JPH08213740A - Surface treatment for circuit board - Google Patents

Abstract

PURPOSE: To enhance the reliability of electrical joint on the surface without having any thermal effect on the region of a circuit board except the conductor part. CONSTITUTION: A circuit board comprises a basic material of modified polyimide resin, and a conductor part including a cavity and an inner lead formed by laminating a plurality of layers of metal material. The circuit board is then irradiated with short pulse laser light in order to remove foreign matters from the surface of the conductor. Finally, only the uppermost surface is fused to make the surface smooth and soft thus processing the surface of the circuit board.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for surface treatment of a circuit board, and more particularly, to irradiating a circuit board having a substrate made of an organic material and a conductor portion formed by laminating a metal material on the substrate with laser light. The present invention relates to a surface treatment method of a circuit board for treating a conductor part.

[0002]

2. Description of the Related Art Conventionally, PGA (Pin Grid Array), QF
P (Quard Flat Pakage), COB (Chip On Board)
In various semiconductor package products called etc.,
A conductor portion made of a metal material layer such as copper or gold is formed on a circuit board made of a synthetic resin or the like, and various electronic components such as a semiconductor chip are electrically joined to the conductor portion to form electronic components or The connection between the electronic parts and the external circuit is achieved. The conductor portion formed on the circuit board for such a semiconductor package requires extremely fine processing according to the semiconductor chip and the like, and a weak current or a high-frequency current is passed through the conductor portion, so that its electrical characteristics Requires extremely high performance.

However, the surface of the conductor portion on the circuit board is contaminated or the surface of the conductor portion becomes metallically inactive due to the influence of the atmosphere for manufacturing the circuit board and other various influences in the manufacturing process. As a result, the insulation resistance value on the surface of the conductor portion increases, and the reliability of electrical connection decreases. Such a reduction in the performance reliability of the surface of the conductor portion causes fatal damage to the characteristics of the entire circuit board.

Therefore, various methods have been proposed to improve the performance reliability of the surface of the conductor by cleaning the circuit board or modifying the surface of the conductor. As a conventional method for cleaning the conductor portion, generally, a wet chemical method using a chemical such as CFC is often adopted. However, in recent years, due to global environmental problems and the like, a cleaning method using chlorofluorocarbon has become a problem, and a method not using fluorocarbon is required. Therefore, a cleaning method using pure water or a cleaning method using a surface active agent has been proposed in place of cleaning with CFCs.

However, these cleaning methods cannot completely remove contaminants existing on the conductor surface.
Further, there is a problem that the cleaning agent remains on the surface of the conductor portion, and rather deteriorates the characteristics of the conductor portion. Further, these methods can be applied as long as the contaminant is attached to the surface of the conductor portion, but the cleaning method as described above can be applied to the case where the conductor surface is metallically inactive. Then, the reliability of the electrical connection cannot be restored.

Therefore, as a dry surface treatment method replacing the above-mentioned wet cleaning method, in recent years, the surface of the conductor portion is irradiated with laser light to remove organic pollutants to improve the performance reliability, and the conductor portion is also improved. A method of recovering the metallic activity of the surface to improve the electrical junction reliability has been proposed. As one example, a method of irradiating a conductor portion composed of a plurality of metal material layers with a laser beam having a pulse width of 1 μsec to form an alloy layer having good solder wettability on the surface is disclosed in JP-A-2-
It is disclosed in Japanese Patent No. 256249. In this conventional circuit board surface treatment method, the surface of the conductor portion is instantaneously melted by high-density laser light and solidified to form an alloy layer with good wettability, and at the same time, remove foreign substances such as organic substances. Evaporate to obtain a clean metal layer.

[0007]

However, in the conventional dry surface treatment method using laser light as described above, there is a problem that the reliability of electrical connection on the surface of the conductor portion is not sufficiently improved. Specifically, since laser light having a long pulse width is used, an intermetallic compound is formed between a plurality of metal material layers, which causes a problem that the resistance value of the entire conductor portion increases. In addition, the amount of laser heat input with sufficient energy is required to form the alloy layer, and as a result, the area other than the conductor portion of the circuit board, such as the resin portion, is thermally affected, and the characteristics of the resin portion and the like are improved. The problem of changing it also arises.

Further, since the surface of the conductor portion is usually formed by plating, and the surface shape thereof has irregularities and changes individually, electrical contamination reliability may not be sufficient only by removing dirt on the surface. Many. Therefore, it was found that the electrical junction reliability can be improved by smoothing only the extreme surface layer. An object of the present invention is to provide a surface treatment method for a circuit board, which can improve the electrical connection reliability of the surface of the conductor section on the circuit board without thermally affecting the area other than the conductor section. To do.

[0009]

According to a first aspect of the present invention, there is provided a surface treatment method for a circuit board, comprising: a circuit board having a substrate made of an organic material; and a conductor portion formed by laminating a metal material on the substrate. A method of irradiating a conductor portion by irradiating laser light includes a laser irradiating step of irradiating a short pulse laser light from a light source onto a circuit board.

According to a second aspect of the present invention, there is provided a surface treatment method for a circuit board according to the first aspect, wherein the outermost surface of the conductor portion is made of gold and has a thickness of 0.2 μm or more. Irradiation energy density of 0.6 ~ 3.0J
/ Cm ² , and the number of times of laser light irradiation is 1 to 50 times. In the surface treatment method for a circuit board according to the invention of claim 3, a circuit board having a substrate made of an organic material and a conductor portion formed by laminating a metal material on the substrate is irradiated with laser light to form a conductor portion. In the processing method, a first laser irradiation step of irradiating the circuit board with a first laser beam to remove foreign matter adhering to the conductor portion, and a first laser irradiation step of the circuit board after the first laser irradiation step. A second laser irradiation step of irradiating a second laser beam having an intensity equal to or higher than the laser beam to surface-treat the conductor portion.

A surface treatment method for a circuit board according to a fourth aspect of the present invention is the method according to the third aspect, wherein the first laser light has an irradiation energy density of 0.2 to 0.6 J / cm ^2. The second laser light is an excimer laser light having an irradiation energy density of 0.6 to 3.0 J / cm ² . A surface treatment method for a circuit board according to the invention of claim 5 is the method according to any one of claims 1 to 4,
Further comprising the step of placing the circuit board in a reduced pressure atmosphere,
In each laser irradiation step, the circuit board arranged in a reduced pressure atmosphere is irradiated with laser light through an optical window.

A surface treatment method for a circuit board according to a sixth aspect of the present invention is the method according to the fifth aspect, further including a plasma generating step of generating plasma under a reduced pressure atmosphere. A surface treatment method for a circuit board according to a seventh aspect of the present invention is the method according to the sixth aspect, further including a plasma control step of controlling power of plasma generated in the plasma generation step.

A surface treatment method for a circuit board according to an eighth aspect of the present invention is the method according to any one of the fifth to seventh aspects, wherein a gas flow forming step of forming a gas flow in the vicinity of the optical window under a reduced pressure atmosphere. Is further included. A surface treatment method for a circuit board according to a ninth aspect of the present invention is the method according to the first aspect, further comprising a step of determining whether or not the conductor portion of the circuit board is larger than a single laser irradiation area before laser irradiation. In addition, in the laser irradiation step, when it is determined that the conductor portion is larger than the laser irradiation area, the mixed portion of the conductor portion mixed with the non-conductor portion on the circuit board is irradiated with laser light, and then the mixed portion is excluded. The conductor is irradiated with laser light.

According to a tenth aspect of the present invention, in the method of surface treatment of a circuit board according to the first aspect, in the laser irradiating step, laser light emitted from a light source is deflected by driving two mirrors. The light is scanned on the circuit board. According to an eleventh aspect of the present invention, in the method for surface treatment of a circuit board according to the tenth aspect, in the laser irradiation step, a mask arranged between a light source and a mirror to limit an irradiation position, and an image of the mask are provided. A lens for forming an image on the circuit board is moved in the optical axis direction in synchronization with the mirror.

According to a twelfth aspect of the present invention, in the method for surface treatment of a circuit board according to the first aspect, in the laser irradiation step, the light source and the circuit board are arranged apart from each other by the sum of their focal lengths. Laser light is emitted through the two lenses thus formed. According to a thirteenth aspect of the present invention, there is provided a surface treatment method for a circuit board according to the first aspect, wherein an irradiation position detecting step of detecting an irradiation position of the laser beam applied to the circuit board in the laser irradiation step, and a detection irradiation position. And a correction step of correcting the irradiation position of the laser light.

According to a fourteenth aspect of the present invention, in the method for surface treatment of a circuit board according to the thirteenth aspect, in the irradiation position detecting step, the detection laser beam emitted from the detection light source is a laser beam emitted from the light source. The same position is irradiated, and the irradiation position of the irradiated detection laser light is detected. A surface treatment method for a circuit board according to a fifteenth aspect of the present invention is the method according to the first aspect, wherein the conductor portion of the circuit board is composed of a plurality of plating layers, and the conductor portion is irradiated with laser light in a laser irradiation step. The method further includes an evaluation step of evaluating the plating adhesion according to the state of the subsequent conductor portion.

[0017]

In the method of surface treatment of a circuit board according to claim 1,
In the laser irradiation step, the circuit board is irradiated with short-pulse laser light from the light source. Here, by irradiating the circuit board with a short-pulse laser light, the energy of the laser light can be applied only to the conductor surface, so that the conductor surface is not affected by the heat on the area other than the conductor. Foreign matter can be removed and only the conductor surface of the conductor can be melted without forming intermetallic compounds between multiple metal material layers to eliminate pinholes and irregularities and smooth the surface of The joint reliability can be improved.

In the surface treatment method for a circuit board according to a second aspect, the outermost surface of the conductor portion is made of gold having a thickness of 0.2 μm or more, and the laser beam irradiation energy density in the laser irradiation step is 0.6 to 3. 0.0 J / cm ² , the number of laser light irradiations is 1
Since the number of times is up to 50 times, it is possible to remove foreign matter on the surface of the conductor portion and smooth the surface of the conductor portion without affecting the metal material laminated under gold even if a plurality of metal materials are laminated.

In the surface treatment method for a circuit board according to a third aspect of the present invention, the circuit board is irradiated with the first laser beam to remove foreign matter adhering to the conductor portion, and then the circuit board is subjected to the second treatment. The surface of the conductor portion is surface-treated by irradiating the laser beam. Here, since the first laser beam removes foreign matter such as dirt on the surface of the conductor portion due to organic matter, the surface of the conductor portion is melted by the second laser beam, so that the electrical connection reliability can be further improved.

In the surface treatment method for a circuit board according to a fourth aspect, the irradiation energy density of the first laser light is 0.2 to.
The excimer laser light is 0.6 J / cm ² , and the irradiation energy density of the second laser light is 0.6 to 3.0 J / cm 2.
^Since the excimer laser light of ² is used, foreign matter can be removed by the excimer laser light of low intensity without heat effect on the circuit board, and then the surface of the conductor part can be melted by excimer laser light of high intensity, resulting in reliable electrical connection. The sex can be improved.

In the surface treatment method for a circuit board according to a fifth aspect, the circuit board arranged in a reduced pressure atmosphere is irradiated with a short pulse laser beam through an optical window. Here, since the laser light irradiation is performed under a reduced pressure atmosphere, the collision between the particles scattered by the irradiation to the area other than the conductor and the atmospheric gas is reduced, and the adhesion of the scattered particles to the conductor can be suppressed. Therefore, even if the conductor portion and the other region are irradiated with the laser light over a large area, the electrical connection reliability can be secured.

In the surface treatment method for a circuit board according to a sixth aspect, the circuit board is irradiated with a short pulse laser beam in a state where plasma is generated in a reduced pressure atmosphere. here,
Since the laser light is irradiated in the plasma atmosphere, the foreign matter adhering to the optical window is removed by the collision of the gas ionized by the plasma, and the scattered particles are gasified and exhausted, so that the amount adhering to the optical window is increased. And the deterioration of the laser transmittance of the optical window is suppressed. Moreover, the scattered matter slightly attached to the surface of the conductor portion due to the collision of the ionized gas can be removed, and the electrical connection reliability can be further improved.

In the method for surface treatment of a circuit board according to a seventh aspect, since the amount of plasma generated is controlled, it is possible to prevent deterioration of the laser transmittance of the optical window and to remove a small amount of scattered matter adhering to the surface of the circuit board. The reliability of the electrical connection can be further improved. In the surface treatment method for a circuit board according to claim 8, since a gas flow is formed in the vicinity of the optical window in a reduced pressure atmosphere, scattered matter is less likely to adhere to the optical window, and the laser transmittance of the optical window is less likely to deteriorate. . Therefore, the circuit board is always irradiated with laser light having a uniform energy density, and high-quality surface treatment can be performed.

In the surface treatment method for a circuit board according to a ninth aspect of the present invention, before the laser irradiation, it is judged whether or not the conductor portion of the circuit board is larger than a single laser irradiation area, and the conductor portion is larger than the laser irradiation area. When it is determined that the laser light is irradiated to the mixed portion of the conductor portion that is mixed with the non-conductor portion on the circuit board,
After that, the conductor portion except the mixed portion is irradiated with laser light. Here, when the conductor portion is larger than the irradiation area, laser light is irradiated from the mixed portion first, so even if particles scattered from the area other than the conductor portion in the mixed portion adhere to the conductor portion excluding the mixed portion The scattered particles can be surely removed, and the reliability of electrical connection can be improved.

In the circuit board surface treatment method according to the tenth aspect, the laser light emitted from the light source is driven on the two mirrors to scan the laser light on the circuit board. Since the laser beam is scanned here, a large area can be processed at a high speed without moving the circuit board, and by limiting the scanning area, only the arbitrary part of the circuit board can be surface-treated.

In the surface treatment method for a circuit board according to the eleventh aspect, the mask and the lens move in the optical axis direction in synchronization with the movement of the mirror. Here, since the mask is arranged, the laser light is not irradiated to the portions other than the conductor portion, the generation of scattered particles can be suppressed, and the mask and the lens are moved in synchronization with the mirror, so that the mirror is driven. The imaging position that changes according to the change in the optical path length can always be set on the substrate, and highly accurate surface treatment can be performed.

In the surface treatment method for a circuit board according to the twelfth aspect, since the two lenses are arranged apart from each other by the sum of the focal lengths, the laser light can be vertically incident on the circuit board and the mask can be arranged. However, the image blur becomes small, and even if there is a step on the circuit board, the surface treatment can be performed accurately. In the circuit board surface treatment method according to the thirteenth aspect, the irradiation position of the laser light with which the circuit board is irradiated is detected, and the irradiation position of the laser light is corrected according to the detected irradiation position.
Here, since the irradiation position is detected and the irradiation position is corrected accordingly, it is possible to always perform accurate surface treatment.

In the circuit board surface treatment method according to the fourteenth aspect, the detection laser light emitted from the detection light source is applied to the same position as the laser light emitted from the light source, and the irradiation position of the applied detection laser light is adjusted. To detect. Here, for example, if visible light is used as the detection laser light, the irradiation position can be detected by an inexpensive detection means such as a CCD camera, so that the irradiation position can be inexpensively and easily detected.

In the circuit board surface treatment method according to the fifteenth aspect, the plating adhesion is evaluated by the state of the conductor portion after the conductor portion is irradiated with the laser beam. Since the quality inspection can be performed simultaneously with the surface treatment, the productivity can be improved and the reliability of the circuit board can be improved.

[0030]

Embodiments of the present invention will be described below with reference to the drawings. 2 and 3 show a PGA board as a specific example of the circuit board. The circuit board 10 has a structure in which two kinds of conductor portions made of a conductor metal are laminated on a rectangular plate-shaped resin base material 11 made of a modified polyimide resin. On the upper surface of the resin base material 11, there are formed cavities 12, which are first conductor portions that are recessed in a rectangular shape, at four equal intervals, for example. In this cavity 12,
A semiconductor chip (not shown) on which an integrated circuit is formed is housed. Around the four sides of the cavity 12, a large number of inner leads 13, which are second conductor portions in the form of small strips, are formed side by side. The inner lead 13 is connected to a conductor circuit connected to a terminal pin (not shown). Further, each terminal of the semiconductor chip housed in the cavity 12 is connected to the inner lead 13 by a bonding wire. The inner lead 13 is
As shown in FIG. 2, the resin base material 11 is mixed in a region of, for example, 1 mm × 15 mm, and the resin base material 11 is a mixed region in which conductor portions are mixed. Also, cavity 1
2 is an area of, for example, 15 mm × 15 mm, and is an area where only the conductor portion exists.

As shown in FIG. 3, the cavity 12 and the inner lead 13, which are conductors, are made of resin.
In this structure, an electrolytic copper plating layer 15, a nickel plating layer 16, and a gold plating layer 17 are laminated in this order on a copper foil layer 14 attached to the upper surface of. The gold plating layer 17 is formed, for example, by gold plating having a thickness of 0.2 μm or more, and preferably by gold plating having a thickness of 0.5 μm or more. Here, the thickness of the gold plating layer 17 is set to 0.2 μm or more because when the thickness is 0.2 μm or less, the underlying nickel plating layer 16 is formed when laser light is irradiated at an energy density described later.
This is because there is a risk that it will be thermally affected.

FIG. 1 shows the overall structure of a surface treatment apparatus used for carrying out one embodiment of the present invention. The surface treatment device includes an excimer laser irradiation device 30 and an XY table 60. A large number of circuit boards 10 are mounted on the XY table 60. The excimer laser irradiation device 30 irradiates the circuit board 10 with short-pulse excimer laser light R. The laser light R is applied to the circuit board 10 via the mirror 32 and the image forming lens 34. The laser light R is KrF excimer laser light having a wavelength of 248 nm, has a pulse width of about 30 nsec, and a repetition frequency of 1 to 200 Hz (when processing the circuit board 10 with a plurality of pulses as shown in FIG. Cycle is 1 sec
~ 5 msec). The irradiation energy density is
0.6~3.0J / cm ² about is set on, the irradiation area is, for example, 3 mm □.

As described above, when the conductor portion is irradiated with the short-pulse laser light, the energy of the laser light acts only on the pole surface of the conductor portion because the heat capacity is small in a short time. As a result, heat is not transmitted to the deep part of the conductor part, and even if the conductor part is composed of a plurality of metal layers, intermetallic compounds are less likely to be formed between the layers, and the resistance value of the entire conductor part is reduced. It is less likely to increase and the reliability of electrical connection of the conductor portion is improved. Further, as shown in FIG. 3B, the organic substances attached to the surface of the conductor portion are evaporated and removed, and the metal deposits on the surface of the conductor portion are diffused inside the conductor portion, so that the amount of impurities on the surface is reduced. it can. Further, since only the extreme surface of the conductor portion can be melted, the surface can be smoothed, the number of pinholes on the surface can be reduced, and the surface can be softened. Furthermore, since only the conductor portion is heated, the resin base material 11 is less likely to be affected by heat, and the characteristics of the resin base material 11 are less likely to change.

As described above, by the short pulse laser beam,
The surface is modified by removing contaminants on the surface of the conductor and melting the pole surface of the conductor, thereby smoothing the pole surface and activating the metal. Laser beam R
The following method is adopted as the irradiation method. Oscillation of a short pulse laser is continuously repeated at regular intervals (for example, 1 to 200 Hz) by the laser irradiation device 30 (for example, 1 to
The circuit board 10 is moved together with (50 times). The circuit board 10 is continuously moved while performing such oscillation,
The laser beam R is applied to the entire irradiation pattern of the circuit board 10. If such a method is adopted, the work can be efficiently performed without interrupting the irradiation of the laser light R.

FIG. 5 is a schematic view showing an embodiment in which the laser light is irradiated in two steps. In the circuit board, the organic matter stain 20 adheres to the surface of the conductor portion 12 (13) inevitably in the process. Therefore, first, the first laser beam is irradiated to remove the organic contaminant 20. This improves the connection reliability of wire bonding. Since this first laser light has a low energy density, it has little effect on the conductor portion. Therefore, laser light is irradiated until the organic substances are completely removed. Here, the irradiation energy density of the first laser light is 0.2 to 0.6 J / cm ² , and the irradiation frequency is 1
~ 500 times. The irradiation interval is the same as the above, and is 1 to 200 Hz.

As shown in FIG. 3, a plating layer is usually formed on the surface of the conductor portion, and the surface condition (grain size of plating, surface irregularities, amount of impurities in plating) varies depending on the lot. Is large, the second laser beam is irradiated to melt the conductor surface of the conductor portion to reduce variations in the surface state and improve wire bonding characteristics (electrical bonding reliability). That is, after removing the dirt, the high density second laser beam melts the extreme surface of the conductor in an extremely short time, smoothes the surface without softening impurities such as organic substances into the interior, and softens it. Form a surface with few pinholes. Here, the irradiation energy density of the second laser light is
0.6 to 3.0 J / cm ² , and the irradiation frequency is 1 to 50
Times.

Although it is possible to remove the dirt of the organic substance by the second laser beam, if the dirt 20 is thick, the dirt cannot be completely removed if the number of laser irradiations is small. Further, if the number of times of laser irradiation is increased, the circuit board is thermally affected, and the electrical characteristics of the circuit deteriorate. Therefore, the organic contaminant 20 can be removed by increasing the number of laser irradiations with a laser beam having a weak energy density, and improving the surface condition by reducing the number of laser irradiations with a laser having a strong energy density. The electrical junction reliability can be improved without deteriorating. Further, in the above two embodiments, a mask for limiting the irradiation pattern to the conductor portion is arranged between the mirror 32 and the laser irradiation device 30,
The mask may be moved in synchronization with the XY table 60.

FIG. 6 shows an embodiment in which a circuit board arranged in a vacuum chamber is irradiated with short pulse laser light. Normally, the conductor portion is formed only on a necessary portion on the resin base material 11 on the circuit board 10, so that the conductor portion and the resin base material 11 are mixed. For this reason, when it is attempted to irradiate only the conductor portion with the laser light, the control of the laser light irradiation system becomes complicated. Further, if only the conductor portion is irradiated, the area that can be irradiated at one time becomes small, which is problematic from the viewpoint of productivity. Therefore, in this embodiment, the area that can be irradiated at one time is set to 3 mm □, and the conductor portion and the resin base material 11 are collectively irradiated so that a large area can be processed at one time.

The surface treatment apparatus used for carrying out this embodiment comprises a box-shaped vacuum chamber 1 in which an optical window 4 is arranged on the upper outer wall. A vacuum pump 2 is connected to the vacuum chamber 1, and the inside of the vacuum chamber 1 is maintained at a vacuum degree of about 0.1 to 0.01 Torr by the vacuum pump 2. A laser irradiation device 30 is arranged above the optical window. In addition, here, the mirror 32 and the lens 34 for image formation are used.
Are not shown. Inside the vacuum chamber 1,
The substrate holding portion 5 for holding the circuit board 10 has an optical window 4.
Are located opposite to.

When the conductor portion and the resin base material 11 are collectively irradiated with the laser light R, the scattered matter generated from the resin base material 11 collides with the atmospheric gas and adheres to the surface of the conductor portion. In order to prevent this, while the circuit board 10 is placed in the vacuum chamber 1 under a reduced pressure atmosphere, short-pulse laser light having a wide irradiation range is collectively irradiated to the circuit board 10. In addition,
The atmosphere gas may be air, but may be He, Ar, N gas. When the circuit board 10 is arranged in the depressurized atmosphere as described above, even if the scattered material from the resin base material 11 jumps out of the board 10 at a high speed, it is less likely to collide with the atmospheric gas, and the amount of adhesion to the conductor portion is reduced.

FIG. 7 shows an embodiment in which the circuit board is irradiated with short pulse laser light while generating plasma under a reduced pressure atmosphere. When the laser light is irradiated in the reduced pressure atmosphere, scattered matter from the resin base material 11 adheres to the optical window 4, causing a problem that the laser transmittance of the optical window 4 decreases. Therefore, in this embodiment, plasma is generated under a reduced pressure atmosphere to reduce the adherence of scattered matter to the optical window 4 by the chemical action and the physical action.

The surface treatment apparatus is provided with a plasma electrode 7 arranged between the optical window 4 and the substrate holding section 5 in addition to the apparatus shown in FIG. The plasma electrode 7 is connected to a high frequency plasma power source 9 arranged outside the vacuum chamber 1. The plasma electrode 7 is made of stainless steel and is 10
It is a coil-shaped electrode having a winding diameter of 0 to 250 mm and a length of 50 mm. The high-frequency plasma power source 9 applies a high-frequency voltage to the plasma electrode to output 20 to 500 W from the plasma electrode 7.
To generate plasma.

In this embodiment, the laser light R is applied to the circuit board 1
When 0 is irradiated, scattered matter is generated from the resin base material 11 and adheres to the optical window and the conductor portion. Even if the scattered matter adheres to the optical window 4, it is physically removed by etching due to collision with the ionized atmospheric gas. Further, the scattered matter scattered in the plasma is gasified and exhausted, so that the amount of adhesion to the optical window 4 is also reduced. As a result, the laser transmittance of the optical window 4 is less likely to decrease, and the laser light R having a uniform energy is obtained.
Can stably reach the circuit board 10 for a long period of time, and stable surface treatment can be performed.

Further, scattered matter slightly attached to the conductor portion can be removed by the etching action. The slight attachment of the scattered matter to the conductor portion does not affect the wire bonding so much. However, as shown in FIG. 8, when the semiconductor chip 22 is die-bonded to the cavity 12, the adhering substance may be dissolved in the solvent 21 for die-bonding, and the viscosity of the solvent 21 may be lowered to facilitate the flow. When the solvent 21 flows to the inner leads 13, a problem such as a short circuit occurs. Therefore, by removing such a slight adhered substance, the electrical connection reliability can be further improved.

FIG. 9 shows an embodiment of irradiating short pulse laser light while controlling plasma. The surface treatment apparatus according to this embodiment is provided with a moving mechanism 7a for moving the plasma electrode 7 up and down, in addition to the apparatus of the embodiment shown in FIG. As the moving mechanism 7a, for example, a driving mechanism such as a motor may be used. By moving the plasma electrode 7 up and down in this manner, appropriate plasma power can be made to reach both the optical window 4 and the circuit board 10. In addition to controlling the plasma by changing the position of the plasma electrode, the plasma may be controlled by applying a bias voltage to the circuit board or applying a magnetic field to the plasma.

In this embodiment, the plasma can be controlled more appropriately than in the embodiment shown in FIG. 7, so that the scattered matter adhering to the optical window 4 and the conductor can be further removed, and the electrical connection reliability can be further improved. FIG. 10 shows an embodiment in which laser light is emitted while forming a gas flow near the optical window.

The surface treatment apparatus according to this embodiment has the structure shown in FIG.
In addition to the apparatus of the embodiment shown in FIG. 1, a nozzle 18 is arranged around the optical window 4. A gas cylinder 19 filled with an atmospheric gas (for example, clean air) is connected to the nozzle 18. In this embodiment, a gas is caused to flow in the vicinity of the optical window 4 to prevent the scattered matter from adhering to the optical window 4. At this time, the inside of the vacuum chamber 1 is constantly evacuated by the vacuum pump 2,
Make sure that the atmospheric pressure does not increase due to the inflow of gas. Further, the gas flow rate at this time may be such that the degree of vacuum (atmospheric pressure) in the vacuum chamber 1 is not affected. Specifically, although it is related to the exhaust capacity, about 1 liter / minute is desirable. The degree of vacuum in the vacuum chamber 1 is 0.
05 Torr is enough. It should be noted that whatever the kind of gas, it is effective in preventing the adherence of scattered matter. However, the reactive gas may react with the circuit board 10 and corrode the circuit board 10. Therefore, an atmospheric gas (air) or an inert gas is desirable.

In this embodiment, since the scattered gas is prevented from adhering to the optical window 4 by the gas flow, the laser transmittance is less likely to decrease, and the circuit board 10 is always irradiated with laser light having a uniform energy density. Therefore, high quality surface treatment can be performed. FIG. 11 shows an embodiment in which the inner lead 13 and the cavity 12 are separately irradiated in the surface treatment apparatus shown in FIG. The area where the inner lead 13 is formed is
As shown in FIG. 2, this is a region in which the conductor portion and the resin base material 11 are mixed. When irradiating the inner lead 13, both of them are simultaneously irradiated with a laser beam. However, since the cavity 12 has only the conductor portion, the resin base material 11 is not irradiated when the cavity 12 is irradiated.

Therefore, as shown in FIG.
In step S1, it is determined whether the conductor portion has a larger laser light irradiation region (one-time irradiation area). When it is determined that the conductor portion is large, the process proceeds to step S2, and first,
The XY table 60 is controlled so that only the mixed area where the inner leads 13 are formed is irradiated. As a result, the resin component is scattered from the resin base material 11 in the mixed area. The scattered resin component adheres to the cavity 12. In step S3, the XY table 60 is controlled so that the cavity 12 is irradiated with the laser light. As a result, the resin scattered matter attached to the cavity 12 is removed, and the metal surface layer is melted and reformed. When it is determined that the conductor portion is smaller than the irradiation area, steps S1 to S4 are performed.
1 shift and irradiate the whole. When the laser beam is scanned by the galvano scanning mechanism, the galvano scanning mechanism may be controlled in steps S2 and S3.

By irradiating the laser beam in such a procedure, the resin component is not dissolved in the solvent for die bonding as described in FIG. 8, and the short circuit due to the solvent can be prevented. FIG. 12 shows an embodiment in which laser light is scanned. The surface treatment apparatus of this embodiment has an optical window 4 on the upper outer wall.
And a laser irradiation device 30 arranged above the vacuum chamber 1. A laser scanning mechanism 31 is arranged between the vacuum chamber 1 and the laser irradiation device 30. Laser scanning mechanism 31
Has a condenser lens 34 arranged below the laser irradiation device 30 and two rotatable Galvano mirrors 36 and 37 for scanning the condensed laser light. The rotation angles of the Galvano mirrors 36 and 37 are controlled by a servo mechanism (not shown), and the irradiation angle of the circuit board 10 can be arbitrarily set from the emission angle of the laser light to the mirrors 36 and 37. Here, a large area can be processed at a high speed without moving the circuit board 10, and the surface of only an arbitrary place can be processed by controlling the mirrors 36 and 37.

FIG. 13 shows an embodiment in which a mask is arranged between the laser irradiation device and the circuit board and the conductor portion is surface-treated with high precision. The laser scanning mechanism 31 of this surface treatment apparatus includes a mask 38 arranged to face the laser irradiation apparatus 30 and a lens 34 arranged to face the mask 38.
And two rotating Galvano mirrors 36 and 37. The mask 38 and the lens 34 move in the optical axis direction in synchronization with the galvanometer mirrors 36 and 37.
a and 34a respectively.

Normally, when an image of the mask 38 is formed and surface treatment is performed, the distance a from the mask 38 to the lens 34 and the processing point from the lens 34 (surface of the circuit board 10).
A relational expression of 1 / a + 1 / b = 1 / f is established between the distance b up to and the focal point f of the lens 34.

When laser scanning is performed using a galvanometer mirror, the optical path length b is such that the central portion A and the peripheral portion B on the circuit board 10 are
Therefore, the pattern image of the mask 38 may be blurred and accurate processing may not be performed. Therefore, in this embodiment, the mask 38 and the lens 34 are moved according to the change in the optical path length b so that the pattern image of the mask 38 is not always blurred. For example, central area A and peripheral area B
If the optical path lengths differ by 10 mm, the mask 38 and the lens 34 may both be moved by 10 mm with respect to the mirror 36.

FIG. 14 shows that even if the conductor portion has a step,
An example is shown in which the conductor portion is surface-treated accurately. This surface treatment device includes a laser irradiation device 30, a mirror 36, two lenses 34 for collimating the irradiated laser light,
And 39. The two lenses 34 and 39 are arranged between the mirror 36 and the circuit board 10. A cavity 12 is recessed in the circuit board 10, and there is a step between the inner lead 13 and the cavity 12.

In general, as the number of layers of the circuit board 10 increases, the irradiation position with respect to the optical path length of the circuit board 10 may change, so that a step occurs within one pulse of the laser light, making it difficult to perform high-precision surface treatment. Become. Therefore, in this embodiment, the laser light is made to enter the circuit board 10 perpendicularly.
The optical system is arranged so that the energy density is constant even with respect to the step of the circuit board 10 by combining a plurality of lenses. When the focal lengths of the two lenses 34 and 39 are f1 and f2 and the distance is L, the two lenses 34 and 39 are arranged so as to have the following relationship.

F1 + f2 = L Here, since the laser light is incident perpendicularly on the circuit board 10, even if there is a step on the circuit board 10, accurate surface treatment can be performed. Actually, when a lens having a focal length of f1 = 400 and f2 = 100 with respect to a step of 1 mm was used, surface treatment with high accuracy was achieved up to a step of 2 mm.

15 to 17 show an embodiment in which the laser irradiation position is detected and the position is corrected. In general, the laser optical system may change the optical path length and change the laser irradiation position due to changes in ambient temperature and changes with time.
Also, due to changes in the discharge state of the laser oscillator and the resonator,
The laser emission position may change and the processing position may change. Therefore, in these embodiments, the laser irradiation position is directly observed on the circuit board 10 and the irradiation position is corrected when the irradiation position changes.

The embodiment shown in FIG. 15 shows a case where the circuit board 10 is moved to fix the laser beam irradiation position. This surface treatment apparatus includes a mask 38 and a detector 50 arranged on an XY table 60 and having a sensitivity characteristic with respect to the wavelength of excimer laser light. In addition,
The lens 34 has the same function as the lens 34 (FIG. 1) of FIG. 1, although the position is different. The detector 50 is arranged so that the irradiation position can be seen. Other configurations are similar to those of the embodiment shown in FIG. The detection and correction timing may be performed, for example, once a hour.

When the KrF excimer laser is irradiated, the detector 50 and its optical system are preferably UV-compatible. Here, when the irradiation position is displaced within the field of view of the detector 50, the position of the XY table 60 may be corrected according to the displacement amount. The embodiment shown in FIG. 16 shows a case where the circuit board 10 is fixed by scanning laser light. This surface treatment apparatus is obtained by adding a detector 50 to the apparatus of the embodiment shown in FIG. The detector 50 is a scanner control system 5 that controls the galvanometer mirrors 36 and 37.
The rotation is controlled in synchronization with 1. When the irradiation position changes, the deviation amount is detected, and the irradiation position is corrected by the scanner control system 51 according to the detected deviation amount.

FIG. 17 shows an embodiment in which a normal visible light camera is used as a detector instead of a special detector for ultraviolet rays. This surface treatment device is a He-Ne laser light (wavelength 633n) that is visible light for irradiation position detection.
m) is further provided with a detection laser irradiation device 52, a mirror 54, a mirror 53, and a detector 50. The mirror 54 is disposed so as to face the detection laser irradiation device 52, and
It transmits e-Ne laser light and reflects KrF excimer laser light. The mirror 53 is arranged so as to face the laser irradiation device 30, and reflects the excimer laser light toward the mirror 54. The detector 50 is, for example, a CCD camera,
The laser irradiation position is arranged at the center of the visual field. The two irradiation devices 3 are arranged so that the optical axis of the laser irradiation device 30 and the optical axis of the detection laser irradiation device 52 coincide with each other.
0 and 52 are arranged.

Here, since the visible light is applied to the laser irradiation position, the cost of the detector is low and the irradiation position can be easily detected. Further, the irradiation position can be reliably detected even if the wavelength of the processing laser light changes. FIG.
Shows an example in which the plating adhesion can be evaluated by surface-treating with laser light.

In the circuit board 10 in which the conductor portion is formed of a plurality of plating layers, if the plating adhesion is weakened due to the presence of the impurities 26 between the plating layers, the plating is separated by laser irradiation (FIG. 18B). Further, if impurities are present between the plating layers even if they are not peeled off, they diffuse to the plating surface for a long period of time, and the electrical connection reliability of the circuit board deteriorates. Therefore, by setting the irradiation energy density and the number of laser irradiations, it becomes possible to evaluate the plating adhesion of the circuit board due to the laser light irradiation.

In this example, in order to simultaneously evaluate the surface treatment and the plating adhesion of the circuit board 10 with the apparatus shown in FIG. 1, a KrF excimer laser was used and the irradiation energy density was 1.0 to 1.4 J. / Cm ² , laser irradiation frequency 1 to
The adhesion of plating was evaluated under irradiation conditions of 5 shots. As shown in FIG. 18, the circuit board 10 has a structure in which a copper foil 14 is pasted onto a resin base material 11 made of a glass cloth base material modified polyimide resin, and an electrolytic copper plating layer 15, a nickel plating layer 16 and a gold plating are applied thereon. Layers 17 were each laminated. The thickness of each plating layer is 10 μm for the copper plating layer 15, 5 μm for the nickel plating layer 16 and 1 μm for the gold plating layer 17.
The place where the impurities 26 adhere and the peeling of the plating occurs is mainly between the gold plating layer 17 and the nickel plating layer 16.

When the laser irradiation is carried out under such conditions, the surface can be modified to improve the electrical bonding reliability, the plating adhesion can be evaluated, and the one in which the plating is peeled off is immediately removed. It can be selected as a good product. Here, laser irradiation makes it possible to detect impurities and defects between plating layers that were difficult to detect in the past, and it is possible to detect circuit boards with low reliability that are difficult to maintain in the long-term in advance, and the final product. The reliability of can be improved. Moreover, since quality inspection can be performed simultaneously with surface modification, productivity is also improved.

[0065]

According to the surface treatment method for a circuit board according to the first aspect of the present invention, by irradiating the circuit board with a short-pulse laser beam, the energy of the laser beam can be applied only to the surface of the conductor portion. Foreign matter on the surface of the conductor can be removed without affecting the area other than the area by heat.
Without forming an intermetallic compound between multiple metal material layers, only the conductor surface can be melted to eliminate pinholes and unevenness, and the surface can be made smooth, improving the electrical connection reliability of the conductor surface. it can.

In the surface treatment method for a circuit board according to claim 2, the outermost surface of the conductor portion is made of gold having a thickness of 0.2 μm or more, and the irradiation energy density of the laser beam in the laser irradiation step is 0.6 to 3. 0.0 J / cm ² , the number of laser light irradiations is 1
Since the number of times is up to 50 times, it is possible to remove foreign matter on the surface of the conductor portion and smooth the surface of the conductor portion without affecting the metal material laminated under gold even if a plurality of metal materials are laminated.

In the surface treatment method for a circuit board according to a third aspect of the present invention, the first laser beam is used to remove foreign matters such as dirt on the surface of the conductor portion by organic matter, and then the surface of the conductor portion is melted with the second laser beam. Therefore, the reliability of electrical connection can be further improved. In the method of surface treating a circuit board according to claim 4,
Laser light has an irradiation energy density of 0.2 to 0.6 J /
an excimer laser beam cm ^2, because the second laser beam irradiation energy density of the excimer laser beam 0.6~3.0J / cm ^2, the thermal influence on the circuit board with strength is weak excimer laser beam The foreign matter can be removed without being given, and the surface of the conductor portion can be subsequently melted by the strong excimer laser light, and the electrical connection reliability can be further improved.

In the surface treatment method for a circuit board according to the fifth aspect, since the laser light irradiation is performed in a reduced pressure atmosphere, the collision between the particles scattered by the irradiation to the area other than the conductor and the atmospheric gas is reduced. Further, it is possible to suppress the adhesion of scattered particles to the conductor portion. Therefore, even if the conductor portion and the other region are irradiated with the laser light over a large area, the electrical connection reliability can be secured.

In the surface treatment method for a circuit board according to the sixth aspect, since the laser beam is irradiated in the plasma atmosphere, the foreign matter attached to the optical window is removed and scattered by the collision of the gas ionized by the plasma. When the particles are gasified and exhausted, the amount attached to the optical window is reduced, and deterioration of the laser transmittance of the optical window is suppressed. Moreover, the scattered matter slightly attached to the surface of the conductor portion due to the collision of the ionized gas can be removed, and the electrical connection reliability can be further improved.

In the surface treatment method for a circuit board according to the seventh aspect, since the amount of generated plasma is controlled, it is possible to surely remove a small amount of scattered matter adhering to the surface of the circuit board, and to improve the electrical connection reliability. Can be improved. In the surface treatment method for a circuit board according to claim 8, since a gas flow is formed in the vicinity of the optical window in a reduced pressure atmosphere, scattered matter is less likely to adhere to the optical window, and the laser transmittance of the optical window is less likely to deteriorate. . Therefore,
The circuit board is always irradiated with laser light having a uniform energy density, and high-quality surface treatment can be performed.

In the surface treatment method for a circuit board according to the ninth aspect, when the conductor portion is larger than the irradiation area, the mixed portion is irradiated with laser light first, so that the particles scattered from the area other than the conductor portion in the mixed portion. Even if adheres to the conductor portion excluding the mixed portion, the adhered scattered particles can be reliably removed, and the electrical connection reliability can be improved. In the surface treatment method for a circuit board according to the tenth aspect, since the laser beam is scanned, a large area can be processed at high speed without moving the circuit board, and by limiting the scanning region, an arbitrary circuit board can be processed. Only the place can be surface treated.

In the method for surface treatment of a circuit board according to the eleventh aspect, since the mask is arranged, the laser beam is not radiated to the portions other than the conductor portion, the generation of scattered particles can be suppressed, and the mask and the lens are mirrored. By moving in synchronization with, the imaging position that changes according to the change in the optical path length due to the driving of the mirror can always be set on the substrate, and highly accurate surface treatment can be performed.

In the surface treatment method for a circuit board according to the twelfth aspect, since the two lenses are arranged apart from each other by the sum of the focal lengths, the laser light can be vertically incident on the circuit board and the mask can be arranged. However, the image blur becomes small, and even if there is a step on the circuit board, the surface treatment can be performed accurately. In the surface treatment method for a circuit board according to the thirteenth aspect, since the irradiation position is detected and the irradiation position is corrected accordingly, the surface treatment can be always performed with high accuracy.

In the surface treatment method for a circuit board according to claim 14, if visible light is used as the detection laser light,
Since the irradiation position can be detected by an inexpensive detecting means such as a CCD camera, the irradiation position can be easily detected at low cost. In the surface treatment method for a circuit board according to the fifteenth aspect, since the quality inspection can be performed simultaneously with the surface treatment, the productivity can be improved and the reliability of the circuit board can be improved.

[Brief description of drawings]

FIG. 1 is a perspective view showing a surface treatment apparatus used for carrying out a method of the present invention.

FIG. 2 is a plan view showing an example of a circuit board.

FIG. 3 is an enlarged cross-sectional view of a circuit board.

FIG. 4 is a graph showing a repetition period and a pulse width of an example in which laser irradiation is repeated with short pulses.

FIG. 5 is a schematic diagram showing an irradiation procedure of an example in which laser irradiation is performed twice.

FIG. 6 is a schematic sectional view showing an example in which laser irradiation is performed in a reduced pressure atmosphere.

FIG. 7 is a schematic sectional view showing an example in which laser irradiation is performed while generating plasma in a reduced pressure atmosphere.

FIG. 8 is a diagram showing an influence when scattered matter adheres to the cavity.

FIG. 9 is a schematic sectional view showing an example in which laser irradiation is performed while generating controlled plasma in a reduced pressure atmosphere.

FIG. 10 is a schematic cross-sectional view showing an example in which laser irradiation is performed in a reduced pressure atmosphere while ejecting gas around an optical window.

FIG. 11 is a flowchart illustrating an example in which laser irradiation is first performed on an inner lead in a conductor portion.

FIG. 12 is a schematic sectional view showing an example in which a laser beam is scanned by a galvano scan optical system.

FIG. 13 is a schematic sectional view showing an example in which an optical system including a mask and a lens is moved to scan with laser light.

FIG. 14 is a schematic cross-sectional view showing an example in which surface treatment can be performed accurately even when there is a step in the conductor portion.

FIG. 15 is a schematic diagram showing an embodiment in which an irradiation position is detected and the irradiation position is corrected.

FIG. 16 is a schematic view showing another embodiment for detecting the irradiation position and correcting the irradiation position.

FIG. 17 is a schematic diagram showing an embodiment in which an irradiation position is detected by visible light and the irradiation position is corrected.

FIG. 18 is a sectional view illustrating an example in which surface treatment is performed while evaluating plating adhesion.

[Explanation of symbols]

 1 Vacuum Chamber 2 Vacuum Pump 4 Optical Window 7 Plasma Electrode 10 Circuit Board 11 Resin Base Material 12 Cavity 13 Inner Lead 17 Gold Plating Layer 18 Nozzle 19 Gas Cylinder 20 Dirt 30 Laser Irradiator 31 Laser Scanning Mechanism 34, 39 Lens 36, 37 Galvano Mirror 38 mask 50 detector 52 detection laser irradiation device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshimitsu Nakamura 1048, Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Works, Ltd.

Claims (15)

[Claims] 1. A method for surface treatment of a circuit board, wherein a circuit board having an organic material substrate and a conductor portion formed by laminating a metal material on the substrate is irradiated with laser light to treat the conductor portion. 3. A surface treatment method for a circuit board, comprising: a laser irradiation step of irradiating the circuit board with a short-pulse laser beam from a light source. 2. The outermost surface of the conductor portion is made of gold having a thickness of 0.2 μm or more, and the irradiation energy density of the laser light in the laser irradiation step is 0.6 to 3.0 J / cm ² , the laser light The method for surface treatment of a circuit board according to claim 1, wherein the number of times of irradiation is 1 to 50 times. 3. A surface treatment method for a circuit board, wherein a circuit board having an organic material substrate and a conductor portion formed by laminating a metal material on the substrate is irradiated with laser light to treat the conductor portion. In a first laser irradiation step of irradiating the circuit board with a first laser beam to remove foreign matter adhering to the conductor portion, and after the first laser irradiation step, the first laser beam is applied to the circuit board. Second laser irradiation step of irradiating a second laser beam having an intensity equal to or higher than the laser beam to subject the conductor portion to surface treatment. 4. The first laser light is an excimer laser light having an irradiation energy density of 0.2 to 0.6 J / cm ² , and the second laser light has an irradiation energy density of 0.6.
The surface treatment method for a circuit board according to claim 3, wherein the excimer laser light is about 3.0 J / cm ² . 5. The method further comprises the step of arranging the circuit board in a reduced pressure atmosphere, wherein in each of the laser irradiation steps, the circuit board arranged in the reduced pressure atmosphere is irradiated with the laser light through an optical window. Item 5. The surface treatment method for a circuit board according to any one of Items 1 to 4. 6. The surface treatment method for a circuit board according to claim 5, further comprising a plasma generating step of generating plasma in the reduced pressure atmosphere. 7. A plasma control step of controlling the power of plasma generated in the plasma generation step,
The surface treatment method for a circuit board according to claim 6. 8. The surface treatment method for a circuit board according to claim 5, further comprising a gas flow forming step of forming a gas flow in the vicinity of the optical window under the reduced pressure atmosphere. 9. The method further comprises the step of determining whether or not the conductor portion of the circuit board is larger than a single laser irradiation area before the laser irradiation, in the laser irradiation step, the conductor portion is the laser irradiation area. When it is determined to be larger, a laser beam is irradiated to a mixed part of the conductor part mixed with a non-conductor part on the circuit board, and then a laser beam is irradiated to the conductor part excluding the mixed part. The surface treatment method for a circuit board according to 1. 10. The surface treatment method for a circuit board according to claim 1, wherein in the laser irradiation step, two mirrors are driven by the laser light emitted from the light source to scan the laser light on the circuit board. . 11. A mask arranged between the light source and the mirror in the laser irradiation step for limiting an irradiation position,
A lens for forming an image of the mask on the circuit board is moved in the optical axis direction in synchronization with the mirror.
The surface treatment method for a circuit board according to claim 10. 12. In the laser irradiation step, laser light is irradiated between the light source and the circuit board via two lenses that are arranged apart from each other by the sum of their focal lengths.
The surface treatment method for a circuit board according to claim 1. 13. An irradiation position detecting step of detecting an irradiation position of the laser light applied to the circuit board in the laser irradiation step, and a correction step of correcting the irradiation position of the laser light according to the detected irradiation position. The surface treatment method for a circuit board according to claim 1, further comprising: 14. In the irradiation position detecting step, the detection laser light emitted from a detection light source that emits the detection laser light toward the circuit board is applied to the same position as the laser light emitted from the light source, and the irradiation is performed. 14. The surface treatment method for a circuit board according to claim 13, wherein the irradiation position of the detected laser light is detected. 15. An evaluation step for evaluating plating adhesion according to a state of the conductor portion after the conductor portion of the circuit board is composed of a plurality of plating layers, and the conductor portion is irradiated with laser light in the laser irradiation step. The surface treatment method for a circuit board according to claim 1, further comprising: