JPH02177497A - Manufacture of flexible printed wiring board - Google Patents

Abstract

PURPOSE:To prevent remainder of bubbles, immersion of adhesive, contamination with volatile component and to pressadhere a cover lay uniformly by forming an intermediate layer of thermoplastic resin having lower softening point than the melt starting temperature of the adhesive coating the cover lay, employing a composite sheet of three layers as a cushion, and press-molding it. CONSTITUTION:A cover lay 7 is placed on a flexible printed wiring board 8 having a circuit 3 through an adhesive 2 on a base film 1, the cover lay is thermally press-adhered through a stainless mirror-surface plate 9 with a 3-layer composite sheet 6 made of upper and lower surface layers of thermoplastic resin having a higher melting point than the melt starting temperature of adhesive 4 and an intermediate layer of thermoplastic resin having lower softening temperature than the melt starting temperature of the adhesive 4 as a cushion to form a flexible circuit board. The low softening point part is softened at the lower temperature than that of the adhesive to bury the end face of the cover lay, the conductor exposed part. Even after softening, it has suitable viscoelasticity to prevent bubbles from remaining. The high softening point part imparts mold releasing properties to the cover lay, the conductor and the layer sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, a flexible printed wiring board is manufactured using a layered sheet in order to uniformly press a coverlay without leaving bubbles, adhesive seepage, or contaminating circuits due to volatile components. It's about how to do it.

(Prior art) The manufacturing process for flexible printed wiring boards involves bonding a heat-resistant film such as polyimide and copper foil with an adhesive, patterning the copper, and then applying a heat-resistant film on top of the copper foil with an adhesive. Heat and press. Conventionally, heat-resistant rubber, kraft paper, high melting point thermoplastic film, or combinations thereof have been used as the kungjon material used in such coverlay thermocompression bonding. In this method, the end surface of the coverlay cannot be sufficiently buried, resulting in adhesive seepage and contamination of the circuit by volatile matter, making surface treatment impossible.

Also, depending on the melt viscosity of the adhesive, bubbles may remain.

[Problem to be solved by the invention]

An object of the present invention is to provide a method for manufacturing a flexible printed wiring board in which a coverlay is evenly bonded without contaminating the circuit due to residual air bubbles, adhesive seepage, or volatile matter.

(Means for Solving the Problems) The present invention provides a method for applying heat having a softening point lower than the melting start temperature of the adhesive applied to the coverlay in the step of press-bonding the printed circuit surface of the flexible printed wiring board and the coverlay. Manufacture of a flexible printed wiring board characterized by compression molding using a three-layer composite sheet as a cushion, with an intermediate layer made of a plastic resin and a surface layer made of a thermoplastic resin having a melting point higher than the melting start temperature of the adhesive. It's a method.

In the present invention, low-density polyethylene (LDPE), ethylene-vinyl acetate (EVA), flexible vinyl chloride (PVC), and ethylene methylmethacrylate (E
MMA), polypropylene (PP), polyethylene terephthalate (P
ET), polymethylpentene (PMP), polyvinylidene fluoride (PVF), high density polyethylene (HDPE)
PP-PVC-PPSPP-EMMA-PP, PP-PVC-PPSPP-EMMA-PP, etc.
PP-LDPE-PPS PMPEMMA-PP,P
P-EVA-PP can be raised.

[Function] In the present invention, the portion having a low softening point softens at a lower temperature than the adhesive, and is embedded in the end face of the coverlay and the exposed portion of the conductor. Therefore, when the adhesive melts or volatile matter is generated, the conductor is covered to prevent the adhesive from seeping out and contaminating the conductor with volatile matter.

Furthermore, since it has appropriate viscoelasticity even after softening, it prevents bubbles from remaining.

The portion having a high softening point is a portion having mold releasability for coverlays, conductors, and layered sheets.

The present invention will be explained in detail with reference to the drawings. As shown in Figures 1 and 2, a copper foil or the like is attached to a base film (1) made of polyester, polyimide, etc. via an adhesive (2),
A coverlay (7) consisting of a coverlay film (5) coated with an adhesive (4) is placed on the circuit (3) side of a flexible printed wiring board (8) having a circuit (3) obtained by etching. Further, upper and lower surface layers are made of a thermoplastic resin having a melting point higher than the melting start temperature of the adhesive (4), and an intermediate layer has a softening point lower than the melting start temperature of the adhesive (4). A three-layer composite sheet (6) made of thermoplastic resin is used as a cushion, all layers are sandwiched between stainless steel mirror plates (9), heated and pressurized, and a coverlay is thermocompression bonded to form a sheet as shown in Figure 1. A flexible printed wiring board with a coverlay is created.

〔Example〕

[Example-1] A circuit (
3) Flexo pull print layout! 9 J7i (
8) Coverlay film with adhesive (4) on top (
A coverlay (7) consisting of 5) is placed on top, and further,
Figure 1 shows a three-layer composite sheet (6) consisting of PP for the upper and lower surface layers and LDPE for the middle layer as a cushion, sandwiched between stainless steel mirror plates (9), heated and pressurized, and a coverlay bonded by thermocompression. Keyaki shown created a flexible printed wiring board. The results are shown in the table.

[Example-2] Three layers? The upper and lower surface layers of the M notebook are PP, and the middle layer is E.
Using MMA as a three-layer sheet, Example-1
Similarly, a flexible printed wiring board was created by thermocompression bonding the coverlay. The results are shown in the table.

[Example-3] A three-layer composite sheet in which the upper layer was PP, the lower layer was PMP, and the middle layer was EMMA was used as a three-layer sheet, and Example-
A coverlay was thermocompression bonded in the same manner as in 1 to create a flexible printed wiring board. The results are shown in the table.

[Example-4] The upper and lower surface layers of the three-layer composite sheet are PP, and the middle layer is Pv.
Using C as 311 sheet, Example-1
In the same manner as above, a coverlay was thermocompression bonded to create a flexible printed wiring board. The results are shown in the table.

(Comparative Example-1) As shown in Fig. 3, a heat-resistant rubber was used as a cushion and a coverlay was thermocompression bonded to create a flexible printed wiring board.The results are shown in the table.

[Comparative Example-2] As shown in FIG. 4, a flexible printed wiring board was prepared by thermocompression bonding a coverlay using kraft paper as a cushioning material. The results are shown in the table.

Table 1 This method enables uniform crimping of the coverlay without contamination of the conductor by volatile matter, and is suitable as a manufacturing method for crimping the coverlay of a flexible printed wiring board.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a flexible printed wiring board obtained according to the present invention. FIG. 2 is a sectional view showing the structure of coverlay thermocompression bonding according to the method of the present invention, and FIG. 3 is a sectional view showing the structure of coverlay thermocompression bonding in Comparative Example 1. FIG. 4 is a sectional view showing the structure of coverlay thermocompression bonding in Comparative Example 2. The table shows that in the coverlay thermocompression bonding according to the present invention, there was no contamination of the copper terminals, there was little adhesive seepage, and the adhesive between the heat-resistant films was good. In particular, Example-2
The adhesive properties were good regardless of the adhesive formulation. (Effect of the invention) The present invention prevents air bubbles from remaining, adhesive oozing out, and patent applicant: Sumitomo Bakelite Co., Ltd. 2. Invention?,!4; Manufacturing method of flexible printed wiring board 3° correction Tom11τP1・Which relationship Special PI' Applicant address Tokyo fiBIu-ku 3 [Ro 3-11-36 April 11, 7] 4. Date of amendment order: March 20, 1999] (Date of shipment) [How to glue flexible printed wiring boards].

Claims (1)

[Claims] (1) In the process of press-bonding the printed circuit surface of the flexible printed wiring board and the coverlay, a thermoplastic resin having a softening point lower than the melting start temperature of the adhesive applied to the coverlay is used as an intermediate layer to bond the coverlay. 1. A method for producing a flexible printed wiring board, characterized in that a three-layer composite sheet with a surface layer made of a thermoplastic resin having a melting point higher than the melting start temperature of the agent is used as a cushion and pressure-molded.