JPH04351546A - Cushioning material - Google Patents

Abstract

PURPOSE:To improve workability and quality of a product by improving a cushioning material used at a process for hot contact bonding of a coverlay film on the surface of the following laminate after a circuit is formed on a copper-clad laminate to be used as a base of a flexible printed circuit(FPC). CONSTITUTION:A cushioning material is prepd. by laminating integrally a propylene resin sheet 1 on both upper and lower faces of a kraft paper 2 as an intermediate layer. In addition, an FPC wherein an adhesive material of a coverlay film is embedded in a circuit without gap and which has no dimensional failure and excellent quality can be prepd. The workability is remarkably improved as a hardly processable propylene resin sheet is not independently handled. The cushioning material and the FPC can be easily separated after thermocompression.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cushioning material used in a coverlay film thermocompression bonding process when manufacturing a flexible printed circuit (hereinafter abbreviated as "FPC").

0002

[Prior Art] When manufacturing FPC, usually after forming a circuit on a base copper clad laminate (hereinafter abbreviated as "CCL"), a coverlay film is attached to the surface for the purpose of insulation and protection of the circuit. is being carried out. This coverlay film is made of polyimide film or polyester film with a thickness of about 25 to 125 μm.
An adhesive coated with a thickness of about 10 to 35 μm is used. Then, the adhesive of the coverlay film bonded to the CCL is completely embedded in the gap between the circuits, and in order to harden the adhesive, the coverlay film is bonded using a heat press machine. The process is carried out under pressure at a temperature of about 140 to 180°C.

[0003] In this thermocompression bonding process, since the FPC has irregularities of the circuit and land parts and terminal parts to which the coverlay film is not attached, the coverlay film is closely attached to the irregularities of the circuit without any gaps, and the lands are Cushioning material is used to prevent adhesive from seeping out at the parts and terminals. First of all, this cushion material is made of CC
The surface circuit of L is covered with a coverlay film, and then the C
When applying heat and pressure to CL, it is used by interposing it between the mirror plate and the coverlay film.

[0004] Conventionally, this cushioning material has been made of silicone rubber sheets, vinyl chloride sheets, EVA (ethylene-vinyl acetate copolymer) sheets, etc., with a thickness of 25 to 50 μm for the purpose of releasing the coverlay film from the mold. Release films such as polypropylene films were also used.

[0005]

[Problems to be Solved by the Invention] However, when sheets such as silicone rubber sheets, vinyl chloride sheets, EVA sheets, and release films are used in combination, (1
) Difficult to handle the release film, poor workability, (
2) It is difficult to peel off the release film from the FPC after thermocompression bonding. (3) When thermocompression bonding is performed on double-sided FPC, the release films of the cushioning material used on the top and bottom surfaces of the FPC may overlap each other. (4) Due to the difference in thermal properties between the sheet and the release film, depending on the combination of these, components such as additives and oligomers in the release film may adhere to the FPC surface. (5) If a resin such as a vinyl chloride sheet or EVA sheet is used, the sheet may melt and flow during the thermocompression bonding process, causing wrinkles to form during the thermocompression bonding process. There were problems such as staining the mirror plate of the mirror and causing product defects, and the workability of removing the stain worsened.

The present invention was made in view of the above circumstances, and aims to provide a cushioning material that improves workability in the process of thermocompression bonding a coverlay film and improves the quality of the resulting product. do.

[0007]

[Means for Solving the Problems] The cushioning material of the present invention uses kraft paper as an intermediate layer, and propylene resin sheets consisting of a single layer or multiple layers are laminated together on the upper and lower surfaces of the intermediate layer through an adhesive layer. This is the solution to the above problem.

[0008] This invention will be explained in detail below. FIG. 1 shows an embodiment of the cushioning material of the present invention. The cushioning material of the present invention has a kraft paper 2 as an intermediate layer, and propylene resin sheets 1 are integrally laminated on the upper and lower surfaces of the kraft paper 2 via an adhesive 3.

The above propylene resin sheet 1 has a thickness of 9 mm.
It is formed to a thickness of 0 to 200 μm, and can be formed by one film formation, or by laminating thin films into multiple layers using heat fusion or adhesive 3. You can also do that. As the adhesive 3 used here, any of epoxy, urethane, and acrylic adhesives can be used. Further, the adhesive 3 is applied to a thickness of about 2 to 10 μm.

The propylene resin used to form the propylene resin sheet 1 may be a copolymer of propylene and another olefin, but a propylene homopolymer is more preferred. In addition, when propylene resin contains trace amounts of halogen elements such as chlorine, corrosive gas is generated when heated, resulting in CCL
Copper may be corroded, so in order to prevent this, the propylene resin used in JP-A-59-209644
It is preferable to use one containing a halogen scavenger as disclosed in Japanese Patent Publication No. Furthermore, the propylene resin sheet 1 undergoes heat shrinkage during the FPC thermocompression bonding process, resulting in FPC
In order to prevent the occurrence of dimensional defects in the PC, it is preferable that the propylene resin film is formed in a state as close to non-stretching as possible, without stretching as much as possible. Further, for the same reason, when the propylene resin sheet 1 is laminated and integrated with the kraft paper 2, it is preferable that the sheet be bonded in a non-stretched state as much as possible without stretching.

As the above-mentioned kraft paper 2, a neutral virgin paper that does not cause discoloration of the copper surface of the FPC is suitable, and a paper that contains as little organic binder as possible is suitable. Also, the thickness is 50 to 350 μm
are used.

[0012] Also, as the adhesive 3 for bonding the propylene resin sheet 1 and the kraft paper 2, epoxy,
Either urethane or acrylic may be used, and the coating is applied to a thickness of 2 to 10 μm.

[0013]

EXAMPLE A cushioning material was prepared by adhering a 50 μm thick polypropylene sheet 1 to both sides of a 250 μm thick kraft paper 2 via a 10 μm thick adhesive layer 3. Using this cushioning material, a coverlay film was thermocompression bonded to the surface of CCL. First, a CCL with a circuit formed on its surface is covered with a coverlay film, and while the surface is pressed with a cushioning material, heat and pressure are applied to the CCL from both the top and bottom using a hot press plate equipped with a mirror plate as an action surface. was activated. FP obtained in this way
In case C, the surface circuit embedding property of the coverlay film was good, and no dimensional defects were observed. Further, no wrinkles or foreign matter were observed on the FPC or the mirror plate. Furthermore, after thermocompression bonding, the cushioning material could be easily removed from the FPC.

[0014]

As explained above, the cushioning material of the present invention has kraft paper as an intermediate layer, and propylene resin sheets are integrally laminated on both upper and lower surfaces of the intermediate layer through an adhesive. Therefore, the propylene-based resin sheet with cushioning properties acts to fill in the uneven portions of the surface circuit of the FPC, and the kraft paper suppresses the lateral elongation of the propylene-based resin sheet that occurs during thermocompression bonding. Excellent quality F with good circuit embedding properties, stable adhesive seepage amount, and no dimensional defects.
PCs can be manufactured.

[0015] Since this cushioning material is made by integrating kraft paper and a propylene resin sheet, the propylene resin sheet, which is difficult to handle, does not need to be handled alone, and workability is significantly improved. In addition, there is no risk that the resin constituting the cushioning material will melt and flow, improving workability and producing products of stable quality.

In addition, the propylene resin sheet constituting this cushioning material has mold releasability, and is used after being formed to an appropriate thickness to obtain the required cushioning properties, so that the rigidity of the kraft paper can be improved. Due to this and the elasticity of the propylene resin sheet, this cushioning material can be easily peeled off from the FPC after thermocompression bonding. Alternatively, in the same manner, when manufacturing a double-sided FPC, the cushioning material applied to both sides of the FPC can be easily peeled off after thermocompression bonding.

In addition, since the kraft paper is sandwiched between propylene resin sheets, there is no risk of its fibers adhering to external objects, so even if it is used in a roll, there will be problems such as damaging the coverlay film. Nor. Furthermore, there is no fear that wrinkles will occur in the FPC or residue will adhere to the product due to differences in thermal properties between the sheet as a cushioning material and the release film.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the cushioning material of the present invention.

[Explanation of symbols]

1 Propylene resin sheet 2. Kraft paper 3 Adhesive material

Claims (1)

[Claims] Claim 1: A cushioning material used when thermocompression bonding a coverlay film covering the surface circuit of a flexible printed circuit, comprising a single layer or multiple layers on the upper and lower surfaces of the intermediate layer of kraft paper. A cushioning material made by integrally laminating propylene resin sheets with an adhesive layer interposed therebetween.