JP3088050B2 - Multilayer circuit board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer circuit board suitable for mounting components in a surface mounting method.

[0002]

2. Description of the Related Art In recent years, electronic devices have been increasingly integrated with component parts, and accordingly, the method of mounting components on a multilayer circuit board used by being incorporated into electronic devices has been changed from an insertion system to a surface mounting system. And has transitioned. With the shift to the surface mounting method, there is an increasing demand for improved reliability of the multilayer circuit board. For example, through-hole reliability is required to be 100 cycles or more in a thermal shock test, and moisture migration resistance is required to be 1000 hours / 10 ⁸ Ω or more. The coefficient of linear expansion of the multilayer circuit board is 10p
pm / ° C. or less is required. This is for LSIs and resistors such as leadless chip carriers and flip chips,
Since components with low linear expansion coefficient, such as capacitors, are soldered directly to the surface of the multilayer circuit board, it is necessary to prevent the occurrence of cracks in the solder connection part due to mismatch of the linear expansion coefficient between these components and the multilayer circuit board. That's why. Conventionally manufactured multilayer circuit boards have a NE in which an insulating layer between a surface and an inner circuit layer is formed of a glass fiber woven fabric base epoxy resin.
It corresponds to the MA standard FR-4, and its configuration is as follows. (1) The glass fiber woven fabric has an E glass composition (SiO ₂ : 5).
4% by weight, Al ₂ O ₃ : 12% by weight, MgO: 1%, Ca
O: 23%, Na ₂ O: 1%, B ₂ O ₃ : 9%). (2) Epoxy resin uses dicyandiamide as a curing agent, and has a glass transition temperature of about 130 ° C. when viewed as a multilayer circuit board. (3) The resin content of the insulating layer is generally about 48% by weight. (4) In order to increase the connection area between the through-hole plating and the inner-layer circuit to enhance the reliability of the through-hole, the copper foil constituting the inner-layer circuit is usually 35 μm thick. The performance of these multilayer circuit boards equivalent to FR-4 is good for through-hole reliability, but the moisture migration resistance is 600 hours, the linear expansion coefficient is about 15 ppm / ° C., and the reliability at the time of surface mounting of components is high. Has left the problem. As for the moisture migration resistance, since the raw material of the epoxy resin commonly used is epichlorohydrin, etc., the extracted water conductivity measured by grinding the cured resin is large. Can not. There have been many attempts to reduce the linear expansion coefficient of a multilayer circuit board, but no industrially preferred one has been found. For example, a multilayer circuit board using a woven fabric such as quartz glass fiber, aramid fiber, graphite fiber, or carbon fiber having a small linear expansion coefficient as a base material has been proposed. However, those using quartz glass fiber are hard, very difficult to drill, and are expensive. In the case of using aramid fiber, when a hole is drilled, a fiber fluff remains on the inner wall of the hole, which hinders plating of a through hole and also causes a problem in moisture resistance. Those using graphite fibers cannot be used for a multilayer circuit board requiring insulation because the fibers themselves have conductivity.

[0003]

As described above, the conventional F
In a multilayer circuit board equivalent to R-4, there has not been found any one having a good balance of characteristics such as good moisture migration resistance and small linear expansion coefficient. The problem to be solved by the present invention is to provide a multilayer circuit board having a circuit on the surface and an inner layer and an insulating layer between circuit layers made of a glass fiber woven fabric base epoxy resin, while ensuring moisture migration resistance and line resistance. The object is to reduce the expansion coefficient and improve the reliability of surface mounting.

[0004]

In order to solve the above-mentioned problems, a multilayer circuit board according to the present invention has a circuit on a surface and an inner layer, and an insulating layer between circuit layers is made of a glass fiber woven fabric base epoxy resin. (1) The glass fiber woven fabric has a glass composition of SiO ₂ : 50 to 75% by weight, A
l ₂ O ₃ : 15 to 35% by weight, alkaline earth metal oxide:
5 to 15% by weight, alkali metal oxide: less than 3% by weight, (2) epoxy resin has a glass transition temperature of 140 ° C. or more as a multilayer circuit board using a phenol resin as a curing agent, and (3) insulating. The average resin content of the entire layer is 35
(4) The thickness of the copper foil forming the inner layer circuit is not more than 20 μm. The average resin content of the entire insulating layer is 35 to 45% by weight,
It is desirable to make the resin content of the insulating layer that bonds the inner layer circuit board and the surface circuit larger than the resin content of the insulating layer that forms the inner layer circuit board. When the inner circuit is composed of a plurality of inner circuit boards, it is desirable to increase the resin content of the insulating layer that bonds the inner circuit boards together.

[0005]

In general, the coefficient of linear expansion α of a multilayer circuit board is determined by the ratio of each component contained, based on the SCHEPARY empirical formula as shown in (Equation 1). By reducing the component having a large coefficient of linear expansion, the coefficient of linear expansion of the multilayer circuit board as a whole is reduced, and the multilayer circuit board according to the present invention uses a glass fiber woven fabric having a small coefficient of linear expansion for the base material and The linear expansion coefficient is reduced by reducing the content of the inner layer copper foil and the epoxy resin, which are components having a large expansion coefficient, and the reliability of other characteristics is secured.

[0006]

(Equation 1)

The glass fiber woven fabric used in the multilayer circuit board according to the present invention is basically disclosed in Japanese Patent Application Laid-Open No. Hei 3-112650, and has a linear expansion coefficient of the conventional FR.
-4: 3 ppm / ° C., which is about half that of the glass fiber woven fabric used for the multilayer circuit board, and there is no practical problem in drilling workability. In the glass component composition of the glass fiber woven fabric, when the SiO ₂ ratio does not reach 50% by weight, the coefficient of thermal expansion increases, and when it exceeds 75% by weight, not only does the furnace corrode greatly when spinning glass fibers, Abrasion of the drill during drilling increases, and the workability of the multilayer circuit board deteriorates. If the Al ₂ O ₃ ratio does not reach 15% by weight, the coefficient of thermal expansion increases, and if it exceeds 35% by weight, drill wear during drilling increases. If the proportion of the alkaline earth metal oxide does not reach 5% by weight, the corrosion of the furnace increases when spinning glass fibers, and the wear of the drill during drilling increases. When the ratio of the alkaline earth metal compound exceeds 15% by weight, the coefficient of thermal expansion increases. If the ratio of the alkali metal oxide is 3% by weight or more, the thermal expansion coefficient increases and the electrical characteristics during moisture absorption deteriorate. These facts are as disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 3-112650.

The copper foil constituting the circuit has a linear expansion coefficient of 17
Although it is as large as ppm / ° C., the content of the copper foil occupied particularly in the circuit of the inner layer is reduced, that is, the thickness of the copper foil is reduced to 20 μm or less. It has a big effect on making it smaller. If the thickness of the copper foil constituting the inner layer circuit is reduced, the connection area between the through-hole plating and the inner layer circuit is reduced,
There is a concern that the reliability of the through-hole may be reduced, but this problem is solved by setting the glass transition temperature of the resin to 140 ° C. or higher. When a drilling process for through-hole plating is performed, the drill blade and the inner wall of the multilayer circuit board are rubbed, and the inner wall of the hole becomes a temperature exceeding 130 ° C. The molten resin generated at that time adheres to the copper foil cross section of the inner layer circuit, and if through-hole plating is performed in such a state, the connection area between the through-hole plating and the inner layer circuit becomes smaller and the reliability of the through-hole decreases. You are worried. However, in the multilayer circuit board according to the present invention, since the resin has a glass transition temperature of 140 ° C. or higher when viewed as a multilayer circuit board, the resin melt generated at the time of drilling is significantly reduced to reduce the through-hole reliability. Is secured. Furthermore, since the glass transition temperature is high, the deformation of the multilayer circuit board in the thickness direction due to high-temperature thermal shock is reduced, and the through-hole reliability can be secured while using a thin copper foil for the inner layer circuit. It has become.

The thermal expansion coefficient is set at a target value of 10 ppm / ° C.
In order to make the content below, in addition to the above requirements, it is necessary to make the resin content of the insulating layer of the multilayer circuit board 45% by weight or less. If the resin content is reduced, there is a concern that the moisture migration resistance may be reduced, but this is addressed by curing the epoxy resin with a phenol resin. Migration is a phenomenon in which copper is ionized when a DC voltage is applied and dissolves and precipitates in a multilayer circuit board to cause insulation deterioration, but is affected by the resin content of the insulating layer and the ionic impurity content in the resin. . In particular, when the resin content of the insulating layer is limited as described above, the influence of the ionic impurity content becomes large. The present invention is based on a new finding that the extraction water conductivity of a cured resin, which is a measure of the content of ionic impurities in the resin, is smaller when a phenol resin is used as a curing agent. However, there is naturally a limit to reducing the content of the resin having a moisture-proof effect in the insulating layer. If the content is less than 35% by weight, the moisture migration resistance cannot be maintained even when a phenol resin is used as a curing agent. Although the average resin content of the entire insulating layer needs to be 35 to 45% by weight, the resin content of the insulating layer that bonds the inner layer circuit board and the surface circuit is determined by the resin content of the insulating layer forming the inner layer circuit board. When the content is increased, the irregularities on the surface of the inner layer circuit can be easily filled with the resin, and voids can be prevented from remaining in the inner layer.

As described above, the multilayer circuit board according to the present invention eliminates the factor that increases the coefficient of linear expansion, and also solves the problem of reduced through-hole reliability that may be caused by the factor. , Above (1)-
This can be achieved only when all the requirements of (4) are satisfied.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The epoxy resin used in the multilayer circuit board according to the present invention has a glass transition temperature of 140 ° C. or higher when viewed as a molded multilayer circuit board, and is preferably a resin having a low ionic impurity content. . Ordinary epibis epoxy resins, polyfunctional epoxy resins and the like are preferred. The phenolic resin used as the curing agent is various resol type phenolic resins and novolak type phenolic resins, preferably phenol novolak resins, bisphenol novolak resins and the like. The copper foil that constitutes the inner layer circuit is
As long as the thickness is 20 μm or less, there is no particular limitation on types such as an electrolytic foil and a rolled foil. Hereinafter, examples, reference examples, and conventional examples according to the present invention will be described in detail.

(Example 1) 54% by weight of SiO ₂ , Al ₂
0.1 m thick made of glass fiber composed of 30% by weight of O ₃ , 13% by weight of MgO, and 3% by weight of CaO.
A glass fiber woven fabric a having a thickness of 0.1 m and a glass fiber woven fabric b having a thickness of 0.18 mm were prepared. 200 g of brominated epibis epoxy resin (YDB-500EK80 manufactured by Toto Kasei) and epibis epoxy resin (Ep-1001EK manufactured by Yuka Shell)
75) 43 g, cresol novolak type epoxy resin (YDCN-704EK75 manufactured by Toto Kasei) 170 g,
Phenol novolak resin (TD-2 manufactured by Dainippon Ink and Chemicals, Inc.
090EK60) and 0.5 g of 2-ethyl 4-methylimidazole (catalyst) were uniformly dissolved to prepare Varnish A. Varnish A is impregnated into glass fiber woven fabric a and dried, and prepreg a having a resin content of 43% by weight (for bonding)
Was prepared. Further, the varnish A is impregnated into a glass fiber woven fabric b and dried, and a prepreg b having a resin content of 35% by weight is used.
(For inner layer circuit board) was prepared. Next, prepreg b is changed to 2
An electrolytic copper foil having a thickness of 18 μm is laminated on both sides of the laminated sheet, and laminated and molded by a heat medium oil press at a temperature of 200 ° C. and a pressure of 40 kg / cm ² for 90 minutes to obtain a copper-clad laminate having a thickness of 0.4 mm. Was. After the copper foil of the copper-clad laminate is etched and blackened by a predetermined method to form an inner circuit board, two prepregs a and two 18 μm-thick electrolytic copper foils are further laminated on both surfaces of the copper foil. Laminating and forming were performed at a temperature of 200 ° C. and a pressure of 40 kg / cm ² for 60 minutes by a medium oil press to obtain a multilayer circuit board having a thickness of 0.9 mm.

Example 2 200 g of a brominated epibis epoxy resin (YDB-500EK80 manufactured by Toto Kasei)
Epibis epoxy resin (Ep-100 made by Yuka Shell)
1EK75) 43 g, cresol novola type epoxy resin (YDCN-704EK75 manufactured by Toto Kasei) 170
g, bisphenol novolak resin (Yukaka Shell Y
LH-129EK60) and 0.4 g of 2-ethyl 4-methylimidazole (catalyst) were uniformly dissolved to prepare Varnish B. Using varnish B, a multilayer circuit board having a thickness of 0.9 mm was obtained in the same process as in Example 1.

Example 3 A multilayer circuit board having a thickness of 0.9 mm was prepared in the same manner as in Example 1 except that an electrolytic copper foil having a thickness of 9 μm was used as the copper foil of the inner layer circuit board.

Reference Example 1 The same process as in Example 1 was carried out except that the resin content of the prepreg b for the inner layer circuit board was 30% by weight, and the resin content of the prepreg a for bonding was 3%.
A multilayer circuit board having a thickness of 0.9 mm was set at 6% by weight.

Reference Example 2 200 g of a brominated epibis epoxy resin (YDB-500EK80 manufactured by Toto Kasei)
Epibis epoxy resin (Ep-100 made by Yuka Shell)
1EK75) 128 g, cresol novolak type epoxy resin (YDCN-704EK75 manufactured by Toto Kasei) 85
g, dicyandiamide 9g dissolved in methyl glycol 100g, 2-ethyl 4-methylimidazole (catalyst)
0.6 g was uniformly dissolved to prepare Varnish C. Varnish C
To obtain a multilayer circuit board having a thickness of 0.9 mm in the same process as in Example 1.

Reference Example 3 The same process as in Example 1 was carried out except that the resin content of the prepreg b for the inner layer circuit board was 45% by weight, and the resin content of the prepreg a for bonding was 5%.
A multilayer circuit board having a thickness of 0.9 mm was set at 0% by weight.

REFERENCE EXAMPLE 4 A multilayer circuit board having a thickness of 0.9 mm was prepared in the same manner as in Example 1, except that an electrolytic copper foil having a thickness of 35 μm was used as the copper foil for the inner layer circuit board.

Reference Example 5 E Glass Composition Thickness 0.1 mm
Was prepared. This was impregnated with varnish A and dried to prepare a prepreg having a resin content of 35% by weight (for an inner layer circuit board) and a prepreg having a resin content of 43% by weight (for bonding). Hereinafter, a multilayer circuit board having a thickness of 0.9 mm was obtained in the same steps as in Example 1.

(Conventional Example 1) E glass composition thickness 0.1 mm
Was prepared. This was impregnated with varnish C and dried to prepare a prepreg having a resin content of 45% by weight (for an inner circuit board) and a prepreg having a resin content of 50% by weight (for bonding). Hereinafter, the same steps as in Example 1 were performed, except that the copper foil for the inner layer circuit board was a multilayer circuit board having a thickness of 0.9 mm using an electrolytic copper foil having a thickness of 35 μm.

(Example 4) The resin content of prepreg a in Example 1 was 40% by weight, and the resin content of prepreg b was 30% by weight. Of a multilayer circuit board.

(Example 5) The resin content of prepreg a in Example 1 was set to 50% by weight and the resin content of prepreg b was set to 40% by weight. Of a multilayer circuit board.

(Example 6) With the same resin content of the prepregs a and b in Example 1 as 38% by weight, a multilayer circuit board having a thickness of 0.9 mm was obtained in the same process as in Example 1.

Example 7 200 g of a brominated epibis epoxy resin (YDB-500EK80 manufactured by Toto Kasei)
Epibis epoxy resin (Ep-100 made by Yuka Shell)
1EK75) 128 g, cresol novola type epoxy resin (YDCN-704EK75 manufactured by Toto Kasei) 85
g, bisphenol novolak resin (Yukaka Shell Y
80 g of LH-129EK60) and 0.4 g of 2-ethyl 4-methylimidazole (catalyst) were uniformly dissolved to prepare Varnish D.
Was prepared. Using varnish D, a multilayer circuit board having a thickness of 0.9 mm was obtained in the same steps as in Example 1 below.

Tables 1 and 2 show the characteristics of the multilayer circuit boards in Examples 1 to 7, Reference Examples 1 to 5, and Conventional Example 1. In the table, each characteristic was evaluated as follows. (1) Tg temperature (glass transition temperature): The inflection point of the coefficient of linear expansion in the thickness direction of the multilayer circuit board is measured by the TMA method. (2) Moisture migration resistance: The pattern of FIG. (Through hole hole diameter 0.3m
m, hole wall spacing 0.3mm, through-hole plating thickness 25μ
m), measuring the time until the insulation resistance becomes 10 ⁸ Ω or less while continuously applying a voltage of 50 V DC in an atmosphere of 85 ° C./85% RH. (3) Linear expansion coefficient: linear expansion in the vertical direction of the multilayer circuit board The coefficient is measured in the range of 30 to 80 ° C. (4) Through-hole reliability: 260 ° C for 5 seconds to 20 ° C for 500 continuous through-holes (hole diameter 1.0 mm, through-hole plating thickness 25 µm) Cycle until thermal conduction is repeated by applying thermal shock repeatedly for 20 seconds (5) Drill wear rate: UC-35 with a drill diameter of 1.0 mmφ
(Union Tool Co., Ltd.) was used to stack three multilayer circuit boards and measure the wear rate of the drill bit after drilling 5,000 hits. (6) Extracted water conductivity: about 200 mesh of multilayer circuit board 2 g of the pulverized water is submerged in 20 g of pure water in a container made of a fluororesin, and the container is sealed and subjected to a pressure cooker treatment at 121 ° C. for 168 hours. The measurement was performed by measuring the conductivity. (7) Number of voids: A copper-clad laminate having 125 copper-etched portions removed by 1 cm square was provided as an inner circuit board for convenience, and was not completely filled with resin after being formed into a multilayer circuit board. Count locations

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

As is clear from Table 1, the multilayer circuit board according to the present invention has a small thermal expansion in the surface direction, good moisture migration resistance, and excellent connection reliability during surface mounting. Things. While the resin content of the entire insulating layer of the multilayer circuit board is in the range of 35 to 45% by weight, the insulating layer (the inner circuit board) for bonding the inner circuit and the surface circuit is determined based on the resin content of the insulating layer of the inner circuit board. If the resin content is increased, the insulating layer is also included when bonding them together.
It is excellent in that voids in the inner layer are reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an inner layer circuit pattern of a multilayer circuit board for evaluating the resistance to moisture migration.

Continuation of the front page (56) References JP-A-3-112650 (JP, A) JP-A-63-232490 (JP, A) JP-A-63-108797 (JP, A) JP-A-60-257591 (JP , A) JP-A-4-329695 (JP, A)

Claims (3)

(57) [Claims] 1. A multilayer circuit board having a circuit on a surface and an inner layer and an insulating layer between circuit layers made of a glass fiber woven fabric base epoxy resin, wherein: (1) the glass fiber woven fabric has a glass composition SiO ₂ :
50-75 wt%, Al ₂ O _3: 15 to 35 wt%, the alkaline earth metal oxide: 5 to 15 wt%, alkali metal oxides: less than 3 wt%, (2) an epoxy resin, phenol The glass transition temperature of the multilayer circuit board using the resin as a curing agent is 140 ° C. or higher. (3) The average resin content of the entire insulating layer is 35 to
(4) A multilayer circuit board, wherein the thickness of the copper foil constituting the inner layer circuit is 20 μm or less. 2. The multi-layer circuit board according to claim 1, wherein the resin content of the insulating layer that bonds the inner circuit board to the surface circuit is larger than the resin content of the insulating layer forming the inner circuit board. 3. The multilayer according to claim 1, wherein the resin content of the insulating layer that bonds the inner circuit boards to each other and the circuit of the surface and the inner layer circuit board is larger than the resin content of the insulating layer constituting the inner circuit board. Circuit board.