JPH04206111A - Bonding sheet - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a bonding sheet for flexible printed circuits.

(Prior Art) In recent years, demand for printed circuit boards has increased as electrical products have become lighter, thinner, smaller, and more sophisticated, and the range of use of flexible circuit boards has expanded in particular.

In particular, as high-density packaging advances and the demand for multilayer flexible printed circuit boards increases, the demand for bonding sheets used to bond each layer increases, and further improvements in performance such as adhesiveness and flexibility are desired. It is rare.

Conventional bonding sheets have a single layer structure with only a semi-cured adhesive layer, so each flexible printed circuit board is laminated as a multilayer board.

Coverlay film had become essential.

As shown in Figure 2, the flexible printed circuit multilayer board created with this configuration has the thickness of the coverlay film and bonding sheet added to the thickness of the circuit board.
This impairs the flexibility of flexible printed circuit boards and makes it difficult to improve the flexibility of multilayer boards. Furthermore, conventional bonding sheets did not have sufficient adhesion to the insulating film used in the coverlay film.

(Problems to be Solved by the Invention) The present invention aims to solve the above-mentioned drawbacks, improve the flexibility of a multilayer board for a flexible printed circuit, and provide a bonding sheet for a flexible printed circuit with excellent adhesive properties. It is.

(Means for Solving the Problems) The present inventors have carried out extensive research in order to solve the above problems, and as a result, they have arrived at the present invention. The gist of the present invention is to provide a bonding method in which an insulating film treated with low temperature plasma has a semi-cured adhesive layer on both sides, and a release film or release paper is pressed onto the outer surface of the adhesive. It's on the sheet.

Examples of the insulating film used in the present invention include films of polyimide, polyethylene terephthalate, polyphenylene sulfide, polyparabanic acid, polyether/etherketone, etc. Among them, polyimide films are preferably used. In the present invention, in order to improve adhesion to the adhesive, it is necessary to subject the insulating film to low-temperature plasma treatment using an inorganic gas in advance.

The method of low-temperature plasma treatment includes placing the insulating film in a low-temperature plasma treatment device that can reduce pressure, creating an inorganic gas atmosphere inside the device, and maintaining the pressure at 0.001 to 10 torr, preferably 0.01 to 1 torr. In this state, a direct current or alternating current of around 0.1 to 10 kV is applied between the electrodes to generate a glow discharge, thereby generating low-temperature plasma of inorganic gas, and continuously plasma-treating the surface while moving the insulating film one after another. However, the plasma treatment time is preferably approximately 0.1 to 100 seconds. As inorganic waste,
Inert gases such as helium, neon, alcon, etc., and oxygen, nitrogen, carbon oxide, carbon dioxide, ammonia, air, etc. are used, but these are not limited to one type, and it is optional to use a mixture of two or more types. It will be held on.

Adhesives used in the present invention include epoxy phenol/polyester and NBR/phenol.

Rigid resins include epoxy phenol/NBR, NBR/epoxy, epoxy/polyester, epoxy/acrylic, and acrylic.

The release film and release paper used in the present invention include polyethylene film, polypropylene film,
Examples include TPX film, polyester film with a silicone release agent, film-coated paper of polyolefin such as polyethylene and polypropylene, and vinylidene chloride film-coated paper.

The bonding sheet of the present invention is prepared by first applying the adhesive onto a release film (or release paper) to a thickness of 20 to 50 μm in a dry state.
Apply the adhesive until it is semi-cured. At this time, heating can be performed for a short time at about 80 to 150°C if necessary. Further, a release film (or release paper) is attached to this and wound up into a roll. Alternatively, the product is simply wound into a roll without attaching a release film (or paper). This is called A-roll. Next, apply the adhesive on one side of the insulating film for 20 to 50 minutes in a dry state.
Apply to a thickness of μm and bring the adhesive to a semi-cured state.

At this time, heating can be performed for a short time at about 80 to 150°C if necessary.

Furthermore, a release film (or release paper) is attached to this and wound up into a roll. This is called B-roll. Finally, if release film (or release paper) is pasted on both sides of the A roll, peel off the release film (or release paper) on one side and use the exposed adhesive side of the A roll. If the release film (or release paper) is attached to only one side, the exposed adhesive side where the release film (or release paper) is not attached is not coated with the adhesive of the B-roll insulation film. The bonding sheet of the present invention is manufactured by laminating it on one side and winding it up into a roll. In this case, the manufacturing order of the A roll and B roll may be reversed.

Next, the present invention will be specifically explained with reference to Examples.
First, an example of manufacturing an insulating film treated with low temperature plasma, which is the starting material of the present invention, will be described.

A 25 an square, 25 μm thick Kapton film (trade name of polyimide film manufactured by Dupont) was placed in a low-temperature plasma processing apparatus, and oxygen was introduced at a vacuum degree of 0.2 torr.
An AC voltage of 110 kHz, 1.5 kV was applied to the electrodes to generate glow discharge, and low-temperature plasma treatment was performed for 20 seconds. The Kapton film was placed on the lower electrode of the upper and lower opposing electrodes, and the gap between the electrodes was 10 aa. This was called low temperature plasma A treatment.

Similarly, low-temperature plasma treatment was performed using argon and argon-oxygen mixed gas at a pressure of 0.2 Torr.

The former was treated as a low temperature plasma B treatment, and the latter was treated as a low temperature plasma C treatment.3 The examples described below are of course not intended to limit the scope of the present invention.

Example 1 A heat-resistant epoxy adhesive (MEK solution with a solid content of 30%) was applied to a polyethylene terephthalate film with a thickness of 25 μm, one side of which was treated with silicone mold release, so that the coating thickness after drying was 30 μm.
Apply to a thickness of μm, 80''CX 2 minutes, 120℃
The adhesive was heated and dried in two stages of x5 minutes to remove the solvent and bring the adhesive into a semi-cured state.

A release paper was laminated onto this by pressure bonding using a roll laminator at a temperature of 50°C, a linear pressure of 5 kg/cm, and a speed of 2 m/min.

This is made into a laminated product.

Next, a heat-resistant epoxy adhesive (MEK solution with a solid content of 30%) is applied to a 25 μm thick polyimide film that has been treated with low-temperature plasma A on both sides so that the coating thickness after drying is 30 μm, and laminated onto the above. A B laminate product was created through the same process as the product.

Furthermore, the release paper of the A laminate was peeled off, and the adhesive side of the A laminate and the non-adhesive polyimide side of the B laminate were stacked together using a roll laminator at a temperature of 50°C and a linear pressure of 5.
kg/rxr and a speed of 2 m/min to create a bonding sheet.

In order to measure the properties of this bonde ink sheet, the release paper and release film were removed from this sheet, and it was laminated on the glossy side of 35 μm thick electrolytic copper foil, and pressed under 160
A laminated product was produced by pressing at 50 kg/ci for 30 minutes at ℃. Table 1 shows the properties of the flexible laminate thus obtained.

In addition, in order to adjust the flexibility of this bonding sheet, a single-sided flexible copper-clad laminate (composition: 35 μm thick) was used.
Rolled fR foil, 25 μm thick polyimide film, adhesive thickness 20 μm) and coverlay film (composition: 25 μm thick)
(μm polyimide film, adhesive thickness 30 μm) and this bonding sheet with release paper and release film removed, press condition 160℃, 50kg
/a&, Pressed in 30 minutes to create a laminate corresponding to the 4-layer board of the flexible printed circuit board shown in Figure 1,
I adjusted the flexibility of this. The results are shown in Table 1.

Example 2 A bonding sheet and a laminate were produced in the same manner as in Example 1 except that a polyimide film treated with low-temperature plasma B was used.

Example 3 A bonding sheet and a laminate were produced in the same manner as in Example 1 except that a polyimide film treated with low-temperature plasma C was used.

Comparative Example 1 Using an untreated polyimide film, the rest was the same as Example 1.
A bonding sheet and a laminate were prepared in the same manner as above.

The four-layer board in this case had the structure shown in FIG.

Comparative Example 2 A sheet similar to the laminated product of Example 1 was prepared as a bonding sheet, and a laminate was made in the same manner as in Example 1 using this sheet.

Table 1 (Test method) l) Peel strength Tested according to JIS C6481. ], The copper foil is peeled off from a sample with a width of 0 mm in a 90 degree direction at a speed of 50 nn/min.

(2) Soldering heat resistance Float the sample on a solder bath at 260°C for 30 seconds and observe any blisters.

1ij) Flexibility radius of curvature 2c! Wrap it around the cylinder No. 11 five times, and observe the appearance of the wrapped material and the appearance of the laminate when unwound.

(Effects of the Invention) The present invention has made it possible to provide a bonding sheet with excellent adhesive properties. When manufacturing a flexible printed circuit multilayer board using the bonding sheet of the present invention, the coverlay film can be reduced compared to when manufacturing a multilayer board using a conventional bonding sheet, so the overall thickness of the multilayer board can be reduced. The present invention has extremely high industrial utility value because it is thinner by the thickness of the film and improves flexibility, and the step of bonding the coverlay film is omitted, which in turn leads to a reduction in raw material costs.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing the structure of a four-layer laminate product using the bonding sheet of the present invention. FIG. 2 is a longitudinal sectional view showing the structure of a four-layer laminate product using a conventional bonding sheet. Figure 1 Figure 2

Claims (1)

[Claims] A bonding sheet comprising a semi-cured adhesive layer on both sides of an insulating film treated with low-temperature plasma, and a release film or release paper pressure-bonded to the outer surface of the adhesive.