JPH0360095A - Manufacture of multilayer printed circuit board - Google Patents

Abstract

PURPOSE:To omit through hole forming, patterning process after multilayers are formed, and to eliminate troubles such as smear malfunction, oxidation of inner layer conductors by forming a conductive part at arbitrary opposed positions on the conductors of a printed circuit board, superposing the opposed parts, heating while pressurizing, or heating and ultrasonically vibrating to adhere them, and filling adhesive liquid between the opposed faces by vacuum immersing. CONSTITUTION:Through holes 15, 19, and copper foil layers 13, 14, 17, 18 of patterns required for both both-side printed circuit boards 12, 16 are formed thereon. The boards are held by upper and lower flat stainless steel plates by opposing the bumps, and heated while pressurizing. Then, opposed solder bumps 20 are fusion-adhered while being collapsed by the pressurizing, and the boards 12, 16 are adhered by solder bump fusion-adhering 21. Then, the boards are placed in a vacuum vessel 22, the vessel is evacuated completely, a resin supply port 24 is opened whole holding a vacuum state, and adhesive resin liquid 25 is filled in the vessel 22 until the boards are dipped. Then, when the vessel 22 is returned to the atmospheric pressure, the liquid 25 is filled in the gap of the bump connecting faces and the holes 15.

Description

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

(Prior Art) FIGS. 2(a), 2(b), and 2(c) show cross-sectional views of a method for manufacturing a four-layer printed wiring board as an example of a conventional multilayer printed wiring board.

In the figure, 1 is the upper single-sided printed wiring board, 2 is the copper foil layer on the upper single-sided printed wiring board 1, 3 is the lower single-sided printed wiring board, 4 is the copper foil layer on the lower single-sided printed wiring board 3, and 5 is the copper foil layer on the lower single-sided printed wiring board 3.
is an internal double-sided printed wiring board, 6 is an upper pattern on the internal double-sided printed wiring board 5, 7 is a lower pattern on the internal double-sided printed wiring board 5, 8 is an interlayer adhesive sheet, 9 is an interlayer adhesive layer, and 10 is the bottom of the through hole. Hole 11 indicates a through hole for interlayer conduction 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, generally using 70tim to ensure through-hole reliability.
Like a normal double-sided printed wiring board, the required double-sided patterns are formed. Single-sided printed wiring boards 1 and 3 are stacked on top and bottom of this double-sided printed wiring board 5 with an interlayer adhesive sheet 8 called prepreg in between. At this stage, the copper foil layers 2 and 4 of the single-sided printed wiring boards 1 and 3 are not patterned. Further, the thickness of the copper foil layer 2.4 is not limited by manufacturing restrictions, and a commonly used thickness of 18 to 35 μm is sufficient. After applying pressure to the top and bottom of the stacked items,
Sandwiched between stainless steel plates (not shown) that can withstand heating, for example, 170°C and 30 kg for epoxy resin.
f 7cm2.Cure by applying pressure and heating for 90 minutes to form interlayer adhesion. Thereafter, as shown in FIG. 2(b), a pilot hole 10 for a through hole is made for interlayer conductive connection. After drilling the holes, as shown in FIG. 2(C), copper is deposited by plating in the same way as for ordinary double-sided printed wiring boards to obtain conduction between the eyebrows and to complete the through-holes 11 for interlayer connection.

Furthermore, the upper and lower steel foil layers 2 and 4 are then patterned,
The printed wiring board is completed.

(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 the eyebrows. However, in the conventional method, after performing interlayer adhesion for multilayering, through-holes are formed to establish a conductive connection between the eyebrows. As a result, treatments such as plating liquid seep into the inner layer, which has the adverse effect of accelerating deterioration of the inner layer conductor. Furthermore, there are drawbacks such as an air layer remaining between the layers and peeling between the layers due to expansion of the air layer during heating in a post-process. The present invention provides a method to overcome these drawbacks.

(Means for Solving the Problems) In the present invention, conductive portions are formed at arbitrary opposing locations on the conductor of a printed wiring board, the opposing surfaces are overlapped, and heated while pressurizing, or heated and ultrasonic vibration. The adhesive liquid is filled between the opposing surfaces by vacuum impregnation.

(Example) FIGS. 1(a) to 1(d) show cross-sectional views of an example 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, 15 is a through hole for electrically connecting the double-sided patterns on the double-sided printed wiring board 12, 16 is a double-sided printed wiring board; 17.
18 is a patterned copper foil layer on the double-sided printed wiring board 16, 19 is a through hole for electrically connecting the double-sided patterns on the double-sided printed wiring board, 20 is a solder bump, 21 is a solder bump fusion, and 22 is a vacuum. 23 is an exhaust port, 24 is a resin supply port, and 25 is an adhesive resin liquid.

In FIG. 1(a), a double-sided printed wiring board 12.1
6 is a normal double-sided printed circuit board on which necessary through holes 15.degree. 19 and double-sided patterned copper foils N13 and 14.17.degree. 18 are formed.

There are no restrictions on the thickness of the copper foil layers 13, 14, 17, and 18 of the double-sided pattern, and the commonly used thickness of 18 to 35 μm is sufficient. Solder bumps 20 are formed at four connection points on the copper foil layer 14.17 on the opposing side of the double-sided printed wiring board 12.16 by, for example, printing cream solder or solder reflow. General eutectic solder is used for the solder.

The thus obtained substrate is placed with the bumps facing each other as shown in FIG. 1(a), the top and bottom are sandwiched between flat stainless steel plates (not shown), etc., and heated while being pressurized. The conditions require a temperature of 2200°C which exceeds the solder melting point. Next, as shown in FIG. 1(b), the solder bumps 20 facing each other at this time
The solder bumps are fused while being crushed due to pressure, and a solder bump fusion 21 is obtained. In this state, the facing double-sided printed wiring boards 12 and 16 are bonded together by solder bump fusion 21.

Next, vacuum impregnation is performed. FIG. 1(c) shows this situation, in which the substrate is placed in the vacuum container 22 and the resin supply port 2
4, open the exhaust port 23, and perform exhaustion using a vacuum pump (not shown). After the evacuation is completed, the resin supply port 24 is opened and the vacuum container 2 is opened while maintaining the vacuum state, as shown in FIG. 1(d).
2 is filled with adhesive resin liquid 25 until the substrate is immersed.

After that, when the inside of the vacuum container 22 is returned to atmospheric pressure, the adhesive resin 1
The skin 25 is filled. The gap between the bump connection surfaces depends on the thickness of the copper foil on the printed wiring board and the height of the bump, but it is several tens of thousands.
Since the thickness is approximately 100 μm, even if the substrate is taken out from the adhesive resin liquid 25, the adhesive resin in the gap remains filled.

Also, the inside of the through hole 15 is also covered with adhesive resin liquid 2 due to surface tension.
It is filled with 5. Therefore, after filling, the substrate is taken out, unnecessary portions of the adhesive resin liquid 25 are wiped, and the adhesive resin liquid 25 is cured to complete interlayer adhesion.

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. That is, by forming solder bumps on opposing surfaces and fusing the solder bumps for all layers or for each opposing surface, a multilayered board can be created, as shown in Figures 1(c) and 1(d) below.
It can be obtained by performing the following steps. It is also possible to impregnate and harden the adhesive resin on each opposing surface. On this occasion,
It is also effective to use tape or other methods to prevent the resin from getting wet where necessary.

Although the above example shows an example in which solder bumps are fused by heating, it is also possible to fuse the solder bumps at a low heating temperature by simultaneously applying ultrasonic waves. It is also clear that the same problem occurs even if conductive paste or the like is used for the solder bumps.

Furthermore, regarding vacuum impregnation, an adhesive resin is placed in a vacuum container from the beginning in order to also defoam the resin, and the vacuum container is held at a position where the substrate is not impregnated with the adhesive resin before being evacuated. After evacuation, a similar resin impregnation can be obtained by immersing the substrate in an adhesive resin in a vacuum state, and then returning the inside of the vacuum container to atmospheric pressure. Alternatively, it is clear that vacuum impregnation can be performed by placing an adhesive resin in a vacuum container, immersing the substrate, and then evacuating the container in this state.

(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 between the multilayer PCCs during standby, a structure is obtained in which there is no risk of peeling off due to expansion of internal air bubbles due to heating in the post-process of the completed multilayer board, or of progression of unbonded parts. That is, a highly reliable multilayer board can be obtained.

[Brief explanation of drawings]

FIGS. 1(a) to (d) are cross-sectional views showing one embodiment of the manufacturing process of a four-layer multilayer board according to the present invention, and FIGS. 2(a) to (c)
1 is a sectional view showing an example of a manufacturing process of a four-layer multilayer board according to the prior art. 1.3... Single-sided printed wiring board, 2.4.6°7.
...Copper foil layer, 5...Double-sided printed wiring board, 8...
Interlayer adhesive sheet, 9... Interlayer adhesive layer, 10... Through hole prepared hole, 11... Interlayer, connection through hole,
12.16...Double-sided printed wiring board, 13,14.
'17.18...Copper foil layer, 15.19...Through hole, 2o...Solder bump, 21 ・Solder bump fusion, 22...Vacuum container, 23...Exhaust port, 24...
-Resin supply port, 25...Adhesive resin liquid.

Claims (1)

[Claims] In multilayer boards made by stacking multiple printed wiring boards,
forming solder bumps at arbitrary opposing locations on the conductors of the plurality of printed wiring boards, overlapping the solder bumps,
means for joining the plurality of printed wiring boards by applying heating or heating and ultrasonic vibration while applying pressure from above and below the plurality of printed wiring boards to fuse the solder bumps; and a plurality of printed wiring boards that are joined together. A method for manufacturing a multilayer printed wiring board, characterized in that adhesive liquid is filled between the boards by vacuum impregnation.