JPS6346593B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a flexible printed wiring board. Flexible printed circuit boards have recently become popular in electronic desk calculators because they can be smaller and lighter, simplify wiring layouts, simplify wiring work, and improve circuit characteristics and reliability compared to ordinary electric wires and rigid boards. It has come to be widely used for the internal wiring of telephones, cameras, and automobile wiring panels. Flexible printed wiring boards are broadly classified into flexible flat cables, single-sided/double-sided flexible printed wiring boards, and multilayer flexible printed wiring boards, and all of them are made by adhesively bonding copper foil to one or both sides of a flexible insulating base film. It is manufactured by pasting the copper foil together via a copper foil, etching a wiring pattern based on the circuit design, etc. to reproduce the copper foil as an electrical circuit, and then providing an overlay film or overcoat in the necessary places on the copper foil. The overlay film is made by laminating a polyester film, polyimide film, etc. to a base film on which a circuit is formed via a polyimide-based, epoxy-based, polyester-based, or phenol-butyral-based thermosetting adhesive, and then heat-curing the adhesive. It is formed by Further, as a method of providing an overcoat, a method of applying a thermosetting paint made of a liquid resin such as an epoxy type or a urethane type and curing it by heating has also been adopted. Since flexible printed wiring boards require soldering, thermosetting adhesives or thermosetting paints as described above are used in these methods. If these materials are moved or stacked before being cured by heating, problems may occur such as the overlay film being rubbed away from a predetermined position or the uncured overcoat coming into contact with other objects and peeling off. Therefore, methods using these materials have the disadvantage that it is difficult to serialize the manufacturing process of flexible printed wiring boards to achieve mass production and rationalization. We focused on the fact that electron beam curing type resins can be cured instantly by electron beam irradiation, and applied this type of resin as an overcoat for flexible printed wiring boards to solve the above drawbacks. I considered it as much as possible. So far, many types of functional monomers (eg, acrylic, silicone, epoxy, etc.) or oligomers having functional groups have been known as electron beam-curable resins. We have investigated various formulations using electron beam curable resins as paints, but when forming an overcoat by irradiating electron beams, it is difficult to achieve a balance between solder resistance and flexibility. It was very difficult. In other words, a composition that can withstand being immersed in solder will only yield a hard and brittle product that will break easily when folded.
A formulation that would not break when bent was only possible to obtain a formulation that foamed or shriveled when immersed in a solder bath. As a result of further investigation, we found that if the surface of the film with copper foil circuits was treated with a certain type of primer before overcoating with electron beam curing paint, the physical properties of the coating film after electron beam curing would be improved. We have discovered an unexpected phenomenon in which the overcoat has both flexibility that does not break even when bent, and heat resistance that can withstand soldering. The present invention was made based on the above findings, and
The gist of this is that a silane coupling containing an unsaturated double bond such as a vinyl group or an acrylic group, or an epoxy group or an amino group is applied to the surface of an insulating base film having a circuit formed of copper foil. After applying the agent, overcoat with a paint that can be cured by irradiating it with an electron beam.
The method of manufacturing a flexible printed wiring board is characterized in that the coating material is then cured by irradiation with an electron beam. The silane coupling agent referred to in the present invention specifically includes unsaturated double bonds such as vinyl groups and acrylic groups, such as vinyltriethoxysilane and γ-methacryloxypropyltrimethoxysilane used as primers. Silane coupling agents containing epoxy groups, such as γ-glycidoxypropyltrimethoxysilane, and amino acids such as N-β (aminoethyl) γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, etc. Silane coupling agents containing groups are effective. Further, as the paint which can be cured by irradiation with an electron beam as referred to in the present invention, a paint consisting of a resin and a reactive diluent as shown below is used. That is, unsaturated polyester resins or modified products of unsaturated polyesters (for example, urethanized products of unsaturated polyesters with diisocyanates, vinylized products with hydroxyalkyl acrylates, siliconized products with cyclic siloxanes having reactive hydroxyl groups or hydrocarbon oxy groups) One or two vinyl monomers such as styrene, vinyltoluene, α-methylstyrene, divinylbenzene, methyl methacrylate, methyl acrylate, butyl methacrylate, butyl acrylate, hydroxypropyl methacrylate, glycidyl methacrylate, etc.
Modified products of epoxy resin (for example, epoxy resin esters obtained by adding unsaturated dibasic acids such as maleic anhydride and itaconic anhydride to epoxy groups and secondary hydroxyl groups)
containing one or more of the above vinyl monomers, reactive modified acrylic resins (for example, telomerized polyamide acrylate obtained by reacting glycidyl methacrylate with polyamide with terminal carboxy, polyfunctional epoxy compound with acrylic Epoxy acrylate obtained by adding acid or other α/β unsaturated carboxylic acid, urethane acrylate obtained by addition reaction of hydroxyethyl methacrylate etc. to a polyfunctional isocyanate compound, hydroxy methacrylate with silicone containing a hydroxyl group or methoxy group, etc. non-silicone acrylate obtained by condensation),
Or the vinyl monomer is added to an ester acrylate or an ester methacrylate (for example, an oligomer so-called functional oligoester acrylate such as ethylene glycol methacrylate or tetraethylene glycol methacrylate) having two or more acryloyl or methacryloyl groups in the molecule. For example, one or more of these may be blended, or a saturated prepolymer such as an acrylic prepolymer may be dissolved in the functional oligoester. Furthermore, in the present invention, the functional oligoester can be used alone as a coating material. Moreover, it is also possible to add to the above-mentioned coating material, if necessary, fillers such as pigments, dyes, organic and inorganic fillers, and surface treatment agents such as alkyl titanates and methacrylate chromium chloride. The above-mentioned coating material may be applied to the base film having the circuit by a method commonly referred to as brush coating, roller coating, flow coating, or a silk screen method. The irradiation dose of the electron beam used in the present invention varies depending on the composition of the paint, but may be from 0.5 to 20 megarats (Mrad), preferably from 1.0 to 10 megarats. Examples Various primers shown in Table 1 were diluted with ethyl alcohol or water, applied to a polyimide film having a circuit formed of copper foil, and air-dried. After the primer was applied in this manner, a paint having the composition shown in Table 2 was overcoated, and an electron beam of 10 megarads was irradiated to cure the paint, thereby producing a flexible printed wiring board. The flexible printed wiring board obtained in this way
Solder resistance was tested by immersing it in a 280°C solder bath for 10 seconds. The results were as shown in Table 3. In other words, without pretreatment, that is, without applying a primer (Comparative Example 1), the overcoat film was torn due to solder immersion, whereas
Overcoated after applying KBE1003, KBM503, KBM403, KBM603 (Example 1,
No changes were observed in samples 2, 3, and 4) even after immersion in solder, and it was found that they had a remarkable effect of improving the coating film. Also, on the bare copper foil surface that has not been coated with paint,
It was also found that solder could be applied even with these primers applied. KC223 could not improve the physical properties of the coating film, and the solder did not adhere to bare copper foil, making it completely unusable (Comparative Example 2).

【table】

【table】

[Table] Others KBM803, EDTA, NP-ACo, St-
Neither Am nor the like had any effect on improving the physical properties of the coating film. (Comparative Examples 3 to 6). Although the reason is not well understood, the vinyl group of the present invention,
Only when pretreated with a silane coupling agent containing an unsaturated double bond such as an acrylic group, an epoxy group, or an amino group, the physical properties of the coating film are significantly improved.
Moreover, the adhesion of solder to copper in areas without a coating film did not deteriorate, and a good flexible printed wiring board was obtained. The present invention has made it possible for the first time to apply an electron beam curing paint as an overcoat for flexible printed wiring boards, and has greatly streamlined the method of manufacturing flexible printed wiring boards.

Claims (1)

[Claims] 1. After applying a silane coupling agent containing an unsaturated double bond such as a vinyl group or an acrylic group, or an epoxy group or an amino group to the surface of an insulating base film having a circuit formed of copper foil, an electron beam is applied. 1. A method for producing a flexible printed wiring board, which comprises overcoating with a paint that can be cured by irradiation with irradiation, and then curing the paint by irradiating with an electron beam of 0.5 to 20 Mrad.