JPH0568875B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a flexible printed wiring board that has excellent mechanical properties such as bending resistance and heat resistance such as solder heat resistance. So-called printed wiring boards, which are constructed by laminating conductors made of metal foil such as copper foil on an insulating base material, are used in large quantities in the electrical and electronic industry fields, such as various home appliances, computers, communication equipment, and various instruments. used in For example, polyimide film, polyester film, and "Teflon" film are used as insulating base materials for flexible printed wiring boards, but polyimide film requires the use of a solvent to dissolve the resin during manufacturing, and the solvent Not only is it complicated to collect and dispose of, making it undesirable in terms of pollution and hygiene, but it is also expensive and its dimensions and electrical properties change significantly when moisture is absorbed.Polyester film has poor heat resistance such as soldering heat resistance, and "Teflon" film has It has the drawbacks of being expensive and having poor adhesion to metal foil and poor processability. In addition, recently polyphenylene sulfide resin (hereinafter abbreviated as PPS)
It has attracted attention for its excellent chemical resistance, heat resistance, electrical properties, and non-flammability, and has been used as an insulating base material for printed wiring boards (for example, Japanese Patent Application Laid-Open No. 54-85380
Publication No. 2) has also been proposed. However, although PPS has the above-mentioned excellent performance, the toughness of the film or sheet deteriorates significantly due to crystallization, and impact resistance etc. cannot be improved even if a fibrous reinforcing agent such as glass fiber is included. However, there is a problem in that it does not exhibit any bending resistance or breakage resistance, and it is difficult to provide a flexible printed wiring board. Therefore, the present inventors aimed to improve the mechanical properties such as bending fatigue resistance and breakage resistance, and the heat resistance such as soldering heat resistance of conventional printed wiring boards using PPS as an insulating base material. As a result of extensive research, we have found that by heat-treating the material PPS under specific conditions to bring its crystallization peak temperature to 160℃ or less, and using it as an insulating base material, we can maintain the excellent performance of PPS and still achieve the above purpose. The present invention was achieved by discovering that it is possible to obtain a printed wiring board that matches the above. That is, in the present invention, a PPS powder or a substantially non-oriented PPS sheet is heat-treated in the presence of oxygen at a temperature higher than the melting point of the resin so that its crystallization peak temperature is 160°C or lower, and then The present invention provides a printed wiring board in which a sheet obtained by compression molding as required is used as an insulating base material, and a metal foil is bonded to at least one surface of the insulating base material. What is the structural formula of PPS used in the present invention?

A polymer containing 90 mol% or more, preferably 95 mol% or more of repeating units represented by the formula, at a temperature of 300°C and an apparent shear rate of 200sec ^-1
Melt viscosity measured under the conditions of 50 to 50000 poise,
Particularly suitable is one in the range of 100 to 20,000 poise. The PPS used includes granular fillers such as talc, fused silica, mica, and glass beads, normal additives such as lubricants, crystal nucleating agents, colorants, and mold release agents, and flexible wholly aromatic polyamide fibers. , organic fibers that do not reduce the bending durability of the base material of the present invention, and auxiliary agents such as peroxides that promote the heat treatment effect of the present invention, and within a range that does not impede the purpose of the present invention. It is also possible to blend small proportions of other types of polymers. The PPS powder or granules in the present invention are powders, chips, pellets, etc., and the PPS sheet-like material is a plate-like or film-like material having a thickness of 1 mm or less and made of substantially non-oriented PPS. This PPS sheet-like product can be formed by extrusion molding, compression molding, etc., but it is appropriate to manufacture it by extrusion molding. Further, the term "substantially non-oriented" in this sheet-like material means that no operations such as active stretching or rolling to orient the molecular chains are applied. The insulating base material of the present invention is made by preparing the above-mentioned PPS powder or granular material or substantially non-oriented PPS sheet material in the presence of oxygen.
At temperatures above the melting point of PPS, especially between 280 and 450℃,
It can be obtained by heat-treating PPS so that its crystallization peak temperature is 160°C or less, and then compression molding if necessary. The melting point and crystallization peak temperature of PPS herein mean values measured by the following method. That is, a differential scanning calorimeter (manufactured by PerkinElmer, DSC
-IB type), approximately 10 mg of PPS was heated as a sample in a nitrogen gas atmosphere at a heating rate of 20°C/min.
When the temperature reaches 360°C, hold it for 5 minutes and then lower the temperature at a cooling rate of 20°C/min. The peak of the endothermic peak that appears when the temperature rises is the melting point, and the peak of the exothermic peak that appears when the temperature falls is the crystallization peak temperature. . The heat treatment temperature of PPS must be higher than the melting point of PPS.
If heat treatment is performed at a temperature below the melting point, the peak crystallization temperature of PPS cannot be lowered to 160℃ or less,
It is not possible to obtain a printed wiring board with excellent mechanical properties such as bending fatigue resistance. Note that the upper limit of the heat treatment temperature is about 450°C, and it is not appropriate to set it higher than necessary. It is also essential that the heat treatment be performed in the presence of oxygen, and when heat treatment is performed under reduced pressure or in an inert gas atmosphere such as nitrogen,
The crystallization peak temperature of PPS cannot be lowered to 160° C. or lower, and the object of the present invention is not achieved. The heat treatment time varies depending on the heat treatment temperature, and the higher the treatment temperature, the shorter the time. However, the combination of treatment temperature and treatment time should be set so that the PPS crystallization peak temperature is 160°C or less, and the crystallization If the heat treatment is stopped when the peak temperature is 160°C or higher, the effect of improving bending fatigue resistance will not be sufficient. Note that the crystallization peak temperature of 160° C. or lower as used in the present invention includes a case where the crystallization peak temperature is substantially no longer observed as the heat treatment progresses. Specific methods for obtaining a PPS sheet as an insulating base material include the following methods (1) to (3). (1) Spread PPS powder evenly into a flat container with an open top and place it in a heat treatment device.
After heat treatment under the above conditions, the product is cooled and then reheated, or the product is maintained above the melting point and subjected to compression molding to obtain a sheet. (2) After uniformly scattering PPS powder onto a metal conveyor belt and heat-treating it by continuously passing it through a heating device set at a temperature higher than the melting point of PPS, the powder is placed between a pair of metal belts immediately after the heating device. A method in which powder and granules are introduced into a metal belt and continuously compression-molded while applying pressure from both sides to obtain a sheet. (3) A method in which at least a portion of the periphery of a PPS sheet is supported with clamps, etc., and then placed in a heating device and heat treated. In methods (1) and (2) above, the PPS powder after heat treatment has a markedly increased melt viscosity, so it is melt-molded by ordinary injection molding or extrusion molding to obtain a sheet. However, it is difficult to subject the product to compression molding, and a compression molding method must be used.
In addition, in method (3) above, the sheet-like material after heat treatment can be used as an insulating base material as it is, but if necessary, it can be compression molded again to adjust the surface smoothness etc. before being used as an insulating base material. It is also possible.
However, in order to obtain a sheet with good flatness in method (3) above, it is necessary to use some kind of support or to prepare the sheet in advance so that it has self-supporting properties.
It is preferable to start the heat treatment at a temperature below the melting point of PPS, for example about 250° C., and then perform the heat treatment at a temperature above the melting point of PPS. Note that method (3) can also be made continuous by placing the PPS sheet on a stainless steel belt and passing it through a heating device. Equipment used for heat treatment includes hot air ovens, infrared heating furnaces, and combinations thereof. The PPS sheet obtained by heat treatment in this way is
Compared to conventional PPS films and sheets, it has a crystallization peak temperature of 160℃ or less, which makes it extremely difficult to crystallize, and the number of bending fatigue cycles is 20.
It has excellent performance of more than 10 times. In other words, PPS sheets obtained by conventional extrusion molding have such poor breakage resistance that they break after being bent once, but the PPS sheets obtained through the above heat treatment of the present invention do not break even after being folded 20 times or more. ,
An insulating substrate for printed wiring boards with excellent mechanical properties and flexibility can be obtained without containing a fibrous reinforcing agent such as glass fiber. There is no particular restriction on the thickness of the above-mentioned PPS sheet used as an insulating base material in the printed wiring board of the present invention, and a range of 0.05 to 5.0 mm is usually selected. In some cases, in order to increase the thickness of the sheet, it is also possible to further laminate a sheet made of another resin on one side of the sheet for practical use. In the printed wiring board of the present invention, the metal foil provided on the insulating substrate may include copper foil, aluminum foil,
Examples include silver foil, but copper foil is the most representative. Bonding of the metal foil onto the insulating substrate can be performed simultaneously with compression molding in methods (1) and (2), and can be performed at any time after heat treatment in method (3). There are no particular restrictions on the specific means for bonding and forming metal foils. An additive method in which copper foil etc. are plated in a pattern, a stamping foil method in which copper foil etc. punched out in a pattern are bonded to an insulating base material, etc. can be used. In addition, in the present invention, excellent adhesive strength can be expected without using an adhesive when joining the insulating base material and the metal foil, but even better adhesive strength can be obtained if an adhesive is used as necessary. is obtained. The printed wiring board of the present invention thus obtained retains excellent properties such as heat resistance represented by solder resistance, chemical resistance, electrical properties, and nonflammability, and is also a printed wiring board using conventional PPS as an insulating base material. It is more flexible and has excellent bending fatigue resistance, breakage resistance, and heat solder resistance, and is expected to be applied to various electronic and electrical applications. The present invention will be further explained with reference to Examples below. In addition, the number of bending fatigue times in the examples is JISP8115.
This is a value measured using an MIT type testing machine in accordance with . Examples 1 to 6 and Comparative Examples 1 to 4 32.6 kg of sodium sulfide was added to the autoclave.
(250 mol, including 40 wt% water of crystallization), 100 g of sodium hydroxide, 36.1 Kg (250 mol) of sodium benzoate, and N-methyl-2-pyrrolidone (hereinafter
79.2 kg of NMP (abbreviated as NMP) was charged, and the temperature was gradually raised to 205°C while stirring, and 7.0 kg of distillate containing 6.9 kg of water was removed. In the residual mixture, 1,4-dichlorobenzene 37.5
Add Kg (255 mol) and NMP20.0Kg, 265℃
It was heated for 4 hours. The reaction product was washed 8 times with hot water and dried at 80°C for 24 hours using a vacuum drier to obtain 21.1 kg of powdered highly polymerized PPS having a melt viscosity of 2900 poise and a melting point of 277°C. Using the above PPS, the thickness is 200mμ by extrusion molding.
created a film. The periphery of the film was supported by a jig, and heat treated under the conditions shown in Table 1 using an oven at atmospheric pressure. However, the treatment in the present invention includes, as a pretreatment,
After processing in advance at 270°C for 1 hour, the temperature was raised stepwise. Meanwhile, 40% by weight of butylene terephthalate units,
An adhesive (dissolved in a monochlorobenzene/methanol mixed solvent) consisting of 70 parts of a polyesteramide resin consisting of 27% by weight of butylene isophthalate units and 33% by weight of dodecane amide units and 30 parts of a bisphenol type epoxy resin was used as a commercially available adhesive. Copper foil with adhesive was prepared by coating it on electrolytic copper foil (thickness 35μ) for printed wiring and drying it. Next, the above film and copper foil coated with adhesive were laminated, heated and pressed at 130°C, and the adhesive was further heat-cured to produce a copper-clad laminate film (printed wiring board). Table 1 shows the results of evaluating the properties of the obtained copper-clad laminated film.

[Table] As is clear from Table 1, the melting point of PPS (277
℃) or less (Comparative Examples 1 to 4)
It can be seen that the number of bending fatigue cycles is small and the soldering heat resistance is poor, but the films treated at temperatures above the melting point of PPS (Examples 1 to 6) have extremely high bending fatigue cycles and have excellent soldering heat resistance. Also, very good values were obtained for adhesive peel strength. Examples 7 to 9 and Comparative Examples 5 to 6 The same PPS film as in Example 1 was used, and the film was heat-treated in an oven under the conditions shown in Table 2. Electrolytic copper foil for printed wiring boards (thickness: 35μ) was applied to the film. of,
They are stacked one on top of the other, inserted into a mold heated to 330°C, and pressurized with a pressure of 20 kg/cm ² using a compression molding machine to heat-fuse the polymer to the copper foil, then cooled and laminated with copper clad. I got the film. Table 2 shows the results of evaluating the properties of the obtained copper-clad laminate film.

[Table] As is clear from Table 2, the copper-clad laminate film of the present invention has extremely high adhesive strength and excellent solder heat resistance even when copper foil is bonded by thermal fusion of polymer. I understand that. Example 10 The copper foil of a copper-clad laminate film prepared in the same manner as in Example 9 was removed by etching, and dimensional changes due to water absorption at room temperature and relative humidity 80% were measured. For comparison, polyimide film (“Kapton”)
As a result of measuring the dimensional change in the same way for 200H),
Compared to 0.17% for polyimide film, the PPS film of the present invention had an extremely excellent dimensional stability when absorbing moisture, with a content of 0.015%. Example 11 and Comparative Examples 7 to 8 Powdered PPS obtained in the same manner as in Example 1 was uniformly spread on a flat iron plate and heated in the presence of oxygen (in the air, in an oven) and under reduced pressure (vacuum). Medium, 30mmHg)
300℃ under nitrogen atmosphere (nitrogen blow),
After heat treatment for 1 hour, electrolytic copper foil for printed wiring boards (thickness 35μ) was layered on top of this PPS.
It was inserted into a compression molding machine with a mold heated to 330°C, and pressurized at a pressure of 20 kg/cm ² to thermally fuse the PPS and copper foil, and then cooled to create a copper-clad laminate film. . Table 3 shows the results of evaluating the properties of the obtained copper-clad laminated film.

[Table] As is clear from Table 3, no improvement in bending fatigue properties was observed in the heat treatment in vacuum or nitrogen atmosphere. It can be seen that the products heat-treated in the presence of oxygen of the present invention have a low crystallization peak temperature, a significantly improved number of bending fatigue cycles, and excellent soldering heat resistance.

Claims (1)

[Claims] 1 Polyphenylene sulfide resin powder or a substantially non-oriented polyphenylene sulfide resin sheet is heated in the presence of oxygen to a temperature higher than the melting point of the resin so that its crystallization peak temperature is 160°C or lower. 1. A printed wiring board comprising a sheet obtained by heat treatment at a temperature of , followed by compression molding if necessary, as an insulating base material, and a metal foil bonded to at least one surface of the sheet.