JPH038596B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention provides a cover made by pasting a coverlay based on a resin with lower heat resistance and a higher heat shrinkage rate on the circuit surface of a flexible circuit board based on a heat-resistant resin. The present invention relates to a method of manufacturing a flexible circuit board with a lay. [Technical background of the invention and its problems] In recent years, with the development of the electronics industry, there has been a demand for smaller, lighter, and higher density internal wiring of devices, and the use of flexible circuit boards that can be bent and three-dimensionally wired has increased. I've been doing it. Such flexible circuit boards have traditionally been used by laminating a plastic film with an adhesive layer called a coverlay on the circuit surface. In particular, flexible circuit boards that require soldering are made using a polyimide resin base. A structure in which a polyimide resin-based coverlay is adhered to the circuit surface of a flexible circuit board is often used. By the way, recently, for applications where the soldering iron is applied only to the exposed part of the circuit and the coverlay is not directly touched by the hot iron tip or molten solder, from the point of view of economic efficiency, polyimide resin is being used which is more heat resistant than polyimide resin. A flexible circuit board with a coverlay attached to it is being considered, which is made of polyester resin, which is inferior in quality but inexpensive. However, when manufacturing such polyester resin-based flexible circuit boards with coverlays using commonly used flat plate molds, there is a drawback that good appearance and characteristics cannot be obtained. . That is, as shown in FIG. 1, a polyester resin-based coverlay 3 is stacked on a polyimide resin-based flexible circuit board 1 and a circuit 2 surface with the adhesive layer inside, and then this is placed between a pair of flat plate molds 4,
When heat-pressure molding is performed by sandwiching the circuit board between 4' and 4', the heat shrinkage rate of polyester resin is higher than that of polyimide resin. Large warping (curl) and deformation occurred with the coverlay 3 on the inside. [Object of the Invention] The present invention was made to solve these drawbacks, and its object is to manufacture a flexible circuit board with a coverlay that has a smooth surface and is free from curls and deformation. [Summary of the Invention] That is, the method for manufacturing a flexible circuit board with a coverlay according to the present invention includes a method of manufacturing a flexible circuit board with a coverlay, in which a synthetic resin made of a synthetic resin having a higher thermal shrinkage rate than the heat-resistant resin is placed on the circuit surface of a flexible circuit board based on a heat-resistant resin. When pasting the coverlay, the flexible circuit board and the coverlay are placed between a mold having a concave and convex curved surface with a radius of curvature of 50 to 1000 mm, with the flexible circuit board on the convex side and the coverlay on the convex side. It is characterized by being sandwiched so that the concave side is formed, and bonded together under heat and pressure. The flexible circuit board based on heat-resistant resin used in the present invention is made of a resin with excellent heat resistance such as polyimide resin, and has a thickness of 0.010~
One side of a 0.130mm film is surface-treated as necessary, a metal foil is pasted on top of this using an adhesive, and a circuit is formed by etching the metal foil. Adhesives used for the above coverlay include:
Metal foils for circuit formation include epoxy, polyester, polyimide, rubber-epoxy, rubber-phenol, rubber-epoxyphenol, and epoxy-polyester.
They are made of copper, nickel, stainless steel, or aluminum and have a thickness of 0.010 to 0.150 mm.
Note that it is preferable that the bonding surface of the metal foil is subjected to surface treatment if necessary. For a coverlay based on a resin with lower heat resistance and higher heat shrinkage rate than the above-mentioned heat-resistant resin used in the present invention, for example, one side of a polyester resin film with a thickness of 0.010 to 0.130 mm may be surface-treated as necessary. There are adhesives on which an adhesive layer of epoxy, polyester, polyimide, rubber-epoxy, rubber-phenol, rubber-epoxy-phenol, epoxy-polyester, etc. is provided. The mold used in the present invention has a pair of opposing molding surfaces, a concave arc shape and a convex arc shape, with a curvature radius of 50 to 1000 mm, more preferably 100 to 700 mm. The reason why the radius of curvature of the molding surface of the mold is limited to the above range in the present invention is as follows. In other words, if the radius of curvature of the molding surface is less than 50 mm,
When a polyimide resin-based flexible circuit board is sandwiched with the convex arc-shaped molding surface side, the deformation imparted during molding is greater than the deformation resulting from the difference in heat shrinkage rate between the polyester resin and polyimide resin. If the radius of curvature exceeds 1000 mm, the mold becomes similar to a conventional flat plate mold, and curling and deformation cannot be sufficiently prevented. . When using a concave arc-shaped or convex arc-shaped mold with a cross-section of the molding surface having a radius of curvature of 150 to 1000 mm, the deformation during hot-pressure molding and the heat shrinkage force between the polyester resin and polyimide resin at this time will be reduced. The deformations in the opposite directions due to the differences are almost equal, and a flexible circuit board with a coverlay that is free from curling or deformation and has excellent smoothness can be obtained. To carry out the invention, as shown in FIG.
First, on the circuit 6 side of the flexible circuit board 5 based on the heat-resistant resin, a coverlay 7 based on a resin with a higher heat shrinkage rate, such as the polyester resin, is layered with the adhesive layer on the inside.
The flexible circuit board 5 is placed between the molding surfaces 9 and 9' of the molds 8 and 8', each having a concave arc shape and a convex arc shape in cross section.
is placed on the convex arc-shaped molding surface 9 side, and the cover lay 7 is placed on the concave arc-shaped molding surface 9' side. At this time, a cushioning material or mold release agent such as kraft paper, linter paper, silicone rubber sheet, or Teflon sheet containing glass cloth is inserted between the molds 8 and 8', the flexible circuit board 5, and the coverlay 7. You can also do that. Next, while heating the molds 8 and 8' to a temperature of 120 to 180°C, a pressure of 5 to 100 kg/cm ² is applied for 1 to 100 minutes to form the flexible circuit board 5 and coverlay 7.
By heating and pressurizing, a flexible circuit board with a coverlay without curling or deformation can be obtained. In the present invention, the flexible circuit board and the coverlay may be passed through a heating roll to be preliminarily bonded together before the heat-pressing molding step, and the cover obtained after the heat-pressing molding is further bonded. The flexible circuit board with a lay may be subjected to post-heating treatment by passing it through a dryer or the like. By employing these methods, a flexible circuit board with a coverlay in which the flexible circuit board 55 and the coverlay 7 are bonded more completely can be obtained. [Embodiments of the Invention] Examples of the present invention will be described below. Example 1 A 0.035 mm thick copper foil was pasted on one side of a 0.025 mm thick polyimide resin film via an epoxy adhesive layer, and a circuit was formed by etching the copper foil to form a polyimide resin-based flexible circuit board. was manufactured. The following thickness on the circuit side of this flexible circuit board
A polyester resin base coverlay consisting of a 0.025 mm polyester resin film with an epoxy adhesive layer on one side is stacked with the adhesive layer on the inside, and the cross section is shaped into a concave arc shape and a convex arc shape with a radius of curvature of 300 mm. A 10 mm thick silicone rubber sheet is sandwiched between the opposing surfaces of a mold having a pair of molding surfaces, with the flexible circuit board facing toward the convex arc-shaped molding surface and the coverlay facing toward the concave arc-shaped molding surface. The flexible circuit board and coverlay are bonded together by applying pressure of 40Kg/cm ² for 30 minutes while heating to 160℃ to produce a polyimide resin-based flexible circuit board with a polyester resin-based coverlay. did. Example 2 One side of a polyimide resin film with a thickness of 0.050 mm was coated with a rubber-epoxy adhesive layer to a thickness of 0.070 mm.
A polyimide resin-based flexible circuit board was manufactured by bonding copper foils of 1 mm thick and etching the copper foils to form a circuit. Next, on the circuit surface of this flexible circuit board, a polyester resin base coverlay consisting of a 0.050 mm thick polyester resin film with a rubber-epoxy adhesive layer on one side is superimposed with the adhesive layer on the inside. The flexible circuit board is on the convex arc-shaped molding surface side, and the coverlay is on the concave arc-shaped molding surface side between the molding surfaces of the mold, which has a pair of molding surfaces with a concave arc shape and a convex arc shape in cross section with a radius of curvature of 200 mm. A polyimide resin-based flexible circuit board with a polyester resin-based coverlay was sandwiched between 10mm-thick silicone rubber sheets and heated to a temperature of 160℃ while applying a pressure of 40Kg/ ^cm2 for 30 minutes. was manufactured. Comparative Example 1 The same polyester resin coverlay used in Example 1 was superimposed on the circuit surface of a polyimide resin-based flexible circuit board manufactured in the same manner as in Example 1, and a 10 mm thick silicone rubber sheet was interposed between the layers. The flexible circuit board and coverlay were sandwiched between a pair of stainless steel flat plates with a thickness of 2.0 mm, heated to a temperature of 160°C, and a pressure of 40 kg/cm ² was applied from the outside to the flat plate for 30 minutes to adhere the flexible circuit board and coverlay together. A polyimide resin-based flexible circuit board with a polyester resin-based coverlay was manufactured. Comparative Example 2 The same polyester resin-based coverlay was layered on the circuit surface of the same polyimide resin-based flexible circuit board as used in Example 1, and the flexible circuit was placed between the same molding surfaces of the same mold as used in Example 1. A 10 mm thick silicone rubber sheet is sandwiched between the plates so that the concave arc-shaped molding surface is on the side and the cover lay is on the convex arc-shaped molding surface, and the polyester resin base cover is formed by heat and pressure molding under the same conditions. A polyimide resin-based flexible circuit board with a lay was manufactured. Next, the curl of the polyimide resin-based flexible circuit board with the polyester resin-based coverlay obtained in the above Examples and Comparative Examples was measured as follows. That is, as shown in Fig. 4, a 200 x 200 mm test piece 10 cut out from these flexible circuit boards was placed on a surface plate 11 with the coverlay surface facing upward in an atmosphere of 20°C and 65% temperature. The sample was allowed to stand still, and the maximum lifting dimension was measured using a height gauge 12. The measurement results are shown in the table below.

[Table] [Effects of the Invention] As is clear from the above examples, according to the present invention, a heat-resistant resin-based flexible circuit board with a coverlay that is free from curling and deformation can be obtained.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view showing a conventional manufacturing method of a polyimide resin-based flexible circuit board with a polyester resin-based coverlay, and Figure 2 is a cross-sectional view of a polyimide resin-based flexible circuit board with a polyester resin-based coverlay obtained by the conventional method. figure,
FIG. 3 is a sectional view for explaining the method of the present invention;
FIG. 4 is an explanatory diagram showing a method for measuring curl. 1...Flexible circuit board, 3...Coverlay, 4, 4'...Flat plate mold, 5...Heat-resistant resin-based flexible circuit board, 7...Resin-based coverlay with a higher heat shrinkage rate than heat-resistant resin ,8,
8'... Mold, 10... Test piece, 11... Surface plate,
12...Height gauge.

Claims (1)

[Claims] 1. When attaching a coverlay made of a synthetic resin with a higher thermal shrinkage rate than the heat-resistant resin on the circuit surface of a flexible circuit board based on a heat-resistant resin, the flexible circuit board and The coverlay is sandwiched between a mold having a concave and convex pair of curved molding surfaces with a radius of curvature of 50 to 1000 mm, with the flexible circuit board facing the convex side and the coverlay facing the concave side, and heated together. A method for manufacturing a flexible circuit board with a coverlay, which is characterized by pressure bonding. 2. The method for manufacturing a flexible circuit board with a coverlay according to claim 1, wherein the heat-resistant resin is a polyimide resin. 3. The method for manufacturing a flexible circuit board with a coverlay according to claim 1 or 2, wherein the coverlay is made of polyester resin.