JPH0680893B2 - Method for manufacturing metal-based double-sided flexible circuit board - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a flexible circuit board using an aluminum foil as a base member, and more specifically, to both sides of such a metal base member. In particular, the present invention relates to a method of manufacturing a metal-based double-sided flexible circuit board having a novel through-hole conductive structure between circuit wiring patterns formed under insulation.

“Prior Art” Flexible circuit boards that use metal foil such as aluminum foil as a base member ensure the dimensional stability that occurs when attempting to form circuit wiring patterns with high density and at the same time improve heat resistance, etc. Was developed with the aim of, for example, a conductive foil such as a copper foil is uniformly adhered to one or both sides of an aluminum foil base member via an insulating adhesive layer, and typically, this conductive foil is used. The foil is subjected to photo-etching treatment to form a desired circuit wiring pattern. In such a metal foil-based flexible circuit board, a required circuit wiring pattern can be simply and densely formed on one or both sides of the base member, but the base member is made of a metal foil. For convenience, unlike other general flexible circuit boards in which the base member is a resin film, for example, a conductive structure between the circuit wiring patterns on both surfaces cannot be easily adopted.

"Problems to be solved by the invention" However, the high density miniaturization and heat resistance of the circuit wiring pattern based on good dimensional stability, which is an inherent characteristic of this type of metal foil-based flexible circuit board, are retained. If, on the other hand, it is possible to simply and surely introduce a conductive structure on both sides, rational wiring processing between circuit wiring patterns formed on both sides will be further enhanced, and a highly functional metal foil-based double-sided flexible circuit. It becomes possible to provide a substrate. In a double-sided flexible circuit board using a metal foil base member, the factor that makes the conduction structure difficult is that the circuit wiring patterns on both sides are finely sized while sufficiently achieving high density miniaturization of the circuit wiring patterns. It seems that a substantially effective means for obtaining mutual conduction in the state where the region is subjected to the insulation treatment of the metal foil base member cannot be easily established.

[Means for Solving the Problems] Therefore, the present invention has a conductive foil adhered to both surfaces of an aluminum foil base member via an insulating adhesive layer, and is acid resistant so as to be peelable on each surface of the conductive foil. A protective layer was applied, a through hole was formed at a required location of this laminate, and an oxide insulating film was formed on the end face of the aluminum foil base member exposed on the inner peripheral surface of the through hole by anodizing. After that, through hole plating is applied to the inner peripheral surface of the above through hole,
Next, after peeling and removing each of the acid-resistant protective layers, a metal-based double-sided flexible circuit board including a step of forming a required circuit wiring pattern on the conductive foils corresponding to the conductive portions by the through-hole plating It provides the law. The above-mentioned oxide insulating film to be formed on the exposed surface of the aluminum foil metal base member on the inner peripheral surface of the required through hole is high while maintaining sufficient electrical insulation characteristics before forming the required circuit wiring pattern on both sides. Since it can be stably and firmly formed with reproducibility, in combination with the use of a peelable acid-resistant protective layer, it has the required through-hole conduction structure only on the inner peripheral surface of the through-hole, while having good dimensions. It is possible to provide a high-density, miniaturized high-performance double-sided flexible circuit board based on stability with good quality and at a low cost.

"Embodiment" FIGS. 1 (1) to 1 (4) are manufacturing process diagrams for explaining problems of a metal-based double-sided flexible circuit board of this type,
As shown in FIG. 1A, an aluminum foil base member 1 is prepared as a metal base member, and copper foil or the like is provided on both surfaces of the base member 1 with an adhesive layer 2 preferably having heat resistance and good electric insulation. After the conductive foils typified by 1) are evenly adhered and bonded, photoetching means is optionally applied to the conductive foils on both surfaces to form the required circuit wiring patterns 3 and 4 on the both surfaces as appropriate. Next, in order to make the through holes conductive, both circuit wiring patterns 3 and 4 at the required places as shown in (2) of the same figure.
The common through hole 5 is drilled by means such as drilling or punching, but the through hole 5 can be formed before the patterning process of the circuit wiring patterns 3 and 4. At this stage, the inner peripheral surface and the edge portion of the through hole 5 are subjected to an appropriate surface conditioning treatment including deburring by means such as soft etching or shot blasting. Since the end surface of the aluminum foil base member 1 as the base member is uniformly exposed on the inner peripheral surface of the through hole 5, the aluminum anodizing treatment is performed on the end surface as shown in FIG. The oxide insulating coating 6 can be firmly and stably formed on the exposed portion. Therefore, after the insulation treatment of the aluminum foil base member 1 in the through hole 5 is completed, through hole plating 7 is applied as shown in FIG. 4 (4) to achieve the conduction between the circuit wiring patterns 3 and 4 on both sides. The Rukoto.

However, in such a manufacturing method, each circuit wiring pattern 3,
Since the through-hole plating 7 is evenly adhered to the surface of 4, it is difficult to use it in applications where flexibility is impeded and high flexibility is required. The present invention has improved such a point.

FIGS. 2 (1) to (5) show one embodiment of the present invention. As described above, both surfaces of the aluminum foil base member 1 as the metal base member are preferably heat resistant and have good electric insulation. Prepared is one in which conductive foils 3A, 4A such as copper foil are evenly adhered and bonded via different adhesive layers 7. Then, before the patterning process, the peelable acid-resistant protective layers 8 and 9 are provided on the surfaces of the both conductive foils 3A and 4A as shown in Fig. 1 (1). After the perforation treatment of No. 5 and the above-mentioned surface treatment, the oxide insulating film 6 is similarly formed by the above means as shown in FIG. When the through hole plating 10 is applied as shown in 3) to provide a conductive structure and both protective layers 8 and 9 to which the through hole plating 10 is attached are peeled and removed, only the inner peripheral surface of the through hole 5 is removed as shown in FIG. It is possible to obtain a laminate having the through-hole plating 10 deposited thereon. After that, the circuit wiring patterns 3 and 4 having the through-hole conduction structure as shown in FIG. 5 can be formed by subjecting the conductive foils 3A and 4A to photoetching. Since the metal-based double-sided flexible circuit board of this structure is provided with the acid-resistant protective layers 8 and 9 which can be peeled off on the surfaces of the conductive foils 3A and 4A before the through-hole plating treatment, the circuit wiring pattern 3 and Since the through-hole plating does not adhere to the surface of No. 4, it has the feature that it is advantageous for use in applications requiring high bending characteristics.

[Advantages of the Invention] In the method for manufacturing a metal-based double-sided flexible circuit board according to the present invention, aluminum foil is used as a flexible base member, and the necessary circuit wiring patterns to be formed on both sides of the aluminum foil are appropriately positioned at necessary mutual locations. Since it is easy to form a through hole and to easily provide a simple and reliable oxide insulating coating on the end face of the aluminum foil base member exposed on the inner peripheral surface of the through hole by anodizing means, such a through hole conducting structure By the introduction of the above, there is an advantage that the function of this type of metal-based double-sided flexible circuit board can be further enhanced and a good quality product can be provided.

Further, according to the present invention, since the peelable acid-resistant protective layer is provided on the surface of each conductive foil before the through-hole plating treatment, the through-hole conductive structure is formed only on the inner peripheral surface of the through-hole. Since the through-hole plating does not adhere to the surface of the circuit wiring pattern, it is advantageous for use in applications requiring high bending characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 (1) to 1 (4) are conceptual manufacturing process diagrams for explaining problems of a metal-based double-sided flexible circuit board of this type, and FIG. (1)-(5) is a conceptual manufacturing process drawing of a metal-based double-sided flexible circuit board according to an embodiment of the present invention. 1: Metal foil base member 2: Heat-resistant insulation adhesive layer 3, 4: Circuit wiring pattern 5: Through hole 6: Oxide insulation coating 7, 10: Through hole plating 8, 9: Peelable protective layer

Claims (1)

[Claims] 1. An aluminum foil base member is coated with conductive foils on both sides thereof via insulating adhesive layers, and an acid-resistant protective layer is releasably attached to each surface of the conductive foils. After forming a through hole at a corresponding portion and forming an oxide insulating film on the end surface of the aluminum foil base member exposed on the inner peripheral surface of the through hole by anodizing treatment, the through hole is formed on the inner peripheral surface of the through hole. Metal base double-sided flexibility including a step of forming a required circuit wiring pattern on both conductive foils corresponding to the conductive points by the above through-hole plating after plating and then peeling off and removing each of the acid resistant protective layers Circuit board manufacturing method.