JPH0360097A - Manufacture of multilayer printed circuit board - Google Patents

Abstract

PURPOSE:To omit through hole forming, patterning after multilayers are formed, and to eliminate smear malfuncion, oxidation of inner layer conductors by superposing solder bumps formed on opposed printed circuit boards, heating while pressurizing, or heating and ultrasonically vibrating in adhesive resin liquid to fusion-adhere the bumps, and curing the adhesive resin. CONSTITUTION:Double-sided printed circuit boards 12, 16 have through holes 15, 19, and patterned copper foil layers 13, 14, 17, 18 on both sides. Solder bumps 20 for electrical connection are formed on the layers 14, 17 of the opposed faces of the boards 12, 16. The boards are dipped in adhesive resin liquids 23 in a vessel 22, the bumps 20 are opposed, superposed, pressed, and removed as they are. In this case, the liquid 23 in the gap between the boards 12, 16 remains filled, and the liquid 23 is filled in the holes 15, 19 by surface tension. The superposed boards removed in this manner are held by upper and lower flat stainless steel plates, and heated while pressurizing. Then, opposed solder bumps 20 are fusion-adhered by processing and heating to form solder bump fusion-adhered part 21, the adhesive resin liquid 23 is cured to form an adhesive layer 24.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a multilayer printed wiring board relating to interlayer conductor connection and interlayer adhesion.

(Conventional technology) Whistle circle I! 1←1° shows a cross-sectional view of a method for manufacturing a four-layer printed wiring board.

In the figure, 1 is an upper single-sided printed wiring board, 2 is a copper foil layer on the upper single-sided printed wiring board 1, 3 is a lower single-sided printed wiring board, 4 is a copper foil layer on the lower single-sided printed wiring board 3,
5 is an internal double-sided printed wiring board, 6 is a patterned copper foil layer on the internal double-sided printed wiring board 5, 7 is a patterned copper foil layer on the internal double-sided printed wiring board 5, 8 is an interlayer adhesive sheet, and 9 is a patterned copper foil layer on the internal double-sided printed wiring board 5. In the interlayer adhesive layer, 10 indicates a pilot hole for a through hole, and 11 indicates a through hole for interlayer conductive connection.

Figure 2(a) is a cross-sectional view showing the configuration before bonding.
The internal double-sided printed wiring board 5 has a copper foil layer with a thickness of 6°7 to ensure through-hole reliability, generally using a thickness of 70 μm.
It has the necessary double-sided patterns formed in the same way as a normal double-sided printed wiring board. This double-sided printed wiring board 5
A single-sided printed wiring board 1.3 is stacked on top and bottom of the board with an interlayer adhesive sheet 8 called prepreg in between. At this stage, the thickness of the copper layer 2.4 is not limited by manufacturing, and the generally used copper thickness of 18 to 35 μm is sufficient. It is. The top and bottom of the stacked materials are sandwiched between flat plates made of stainless steel (not shown) that can withstand later pressure and heat. For example, in the case of epoxy resin, it is hardened by pressure and heat at 170°C and 30 kgf/am2.90 minutes. and perform interlayer adhesion. Thereafter, as shown in FIG. 2(b), a pilot hole 10 for a through hole is drilled for interlayer conductive connection. After drilling, as shown in FIG. 2(C), copper is deposited by plating to obtain conduction between the layers and complete the interlayer bonding through hole 11, as shown in FIG. 2(C). Further, the upper and lower copper foil layers 2.4 are then patterned to form a printed wiring board.

(Problems to be Solved by the Invention) Conventionally, in multilayer printed wiring boards, a method using through holes has been used as a method for obtaining conductor connections between layers. In the conventional method, a through-hole type is used to make a conductive connection between the eyebrows with inter-layer adhesion in multilayers, so there are problems with smearing defects in through-hole processing, or wet processing associated with plating and buttering processing, which prevents the inner layer from forming. Processing liquids such as denting liquid seep in, which has the adverse effect of accelerating deterioration of the inner layer conductor. Furthermore, there is a drawback that an air layer remains between the eyebrows and peeling occurs between the eyebrows due to expansion of the air layer during heating in a post-process. The present invention provides a method to overcome these drawbacks.

(Description of Structure and Effects of the Invention) FIG. 1 shows a cross-sectional view of an embodiment of a four-layer printed wiring board according to the present invention. In the figure, 12 is a double-sided printed wiring board, 13.14 is a patterned copper foil layer on the double-sided printed wiring board 12, and 15 is a double-sided printed wiring board 1.
16 is a double-sided printed wiring board, 17.18 is a patterned copper foil layer on the double-sided printed wiring board 16, and 19 is a double-sided printed wiring board 16. A through hole for electrically connecting the pattern, 20 a solder bump, 21 a solder bump fusion part, 22 a container, and 23 an adhesive layer If? ? !
, 24 indicates an adhesive layer, 25 indicates a resin protruding from a gap, and 26 indicates a resin protruding from a through hole.

In FIG. 1(a), a double-sided printed wiring board 12.1
6 are both necessary through holes 15° 19 and double-sided patterned copper foil layer 13. It is a normal double-sided printed circuit board with 14.17°18.

The copper foil layers 13, 14, 17, and 18 of the double-sided pattern are sufficient to have a thickness of 18 to 35 μm, which is commonly used.

Solder bumps 20 are placed at conductive connection points on the steel foil layer 14.17 on the opposite side of this double-sided printed wiring board 12.16.
For example, it is formed by cream solder printing or solder reflow. General eutectic solder is used for the solder.

The substrate obtained in this way is crushed in the adhesive resin liquid 23 in the container 22 as shown in FIG. 1(b), and the adhesive resin is removed. night 23
Inside, stack the solder bumps 20 facing each other and press them together.
Take it out of the adhesive resin liquid 23 as it is. At this time, the double-sided printed wiring board 12. on the side where the solder bumps 20 are facing each other. IAF-”!m-J-IFJ+10 pieces 2r
fxlA 17) Although it is related to the thickness of the blank 20, it is about several tens to 100 μm, so the adhesive resin 'e23 in this gap remains filled. Furthermore, the adhesive resin liquid 23 in the through holes 15 and 19 remains filled due to surface tension. If you are using a wiring board with large holes, use tape, etc. on the side opposite to the solder bumps.
There is a way to highlight it. The top and bottom of the stacked substrates taken out in this way are sandwiched between flat stainless steel plates, etc., and heated while applying pressure to fuse the facing solder bumps 20 together. Thereafter, the temperature required for curing the adhesive resin liquid is applied to complete interlayer adhesion. FIG. 1(C) shows this situation, in which the opposing solder bumps 20 are fused by processing and heating to form a solder bump fused portion 21. Further, the adhesive resin liquid 23 is cured to form an adhesive layer 24, and at the same time, the opposing solder bump 2
Since the gap between the two line boards becomes smaller when the two line boards are fused, a gap-protruding resin 25 and a through-hole protruding resin 26 are formed. Each protruding resin is removed by polishing, cutting, etc.

Since heating is generally performed using an epoxy adhesive resin, a two-stage heating step is advantageous. That is, it is necessary to provide a temperature higher than the solder melting point in the first stage, and a temperature and a holding time for resin curing conditions in the second stage. In this case, if the temperature of the second stage is lower than the first stage and below the melting point of the solder bump, the pressure may be removed. Further, when the solder bumps are fused together, it is possible to fuse them even at a temperature below the solder melting point by using ultrasonic vibration.

Although the above example is an example in which two printed wiring boards are pasted together, the same thing is possible when three or more boards are pasted together. In other words, the formation of solder bumps on the opposing surfaces is completed, and the solder bumps are fused, and the adhesive resin liquid is filled and cured for each layer, or by repeating the above steps for each opposing surface to create a multilayer structure. I can do it. Furthermore, if there is a possibility that air bubbles may remain inside, it is effective to remove air bubbles when the substrate is in the adhesive resin liquid.

(Effects of the invention) Since a multilayer board can be obtained through the above process, there is no through-hole processing or buttering after multilayering, which is seen in conventional multilayer boards, and there is no need for wet smearing or plating, which is a problem with through-holes. This solves problems after multilayering, such as adverse effects such as oxidation of the inner layer conductor due to seepage into the inner layer during processing. Furthermore, since air is not taken in when the multilayer PCC is indirectly dark, a structure can be obtained in which there is no risk of peeling off due to the expansion of internal bubbles due to heating in the post-process of the completed multilayer board, or of the progress of unbonded parts. That is, a highly reliable multilayer board can be obtained.

[Brief explanation of drawings]

FIGS. 1(a) to (c) are cross-sectional views showing one embodiment of the manufacturing process of a multilayer printed circuit board according to the present invention, and FIGS. 2(a) to (c)
C) is a sectional view showing an example of the manufacturing process of a multilayer printed circuit board according to the prior art. 1... Upper single-sided printed wiring board, 2.4, 6°7.
...Copper foil layer, 3...Lower single-sided printed wiring board, 5.
・Internal double-sided printed wiring board, 8... interlayer adhesive sheet, 9... interlayer adhesive layer, 10... through hole pilot hole, 11... through hole for interlayer conduction connection, ], 2.1
．． 6...Double-sided printed wiring board, 13,14.17.
18...Copper foil layer, 15.19...Through hole, 2
0...Solder bump, 21...Solder bump fusion part, 2
2. Container, 23. Adhesive resin liquid, 24 Adhesive layer, 25 Resin protruding from the gap, 26 Seal sealing protruding from the through hole.

Claims (1)

[Claims] In a multilayer board in which a plurality of printed wiring boards are stacked, solder bumps are formed at arbitrary opposing locations on the conductors of both opposing printed wiring boards, the solder bumps are stacked, and pressure is applied in an adhesive resin liquid. A method for manufacturing a multilayer printed wiring board, characterized in that a multilayer printed wiring board is obtained by applying heating or heating and ultrasonic vibration to fuse and connect the solder bumps and harden the adhesive resin.