JPH02177498A - Multilayer printed wiring board - Google Patents

Abstract

PURPOSE:To improve reliability of soldered part of an electronic component and to prevent voids from remaining in an inner layer circuit by forming a glass nonwoven fabric layer immersed with thermosetting resin between the insulating layer of an inner layer plate and the inner layer plate, and between the inner layer plate and an insulating layer in contact with the circuit on the surface, and forming the insulating layer in contact with the circuit of the surface of a glass woven fabric layer immersed with the thermosetting resin. CONSTITUTION:An inner layer insulating layer 1 is formed of a glass nonwoven fabric layer immersed with thermosetting resin. A surface insulating layer 2 in contact with the circuit of the surface is formed of a glass woven layer immersed with thermosetting resin. An interlayer insulating layer 3 in contact between the inner layer plates and between the inner layer plate and the circuit of the surface is formed of a glass nonwoven fabric layer immersed with thermosetting resin. Since the glass nonwoven fabric is softer than the glass woven fabric, particularly the distortion of the hole position due to the bending of a drilling is prevented. The rigidity of a multilayer printed wiring board is reduced, and the reliability of soldered junction part in a cold cycle is improved. The uneven part of the inner layer circuit face is easily buried with resin in the glass nonwoven fabric to prevent voids from remaining.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to multilayer printed wiring boards having circuits in both the inner and surface layers.

Conventional technology In recent years, printed wiring boards used in electronic devices such as personal computers and microcontrollers have replaced single-sided and double-sided printed wiring boards with multilayer printed wiring boards from the viewpoints of higher density, smaller size, higher reliability, and radio wave shielding. progress is being made in the direction of using .

Conventionally, in multilayer printed wiring boards, the insulating layer of the inner layer circuit is made of epoxy resin-impregnated glass fabric. Further, the insulating layer of the outer layer circuit is also generally made of epoxy resin-impregnated glass fabric.

This multilayer printed wiring board is manufactured, for example, as follows. First, a circuit is formed by etching the copper foil of an epoxy resin laminate with a double-sided copper-clad glass woven base material to form a circuit board for the inner layer (inner layer board).

Then, a copper foil is layered on the inner layer plate with an epoxy resin-impregnated glass woven prepreg interposed therebetween, and this is heated and press-molded to be integrated. The copper foil on the surface becomes the outer layer circuit by etching.

The conventional multilayer printed wiring board described above has the following problems.

(1) Drilling (through-hole holes) in the circuit board manufacturing process is usually performed by stacking three to four multilayer printed wiring boards and using an NC drill. Conventionally, multiple layers of woven glass fabric are used, which makes it easy for the drill hole to become misaligned, and the friction of the drill blade is high.

When the drill bit rubs, the walls of the hole formed become rough.
There is a problem that the conduction reliability of the through holes is reduced.

Furthermore, in order to avoid misalignment of the drill holes, it is necessary to reduce the number of stacked multilayer printed wiring boards, but this increases costs.

(2) Since it is composed only of epoxy resin-impregnated glass woven material, the wiring board has high rigidity. For this reason, stress tends to concentrate on the solder joints of mounted electronic components (radial and axial components) when thermal cycles are applied, resulting in the early appearance of solder cracks.

In addition, in the mass production process, it is necessary to cut out a large number of workpieces, and after the processing is completed, the workpieces are bent along pre-formed grooves and cut into individual sizes. However, as mentioned above, since the rigidity is large, there is a problem in this separation ability.

(3) When impregnating a glass woven fabric with an epoxy resin, it is quite difficult to increase the amount of resin deposited to more than 50% by weight, and the amount is generally in the range of 35 to 50% by weight. When there are multiple layers of circuits in the inner layer and the inner layer plates are integrated under heat and pressure via an epoxy resin-impregnated glass fabric, voids remain between the inner layer plates. This is because complicated unevenness is formed between the inner layers due to the thickness of the opposing circuits, and the small amount of resin impregnated into the glass woven fabric cannot sufficiently fill in these unevenness.

In order to fill in the irregularities so that no voids remain, a special process such as vacuum forming is required.

Problems to be Solved by the Invention In view of the above points, an object of the present invention is to provide a multilayer printed wiring board that has excellent drilling workability and can also improve the reliability of solder joints of mounted electronic components. . A further object of the present invention is to provide a multilayer printed wiring board in which no voids remain in the inner layer circuit.

Means for Solving the Problems A multilayer printed wiring board according to the present invention for achieving the above object is characterized by having the following configurations (a) to (c) (see FIG. 1).

(a) The insulation layer of the inner layer board (inner layer insulation layer 1) is coated with thermosetting resin. The glass layer is impregnated with a synthetic resin.

(b) The insulating layer (surface insulating layer 2) in contact with the circuit on the surface,
A glass woven fabric layer impregnated with a thermosetting resin.

(c) The insulating layer (interlayer insulating layer 3) between the inner plates and in contact with the inner plate and the circuit on the surface is a glass nonwoven fabric layer impregnated with a thermosetting resin.

In addition, 4 is an inner layer circuit, and the inner layer board is made by integrating the inner layer circuit 4 into the inner layer insulating layer 1. 5 is a metal foil serving as a circuit on the surface.

Function The present invention can improve drilling workability by making the inner insulating layer mainly composed of a glass nonwoven fabric impregnated with a thermosetting resin. This is because the glass nonwoven fabric is softer than the glass woven fabric, and can prevent hole position shift due to drill bending, especially when drilling holes.

In addition, by using a glass nonwoven fabric for the inner insulating layer, the rigidity of the multilayer printed wiring board is reduced (4.7 to 5
101Gdyne/cm-+ 3~4.5 X I Q
dyne/ctA), the reliability of solder joints during thermal cycles is improved.

Furthermore, the amount of resin attached to the glass nonwoven fabric can be increased to 60 to 90% by weight. Therefore, unevenness on the inner layer circuit surface can be easily filled with the resin in the glass nonwoven fabric.
It is possible to prevent voids from remaining.

Example In carrying out the present invention, the density of the glass nonwoven fabric was 0.
A range of 0.08 to 0.15 g/m is preferred. If the density is low, the volume content of the glass fibers will be low, so when a prepreg is produced by impregnating a glass nonwoven fabric with a resin in the manufacturing process, there is an inconvenience that the surface of the prepreg will become fluffy. In addition, if the density is high, the impregnating property of the resin will decrease, and when the prepreg is produced, the degree of resin adhesion to the surface will increase (superposition), and the glass nonwoven fabric will easily break during molding. In addition, electrical insulation properties tend to deteriorate quickly.

Although a glass nonwoven fabric is used in the multilayer printed wiring board according to the present invention, dimensional changes are somewhat large (especially after heating).

When it is necessary to particularly suppress dimensional changes, it is advisable to use a glass nonwoven fabric constituting the insulating layer of the inner layer plate. In this case, by making the vertical and horizontal directions of the glass woven fabric used for the inner layer board orthogonal to the vertical and horizontal directions of the glass woven fabric in the insulating layer in contact with the surface circuit, the vertical and horizontal differences in dimensional changes of the multilayer printed wiring board can be reduced. Can be done.

Example 1 A 4197-glass nonwoven fabric (density 0.1 g/i) was impregnated with bisphenol type epoxy resin and dried, and the resin adhesion amount was 8.
5% by weight epoxy-glass nonwoven prepreg (A)
prepared. Separately, add the above epoxy resin to 2052/-
An epoxy glass woven fabric prepreg (B) having a resin adhesion of 40% by weight was prepared by impregnating and drying the epoxy-glass woven fabric.

Four plies of prepreg (A) were stacked one on top of the other, copper foil with a thickness of 70 μm was placed on both sides, and hot and pressure molded to obtain a double-sided copper-clad laminate with a thickness of 0.8 m and 1 m.

The copper foil of the double-sided copper-clad laminate was etched by a conventional method to form a predetermined circuit, and the surface of the circuit was subjected to a blackening treatment to obtain an inner layer board.

1. Placing one prepreg (A) and one prepreg (Bl) on both sides of the inner layer board, overlapping 35μ thick copper foil on both sides, and molding them under heat and pressure to form an inner layer circuit. A double-sided copper clad board with a thickness of 5 m/m was manufactured.

Drill holes were drilled in the double-sided copper clad plate according to a predetermined pattern, and through-hole plating was performed on the hole walls by a conventional method to conduct the inner layer circuit and the surface circuit to be formed next. Next, a circuit was formed by etching a predetermined pattern on the copper foil on the surface using a conventional method to obtain a four-layer multilayer printed wiring board with a thickness of 1.5 m/m.

The characteristics of this product are shown in Table 1.

Example 2 3 plies of the prepreg (A) produced in Example 1 were stacked, and 1 prepreg FB+ was placed between the 1st fly and the 2nd ply.
A ply was inserted, copper foils with a thickness of 70 μm were placed on both sides, and molded under heat and pressure to obtain a double-sided copper-clad laminate with a thickness of 0.8 m and 1 m.

The double-sided copper-clad laminate was processed in the same manner as in Example 1 to form an inner layer (the structure of the inner layer is shown in FIG. 2. The inner insulating layer 1 was a combination of a glass woven fabric 6 and a glass nonwoven fabric 7). )
. Furthermore, a four-layer multilayer printed wiring board having a thickness of 1.5 m/m was obtained using the same process as in Example 1.

The characteristics of this product are shown in Table 1.

Example 3 One ply of prepreg (Bl) was placed on both sides of the two plies of prepreg (A) produced in Example 1, and 7 plies of prepreg (Bl) were placed on both sides.
Copper foil with a thickness of 0μ is arranged and molded under heat and pressure to form a sheet of 08 m/m.
A thick double-sided copper-clad laminate was obtained.

The double-sided copper-clad laminate was processed in the same manner as in Example 1 to form an inner layer board (the structure of the inner layer board is shown in FIG. 3).

Furthermore, in the same process as in Example 1, four layers of 1.5 m/m thick were prepared, except that the longitudinal and lateral directions of the glass woven fabric of the inner insulating layer were the same as the longitudinal and lateral directions of the glass woven fabric of the surface insulating layer. A multilayer printed wiring board was obtained.

The characteristics of this product are shown in Table 1.

Example 4 The structure was as in Example 3, except that the longitudinal and lateral directions of the glass woven fabric of the inner insulating layer were perpendicular to the longitudinal and lateral directions of the glass woven fabric of the surface insulating layer. A multilayer printed wiring board was obtained.

The characteristics of this product are shown in Table 1.

Comparative Example 1 Two plies of prepreg + A) were placed on each side of the inner layer board produced in Example 1, and 35μ thick copper foil was placed on both sides, and this was heated and pressure-molded to form a 1-layer board with an inner layer circuit. .6f
A double-sided copper clad board with a thickness of ff/m was manufactured.

This was processed in the same manner as in Example 1, and the result was 1.6 m/Wl.
A multilayer printed wiring board with a thickness of 4 layers was obtained.

The characteristics of this product are shown in Table 1.

Comparative Example 2 Two plies of prepreg (H) were placed on each side of the inner layer board produced in Example 1, and 35μ thick copper foil was placed on both sides, and this was heated and press-molded to have an inner layer circuit. 1.5
A double-sided copper clad board with a thickness of m/m was manufactured.

This was processed in the same manner as in Example 1, and 1.6 m/yn
A multilayer printed wiring board with a thickness of 4 layers was obtained.

The characteristics of this product are shown in Table 1.

Comparative Example 3 4 plies of the prepreg (B) produced in Example 1 were stacked,
Place 70μ thick copper foil on both sides and heat and press mold.
Q: A double-sided copper-clad laminate with a thickness of 3 m/m was obtained.

The copper foil of the double-sided copper-clad laminate was etched by a conventional method to form a predetermined circuit, and the surface of the circuit was subjected to a blackening treatment to obtain an inner layer board.

Two plies of prepreg (Bl) are placed on each side of the inner layer board, and 35μ thick copper foil is further layered on both sides, and this is heated and pressure molded to form a 5 m/m thick double-sided sheet with an inner layer circuit. Manufactured copper clad plates.

Drill holes were drilled in the double-sided copper clad plate according to a predetermined pattern, and through-hole plating was performed on the hole walls by a conventional method to conduct the inner layer circuit and the surface circuit to be formed next. Then,
A circuit was formed by etching a predetermined pattern on the copper foil on the surface using a conventional method to obtain a four-layer multilayer printed wiring board with a thickness of 1.6 ml and 1 m.

The characteristics of this product are shown in Table 1.

*1. Drill: l, Q tax p, 6000 r
3 layers of pmx5Qμ/rev0 multilayer printed wiring boards, 0
．． Sandwich it between a 11-thick A/board and a 1.6U-thick waste board and drill holes.

*Drill holes in 2 or 3 sheets and show the value after 1500 hits. (Measure the blade width direction) *3. The drill is 0.4 ws p, 6000 rpm x 5
0μ/rev0 measurement is based on positional accuracy (
Xmax −Xmin), n = 3 Q.

*4. Microscopic measurement of n=30 on the side of the inner layer 70μ foil circuit.

*5. After soldering the capacitor, heat at -30℃ (0.5Hr).
)j Repeat the cooling and heating cycle at 80℃ (0.5Hr),
Number of times until micro cracks occur in the solder joint.

*6. The dimensional change rate after completion of the leveler, based on the hole drilling after multilayer press molding, was found to be large only in the part made of glass woven fabric with regard to the wall roughness of the drill hole. Comparative example 1 composed only of glass nonwoven fabric
In this case, soldering reliability is poor due to large dimensional changes.

Here, we have taken a four-layer board as an example, but if the inner layer circuit has three or more layers (it has two or more inner layers, and a layer of thermosetting resin-impregnated glass nonwoven fabric is arranged between the inner layers) ) also had the same effect as the example in preventing the generation of voids in the inner layer circuit section. In addition, substantially the same effects as those of the above embodiments were obtained regarding other characteristics.

Effects of the Invention As described above, in the present invention, the inner insulating layer is mainly composed of glass non-woven fabric, and the interlayer insulating layer is made of glass non-woven fabric. Because the roughness is small, through-hole plating can be applied uniformly, which helps improve the reliability of multilayer printed wiring boards. It has the advantage of excellent positional accuracy for drilling holes, and is easy to accommodate small-diameter through holes, and it is also possible to increase the number of stacked multilayer printed wiring boards when drilling holes. Furthermore, since a glass nonwoven fabric is used for the interlayer insulation layer and the inner insulation layer, the rigidity of the multilayer printed wiring board is reduced and the reliability of the solder joints during cooling and heating cycles is improved.

In addition, glass non-woven fabric is used for the interlayer insulating layer and a large amount of resin is attached to it, making it possible to mold multi-layered circuit boards without leaving voids around the inner layer circuits, even on inner layer circuit boards with thick copper foil circuits. It is something that we have.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of a multilayer printed wiring board according to the present invention, and FIGS. 2 and 3 are sectional views showing other configurations of the inner layer board in the same embodiment. 1 is an inner insulating layer, 2 is a surface insulating layer 3 is an interlayer insulating layer, 4 is an inner layer circuit, 5 is a metal foil, 6 is a glass woven fabric, 7 is a glass nonwoven fabric

Claims (4)

[Claims] 1. A multilayer printed wiring board having circuits on an inner layer and a surface, the multilayer printed wiring board having the following configurations (a) to (c). (a) The insulating layer of the inner plate (inner insulating layer) is a glass nonwoven fabric layer impregnated with a thermosetting resin. (b) The insulating layer (board surface insulating layer) in contact with the circuit on the surface is a glass woven fabric layer impregnated with a thermosetting resin. (c) A glass nonwoven fabric layer impregnated with a thermosetting resin is used between the inner plates and between the inner plate and the insulating layer in contact with the circuit on the surface (interlayer insulating layer). 2. 2. The multilayer printed wiring board according to claim 1, wherein the insulating layer of the inner board (inner insulating layer) is a combination of a glass woven fabric and a glass nonwoven fabric, and the center layer of the insulating layer is a glass woven fabric. 3. 2. The multilayer printed wiring board according to claim 1, wherein the insulating layer of the inner board (inner insulating layer) is a combination of glass woven fabric and glass nonwoven fabric, and the surface layer of the insulating layer is glass woven fabric. 4. Claim 2: The longitudinal and lateral directions of the glass woven fabric in the insulating layer (inner insulating layer) of the inner board are orthogonal to the longitudinal and lateral directions of the glass woven fabric in the insulating layer (surface insulating layer) in contact with the circuit on the surface.
Or the multilayer printed wiring board according to 3. 5 The density of the glass nonwoven fabric before being impregnated with the thermosetting resin is 0.
The multilayer printed wiring board according to any one of claims 1 to 4, wherein the multilayer printed wiring board has a thickness of 0.08 to 0.15 g/cm.