JPH0329247B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field] The present invention relates to epoxy resin prepregs and epoxy resin laminates used as materials for printed wiring boards for electronic devices. [Background technology] As electronic devices become more sophisticated and smaller,
It is strongly desired that laminates, which are materials for printed wiring boards used in this application, have improved heat resistance, adhesion to circuits, and drill workability. Laminated boards for printed wiring boards are made by laminating multiple sheets of prepreg prepared by impregnating a base material with thermosetting resin and drying it, and then molding it under heat and pressure. ing. Various types of thermosetting resins can be used here, but epoxy resins are very often used from the viewpoint of adhesion to metal foil circuits. In this case, a prepreg is generally prepared by impregnating a base material with an epoxy resin varnish in which an epoxy resin and a curing agent are dissolved in a solvent, and drying the impregnated base material. Although various types of curing agents for epoxy resins are available, dicyandiamide is often used when manufacturing laminates for printed wiring boards. However, when dicyandiamide is used as a curing agent, it is possible to obtain a laminate with good adhesion to the metal foil circuit, but it has poor heat resistance such as moisture absorption solder heat resistance, and poor drilling workability such as smearing. There is a problem. Therefore, various studies have been conducted on curing agents for epoxy resins, and for example, as curing agents for epoxy resin laminates for printed wiring boards,
Japanese Patent Publication No. 49-23840 discloses dihalogenated diaminodiphenylmethane, and Japanese Patent Publication No. 60-4526 discloses dihalogenated diaminodiphenylmethane.
In the publication, trimethylene glycol di-4-
Aminobenzoates have been proposed and good results can be obtained using these as curing agents. However, the former dihalogenated diaminodiphenylmethane is highly toxic and difficult to widely use, and the latter trimethylene glycol di-4-aminobenzoate is extremely expensive and cannot be used generally. However, neither of these methods can be considered as practical curing agents, and no practical solution has yet been found. [Object of the Invention] The present invention has been made in view of the above points, and provides an epoxy resin prepreg and an epoxy resin laminate that have excellent adhesion to metal foil circuits, as well as excellent heat resistance and drill workability. The purpose is to provide boards. [Disclosure of the invention] However, the epoxy resin prepreg according to the present invention contains dicyandiamide and the general formula in the epoxy resin. (R is an ethyl group or an isopropyl group) and is prepared by impregnating and drying an epoxy resin varnish on a base material. Such an epoxy resin laminate contains dicyandiamide and a general formula of epoxy resin. (R is an ethyl or isopropyl group) epoxy resin prepreg is formed by impregnating and drying a base material with an epoxy resin varnish blended with an aromatic diamine. The present invention will be described in detail below. Examples of the epoxy resin used in the present invention include diglycidyl ether type of bisphenol A, diglycidyl ether type of halogenated bisphenol A, triglycidyl ether type of tris(hydroxyphenyl)methane, and polyglycidyl ether type of phenol novolak. Examples include ether type, polyglycidyl ether type of cresol novolak, polyglycidyl ether type of halogenated phenol novolak, tetraglycidyldiaminophenylmethane, and triglycidyl-p-aminophenol. Epoxy resin curing agents include acid anhydrides, phenols, and amines, but acid anhydrides have problems with the storage stability of prepregs, and phenols have problems with adhesion to metal foil circuits. Therefore, neither of them is suitable for use in printed wiring boards. On the other hand, cured epoxy resins using amines, especially aromatic diamines as curing agents have excellent performance. As mentioned above, among aromatic diamines, dihalogenated diaminodiphenylmethane and trimethylene glycol di-4-aminobenzoate show excellent performance, but on the other hand, as mentioned above, they are not practical. be. Therefore, the present inventors investigated various aromatic diamines and found that the general diamines ( By discovering what is shown in the formula, we have completed the present invention. In the formula, R represents an ethyl group or an isopropyl group, and 4-4' methylene di-
2-6-diethylaniline (the structural formula is shown in the following formula) and 4-4'methylenedi-2-6-diisopropylaniline (the structural formula is shown in the following formula) in which R is an isopropyl group can be used. However, when this aromatic diamine of formula () is used alone as a curing agent, the curing time becomes longer and the curing properties of the epoxy resin are inferior.Also, despite the long curing time, the storage stability of the epoxy resin varnish is was found to be inferior. Therefore, in the present invention, by using aromatic diamine of formula () and dicyandiamide together as a curing agent,
The curability of epoxy resin and the storage stability of epoxy resin varnish are improved. By using the aromatic diamine of the formula () in combination with dicyandiamide in this way, the properties of the cured epoxy resin can be significantly improved compared to when dicyandiamide is used alone as a curing agent. The blending amount of dicyandiamide and the aromatic diamine of the formula () is preferably set in the range of 0.5 to 1.1 equivalents of active hydrogen equivalents of the two types based on 1 equivalent of the epoxy resin. Outside this range, the properties of the cured epoxy resin tend to deteriorate. Here, in the present invention, 1 equivalent of the epoxy resin is obtained as the value obtained by dividing the average molecular weight of the epoxy resin by the number of epoxy groups per molecule, that is, the epoxy equivalent. Also, the blending ratio of dicyandiamide and the aromatic diamine of formula () can be adjusted freely, but the blending amount of the aromatic diamine is set in the range of 0.2 to 0.8 equivalents of active hydrogen per equivalent of epoxy resin. be done.
If the amount is less than 0.2 equivalents, the effect of improving the heat resistance of the epoxy resin laminate is insufficient, and if it exceeds 0.8 equivalents, problems tend to occur in the storage stability of the epoxy resin varnish. Then, an epoxy resin varnish can be prepared by dissolving the epoxy resin, dicyandiamide as a curing agent, and the aromatic diamine of formula () above in a solvent. As a solvent, acetone, methyl ethyl ketone, methyl cellosolve,
Methyl isobutyl ketone, dimethylformamide, etc. can be used. Further, at this time, it is also possible to further mix a curing accelerator to prepare an epoxy resin varnish. As the curing accelerator, tertiary amines, imidazoles, aminotriazoles, phosphines, etc. can be used. The resin concentration of the epoxy resin varnish is arbitrarily set depending on the amount of resin impregnated into the base material. Then, the epoxy resin varnish prepared in this way is impregnated into a base material such as glass cloth according to a conventional method, and then heated and dried to semi-cure the epoxy resin and form an epoxy resin prepreg. create. Then, the epoxy resin is cured by stacking multiple sheets of this epoxy resin prepreg and, if necessary, layering a metal foil such as copper foil on the outer surface of the outermost layer, and molding this under heat and pressure according to a conventional method. , a laminate can be obtained. Furthermore, the epoxy resin prepreg can also be used as an adhesive sheet, etc., instead of as a laminate. Next, the present invention will be specifically explained based on examples. Of course, the present invention is not limited to the following examples. Example 1 First, an epoxy resin varnish was prepared by mixing the following formulation. - Bromated bisphenol A type epoxy resin (epoxy equivalent: 510)...85 parts by weight - Cresol novolac type epoxy resin (epoxy equivalent: 215)...15 parts by weight - 4-4'methylenedi-2-6-diethylaniline (active hydrogen Equivalent: 77.5) …8.37 parts by weight dicyandiamide (active hydrogen equivalent: 21)
...1.24 parts by weight 2-ethyl 4-methylimidazole
…0.10 parts by weight Methyl cellosolve…50 parts by weight Methyl ethyl ketone…70 parts by weight For the epoxy resin varnishes prepared in this way, the varnish gel time at 160°C at the time of blending and after storage for 20 days in an atmosphere at 20°C was determined. Epoxy resin prepreg 1 with a resin content of 50% by weight was prepared by impregnating a glass cloth with a unit weight of 103 g/m ² with this epoxy resin varnish shown in Table 1 and heating it for 9 minutes in a dryer at 155°C. Obtained. Six sheets of this epoxy resin prepreg were stacked, and copper foil with a thickness of 0.070 mm was layered on the top and bottom surfaces, and this was placed between heating plates to maintain a pressure of 20 kg/cm ² and heated to 175°C.
By heating at 195° C. for 30 minutes and then at 195° C. for 90 minutes, a copper-clad laminate 2 for inner layer was created. Patterns 3 having a land diameter of 1.8 mmφ at a pitch of 2.54 mm were formed on both sides of the copper-clad laminate 2 for inner layer by etching. These land patterns 3 are per side.
They were arranged so that there were 7,500 pieces in a size of 250 x 330 mm. Copper-clad laminate 2 for inner layer formed as inner layer material after pattern formation, epoxy resin prepreg 1 made as above and thickness 0.018
By stacking copper foils 4 of 1 mm thick as shown in Figure 1, placing them between heating plates and maintaining a pressure of 20 kg/cm ² , heating and pressurizing them at 175°C for 30 minutes and then at 195°C for 90 minutes,
A four-layer multilayer printed wiring board was created. Example 2 In place of 4-4'methylenedi-2-6-diethylaniline in Example 1, 4-4'methylenedi-2-
6-diisopropylaniline (active hydrogen equivalent
An epoxy resin varnish was prepared in the same manner as in Example 1, except that 10.82 parts by weight of 91.5) was used, and an epoxy resin prepreg was prepared in the same manner as in Example 1 using this epoxy resin varnish. A four-layer multilayer printed wiring board was prepared in the same manner as in Example 1 using the following. Table 1 shows the formulation in this case and the varnish gel time of the obtained epoxy resin varnish. Examples 3 and 4 and Comparative Examples 1 to 5 Brominated bisphenol A type epoxy resin, cresol novolac type epoxy resin, dicyandiamide, 4-4'methylenedi-2-6-diethylaniline, 4-4'methylenedi-2- The amounts of 6-isopropylaniline, 4-4'methylenedi-2-6-dimethylaniline, and dichlorodiaminodiphenylmethane were set as shown in Table 1, and the amounts of curing accelerators and bath agents were set in the examples. An epoxy resin varnish was prepared in the same manner as in Example 1, and an epoxy resin prepreg and a four-layer multilayer printed wiring board were created in the same manner as in Example 1 using this epoxy resin varnish. However, when creating the epoxy resin prepreg, the heating time in a dryer at 155°C was set to be the same as the varnish gel time immediately after compounding. The varnish gel time of the obtained epoxy resin varnish is shown in Table 1. The characteristics of each of the above examples and comparative examples were measured, and the results are shown in Table 1. Measurements and calculations were performed as follows. (A) Rate of change in varnish gel time The varnish gel time 20 days later was divided from the varnish gel time immediately after compounding, and this was expressed as a 100% of the value divided by the varnish gel time immediately after compounding. (B) Peel strength of copper foil The peel strength of a 0.018 mm thick copper foil on a four-layer printed wiring board was measured in accordance with JIS-C-6481. (C) Moisture absorption and solder heat resistance A 50 mm x 50 mm test piece was cut from a 4-layer printed wiring board with the outermost copper foil removed by etching, and placed in a steam oven maintained at a steam pressure of 3 atmospheres.
After the test piece was placed in the test piece for 60 minutes to force moisture absorption, the test piece was immersed in a solder bath at 260°C for 20 seconds to observe the occurrence of blistering. (D) Smear failure rate For a 4-layer printed wiring board, set the drill so that the center is in the center of the land pattern of the inner layer material, and use a drill machine with NC to adjust the drill diameter.
Using a 0.9 mmφ drill, 2,500 holes were drilled in two stacked four-layer printed wiring boards (both the upper and lower four-layer printed wiring boards) at a spindle rotation speed of 60,000 rpm and a feed rate of 3 m/min. After drilling the holes, through-hole plating was applied to the four-layer printed wiring board, and the cross sections of 20 holes (40 holes in total) around the 2500th hole were observed. A case where the inner layer copper foil was covered with 1/4 or more of the total thickness of the epoxy cured product was determined to be a through-hole plating failure, and the failure rate was calculated. Since there are 4 connection points per hole, the number of connection points where more than 1/4 of the inner layer copper foil is covered with epoxy cured material is divided by 160, which is the total number of connection points on the upper and lower plates. , the calculation was made as a 100% of this.

【table】

[Table] The following is confirmed from Table 1. 1) Each example using aromatic diamine of formula () as a curing agent is different from Comparative Example 5 using dichlorodiaminodiphenylmethane as a curing agent.
It has excellent heat resistance and drill workability (hygroscopic solder heat resistance and smearing properties) on a par with other materials. However, as in Example 4, when the amount of aromatic diamine of formula () is small, the effect of improving heat resistance and drill workability is small. 2) When the aromatic diamine of the formula () is blended without dicyandiamide, as in Comparative Examples 2 and 3, the rate of change in gel time of the epoxy resin varnish is large and the storage stability of the epoxy resin varnish is poor. Further, in Comparative Examples 2 and 3, the varnish gel time immediately after blending was long and the curing properties were poor. Furthermore, Example 3
When the aromatic diamine of the formula () is blended in an amount exceeding 0.8 equivalent, the effect of improving the storage stability and curability of the epoxy resin varnish is not large. 3) Even when an aromatic diamine is used as a curing agent, if R in formula () is a methyl group instead of an ethyl group or an isopropyl group, the storage stability of the epoxy resin varnish is poor as in Comparative Example 4. In this way, the cured product of the present invention, which uses aromatic diamine of the formula (2) and dicyandiamide together as a curing agent for epoxy resin, has excellent heat resistance and drilling processability without reducing adhesion to metal foil circuits. Furthermore, the substances used have low toxicity and can be widely used. [Effects of the Invention] As described above, the epoxy resin prepreg and epoxy resin laminate according to the present invention contain dicyandiamide and the general formula in the epoxy resin. (R is an ethyl group or an isopropyl group) is created using an epoxy resin varnish blended with an aromatic diamine. Heat resistance and drilling workability can be improved without reducing adhesion with metal foil circuits.

[Brief explanation of the drawing]

FIG. 1 is a schematic exploded sectional view of an embodiment of the present invention. 1 is an epoxy resin prepreg, and 2 is a copper-clad laminate for the inner layer.

Claims (1)

[Claims] 1. An epoxy resin containing dicyandiamide and the general formula An epoxy resin prepreg characterized in that an epoxy resin varnish prepared by blending with an aromatic diamine represented by (R is an ethyl group or an isopropyl group) is impregnated into a base material and dried. 2 In epoxy resin varnish, the aromatic diamine is equivalent to active hydrogen per equivalent of epoxy resin.
The epoxy resin prepreg according to claim 1, wherein the epoxy resin prepreg is blended in an amount of 0.2 to 0.8 equivalents. 3 Epoxy resin has dicyandiamide and the general formula (R is an ethyl or isopropyl group) epoxy resin prepreg is formed by impregnating and drying a base material with an epoxy resin varnish blended with an aromatic diamine. An epoxy resin laminate board characterized by being formed by laminating layers. 4 In epoxy resin varnish, the aromatic diamine is equivalent to active hydrogen per equivalent of epoxy resin.
The epoxy resin laminate according to claim 3, wherein the epoxy resin laminate is blended in an amount of 0.2 to 0.8 equivalents.