JP2734912B2 - Copper-clad laminate for surface mount printed wiring boards - Google Patents

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 suitable for use as a surface-mount pudding wiring board. Specifically, a surface mount component (Surface Mount) to be mounted on a printed wiring board in which a copper-clad laminate is processed by a circuit
Device; hereinafter referred to as “SMD”) and a novel copper-clad laminate for a surface-mounted printed wiring board that can improve the solder connection reliability of a copper foil circuit of the printed wiring board.

[0002]

2. Description of the Related Art A copper-clad laminate for a printed wiring board is manufactured by integrating a sheet-like base material layer impregnated with a thermosetting resin and a copper foil of a surface layer by heating and pressing. Conventionally, S
As a copper-clad laminate for improving the solder connection reliability between the MD and the copper foil circuit, a copper-clad laminate in which a high elastic modulus elastomer resin layer is interposed immediately below the copper foil (Japanese Patent Laid-Open No. 21724/1990)
No. 0) and those in which an inorganic substance such as alumina or cordierite is sprayed on a copper foil and a layer of these inorganic substances is interposed immediately below the copper foil. In addition, a technique of using a resin having a small coefficient of thermal expansion or a glass cloth having a small coefficient of thermal expansion as a sheet-like substrate is also known.

The technique of interposing an elastomeric resin layer having a high modulus of elasticity is based on the fact that a thermal stress caused by a temperature change applied to a solder connection portion due to a difference in the coefficient of thermal expansion between an SMD and a laminated board is reduced. This suppresses the occurrence of cracks in the solder connection part and improves the reliability of solder connection. In addition, the technology of interposing an inorganic layer such as alumina or cordierite eliminates the influence of the thermal expansion of the laminated board by disposing an inorganic layer having almost no difference in thermal expansion coefficient from that of SMD. Cracks are not generated at the solder connection part. In addition, technology that uses a resin with a low coefficient of thermal expansion or a glass cloth with a small coefficient of thermal expansion reduces the occurrence of thermal stress caused by temperature changes by bringing the coefficient of thermal expansion of the laminate closer to the coefficient of thermal expansion of small SMD. Then, the solder connection reliability is improved.

[0004]

However, in the technique of interposing a high elastic modulus elastomer resin layer of the related art, the use of the high elastic modulus elastomer resin disclosed in the above-mentioned publication requires the recent high-density surface mounting. It cannot be said that it is sufficient for various characteristics required for a laminate for a printed wiring board, for example, reflow heat resistance, moisture and electric resistance, electric corrosion resistance, and smearless small-diameter through holes. In addition, the technology of interposing an inorganic layer such as alumina or cordierite adds a special process called a thermal spraying process in the production of copper foil, which significantly increases the price, the adhesiveness between the sprayed inorganic material layer and the copper foil, In addition, there has been a problem that the adhesiveness between the sheet-like base material impregnated with the thermosetting resin and the inorganic layer is poor. Furthermore, the technology that uses a resin or a glass cloth with a low coefficient of thermal expansion such as T-glass, which has a small coefficient of thermal expansion, still has a large coefficient of thermal expansion of the laminate compared to the SMD, and the solder connection reliability is high despite the high price. There was a problem that the property did not increase. The problem to be solved by the present invention is to further improve the reliability of SMD solder connection, which has been improved from the past, and furthermore, in addition to the above-mentioned various characteristics (reflow heat resistance) of a high-density printed wiring board in recent years. The present invention is to provide a copper-clad laminate for a surface-mounted printed wiring board, which is suitable for requirements of moisture-resistant electric characteristics, electric corrosion resistance and small-diameter through holes.

[0005]

In order to solve the above-mentioned problems, a copper-clad laminate according to the present invention comprises a sheet-like base material layer impregnated with a thermosetting resin and a surface-layer copper foil which are heated and pressed. In the one integrated by molding, the following (a) immediately below the copper foil
(B) A resin layer containing (c) as an essential component is interposed.

(A) Nitrile-butadiene rubber (b) Alkylphenol resin (c) Epoxy resin The nitrile-butadiene rubber (a) is preferably a carboxylated polybutadiene-acrylonitrile copolymer having carboxyl groups at both ends, and Carboxyl groups are epoxidized. The epoxy resin (c) is preferably selected from phenol novolak type epoxy resins, cresol novolak type epoxy resins, and bisphenol A type epoxy resins.

[0007]

By interposing a resin layer having a lower modulus of elasticity than the resin used for the laminate immediately below the copper foil, the resin layer can reduce the stress caused by the difference in thermal expansion coefficient between the SMD and the laminate. Since it is absorbed, it is most effective in suppressing the application of thermal stress to the solder connection. That is, similarly to those conventionally studied, the thermal stress caused by the difference in the coefficient of thermal expansion between the SMD and the laminated board is alleviated by the rubber elasticity of the nitrile butadiene rubber (a), and the solder connection reliability is improved. The alkylphenol resin (b) is oil-soluble because it has an alkyl side chain, and has good compatibility between the nitrile butadiene rubber (a) and the epoxy resin (c). Further, the heat resistance characteristic of the phenol resin improves the reflow heat resistance of the laminate. Furthermore, the use of the alkylphenol resin (b) makes the laminated board more excellent in moisture resistance and heat resistance than when a phenol resin having no alkyl side chain is used. This is presumed to be due to the hydrophobic effect of the alkyl group at the p-position and the steric hindrance caused by the alkyl group causing the main chain to be rigid during the crosslinking reaction of the resin. This improved heat resistance makes it possible to provide a smear-less copper-clad laminate for surface-mounted printed wiring boards that avoids the occurrence of smear in small-diameter through holes, which was a problem with the resin layer interposed directly under the conventional copper foil. It became. The epoxy resin (c) has an effect on the above-mentioned various properties including the moisture-resistant electric property. As the epoxy resin (c), a phenol novolak type epoxy resin, a cresol novolak type epoxy resin, and a bisphenol A type epoxy resin novolak are used. If a resin is selected, the crosslink density of the resin layer is increased, and the reflow heat resistance can be dramatically improved. In addition, smear can be avoided more favorably.

[0008]

Examples The nitrile butadiene rubber (a) is a polybutadiene-acrylonitrile butadiene copolymer, a carboxylated nitrile butadiene rubber at both ends, a polybutadiene-acrylonitrile copolymer at both ends carboxyl, etc. It may have a group. There is no particular limitation as long as it is compatible with epoxy resin or alkylphenol resin or undergoes a crosslinking reaction. Next, the alkylphenol resin (b) is p
-P such as phenol, p-cumylphenol, amylphenol, butylphenol, octylphenol, etc.
-It is a substituted alkylphenol resin, and is not particularly limited as long as it is a phenol resin having a phenolic hydroxyl group and an alkyl group. As the epoxy resin (c), bisphenol A type epoxy resin, novolak resin of bisphenol A type epoxy resin, phenol novolak type or cresol novolak type epoxy resin can be used. The resin layer containing (a), (b) and (c) as essential components may contain a flame retardant such as aluminum hydroxide and magnesium hydroxide.

In order to form the resin layer directly below the copper foil, a resin composition containing the above (a), (b) and (c) as essential components is applied to a copper foil and then dried and semi-cured. May be molded under heat and pressure integrally with the layer of the thermosetting resin-impregnated sheet-like base material. However, the resin composition may be adjusted in its curing speed or the elastic modulus of the resin layer formed immediately below the copper foil. In order to adjust to a predetermined characteristic, imidazoles or a compound thereof, or amines or a compound thereof can be appropriately used as a curing accelerator. Examples of the solvent used in the resin composition include toluene, methyl ethyl ketone, acetone, methyl isobutyl ketone, xylene, ethyl cellosolve, cellosolve acetate, and ethyl acetate. As a result of the study by the present inventors, it is better to use a mixture of two or three types than to use the above various solvents alone,
It was found that the coating properties on the copper foil and the blocking property during loading of the copper foil coated with the resin composition were good. More specifically, when a three-component system of methyl ethyl ketone / toluene / ethyl cellosolve is used, toluene is a good solvent for nitrile butadiene rubber and an alkylphenol resin, and methyl ethyl ketone is a good solvent for an epoxy resin to increase compatibility. In addition, by using ethyl cellosolve having a relatively high boiling point and vapor pressure, it is possible to prevent appearance defects such as avatars and voids on the surface of the coating layer on the copper foil.

Example 1 Carboxylated polybutadiene-acrylonitrile copolymer at both ends (trade name: Hiker CTBN, manufactured by Ube Industries)
/ Epoxy resin (trade name: EP-828EL, manufactured by Yuka Shell Epoxy) / imidazole (2E4MZ, manufactured by Shikoku Chemicals) is pre-reacted at a weight ratio of 100/30 / 0.20 to epoxidize both terminal carboxyl groups. An oligomer of acrylonitrile butadiene rubber was prepared. The acrylonitrile-butadiene rubber oligomer / butylphenol resin / bisphenol A type epoxy resin (trade name: YD-900, manufactured by Toto Kasei) was blended in a weight ratio of 50/20/30, and the resin concentration was 35% by weight.
Methyl ethyl ketone / toluene / ethyl cellosolve
The mixture was diluted with a mixed solvent having a weight ratio of 50/30/20. Imidazole (0.5 part by weight) was added as a curing accelerator, and the mixture was sufficiently stirred to prepare a varnish (a) for application to a copper foil. The varnish (a) was applied to the roughened surface of the 18 μm-thick electrolytic copper foil with a roll coater so that the applied amount became 25 μm in thickness, and then dried so that the volatile content became 3%. Prepare a prepreg laminate structure in which the core material layer is six epoxy resin-impregnated glass nonwoven fabrics, and both surface layers are one epoxy resin-impregnated glass cloth, and the copper foil is coated on the outermost surface so that the coated surface is on the inside. At a pressure of 30 kgf / cm ²
After heating and pressurizing for 90 minutes, cooling for 30 minutes.
A 6 mm composite double-sided copper-clad laminate was obtained.

Example 2 A composite double-sided copper-clad laminate having a thickness of 1.6 mm was obtained in the same manner as in Example 1 except that octylphenol resin was used as the alkylphenol resin of varnish (a).

Example 3 A composite double-sided copper-clad laminate having a thickness of 1.6 mm was obtained in the same manner as in Example 1, except that an o-cresol novolak type epoxy resin was used as the epoxy resin of the varnish (a). .

Example 4 A 1.6 mm-thick composite double-sided copper-clad laminate was prepared in the same manner as in Example 1 except that a novolak resin of diglycidyl etherified bisphenol A was used as the epoxy resin of the varnish (a). Obtained.

Example 5 A double-sided copper-clad laminate having a thickness of 1.6 mm was obtained in the same manner as in Example 1 except that the prepreg laminated structure was constituted only by eight epoxy resin-impregnated glass cloths.

Example 6 A 1.6 mm thick composite was prepared in the same manner as in Example 1, except that a non-epoxidized carboxylated polybutadiene-acrylonitrile copolymer was used as the nitrile butadiene rubber of the varnish (a). A double-sided copper-clad laminate was obtained.

Conventional Example 1 The procedure of Example 1 was repeated, except that a varnish (a) was replaced by a copper foil coated with only a carboxylated polybutadiene-acrylonitrile copolymer at both ends. A composite double-sided copper-clad laminate was obtained.

Conventional Example 2 The procedure of Example 5 was repeated, except that a varnish (a) was replaced by a copper foil coated with only a carboxylated polybutadiene-acrylonitrile at both ends, and the thickness was 1.6 mm. Was obtained.

Conventional Example 3 Instead of varnish (a), carboxylated polybutadiene-acrylonitrile copolymer at both ends / bisphenol A
A 1.6 mm-thick composite double-sided copper-clad laminate was obtained in the same manner as in Example 1 except that a varnish coated with 50/50 parts by weight of a mold epoxy resin was used.

Tables 1 and 2 show the characteristics of the copper-clad laminates in Examples 1 to 6 and Conventional Examples 1 to 3. The evaluation method and evaluation criteria are as follows. (1) Solder connection reliability Using an SMD (square plate type chip fixed resistor) 3.2 mm long x 2.5 mm wide x 0.6 mm thick, -30 ° C ← → 120
The rate of occurrence of cracks in the SMD solder connection after 1000 cycles at a temperature of 100 ° C. (n = 100). (2) Reflow heat resistance The reflow conditions were as follows: preheating at 150 ° C for 2 minutes, 240 ° C-1.
The reflow heating is performed for 0 second. Judgment criteria: ：: no discoloration ○: slight discoloration but no problem in practical use △: remarkable discoloration (3) Solder heat resistance Measure the time required for floating the laminate in a 300 ° C solder bath and blistering (4) Insulation resistance Measured after pressure cooker treatment (121 ° C-2 atmospheres, 6 hours) (5) Electric corrosion resistance 0.5mm pitch comb-shaped pattern is formed, and 60 ° C-95%
Electricity is supplied at a voltage of 50 V for 500 hours in an RH atmosphere. Judgment criteria: ：: no dendrite was generated △: slight dendrite was generated ×: many dendrites were generated (6) Smear generation rate After drilling 1000 hits, after 3000 hits, 6
Occurrence of smear in 100 holes after 000 hits

[0020]

[Table 1]

[0021]

[Table 2]

[0022]

As described above, the copper-clad laminate for a surface-mounted printed wiring board according to the present invention comprises: (a) nitrile butadiene in which the carboxyl group of the carboxylated polybutadiene-acrylonitrile at both ends is epoxidized; Rubber (b) Alkylphenol resin (c) Epoxy resin A resin composition layer as an essential component is formed immediately below the copper foil, so that the solder connection reliability of the SMD is high, and the reflow heat resistance, moisture resistance, It is excellent in electric corrosion resistance and has a remarkable smear-less effect, and can sufficiently cope with recent high-density component mounting processes. Nitrile butadi
Carboxylated polybutadiene at both ends as ene rubber
-The carboxyl group of the acrylonitrile copolymer is
Since the carboxyl group was used,
Non-poxylated carboxylated polybutadi at both ends
Compared with the case of using an ene-acrylonitrile copolymer
Thus, the electric resistance against humidity is excellent. this thing
Indicates the insulation resistance of Examples 1 to 5 and Example 6 shown in Table 1.
Can be understood from the comparison.

Claims (2)

(57) [Claims] 1. A copper-clad laminate in which a sheet-like base material layer impregnated with a thermosetting resin and a surface layer copper foil are integrated by heat and pressure molding, the following (a) (b) (3) A copper-clad laminate for a surface mount printed wiring board, wherein a resin layer containing (c) as an essential component is interposed. (A) Carboxylated polybutadiene-acryloyl at both ends
The carboxyl group of the nitrile copolymer is epoxidized.
Nitrile-butadiene rubber (b) alkylphenol resin (c) an epoxy resin 2. The epoxy resin (c) is a phenol novola.
Epoxy resin, cresol novolak epoxy
Resin, bisphenol A type epoxy resin novolak tree
The copper-clad laminate for a surface mount printed wiring board according to claim 1, which is selected from fats and oils.