JPH0664090A - Copper-plated laminated plate and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve reliability of connecting a component to be connected to a printed circuit board with low thermal expansion coefficient of the board and to process the board by providing a ceramic flame sprayed layer between a copper foil and an aramid fiber nonwoven fabric prepreg layer. CONSTITUTION:Ceramics are flame sprayed to one side surface of a copper foil 1 to form a ceramic layer 2. A prepreg 3 having aramid fiber nonwoven fabric as a base material is so laminated as to be brought into contact with the layer 2, thermally press-molded and integrated. Here, the layer 2 contains cordierite as a base, and is formed by flame spraying the ceramic to one side surface of the foil by plasma flame spraying or gas flame spraying. As resin to be impregnated in the fiber, epoxy resin, melamine resin, etc., are used, and the melamine resin is desirable at a view point of its adhesive properties and electric characteristics.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copper clad laminate used for printed wiring boards and a method for manufacturing the same.

[0002]

2. Description of the Related Art Recently, with downsizing and higher density of electronic equipment, components mounted on a printed wiring board have been changed from a conventional insertion type to an imposition type. Therefore, the surface mounting method is becoming the mainstream as the mounting method on the printed wiring board. Therefore, various requirements are becoming severe for copper clad laminates used as printed wiring boards.

That is, when a component such as a chip is surface-mounted on a printed wiring board, matching of thermal expansion coefficients becomes a problem from the viewpoint of connection reliability. For example, a thin mounting type TSOP (Thin type) has been widely used recently.
Small Outline Package) has a thermal expansion coefficient of approximately 5 x 10
^-6 / ° C. However, the coefficient of thermal expansion of a fiber-reinforced plastic substrate such as a glass cloth-based epoxy resin copper-clad laminate that is widely used as a printed wiring board is about 15 to 17 × 10 ⁻⁶ / ° C. Very expensive compared to that of the parts that are. Therefore, when a component with a low coefficient of thermal expansion is surface-mounted on a printed wiring board with a high coefficient of thermal expansion, a large difference in coefficient of thermal expansion causes cracks in the solder at its connection when the temperature changes. It is not easy to secure practical connection reliability. In order to improve the connection reliability with the chip component, a substrate having an expansion coefficient closer to that of the mounted component, that is, a low thermal expansion coefficient is required.

[0004]

As a substrate material having a low coefficient of thermal expansion, a ceramic substrate such as alumina or aluminum nitride, which is different from the above organic substrate, or a low thermal expansion metal such as Invar or 42 alloy is used as a core. Previously used metal core substrates have been utilized. However, looking at these, because the ceramic substrate is very hard, it cannot be machined like drilling and cutting like the organic substrate,
A large substrate cannot be used, it is heavier than an organic substrate, which is disadvantageous in weight reduction, it is easy to crack due to poor toughness and handling is difficult, or the process of circuit processing and multilayering is complicated and costly. There is a drawback of. Therefore, it has been desired to develop a conventional organic substrate having excellent workability and a low thermal expansion coefficient.

As an organic substrate having a low thermal expansion, a substrate using a low thermal expansion base material such as quartz fiber or aramid fiber has been studied. However, quartz fiber has poor machinability and is expensive. Further, aramid fiber has poor machinability like quartz fiber, has low adhesiveness with resin, and easily absorbs moisture, so that there is a problem that insulation properties and dimensional stability during moisture absorption are deteriorated. Further, although the in-plane coefficient of thermal expansion is low, the coefficient of thermal expansion in the thickness direction is higher than that of a conventional laminated plate of glass fiber base material, and there is a drawback that the through hole connection reliability is poor.

Recently, in order to improve the machinability of aramid fibers, non-woven fabrics of aramid fibers have begun to be used instead of the cloth of aramid fibers. The machinability is improved as compared with cloth, but the problems of adhesiveness with resin and deterioration of characteristics when absorbing moisture cannot be solved. In addition, the resin content is higher than that of cloth, and a sufficiently expensive thermal expansion substrate cannot be obtained. When this is used for a multi-layer board, the thermal expansion of the substrate is further increased due to the effect of the copper foil with a high coefficient of thermal expansion (coefficient of thermal expansion of about 17 × 10 ^-6 / ° C) that forms the inner ground layer. The coefficient becomes high. This is because the elastic modulus of the aramid fiber reinforced epoxy resin is lower than that of the glass fiber reinforced epoxy resin, and is greatly affected by the copper foil. Moreover, when a non-woven fabric is used instead of the cloth, the elastic coefficient is further lowered, and the presence of the copper foil makes the thermal expansion coefficient of the substrate higher than that when the cloth is used. From such a thing,
These fiber substrates have not been widely used.

On the other hand, the present inventors have considered that such a requirement can be met by compounding a ceramic and an organic substrate, and as shown in JP-A-62-152742, a copper foil is used. We have developed a substrate with a ceramic sprayed layer between it and an organic substrate such as glass cloth epoxy resin. Due to the presence of the ceramic layer with a low coefficient of thermal expansion, this board has a lower coefficient of thermal expansion in-plane than organic boards such as conventional glass cloth-based epoxy resin laminates, and reliability of connection with the mounted components. It is effective in improving sex. However, recently, the progress of thinning and densification of parts has made it more likely that the coefficient of thermal expansion of parts becomes lower. Therefore, the demand for low thermal expansion of the substrate is becoming more severe. Therefore, there is an increasing demand for lower thermal expansion of the above substrates. In response to such requirements, even if the ceramic layer formed by thermal spraying as described above and a laminated plate such as a conventional glass cloth base material epoxy resin are combined, the thermal expansion coefficient of the conventional glass cloth base material epoxy resin is It has been found that due to its high temperature, the coefficient of thermal expansion of the entire substrate is limited by the presence of the ceramic layer.

The present invention solves the above problems and enables the same handling as a conventional copper clad laminate based on an organic substrate, and has a sufficiently low coefficient of thermal expansion, and when components are surface-mounted. A substrate having excellent connection reliability is provided.

[0009]

Means for Solving the Problems That is, the present invention provides a ceramic sprayed layer between a copper foil and a prepreg layer having an aramid fiber non-woven fabric as a base material. A ceramic layer is formed by thermally spraying a ceramic on the prepreg, and a prepreg having an aramid fiber nonwoven fabric as a base material is laminated so as to be in contact with the ceramic layer and thermocompression-molded.

The ceramic layer is formed by spraying a ceramic on one surface of a copper foil by plasma spraying or gas spraying. As the ceramic to be sprayed, an electrically insulating ceramic such as alumina, titania, zirconia, magnesia, mullite, spinel, zircon, cordierite, steatite, forsterite, and aluminum titanate can be used. Low cordierite is preferable from the viewpoint of low thermal expansion of the substrate. In addition, cordierite has a relatively low hardness among ceramics, and if it is used, there is a feature that machinability such as drilling workability of a substrate is not significantly impaired. The thickness of the ceramic formed by thermal spraying does not limit the scope of the present invention, but is preferably in the range of 10 to 300 μm. If the thickness of the sprayed ceramic is less than 10 μm, the effect of lowering the thermal expansion of the substrate is not sufficient, and the effect of improving the connection reliability with the mounted parts is reduced.
This is because if it is thicker than μm, the machinability such as drilling workability is deteriorated.

The use of a non-woven fabric of aramid fiber as the fiber of the prepreg means that the thermal expansion coefficient of aramid fiber shows a negative value of about −5 × 10 ⁻⁶ / ° C. and glass fiber (about 5
This is because the coefficient of thermal expansion is extremely lower than that of (10 × 10 ⁻⁶ / ° C.). By using the aramid fiber, the coefficient of thermal expansion of the substrate can be further lowered as compared with the case of using the conventional glass fiber. It should be noted that the reason why a non-woven fabric is used for the aramid fiber instead of the cloth is in consideration of machinability. That is, the cloth of aramid fiber has extremely poor machinability, and it is difficult to perform drilling, shear cutting, punching, etc., which are performed at the time of ordinary printed wiring board processing. In comparison, the use of non-woven fabrics significantly improves their machinability.

As the resin to be impregnated into the aramid fiber nonwoven fabric, thermosetting resins such as epoxy resin, melamine resin, polyimide resin, phenol resin, vinyl ester resin, silicone resin, melamine resin, unsaturated polyester resin, polysulfone and polyether. Thermoplastic resins such as imide, polyether ether ketone, and polyphenylene oxide can be used. Among them, epoxy resin is most suitable from the viewpoint of adhesiveness with aramid fiber and other electrical characteristics.

By adding an inorganic filler to the resin of the prepreg, the resin content of the aramid non-woven fabric base resin can be easily lowered and the elastic modulus can be increased. Therefore, particularly when a multi-layer board is used, it is less likely to be affected by the copper foil, and the coefficient of thermal expansion can be further lowered. Fillers added to the resin include silica, alumina, cordierite, mullite, zircon, spinel,
A powdery substance such as titania, steatite, forsterite, zirconia, calcia, calcium carbonate, aluminum hydroxide, or a fibrous substance such as glass fiber powder or whiskers such as silicon carbide or potassium titanate can be used. The addition amount is preferably 20% by weight or more with respect to the resin. This is because if it is less than 20% by weight, the effects of lowering the thermal expansion of the substrate and increasing the elastic coefficient are not sufficiently exhibited.

[0014]

The ceramic layer formed on the copper foil by thermal spraying is firmly fixed and integrated with the resin of the prepreg during thermocompression molding with the prepreg. The in-plane thermal expansion coefficient of the substrate obtained by combining the ceramic layer, the organic substrate, and the copper foil thus obtained can be calculated from the following formula according to the compounding rule, and the measured values are almost the same. . α: Coefficient of thermal expansion of composite α _CE : Coefficient of thermal expansion of ceramic layer α _M : Coefficient of thermal expansion of organic substrate α _CO : Coefficient of thermal expansion of copper foil E _CE : Elastic coefficient of ceramic layer E _M : Organic substrate modulus of elasticity E _CO: elastic modulus of the copper foil V _CE: volume fraction of the ceramic layer V _M: the volume fraction of the organic substrate V _CO: as is clear from the volume fraction above formula of the copper foil, an organic substrate Since the coefficient of thermal expansion of the ceramic layer is lower than that of, the coefficient of thermal expansion of the substrate in which these are combined is lower than that of the organic substrate. Further, from the above equation, it is effective to lower the coefficient of thermal expansion of the organic substrate in order to further lower the coefficient of thermal expansion of the substrate.

To lower the coefficient of thermal expansion of the organic substrate,
Among the constituents, it is most effective to lower the coefficient of thermal expansion of the fiber base material. That is, the overall thermal expansion coefficient can be further reduced by using the aramid fiber having a thermal expansion coefficient lower than that of the commonly used glass fiber. Further, the substrate thus obtained is porous because the ceramic layer is formed by thermal spraying, and is therefore more excellent in machinability than the sintered body. Furthermore, since the aramid fiber also uses a non-woven fabric instead of a cloth, the life of the tool is slightly inferior, but a printed wiring board can be processed in the same manner as a conventional glass cloth base material epoxy resin laminated board.

Further, as is clear from the above equation, the elastic coefficients of the respective constituents also greatly affect the coefficient of thermal expansion of the substrate. That is, to reduce the coefficient of thermal expansion of the entire substrate,
It is advantageous that the component having a low thermal expansion coefficient has a high elastic coefficient, and the component having a high thermal expansion coefficient has a low elastic coefficient. However, the copper foil has a high coefficient of thermal expansion and an elastic modulus of about 11,000 Kgf / mm ² , which is much higher than that of the substrate. Therefore, if there is a ground layer having a high residual copper rate in a multilayer board or the like, the influence of the copper foil becomes strong, and the thermal expansion coefficient of the board becomes high. This tendency is more remarkable as the elastic modulus of the substrate is lower. However, since the elastic modulus of the laminated board using the aramid fiber is lower than that of the laminated board using the glass fiber, the influence of the copper foil becomes large, and the effect of using the aramid fiber having a low thermal expansion becomes small. Further, when a non-woven fabric is used, the elastic modulus of the substrate is further lowered. Therefore, when a multilayer board is produced from a laminated board using an aramid nonwoven fabric, the expected low coefficient of thermal expansion cannot be obtained due to the presence of the copper foil.

In comparison, the combination with the ceramic sprayed layer according to the present invention can remedy this drawback.
That is, when the ceramic layer and the resin layer having the aramid fiber nonwoven fabric as the base material are combined, the elastic modulus of the substrate becomes higher than that without the ceramic layer because the ceramic has a high elastic modulus. Therefore, it is less likely to be affected by the copper foil, and even when a multilayer board is used, an increase in the coefficient of thermal expansion due to the copper foil can be suppressed, and the effect of the aramid fiber nonwoven fabric can be sufficiently exhibited. Further, by adding an inorganic filler to the resin of the prepreg, the elastic coefficient of the substrate can be further increased, and the thermal expansion coefficient can be further lowered.

By the way, in addition to machinability, the aramid fiber has a drawback that it easily absorbs moisture, and the insulating property is deteriorated during moisture absorption, or the dimensions are largely changed by moisture absorption.
This is another reason why the aramid fiber is not widely used even though the mechanical processing has been improved by the development of the nonwoven fabric. However, this problem can be solved by combining with a ceramic layer formed by thermal spraying as in the present invention. That is, the surface of the layer having the aramid fiber nonwoven fabric as a base material is covered with the ceramic layer by being combined with the ceramic. The ceramic layer formed by thermal spraying has 10 to 20% by volume of pores. However, the pores are sealed when the resin in the prepreg is reduced in viscosity and impregnated during press molding with the prepreg. Therefore, this ceramic layer is less likely to absorb moisture than a general glass cloth-based epoxy resin layer. As described above, the resin layer having the aramid fiber nonwoven fabric as a base material is covered with the ceramic layer having a low moisture absorption, and thus becomes difficult to absorb moisture. Therefore,
The disadvantage of aramid fiber, which is easy to absorb moisture, is also improved by compounding with a ceramic. Further, when the aramid fiber is used, the in-plane thermal expansion coefficient becomes low, but the thermal expansion coefficient in the thickness direction becomes larger than that when the glass fiber is used. Therefore, when it is used for a multilayer board, there is a problem that the reliability of through-hole connection deteriorates. However, when the ceramic layer is combined with the ceramic layer as in the present invention, the coefficient of thermal expansion of the ceramic layer is low, so that the coefficient of thermal expansion in the thickness direction is also low as a whole, and this point is also solved.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.

Example 1 Cordierite was sprayed on a roughened surface of an electrolytic copper foil 1 by a thermal sprayer to form a cordierite layer 2 having a thickness of 100 μm.
A copper foil having a cordierite layer 2 on one surface was obtained. on the other hand,
An aramid fiber nonwoven fabric (Technora, manufactured by Teijin Ltd.) was impregnated with an epoxy resin varnish and dried to obtain a prepreg 3 of an aramid fiber nonwoven fabric-based epoxy resin. Using the prepreg 3 thus prepared and the copper foil 1 having the cordierite layer 2, a laminated board having the structure shown in FIG. 1 was prepared.
The thickness of the copper foil is 18μm, the thickness of the ceramic layer is 100μ
m, the thickness of the central aramid fiber nonwoven fabric base material epoxy resin layer is 0.2 mm, and the total thickness is 0.4 mm. Table 1 shows the test results of the in-plane coefficient of thermal expansion after etching the copper foil and the solder heat resistance after the pressure cooker treatment after etching the copper foil of the thus obtained laminated plate with the copper foil. .

Example 2 100% by weight of resin solids in aramid fiber non-woven fabric
A prepreg was prepared by impregnating the epoxy resin varnish containing the fused silica powder of 1. This prepreg and Example 1
Using the copper foil having a cordierite sprayed layer similar to the above, a laminate having the same configuration as in Example 1 was produced. Table 1 shows the measurement results of the thermal expansion coefficient and solder heat resistance of this laminate.

Comparative Example 1 Using a copper foil having no ceramic layer, a prepreg having an aramid fiber non-woven fabric as a base material was used to prepare a laminate of only the aramid fiber non-woven fabric having no ceramic layer. Table 1 shows the measurement results of the thermal expansion coefficient and solder heat resistance of this laminate.

Comparative Example 2 A glass fiber base epoxy resin laminated plate having a ceramic layer was prepared in the same manner as in the example except that a prepreg using a glass fiber cloth as a base material was used. Table 1 shows the measurement results of the thermal expansion coefficient and solder heat resistance of this laminate.

[0024]

[Table 1] * After each time treatment with pressure cooker (121 ° C, 2 atm), soak in solder layer at 288 ° C for 30 seconds, ○: None
×: Blistering occurred

[0025]

As described above, according to the method of the present invention, it can be handled in the same manner as a conventional copper clad laminate,
Moreover, it is possible to easily obtain a substrate having a low coefficient of thermal expansion and excellent connection reliability with surface mount components. In addition, aramid fiber has a low in-plane coefficient of thermal expansion and is suitable as a substrate material for surface mounting, but it has drawbacks such as machinability, deterioration of characteristics when absorbing moisture, and high coefficient of thermal expansion in the thickness direction. , Was not widely used. Furthermore, since the coefficient of thermal expansion of the substrate is lower than that of the glass fiber substrate laminate, it is easily affected by the copper foil, and in a multilayer board having a ground layer with a high residual copper rate, the presence of copper foil causes aramid. The feature of low thermal expansion of the fiber was not fully exhibited. However, by combining the ceramic layer formed by thermal spraying with the aramid fiber nonwoven fabric as in the present invention, these drawbacks can be improved, and moreover, the conventional ceramic layer and the glass fiber base epoxy resin are combined. The coefficient of thermal expansion of the laminate can be further lowered.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a laminated structure in an example of the present invention.

[Explanation of symbols]

1. Copper foil 2. Cordierite 3. Prepreg

Claims (5)

[Claims] 1. A copper clad laminate comprising a ceramic sprayed layer provided between a copper foil and an aramid fiber nonwoven fabric prepreg layer. 2. A ceramic spray-coated layer is formed by spraying a ceramic on one surface of a copper foil, and a prepreg having an aramid fiber nonwoven fabric as a base material is laminated so as to be in contact with the ceramic spray-coated layer and subjected to thermocompression molding. The method for producing a copper clad laminate according to claim 1. 3. The resin of the prepreg contains 20 inorganic fillers.
The copper-clad laminate according to claim 1 or 2, wherein the copper-clad laminate contains at least wt%, and a method for producing the same. 4. The copper clad laminate according to claim 1, wherein the ceramic layer is mainly composed of cordierite, and the method for producing the same. 5. The copper-clad laminate according to claim 1, wherein the resin of the prepreg is an epoxy resin, and the method for producing the same.