JPH01286390A - Molding method for multilayer printed board - Google Patents

Abstract

PURPOSE:To prevent interlayer voids between printed circuit boards from generating by providing an outer frame for specifying the height of a multilayer printed board, and a plunger for pressurizing a melted adhesive flowing to the periphery of a laminate. CONSTITUTION:After a laminate 4 is interposed between an upper metal mold 11 and a lower metal mold 12 by using a multilayer printed board molding device having an outer frame 23 which can burden the loads of the upper and lower molds, a space surrounded by the molds 11, 12 is evacuated in vacuum, and the air of a fine space between the printed circuit board 1 of the laminate 4 and an insulation adhesive 2 is sufficiently sucked. The molds 11, 12 are heated, the adhesive 2 is melted, the melted adhesive 2' is sufficiently filled in a space surrounded by the molds 11, 12 and the frame 23 by the pressure from the molds 11, 12 side, continuously pressurized until the molds 11, 12 are brought into contact with the frame 23, and the melted adhesive is pressurized to high pressure by a plunger 24 for directly pressurizing the part in contact with the adhesive 2' of the molds 11, 12 when the thickness of the laminate 4 does not vary. Thus, the interlayer voids can be eliminated.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for forming a multilayer printed board, and is particularly directed to preventing the generation of interlayer voids and reducing interlayer misalignment.
The present invention relates to a method for forming a multilayer printed board.

[Prior art] An example of a conventional method for forming a multilayer printed board is disclosed in Japanese Patent Application Laid-open No. 57
As described in Japanese Patent No. 118698, a laminate consisting of alternately laminated printed wiring boards and an insulating adhesive is placed inside a vacuum sealed chamber formed by an upper heating plate, a lower heating plate, and a frame. The mold is inserted between the lower molds, heated and pressurized by the upper and lower hot plates, and molded.

In addition, as another example, in order to obtain the low pressure (hereinafter referred to as vacuum) necessary to prevent the occurrence of interlayer voids, the laminate is placed in a heat-resistant bag while being sandwiched between upper and lower molds, Make a vacuum inside. A method is known in which a multilayer printed board is formed by placing this heat-resistant bag into a high-pressure tank and heating and pressurizing the laminate using high-temperature, high-pressure gas.

[Problems to be Solved by the Invention] Details and problems of the above-described conventional molding method will be explained using the drawings.

FIG. 4 is a perspective view showing an example of a laminate formed by alternately laminating a printed wiring board and an insulating adhesive, and FIG. 5 shows an example of a state in which a multilayer printed board is formed by a conventional method. The principal part sectional view, FIG. 6, is a pressure distribution diagram showing the fluid pressure distribution of the molten adhesive when molding is performed by the method according to FIG. 5.

First, an example of a laminate will be described.

As shown in FIG. 4, this laminate 4 is made by alternately stacking a plurality of printed wiring boards 1 with guide holes 1a drilled in predetermined positions and an insulating adhesive 2, and guiding pins 3 to the guide holes 1a. The positioning between each printed wiring board 1 is performed by inserting the .

Here, the method described in Japanese Unexamined Patent Publication No. 57-118698 will be explained using FIG. It is inserted into the guide holes 5a, 6a drilled in the lower mold 6, and is sandwiched between the upper mold 5 and the lower mold 6 in the shape of a sandwich.
This is attached to an upper hot plate 7. attached to a press (not shown).
It is inserted into the vacuum sealed chamber V formed by the lower hot plate 8 and the vacuum sealed frame 9. Vacuum suction lowers a and 8a are provided in the upper and lower heating plates 7 and 8, respectively, and immediately after the laminate 4 is inserted into the vacuum sealed chamber V, vacuum suction is applied through the suction ports, and this Heat and pressurize. Thereafter, the heat and pressure are removed, the vacuum sealed chamber V is removed, and the upper mold 5. When removed from the lower mold 6, the adhesion between the printed wiring boards 1 of the laminate 4 is completed and a laminate printed wiring board is obtained.

However, in this prior art, since a vacuum sealed chamber V is formed between the upper and lower hot plates 7 and 8, the insulating adhesive 2 may melt while the vacuum cannot be sufficiently suctioned. In such cases, the air in the tiny space left between the printed wiring board 1 and the insulating adhesive 2 cannot be vacuum-sucked, and the air remains in the molten adhesive after molding, causing interlayer voids. This was one of the causes.

In addition to this, 8! Since the area around the layered body 4 is an open space, the fluid pressure of the molten adhesive cannot be raised uniformly over the entire surface of the layered body 4, and the fluid pressure cannot be increased until the adhesive hardens. It is also difficult to maintain. That is, according to the research of the present inventors, as shown in FIG. 6, the fluid pressure p(r) of the molten adhesive is sufficiently high at the in-plane center of the laminate (r valve 0), Inner periphery (
When pressing r), the fluid pressure hardly increases. In addition, in the in-plane peripheral area, water and solvent contained in the molten adhesive may be vaporized at the heating temperature, which is another cause of the generation of interlayer voids.

Nonuniform pressure distribution of the molten adhesive also has an adverse effect on interlayer slippage.

The other conventional techniques mentioned above are intended to prevent the occurrence of interlayer voids. As mentioned above, this method involves placing the laminate in a heat-resistant bag, vacuuming the inside of the bag, and then placing the bag in a high-pressure tank and heating and pressurizing it using high-temperature, high-pressure gas. However, implementing this method requires a high-pressure link and gas heating and pressurizing equipment, which requires a high investment amount and requires considerable care in handling to ensure safety. there were. In addition, the time required for heating and pressurizing is long, so in order to shorten this time it is necessary to develop an adhesive with fast curing properties. It wasn't something.

In addition, the conventional technology does not take into account the adjustment of plate thickness distribution and parallelism during forming.
It is difficult to keep the thickness distribution of multilayer printed boards within a certain range, and this is the main cause of interlayer misalignment.

The present invention solves the above-mentioned problems of the prior art, prevents the occurrence of interlayer voids between printed wiring boards, reduces interlayer misalignment, and provides a highly reliable and highly accurate multilayer printed board at a high yield. The object of the present invention is to provide a method for forming a multilayer printed board that can be easily manufactured.

[Means for Solving the Problems] The structure of the method for forming a multilayer printed board according to the present invention for solving the above problems includes a printed wiring board with guide holes drilled in advance at predetermined positions, and an insulating adhesive. In a method of forming a multilayer printed wiring board by pressurizing and heating a laminate obtained by stacking a plurality of printed wiring boards alternately and positioning each printed wiring board by passing guide pins into the guide holes, l&Ji'J An upper mold and a lower mold that can sandwich the body from above and below in a sandwich shape and heat the laminated body, and these upper and lower molds are relatively close to each other and the upper and lower molds are At the abutting position, an airtight space is formed to confine the laminate therein, and an outer frame defines the height of the multilayer printed board, and the molten adhesive that has flowed out around the laminate in the airtight space is removed. A plunger capable of applying pressure is provided, the laminate is sandwiched between the two molds and the lower mold in a sandwich shape, and this is suppressed by applying pressure from the upper and lower mold sides, After vacuum suctioning the air in the space that will become the sealed space, the insulating adhesive is melted by heating from the upper and lower molds, and the molten adhesive is caused to flow around the laminate by applying pressure, and then further applied. After applying pressure to seal the molten adhesive in the sealed space formed by bringing the upper and lower molds into contact with the outer frame, pressurizing the molten adhesive to a predetermined pressure with the plunger, The pressure is maintained until the adhesive hardens.

More details are as follows.

The above purpose is to provide an upper mold and a lower mold that can heat and cool the laminate, and to crush the laminate by pressure load from the upper mold and lower mold sides. A multilayer structure that can seal the space between the mold and the mold to form a sealed space, and has an outer frame that can receive the load of the upper and lower molds by contacting the upper and lower molds. Using printed board molding equipment, the laminate is sandwiched between the upper and lower molds, and then the space between the upper and lower molds is vacuumed to insulate the laminate from the printed wiring board. Thoroughly vacuum the air in the tiny space between the adhesive and the adhesive. and heating the upper and lower molds to melt the insulating adhesive,
By applying pressure from the upper and lower mold sides, the molten adhesive is sufficiently filled into the space surrounded by the upper and lower molds and the outer frame, and the upper and lower molds and the outer frame come into contact. Pressure is continued until the thickness of the laminate stops changing, and when the thickness of the laminate stops changing, the molten adhesive is removed by plungers arranged so that the portions of the upper and lower molds that come into contact with the molten adhesive can be directly pressurized. The above object is achieved by raising the pressure of the molten adhesive to a predetermined level by increasing the pressure of the molten adhesive with the plunger while measuring the liquid pressure of the molten adhesive. This is also achieved by keeping the pressure constant.

[Function] Before heating the laminate, vacuum suction is applied to the printed wiring board of the laminate, the minute space between the insulating adhesive, and the top.
Remove the air in the space between the lower mold and the insulating adhesive.

As a result, air hardly remains in the laminate, and it is possible to suppress the occurrence of interlayer voids.

Finally, the insulating adhesive of the laminate is melted by heating from the upper mold and lower mold sides. At this time, since the upper mold and the lower mold press the VT layer body with a small pressure, the molten adhesive flows out toward the periphery of the upper and lower molds. Therefore, the thickness of the laminate decreases while changing within the plane. Due to the subsequent pressurization, the laminate is crushed, and the upper mold is lowered and comes into contact with the outer frame, forming a sealed space and sealing the molten adhesive inside the space. After this, the thickness of the single-layer structure does not decrease.

The molten adhesive is then pressurized by a plunger to increase the liquid pressure of the molten adhesive.

By applying this pressure, the liquid pressure of the molten adhesive can be made equal and high everywhere based on the well-known Pascal's principle. Due to this.

Even if there is residual air, it is crushed, and since the liquid pressure is the same everywhere in the stack, interlayer displacement can be significantly reduced. Moreover,
Even if the pressing force of the plunger is further increased, the plate thickness does not change during this period, so the plate thickness of the laminate remains constant within the plane and does not change.

Note that the liquid pressure of the molten adhesive can be made very large by the plunger, but since the actual molten adhesive is not an ideal liquid, the magnitude of the pressure is
This is somewhat different from the liquid pressure calculated from the plunger setting pressure force. Furthermore, it is not always easy to maintain the liquid pressure of the molten adhesive at a high pressure when a gap is created between the upper and lower molds and the outer frame due to damage to the sealing material. In consideration of such a case, the magnitude of the liquid pressure may be maintained at a predetermined pressure by adjusting the pressing force applied to the plunger while measuring the liquid pressure of the molten adhesive.

[Example] The present invention will be explained below by way of examples.

FIG. 1 relates to one embodiment of the present invention. FIG. 2-3 is a schematic front sectional view showing an example of a multilayer printed board forming apparatus used for carrying out the method for forming a multilayer printed board, showing the vicinity of the plunger in FIG. 1, and FIG. teeth,
FIG. 3 is a cross-sectional view of the main part showing a state in which the laminate is inserted between the upper and lower molds, and FIG. 3 is a cross-sectional view of the main part showing a state in which the molten adhesive is pressed by a plunger.

This multilayer printed board forming apparatus 17 includes an upper mold 11 that can sandwich the laminate 4 from above and below in a sandwich-like manner and heat the laminate 4. A lower mold 12 and these upper molds 11. The lower mold 12 is relatively close to the upper mold 119. An outer frame 23 that forms an airtight space V = that confines the laminate 4 therein at a position where it abuts the lower mold 12 and defines the height of the multilayer printed board, and the airtight space v,
J, which has a plunger 24 capable of pressurizing the molten adhesive 2' that has flowed out around the laminate 4.

This will be explained in detail below.

Upper mold 11. The lower mold 12 is the insulating adhesive 2 of the laminate 4.
(See Fig. 4) is configured to be able to be heated and cooled, and the pressurizing cylinder 13
The pressurizing force from the laminate 4 can be transmitted to the laminate 4. Furthermore, these upper molds 11. Guide holes 11a and 12a for inserting guide pins 3 of the laminate 4 for positioning and fixing the laminate 4 are formed in the lower mold 12, respectively. The pressurizing cylinder 13 is fixed to an upper bolster 14, so that the upper bolster 14 can support the reaction force.

The upper bolster 14 and the lower bolster 15 facing it are fixed together by four pillars 16. In order to prevent the heat generated by the heating of the upper mold 11 and the lower mold 12 from being transferred to the side opposite to the laminate, a heat insulating material 18 is provided at the upper part of the upper mold 11 and a heat insulating material 19 is provided at the lower part of the lower mold 12. Each is provided. Further, in order to transmit the pressurizing force of the pressurizing cylinder 13 to the stacked body side, a fixing plate 20 is fixed to the heat insulating material 18, and a fixing plate 21 is fixed to the heat insulating material 19, respectively.

Upper mold 11. In order to seal the space surrounded by the lower mold 12 and the laminate 4, a seal 22 is installed at a position that can surround the laminate 4. An outer frame 23 is installed outside the seal 22 in order to receive the pressurizing force from the pressurizing cylinder 13 when the upper mold 11 is lowered to a predetermined position. After the upper mold 11 comes into contact with the outer frame 23, the thickness of the laminate 4 does not change even if pressure is applied by the pressure cylinder 13.

The plunger 24 is integrated with a plunger pressurizing part 25, which is connected to the lower mold 12. Insulating material 19, fixed plate 21
The tip of the plunger 24 is located outside the laminate 4.

It is arranged so that it can protrude into the space inside the outer frame 23. Further, a seal 34 is fitted around the outer periphery of the plunger 24. With this configuration, the insulating adhesive 2 of the laminate 4 melts and the upper mold 11. Lower mold 1
2. Outer frame 23. After the space surrounded by the laminate 4 is filled and the upper mold 11 comes into contact with the outer frame 23, and the interval between the upper and lower molds does not change (at this time, the closed space VLL
The plunger 24 can press the molten adhesive 2' and maintain it at a high pressure.

Upper mold 11. In order to remove the air in the space surrounded by the lower mold 12 and the outer frame 23, the upper mold 11.
In the space between the lower molds 12, a vacuum suction frame 27 having vacuum seals 26, which are crushed by the relative approach of the upper mold 11° and the lower mold 12, mounted on the upper and lower sides, was installed. This vacuum suction frame 2
7 is connected to a vacuum pump 28 via a vacuum piping 33.

The liquid pressure of the molten adhesive 2' can be measured by a liquid pressure receiving element 29 screwed into the lower mold 12 with a threaded portion so as to face the closed space v. This measured value is sent to an amplification calculator 31 via a signal line 30. This amplification calculator 31 amplifies the pressure signal from the liquid pressure pressure receiving element 29, and compares it with a preset set pressure. If the measured value is low, the signal line 3
The liquid pressure of the molten adhesive 2' can be maintained at the set pressure by sending a rising signal to the plunger pressurizing section 25 via the pressure pump 2, and a reducing signal when the pressure is high.

A method for forming a multilayer printed board according to an embodiment of the present invention will be described using the multilayer printed board forming apparatus 17 configured as described above.

The laminate 4 was inserted between the upper mold 11 and the lower mold 12 (
(Fig. 2) After that, the upper mold 11. Lower mold 12 and vacuum seal 2
6, the upper mold 11 has already been suctioned by the vacuum pump 28 through the vacuum piping 33.
．． Air in the space surrounded by the lower mold 12 and the vacuum suction frame 27 is removed.

Thereby, the air in the minute space between the printed wiring board 1 and the insulating adhesive 2 of the laminate 4 can be removed.

After performing vacuum suction in this manner, the upper mold 11.
When the laminated body 4 is heated by the lower mold 12 and a low pressure is applied by the pressurizing cylinder 13.

The insulating adhesive 2 of the laminate 4 melts and flows out of the laminate 4, but this molten adhesive 2' is blocked by the sealing material 22 and fills the space surrounded by the outer frame 23.

The plunger 24 protrudes into this closed space Vj, pressing the molten adhesive 2' and increasing the liquid pressure (Fig. 3).
The liquid pressure is measured by the liquid pressure receiving element 29, and the pressure signal is sent to the amplification calculator 31. It is then compared with the set pressure, and if the measured value is lower than the set pressure,
The pressure is increased by the plunger pressurizing section 25, and when the pressure is low, the pressure is reduced and maintained at the set pressure. When the molten adhesive 2' is cured, the molding of the multilayer printed board is completed.

According to the embodiment described above, there are the following effects.

(2) Before melting the insulating adhesive 2, the air in the tiny space between the printed wiring board 1 and the insulating adhesive 2 is removed, so that air remains in the laminate 4. There are no interlayer voids.

◎ Since the outer frame 23 is provided to define the distance between the upper mold 11 and the lower mold 12 during molding, interlayer misalignment is reduced, and the thickness of the multilayer printed board is constant, making it possible to adjust the distance between each product. There will be no variation.

O. Since the plunger 24 is used to maintain the liquid pressure of the molten adhesive 2' at a high level, the distribution of liquid pressure within the laminate 4 becomes uniform, and interlayer deviation is significantly reduced. I can do it.

(2) Since the plunger 24 is actuated by feeding back the measured value by the liquid pressure receiving element 29, the fluid pressure of the molten adhesive 2' can always be maintained at the set pressure.

[Effects of the Invention] As explained in detail above, according to the present invention, it is possible to suppress the generation of interlayer voids that conventionally occurred during molding of multilayer printed circuit boards, and to reduce interlayer misalignment between printed wiring boards. This eliminates insulation defects around the through-holes of multilayer printed circuit boards, significantly improving connection reliability, and reducing void defects, which significantly improves manufacturing yields.Reducing misalignment between layers allows for higher precision. effective.

In short, this product has high reliability by preventing interlayer voids between printed wiring boards and reducing interlayer misalignment.

It is possible to provide a method for molding a multilayer printed board that can easily produce a highly accurate multilayer printed board at a high yield.

[Brief explanation of the drawing]

FIG. 1 relates to one embodiment of the present invention. FIG. 2-3 is a schematic front sectional view showing an example of a multilayer printed board forming apparatus used for carrying out the method for forming a multilayer printed board, showing the vicinity of the plunger in FIG. 1, and FIG. teeth,
A sectional view of the main part showing the state in which the laminate is inserted between the upper and lower molds, Fig. 3 is a sectional view of the main part showing the state in which the molten adhesive is pressed by the plunger, and Fig. 4 shows the printed wiring. FIG. 5, a perspective view showing an example of a laminate formed by alternately laminating plates and an insulating adhesive, is produced by a conventional method. FIG. 6 is a cross-sectional view of main parts showing an example of a molded state of a multilayer printed board.
When molding by the method shown in the figure. FIG. 3 is a pressure distribution diagram showing fluid pressure distribution of a molten adhesive. 1...Printed wiring board, 1a...Guide hole, 2...
- Insulating adhesive, 2'... Melt adhesive, 3... Guide pin. 4... Laminate, 11... Upper mold, 12... Lower mold, 17... Multilayer printed board molding device, 23... Outer frame, 24... Plunger, 28... vacuum pump, 29
...Liquid pressure receiving element, 31...Amplification computing unit, Vj
...closed space.

Claims (2)

[Claims] 1. A laminated body made by alternately stacking a plurality of printed wiring boards with guide holes drilled at predetermined positions and an insulating adhesive, and positioning each of the printed wiring boards by passing guide pins through the guide holes, In a method of forming a multilayer printed board by applying pressure and heating, the laminate is sandwiched from above and below, and an upper mold and a lower mold are capable of heating the laminate; an outer frame that defines a height of the multilayer printed board and forms a sealed space that confines the laminate therein at a position where the lower mold is relatively close to and abuts the upper and lower molds; A plunger capable of pressurizing the molten adhesive that has flowed out around the laminate in a closed space is provided, the laminate is sandwiched between the upper mold and the lower mold, and the laminate is sandwiched between the upper mold and the lower mold. , After pressing with pressure from the lower mold side and vacuum suctioning the air in the space including the space that will become the sealed space, the insulating adhesive is melted by heating from the upper and lower molds, and the insulating adhesive is pressurized. The molten adhesive was caused to flow around the laminate, and further pressure was applied to seal the molten adhesive into the sealed space formed by bringing the upper and lower molds into contact with the outer frame. Thereafter, the molten adhesive is pressed to a predetermined pressure by the plunger, and the pressure is maintained until the adhesive hardens. 2. The multilayer according to claim 1, characterized in that the pressing force of the plunger is set to a pressure that can maintain the pressure at a predetermined pressure while measuring the liquid pressure of the molten adhesive in the closed space. How to form printed boards.