JPH053387A - Multilayer printed wiring board for surface mounting - Google Patents

Abstract

PURPOSE:To elevate the reliability of a solder connection part by preventing the solder connection part of a composite type of multilayer printed wiring board surface mounted from cracking. CONSTITUTION:In an object wherein the insulating layer a of an outer layer circuit is made glass woven fabric impregnated with epoxy resin and an insulating layer b, which constitutes an inner layer circuit board, and an adhesive layer between the inner layer circuit board and the insulating layer are made glass unwoven fabric impregnated with epoxy resin, a layer of butyral denatured phenol resin is made in contact with the outer layer circuit inside of this. This layer becomes the shape of rubber at high temperature, and it prevents the solder connection part from cracking caused by stress by absorbing said stress based on the difference of thermal expansion coefficient between the parts mounted on the surface and the insulating layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to surface mount components (Sur
The present invention relates to a multilayer printed wiring board for mounting a face mount device (SMD).

[0002]

2. Description of the Related Art A multilayer printed wiring board on which an SMD such as a ceramic chip is mounted has an SMD coefficient of thermal expansion of 6.5 ×.
Since it is as small as 10 to ⁶ / ° C., the insulating layer of the wiring board is also required to have a small coefficient of thermal expansion in the planar direction. Conventionally used is a glass woven fabric as a base material, which is impregnated with an epoxy resin to form an insulating layer (FR-4), and has a thermal expansion coefficient in the plane direction of (10 to 15). ) × 1
It is 0 to ⁶ / ° C. Further, as a base material for the insulating layer, a composite type multilayer printed wiring board in which a glass woven cloth and a glass nonwoven cloth are combined is proposed as a material having improved drilling properties. A reflow soldering method using cream solder is mainly used for mounting the SMD.

[0003]

In the technique using the glass woven cloth as the base material of the insulating layer, the difference in thermal expansion coefficient between the SMD and the substrate is relatively small. It's not that big, and it's currently supported. However, in a composite type multilayer printed wiring board, the thermal expansion coefficient of the insulating layer in the plane direction is 20 × 10 to ⁶
Since it is as large as / ° C, the difference in expansion and contraction also becomes large,
Large stress acts on the solder connection portion of the SMD, and cracks are likely to occur at the solder connection portion. The problem to be solved by the present invention is to prevent cracks from being generated in a solder connection portion of a composite type multilayer printed wiring board mounted with an SMD by thermal shock, and to enhance reliability of the solder connection portion.

[0004]

In a surface mounting multilayer printed wiring board according to the present invention which solves the above problems, a thermosetting resin impregnated glass woven cloth is used as an insulating layer (a) of an outer layer circuit, and an inner layer circuit board is formed. A thermosetting resin-impregnated glass nonwoven fabric is used as the constituent insulating layer (b) and the adhesive layer between the inner layer circuit board and the insulating layer (a), butyral-modified phenolic resin inside the outer layer circuit and in contact therewith. Is formed. Also, in the case where the number of layers of the circuit exceeds four layers, the thermosetting resin-impregnated glass nonwoven fabric is also used as the adhesive layer between the inner layer circuit boards, in the same manner as described above, inside the outer layer circuit. It is characterized in that a layer of butyral-modified phenolic resin is formed in contact therewith.

[0005]

The above-mentioned butyral-modified phenol resin layer has 1 layer.
The elastic modulus at 00 ° C. is 0.4 Kgf / mm ² , which is considered to be almost rubbery. Therefore, even if the use environment becomes high and the difference in thermal expansion between the substrate and the mounted SMD becomes large, the layer of butyral-modified phenolic resin in the rubber state is deformed, and the heat It is possible to absorb the stress due to the difference in expansion and avoid applying stress to the solder connection portion.

[0006]

EXAMPLES Example 10. Fourteen prepregs obtained by impregnating and drying a 10.18 mm thick glass non-woven fabric with brominated bisphenol A type epoxy resin were placed, and 35 μm copper foil was placed on both sides thereof, and the temperature was 165 ° C. Then, a copper-clad laminate having a thickness of 0.8 mm was manufactured by heat and pressure molding at a pressure of 40 Kgf / cm ² for 50 minutes. A power source ground pattern was printed on the laminated board to perform circuit processing by etching to obtain an inner layer circuit board. The circuit surface was subjected to a blackening treatment in consideration of the adhesiveness in a later process. Separately, a prepreg was prepared by impregnating and drying a 0.18 mm-thick glass woven fabric with a brominated bisphenol A type epoxy resin. One piece of glass nonwoven fabric prepreg was laminated on both sides of the inner layer circuit board, and one piece of the above-mentioned separately prepared glass woven fabric prepreg was laminated on both sides thereof, and the outermost layer was coated with butyral-modified phenolic resin to a thickness of 25 μm. 18
A copper foil having a thickness of μ was arranged and integrated by heat and pressure molding.
The molding conditions are the same as in the case of molding a copper-clad laminate for an inner layer circuit board.

Then, the multilayer printed wiring board was processed in the following steps. After the through hole processing at a predetermined position, an outer layer circuit was formed by etching, and a solder leveler processing was performed as a final finish. In the component soldering process, first, cream solder was applied to the reflow surface, a ceramic resistor was mounted, and soldering was performed in a far infrared hot air oven. Next, a ceramic resistor was fixed to the flow surface with an adhesive and soldered with jet solder.

After observing the initial surface condition of the solder connection portion, a vapor phase cooling / heating cycle test of -40 ° C./30 minutes and 125 ° C./30 minutes was performed to observe the crack generation state of the solder connection portion. The results are shown in Table 2 together with other characteristics.
For reference, the elastic moduli of the insulating layer and the butyral-modified phenolic resin layer are shown. The butyral-modified phenolic resin layer has an elastic modulus of about 1/500 that of the substrate even at 30 ° C.

The butyral-modified phenolic resin layer is
Instead of applying it on the adhesive surface of copper foil, use a sheet of butyral modified phenolic resin, or apply butyral modified phenolic resin on the surface of the glass woven prepreg that will be the insulating layer of the outer layer circuit. You may.

[0010]

[Table 1]

Conventional Example 1 In Example 1, a butyral-modified phenolic resin was not applied to the outermost copper foil, and the other steps were the same as in Example 1 to obtain a multilayer printed wiring board. The characteristics are shown in Table 2.

Conventional Example 2 A multi-layered printed wiring board was obtained through the same steps as in Conventional Example 1 except that the base material forming the insulating layer was made of glass woven cloth. The characteristics are shown in Table 2.

In Table 2, the through hole reliability is 20
C. Silicon oil (immersion for 20 seconds) and 260.degree. C. oil (immersion for 10 seconds) were repeatedly immersed, and the cycle until the increase of conduction resistance occurred was examined. Solder heat resistance is
It was carried out by dipping in a solder bath at 260 ° C.

[0014]

[Table 2]

[0015]

As is clear from Table 2, in the composite type multilayer printed wiring board according to the present invention, the stress due to the difference in thermal expansion between the insulating layer and the surface mount component is absorbed by the butyral-modified phenol resin layer. As a result, it is possible to prevent a crack due to the stress from being generated in the solder connection portion. And other characteristics are also equivalent to the conventional FR-4 multilayer printed wiring board. Also, the butyral modified phenolic resin layer smoothes the insulating layer of the outer layer circuit,
It is possible to improve the accuracy by etching the outer layer circuit. Although the present invention relates to a composite type multilayer printed wiring board, the same technique can be applied to an FR-4 multilayer printed wiring board using a glass woven cloth for all the base materials of the insulating layer. For example, the reliability of the solder connection portion against thermal expansion becomes higher.

Claims (2)

[Claims] 1. A multilayer printed wiring board having circuits in an inner layer and an outer layer, wherein an insulating layer (a) of the outer layer circuit is a thermosetting resin-impregnated glass woven cloth, and an insulating layer (b) constituting the inner layer circuit board, In addition, the adhesive layer between the inner layer circuit board and the insulating layer (a) is a thermosetting resin-impregnated glass non-woven fabric, and a butyral-modified phenolic resin layer is formed inside the outer layer circuit in contact therewith to form a multi-layer surface mount print. Wiring board. 2. A multilayer printed wiring board having a circuit in an inner layer and an outer layer, wherein an insulating layer (a) of the outer layer circuit is a thermosetting resin impregnated glass woven cloth, and an insulating layer (b) constituting the inner layer circuit board, The adhesive layer between the inner layer circuit board and the insulating layer (a) and the adhesive layer between the inner layer circuit boards are thermosetting resin-impregnated glass nonwoven fabrics, and a butyral-modified phenolic resin layer is provided inside the outer layer circuit in contact therewith. The formed multi-layer printed wiring board for surface mounting.