JP2003526205A - Method of making an opening or cavity in a substrate for receiving an electronic component - Google Patents

Abstract

(57) Abstract: A method is provided for forming an opening or cavity in a substrate that receives an electronic component. The method includes providing a patterned opaque mask layer on or adjacent a first major surface of a substrate, wherein the mask layer has openings overlying locations where openings or cavities are to be made in the substrate. Removing material from the substrate by performing laser ablation through the opening, thereby creating an opening or cavity in the substrate of an appropriate size to receive electronic components. .

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION The present invention relates to a method of making an opening or cavity in a substrate. This substrate is preferably of the type which can be equipped with electronic components or integrated circuits. An example of such a substrate is a printed circuit board (PCB).

As the circuit density of electronic components, especially integrated circuits, has increased, so has the problem of connecting them to the connections and conductors of printed circuit boards (PCBs). This problem is especially acute when a large number of interconnects are present (eg in the case of microprocessor devices).

Prior Art Known soldering and wire bonding techniques are costly and require complex equipment to perform the manufacturing process efficiently. Furthermore, it is necessary to heat the solder twice. That is, it is heated first during the manufacture of the PCB and then again during the mounting of the components on the PCB.

Techniques for making openings in a substrate for electronic components are known. See U.S. Pat. No. 3,480,836 for this. Here, a hole is previously punched in the base body, and then a conductor lead having a tab protruding above the cavity is attached. This technique has been further developed, for example in US Pat. No. 4,927,491, where the substrate is a flexible tape.

JP-A-10-098081 discloses the use of a carbon gas laser to cut a peripheral trench to make an opening in a substrate having a copper foil laminated on both sides. There is. Here, the remaining base material is removed in the second step.
The copper foil is then lithographically patterned and etched to create the leads that hold the component.

SUMMARY OF THE INVENTION The present invention provides a relatively small interconnect dimension on a PCB, thereby allowing it to be made relatively thin, and also eliminates the need for synthetic plastic lead chip carriers (PLCC). The purpose is to lose. The invention can also be used to produce relatively low cost chip carriers with beneficial performance.

In a first aspect of the present invention there is provided a method as specified in claims 1-8. In a second aspect of the invention there is provided a substrate as specified in claim 9. In a further aspect of the invention there is provided a device as specified in claim 10.

[0008]   Hereinafter, embodiments of the present invention will be described by way of example with reference to the drawings.

Detailed Description of Certain Advantageous Embodiments FIG. 1 is a general view of a facility 10 for making interconnections to a substrate 12. The installation 10 includes a lasing 14 focused through a suitable lens system 16, which in use reflects off a mirror 18. In a preferred embodiment, a CO ₂ laser with a power of 50-500 W and a beam diameter of 480 μm is used. However, higher power and larger diameter are desirable to increase throughput. Alternatively,
Excimer lasers or YAG lasers can be used.

To fully understand this equipment, it is necessary to consider it in combination with other equipment. These include means for transporting the substrate, such as the flatbed table 24. Photoimaging equipment (not shown) and etching baths (not shown) as a means of selectively removing areas from the first layer of material.
Can be mentioned. The equipment for removing the volume of the substrate may include the laser oscillator 14, an ion beam etching apparatus (not shown), or a plasma etching apparatus (not shown). The means for removing material from the second surface may be a modified etching bath capable of etching the conductor. These are controlled by a series of microprocessors (not shown) in combination with the equipment.

The output of laser 14 is controlled by microprocessor 20. Along with controlling the pulse duration and energy of the laser 14, the microprocessor 20 can adjust the orientation of the mirror 18 and use it to focus the laser 14 through the lens system 16.

Cavities of different depths can be created by a relatively large number of pulses from the energy source or by lengthening the duration of each pulse. Similarly, an array of cavities can be made and the number and size of the cavities in this array of cavities can be varied to make different products or to accommodate different devices.

The substrate 12 shown in detail in FIG. 2 is in the form of a laminated sheet or tape. A flexible substrate 12 sandwiched between two layers 21a and 21b of a metallic material such as copper (or aluminum) comprises a polyethylene (tri-talmate).
te)) (PET). Since the substrate 12 is flexible, it is provided by a roll or drum 22a. Since the base body 12 is flexible, the base body holding the component can be wound on another roll 22b after being connected to the component.

In this embodiment, the substrate has a thickness of 190 μm, but a thickness of 100 μm to 600 μm can be used. Ideally, when inserting a silicon chip, it is polished from the back to a thickness similar to that of the substrate. Alternatively, the thickness of the substrate is selected according to the thickness of the semiconductor chip.

A non-metallic substrate material, such as PET substrate 12, is a metal that catalyzes the base material and coats the base material with a uniform thickness by laminating sheets of metal using adhesive bonding agents. By plating the layers
At least one of its surfaces is coated with a metallic material.

The substrate 12 can be introduced in a partially finished or “green” condition. If the substrate 12 is untreated, it needs to be treated. this is,
This is accomplished by first applying a photoresist to the substrate. It can be applied as a curtain coating with a thin uniform spray, or using other known techniques.

The conductor tracks, interconnects and die bonding sites are photoimaged on both sides. This is a common step in printed circuit board processes.

A circuit pattern is created on the metallized surface of the substrate using photoimaging and etching techniques. The circuit pattern has a coupling point 52. This bond location 52 corresponds to the bond pad size and location of the semiconductor component (not shown) introduced into the cavity created in the substrate and bonded to the interconnect.

On the material side opposite the circuit pattern, bond pads of the corresponding circuit pattern are present in the area corresponding to the dimensions of the semiconductor component to be mounted.

After removing the region from the upper material, the lower polymer layer forming the substrate is removed by laser ablation. Although PET has been mentioned as the polymer for use in the substrate, various other materials are suitable for this application. For example, liquid crystal polymer (
LCP), polyamide, PEN / polyethylene napatamate (napa th)
Almate), polyvinyl chloride, and Mylar ™ can be incorporated into or made from the substrate. Another suitable material for making chip carriers is Thermomount ™ (random strand aramid reinforced laminate material available from Dupont). However, this material has a poor end formability and is very easy to remove.

Laser ablation is very fast, typically 300-800 pulses / sec. The microprocessor 20 changes the speed and duration of the pulses from the laser oscillator 14. This combination allows the vaporization rate to be controlled and adjusted with respect to the particular properties of the substrate material. As a result, due to the M rows by N columns of cavities created over a particular region, the removal occurs at the correct X and Y locations over a known region to a given depth.

Events in the manufacturing process are modular. The substrate is first coated and then photoimaged. Next, etching and stripping are performed. Next, laser removal of the opening or cavity is performed. The next step is wet chemical cleaning and / or plasma cleaning, for example using potassium permanganate solution. Such mechanical tab structure (or contact) made after this cleaning process
Deposit metal on. This is accomplished by immersion alloy deposition from solution. This is an electroless method, but electrolytic plating can be used instead. The alloy selected should be compatible with the application or bonding method selected. Typical materials can include materials based on tin, gold or silver.

During the laser ablation process, material removed from the cavities may redeposit on other parts of the substrate. Such deposits are typically removed during plasma and / or wet cleaning steps. However, when the material to be removed by laser is polyimide, the removal may be difficult. To aid in this removal, an optional sacrificial layer can be deposited on one or more surfaces of the substrate prior to the laser ablation step.
This sacrificial layer may be photoresist, for example. After laser ablation, this layer can be easily removed by plasma and / or wet cleaning to remove any redeposited material simultaneously.

After that, the PCB is cut into a predetermined shape and finished. This contour forming process is
It can be achieved by C routing, die punching, or YAG laser profiling.

The electrodes are preliminarily defined by an etching method. The connector with a series of protrusions, which are spaced apart from each other and side-by-side, into a resistor with components or die connections to be inserted into the cavity or die are made by a metal etching process prior to laser ablation of the dielectric. Alternatively, the electrodes can be laser etched into the metal layer at the bottom of the cavity after removing the dielectric material. Alternatively, changes to the pattern of this pre-etched layer can be made by the laser after the cavity is created (eg by removing the tab and freeing the end of the long structure).

A perforated substrate having contacts defined on one surface is an electronic component (50).
Acts as a stepped recess. The simplest version is one with one or two contacts suitable for receiving a capacitor, for example (Fig. 3a).
. The transistor needs to make three contacts, which is shown in FIG.
It is shown by b. More complex devices, such as integrated circuits (ICs), read only memories (ROMs), random access memories (RAMs) or microprocessors, require many contacts (51). An example of this is shown in Figure 3c.

The long metal bond leads or tabs that make the electrical contact perform two functions. First, they act as electrical paths to / from the component. Secondly, due to their mechanical properties, they hold the part at least during the manufacturing process. For example, the device can be attached by pressing, in which case insertion of the device folds the protruding tabs, creating an elastic clip structure that holds the device in place. Contact tabs coated with silver have been found to be particularly advantageous for this application.

The positioning of each etched area on each surface is important.
However, some error has been tolerated and it has been found that the die positions can be offset to provide a suitable mechanical recess that can receive and hold electrical components.

The component can be bonded to the protruding electrode adjacent to the cavity, for example by ultrasonic and / or pressure bonding. Alternatively, shrink wrap films can be used to press the components against the electrodes, or adhesive tape or tabs can be used.

The present invention can be used to create an array of cavities. The advantage of this method is that multiple devices can be made on a single substrate.

The substrate can be flexible and can be rolled or folded, thereby reducing its bulk and allowing for easy shipping. For example, the substrate can be stored on spools before and / or after manufacture.

The parts can be introduced into the prefabricated cavity by any known technique, for example with a pick-and-place device, by means of an air jet (vacuum) or by hand. The method by creating a vacuum at one surface is particularly convenient. The pressure differential allows electronic components to be placed in their respective cavities, thereby coupling the components (eg semiconductor chips or dies) to the substrate.

When making chip carrier circuits using the present invention, the individual chip carriers are
Die cutting, cutting from a relatively large substrate sheet or tape,
You can take it out.

A particularly advantageous feature of the present invention is that it promotes a flatter chip carrier shape than is normally achievable. The thickness of the chip carrier made by a typical method is
17 μm thicker than the die thickness. However, by using the present invention,
The resulting carrier shape is thinner than conventionally achievable because the part of the substrate that receives the part is removed.

Many different types of electrical and electronic components can be placed in openings or cavities in the substrate. These include resistors, capacitors, inductors,
Mention may be made of transistors, integrated circuits, tuners, waveguides, piezoelectric devices, coils and / or heat sinks. Additionally or alternatively, each aperture or cavity may receive an electro-optical device, such as a liquid crystal device or a light emitting diode. In the latter case, a transparent material such as indium tin oxide (ITO) can be used to create conductive tracks on the surface.

In the embodiment described above, the openings created by laser ablation extend completely through the substrate. Alternatively, the removal can be stopped before all of the substrate has been removed, creating an aperture or cavity that does not penetrate. This technology is a multi-layer P
Useful for creating cavities in CB.

The multilayer PCB has a prepreg dielectric layer, typically 70 μm thick, overlaid with a conductive metal layer. Using a laser removal process to remove such layers,
The bond pad of the subsurface metal layer can be exposed. A flip-chip die with solder bumps is placed on the bond pads so that when the assembly is heated, the solder can flow and bond the chips in place. The advantage of this technique is that the subsurface layers of the multi-layer PCB can be used for input and output of signals to the chip. This reduces the signal conductor length and the propagation delay.

In addition to making openings or cavities for mounting semiconductors or other devices, it is also possible to make via holes at the same time through the PCB. In the preferred embodiment shown in FIG. 4, long metal flaps or tabs (30) are attached to via holes (31).
) At the bottom. The flaps or tabs are longer than the depth of the via holes and are optionally shaped to create jagged edges (32) or barbs or spikes. The flap or tab can be placed in the via by blowing a gas or liquid into the via or by pushing using a solid tool such as a pin. Some of the flaps or tabs that project through the other side of the via hole can be folded onto the conductive tracks on the other side of the PCB to make through-contacts without the use of conventional plating techniques. . In FIG. 4, the jagged end entering the second opening or cavity (33) in the substrate is shown. This can be made by laser ablation or the like. This technique may also be advantageous in conventional PCB manufacturing, even if the opening or cavity that receives the electronic device is not cut in the substrate.

In the embodiments described above, the laser ablation is performed through a patterned metal layer carried by the substrate, but instead with a separate hole having a corresponding hole cut as a mask located adjacent the substrate. It is possible to use a metal sheet of

In the above example, the laser ablation process exposes the long contact protruding into the resulting cavity. Such long metal members need not be electrical contacts, and mechanical structures such as pressure switches can be made.

Although the invention has been described by way of example, variations on the described aspects can be practiced, for example, by using equivalents not disclosed in the description herein.

Finally, the description of the patent application specification, especially the drawings, on which the priority claim of the present application is based, is hereby incorporated by reference.

[Brief description of drawings]

[Figure 1]   FIG. 1 is a diagram of one embodiment of a facility for making interconnects on a substrate.

2a and b are cross-sections and plan views of one component mounted on a substrate made using the equipment of FIG.

[Figs. 3a to 3c]   3a-3c are plan views showing examples of interconnections.

[Figure 4]   FIG. 4 is a diagram showing a method of making a contact portion passing through a via hole.

─────────────────────────────────────────────────── ─── Continued front page    (81) Designated countries EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, I T, LU, MC, NL, PT, SE, TR), OA (BF , BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, G M, KE, LS, MW, MZ, SD, SL, SZ, TZ , UG, ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AE, AG, AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, B Z, CA, CH, CN, CR, CU, CZ, DE, DK , DM, DZ, EE, ES, FI, GB, GD, GE, GH, GM, HR, HU, ID, IL, IN, IS, J P, KE, KG, KP, KR, KZ, LC, LK, LR , LS, LT, LU, LV, MA, MD, MG, MK, MN, MW, MX, MZ, NO, NZ, PL, PT, R O, RU, SD, SE, SG, SI, SK, SL, TJ , TM, TR, TT, TZ, UA, UG, US, UZ, VN, YU, ZA, ZW

Claims (10)

[Claims] 1. (a) on or adjacent to a first major surface of a substrate,
Providing a patterned opaque mask layer, wherein the mask layer has an opening that overlaps where the opening or cavity is created in the substrate; (b) from the substrate by performing laser ablation through the opening. Removing the material, thereby making an opening or cavity in the substrate of a size suitable for receiving the electronic component, the method comprising: or consisting of an opening or cavity in the substrate for receiving the electronic component. 2. The opening or cavity is created by laser ablation only.
The method of claim 1. 3. The method of claim 1, wherein the substrate comprises a dielectric material and the mask layer comprises a metal. 4. The substrate has a further patterned layer on a surface of the first major surface side, the further patterned layer comprising a conductive material. The pattern is defined such that the further patterned layer remains substantially complete when the opening or cavity is made in the substrate, and a portion of the further layer is 2. The method of claim 1, wherein the opening or cavity extends at least partially over one side. 5. The substrate has a layer of electrically conductive material on a surface of the first major surface side, one or more portions of which is provided during or after manufacture of the opening or cavity. The method of claim 1, wherein the selective removal is by laser ablation. 6. The method according to claim 1, wherein the patterned layer is produced by deposition on a substrate and selective removal from the substrate. 7. The method of claim 1, wherein the substrate is long and flexible. 8. A sacrificial layer is provided to cover the first patterned layer and / or the further patterned layer during laser ablation to create the opening or cavity. The method of claim 1, wherein the sacrificial layer is subsequently removed, thereby removing material from the openings or cavities deposited in the sacrificial layer during laser ablation. 9. A substrate having openings or cavities made by the method of claims 1-7. 10. A device comprising a substrate according to claim 8 and an electronic component disposed in the opening or cavity.