JPH04201441A - Cushioning material - Google Patents

Abstract

PURPOSE:To bury without gap an adhesive for a coverlay film in an FPC (flexible printed circuit) and to prevent a film from occurrence of elongation, cracks, wrinkles and defects by laminating directly or through an adhesive layer a vinyl chloride sheet on the upper face of a kraft paper and laminating a release film directly or through an adhesive layer on this vinyl chloride sheet to integrate them. CONSTITUTION:A kraft paper 1a and a vinyl chloride sheet 1c are bonded together through an adhesive layer 1b and in addition, a release film 1d is bonded together with the vinyl chloride sheet 1c through an adhesive layer 1b. As the kraft paper 1a, a neutral virgin paper which has no possibility of discoloring the copper surface of FRC is suitable and in addition, such a product that contains as little as possible an org. binder such as tar which causes seizing to a mirror surface when hot contact bonding is performed is suitable. In addition, as the release film 1d, a film such as polypropylene, polymethylpentene and fluorinated resin is used and as the adhesive layer 1b, such an adhesive that is made of an epoxy, a urethane or an acrylic resin can be used.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to flexible printed circuits (hereinafter referred to as r
(abbreviated as FPcJ) relates to a cushioning material used in the coverlay film thermocompression bonding process during manufacturing.

[Prior Art] When manufacturing FPC, usually after forming a circuit on a base copper clad laminate (hereinafter abbreviated as rCCLj), a polyimide film or a polyester film with a thickness of about 25 to 125μ is used as a protective film. Thickness lO~35
A coverlay film coated with an adhesive of about μm thickness is bonded together for the purpose of insulation and protection of circuits.

At this time, the adhesive of the coverlay film is molded so that it is completely embedded in the gap between the circuits, and in order to harden the adhesive, a heat press is used to heat the film to a temperature of about 140 to 180°C. They are bonded together under pressure at a temperature of .

In this thermocompression bonding process, since the FPC has irregularities in the circuit and lands and terminals to which the coverlay film is not attached, the coverlay film is tightly attached to the irregularities of the circuit without any gaps, and the lands and terminals are Cushioning material is used to prevent adhesive from seeping out.

Conventionally, silicone rubber sheets, Teflon glass cloth, polyethylene sheets, etc. have been used as this cushioning material, either singly or in combination, or with a thickness of 25 to 50 μm for the purpose of releasing from the coverlay film. It is used in combination with a release film such as polypropylene film.

[Problem to be solved by the invention] However, among such conventional cushioning materials,
Although the silicone rubber sheet has excellent cushioning properties, it has the disadvantage that the silicone rubber sheet stretches in the lateral direction during the thermocompression bonding process, which causes the FPC to stretch as well, resulting in dimensional defects and cracks in the FPC. There is.

In addition, when using a polyethylene sheet, it is possible to omit the use of a release film, but the polyethylene sheet melts, flows, and stretches during the thermocompression bonding process, resulting in dimensional defects and cracks in the FPC. There are drawbacks such as the occurrence of

Furthermore, among these, polyethylene sheets have no waist,
Furthermore, silicone rubber sheets are heavy and ugly, making them difficult to handle and causing problems in terms of workability.

On the other hand, when Teflon glass cloth is used alone or in combination with a release film, the Teflon glass cloth suppresses the elongation of the coverlay film during thermocompression bonding, resulting in problems such as dimensional defects and cracks in the FPC. However, the weave of the glass cloth is transferred to the FPC, creating unevenness on the surface, which is unfavorable in terms of appearance.Also, the adhesion at the land and terminal areas is insufficient, resulting in adhesive stains on the coverlay film. It has the disadvantage that it causes leakage.

The present invention has been made in view of the above circumstances, so that in the process of thermocompression bonding the coverlay film, the adhesive of the coverlay film is embedded in the circuit of the FPC without any gaps, and the coverlay film is in a completely adhered state. The purpose of the present invention is to provide a cushioning material that is effective in preventing defects such as elongation, cracks, wrinkles, and scratches, stabilizing and improving quality, and improving workability in a thermocompression bonding process.

[Means for Solving the Problems] The cushioning material of the present invention has a vinyl chloride sheet laminated directly or via an adhesive layer on the upper surface of kraft paper, and a release film is laminated directly or via an adhesive layer on the vinyl chloride sheet. The solution to the above problem was to integrate the materials by laminating them through layers.

[Example] The present invention will be described in detail below. FIG. 1 shows an embodiment of the cushioning material 1 of the present invention, in which a kraft paper 1a and a vinyl chloride sheet lc are pasted together with an adhesive layer lb, and a release film 1d is further applied on the vinyl chloride sheet lc as an adhesive layer. It has a structure in which 1b is bonded together.

The kraft paper 1a is a neutral virgin paper that does not cause discoloration of the copper surface of the FPC4, and furthermore,
A material containing as little organic binder as possible, such as tar, which may cause sticking to the mirror plate during thermocompression bonding, is suitable. Further, a thickness of 50 to 350 μm is used.

In addition, vinyl chloride sheet LC is JES K673
Generally used agricultural vinyl that falls under the four types of agricultural vinyl specified in 2.
00 μm is used.

In addition, as the release film 1d, a pinyl chloride sheet l
A film that is flexible at high temperatures without impairing its adhesion to the FPC 4 (c), such as polypropylene, polymethylpentene, fluorine-based film, etc., is used, and has a thickness of 10 to 50 μm.

Furthermore, as the adhesive layer 1b for bonding the craft paper 1a and the vinyl chloride sheet lc, or the vinyl chloride sheet lc and the release film ld, epoxy, urethane, acrylic, etc. can be used. The thickness of 1b is preferably 3 to 15 μm.

Kraft paper 1a and vinyl chloride sheet lc are both difficult to handle because they have no stiffness, and workability is not good.
By bonding and integrating the components c in advance with the adhesive layer 1b, handling becomes easier and workability improves. Further, by integrally fixing in this manner, the kraft paper 1a suppresses the elongation of the vinyl chloride sheet 1c that occurs during thermocompression bonding, so that it is possible to prevent dimensional defects and cracks in the FPC 4.

However, in the structure of only the kraft paper 1a and the vinyl chloride sheet lc, the vinyl chloride sheet lc and the FP, which is the material to be heat-pressed,
Since the mold releasability after thermocompression bonding with C4 is poor, it is necessary to interpose a mold release film ld, which is a troublesome work.

Therefore, by further laminating the release film ld on the vinyl chloride sheet) lc with the adhesive layer 1b and using it as an integrated sheet, the work process is not only simplified and workability is improved, but also the overall By integrating, it is possible to use a thinner release film ld, and the overall material cost can also be reduced.

FIGS. 2 and 3 show examples of how the cushioning material 1 of the present invention is used.

FIG. 2 is a cross-sectional view schematically showing a state in which an FPC 4 as an object to be pressed and a cushion material 1 of the present invention are assembled in a hot press apparatus.

FPC4 made by covering a CCL4b with a circuit formed on the surface with a coverlay film 4a which is a protective film.
The surface of the material is pressed with a cushioning material 1, and heat and pressure are applied from both the upper and lower directions using the heat press hot plate 2 and the mirror plate 3 located inside the hot press plate 2 to bond the material under thermocompression. At this time, FPC
The release property of CCL 4b is ensured on the upper surface of 4 by the release film ld of the cushion material 1, and the release property of CCL 4b is ensured by interposing a release film ld with a thickness of 40 to 100 μm on the lower surface of the FPC 4. secure.

FIG. 3 is a cross-sectional view showing the state of close contact between the FPC 4, the release film ld, and the cushion material 1 when heat and pressure are applied from both the upper and lower directions during thermocompression bonding.

The vinyl chloride film 1c is deformed along the unevenness of the FPC 4 under high temperature and high pressure, and the coverlay film 4a is transformed into a surface circuit 5.
Attach it tightly without any gaps. In addition, the land portion 6 of the FPC4,
Alternatively, the release film ld is also applied to the edge of the coverlay film 4a formed on the terminal part.
The adhesive 4c of the coverlay film 4a can be prevented from seeping out by closely adhering the coverlay film 4a without any gaps.

In addition, the kraft paper 1a plays a role in filling in the unevenness of the surface circuit 5 of the FPC 4, and has the effect of assisting the vinyl chloride sheet lc to adhere closely to the uneven parts without gaps, especially in the areas with small unevenness. Furthermore, the unevenness on the surface of the mirror plate 3 and the unevenness caused by scratches can be alleviated and absorbed to give the product a beautiful appearance.

Table 1 shows the results of comparing the frequency of defective items and workability when the cushioning material of the present invention and cushioning materials made of other materials are used in the thermocompression bonding process.

Example 1 As Example 1 of the product of the present invention, a cushioning material was made by integrating a 300 μm thick kraft film, a 100 μl thick vinyl chloride sheet, and a 25 μm thick polymethylpentene film.

Example 2 - As Example 2 of the product of the present invention, 300 μm thick kraft sheet, 100 μm thick vinyl chloride sheet, and 12.5 μm thick vinyl chloride sheet were used.
A product that is integrated with a thick polymethylpentene film,
Used as cushioning material.

Comparative Example 1: A 100 μm thick polyethylene sheet alone was used as a cushioning material.

Comparative Example 2: A 1,600-μm-thick silicone rubber sheet was used as a cushioning material, and was used in combination with a 50-μI-thick polymethylpentene film for mold release.

Comparative Example 3: A 1600 μm thick silicone rubber sheet and 300 μl WL Teflon glass cloth were used together as a cushioning material.

Comparative Example 4: A 100 μm thick vinyl chloride sheet was used as a cushioning material, and was used together with a 50 μm thick polymethylpentene film for mold release.

Comparison items include dimensional defects, tears, surface irregularities and wrinkles, surface scratches, adhesive seepage, and circuit embedding defects when thermocompression bonding is applied to FPC using each cushioning material. Frequency and workability are indicated in three stages: ○, △, and ×, from less to more defective items, or from good to bad workability.

As shown in Table 1, when the cushioning material of the present invention is used, products with dimensional defects due to elongation, tears, scratches, unevenness, and wrinkles are more likely to occur than when cushioning materials made of other materials are used. It was confirmed that this method is effective against defects, as well as circuit embeddability and workability.

Furthermore, when comparing the use of the cushioning material of the present invention and the use of a release film alone in terms of workability and cost, it is found that in the work process of a simple single-sided FPC, The work time can be reduced by approximately 15%, and the price of the release film is lower than the conventionally used thickness of 5.
Since it is possible to change the 0 μm film to a 25 μm film or a 12.5 μm film, costs can be significantly reduced.

(Hereinafter, blank space) [Effects of the invention] As explained above, the cushioning material of the present invention can be used to
When heat-compression bonding a coverlay film to a PC, you can not only obtain a high-quality product that has a beautiful appearance because there are no scratches, unevenness, or wrinkles, and also has good circuit embedding, but also eliminates dimensional defects due to stretching. The incidence of product defects such as cracks is reduced. In addition, since the cushioning material can be handled as a container, work efficiency can be improved, and compared to using a separate release film alone,
It is possible to improve workability and reduce material costs.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing one embodiment of the present invention, and Fig. 2 is a sectional view showing an embodiment of the present invention.
FIG. 3 is a schematic cross-sectional view showing a state in which the PC and the cushioning material are assembled into a heat press device, and FIG. 3 is a cross-sectional view showing the state in which the FPC, the release film, and the cushioning material are in close contact with each other during thermocompression bonding. l...Cushion material, Im-kraft paper, lb...
adhesive layer, lc... vinyl chloride sheet, 1d... release film, 4... flexible printed circuit, 4a... coverlay film, 5... surface circuit.

Claims (1)

[Claims] A cushioning material used when thermocompression bonding a coverlay film that covers the surface circuit of a flexible printed circuit.A vinyl chloride sheet is laminated directly or via an adhesive layer on the top surface of kraft paper. A cushioning material characterized by having a release film laminated thereon either directly or through an adhesive layer.