JPS63164396A - Structure and method for double-sided continuity of flexible circuit substrate - 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 technology for conducting circuit wiring patterns formed on both sides of a flexible circuit board. The present invention relates to a double-sided conductive structure for a flexible circuit board and a method therefor, which enables continuity of processes while providing a conductive structure between required circuit wiring patterns.

"Prior Art" As a conventional double-sided conduction method for this type of flexible circuit board, a laminate 11 is prepared in which conductive foil such as copper foil is uniformly bonded to both sides of a flexible insulating base material. Then, after cutting this to any size and stacking the multiple sheets 12 as shown in Figure 3, they are individually drilled using an NC drill so that they match the locations where continuity should be provided between the front and back circuit wiring patterns. Hall 13
Then, as shown in FIG. 4, each laminate 11 is subjected to an electroless through-hole plating process to form through holes 1.
Apply plating to 3. Through such a through-hole plating process, the entire surface of the conductive foils 15 and 16 bonded to both sides of the flexible insulating base material 14 and the through-holes 1
A uniform through-hole plating 17 is applied to the inner circumferential surface of 3 to provide conduction to the conductive foils 15 and 16 on the front and back sides through the through-holes 13, and to further ensure conduction by the through-hole plating 17. Therefore, as shown in FIG. 5, an electrolytic plating layer 18 is formed by electrolytic plating in the next step. The laminate 11 that has been subjected to such through-hole plating treatment is then provided with, for example, a photosensitive film with a release paper on both sides thereof, and subjected to an exposure process using a mask film to form a desired circuit wiring pattern. After the release paper is removed, unnecessary photosensitive film is removed through necessary development and etching steps to form circuit wiring patterns 19 and 20 having through-hole conductive parts as shown in FIG. This method produces double-sided flexible circuit boards.

``Problems to be Solved by the Invention'' According to the above-mentioned conventional double-sided conductive structure of a flexible circuit that involves a through-hole plating process, it is difficult to ensure through-hole conduction due to various factors. This has the disadvantage that reliability is rarely a problem. FIG. 7 is for explaining the problem. First, if a defective portion 13A is left on the inner circumferential surface of the through hole 13 due to dirt or dust adhesion or undulations during through hole processing, such a problem will occur. The electroless through-hole plating 17 is not properly attached to the areas where the electrolytic plating layer 18 is formed.
There is a possibility that the plating layer 18 may not be deposited in that area, or the amount of deposition may be different, resulting in locally thinner areas of the plating layer 18 and leaving incompletely conductive areas. Furthermore, if the adhesive bonding layer 21 between the insulating base material 14 and the conductive foil 15, 16 is not sufficiently cured, the through-hole plating 17 is subjected to breakage stress due to the effect of thermal stress. Since the plating 17 is not originally that thick, there is also the inherent problem of cracking. All of these factors impair the reliability of the through-hole conduction structure and are extremely undesirable.

On the other hand, the above defective portion 13 in the through hole 13
In addition to A, if holes are left behind during through-hole processing, these will likely form protrusions 19 after plating, and such protrusions 19 will bite into or break through the photosensitive film 20. Forms an ultra-thin area of
Such portions may be excessively etched during the etching process, causing etching errors.

Furthermore, according to the double-sided conduction method using through-hole plating as described above, the use of the photosensitive film 20 also involves the problems described above, so it is difficult to use a thin liquid photosensitive resin. However, there are various disadvantages in forming fine circuit wiring patterns. In addition, in the through-hole plating process, as described above, two electrolytic plating layers 18 are used to ensure continuity by the electroless through-hole plating 17.
However, the thickness of the plating layer 18 relative to the conductive foil 15 and 16 becomes unfavorable to the formation of a fine circuit wiring pattern, and the shape of the circuit wiring pattern is changed during the etching process. Etching errors such as thinning or thickening often occur.

"Means for Solving the Problems" The present invention eliminates the disadvantages of the double-sided conductive structure of flexible circuit boards using the through-hole plating method as described above, and continuously produces flexible circuit boards with high continuity reliability. The present invention provides a double-sided conductive structure of a flexible circuit board that can be manufactured in a number of steps, and a method for manufacturing the same. Therefore, in the present invention, without using through-hole plating means, conductive portions at required locations in the circuit wiring pattern formed on the front and back surfaces of the flexible circuit board are formed using a conductive filler and the filler. It consists of an electrolytic plating layer provided on the outer surface and both the front and back circuit wiring pattern surfaces. In this double-sided conduction method for flexible circuit boards, through-holes necessary for conductive parts are formed at the same time using a punch press in correspondence with the conductive parts provided at required locations between the circuit wiring patterns on the front and back sides of the circuit board. It will be done. In other words, through-holes for both-side conduction are sequentially punched in one batch using a punch press in a long laminate in which conductive foil is bonded to both sides of a flexible insulating base material. continuous filling treatment with a conductive filler, and then applying an electrolytic plating layer to both outer surfaces of the filler and conductive foil on both sides in an electrolytic plating process to ensure electrical connection between the filler and the conductive foil, Thereby, preparations are made so that the subsequent steps of deposition of a film or liquid photosensitive layer, exposure and development, and subsequent etching treatment can be performed continuously.

"Example" Hereinafter, the present invention will be further explained with reference to the illustrated embodiment. FIGS. A long laminate is prepared by bonding conductive foils 2 and 3 such as copper foil to both sides of a flexible insulating base material 1 made of a suitable plastic film, and this is rolled out one after another, for example. Then, the required through-holes 4 are punched all at once at the locations corresponding to conduction using a punch press as shown in FIG. 1 (1). After the process of drilling the through-holes 4, if any burrs or the like occur due to the die of the punch press, it is easy to remove the burrs by performing an appropriate surface preparation treatment. For such a through hole 4, for example, as shown in FIG.
By sequentially filling the through holes 4 with the conductive filler 10 supplied to the doctor knife member 9 while inserting the conductive filler in the direction, each through hole 4 is filled as shown in FIG.
The conductive filler 5 can be filled with high efficiency.

As the conductive filler 5, an appropriate material such as copper-based or silver thread paste or solder paste can be used. After the filling process, the conductive foils 2 and 3 are smoothed with a brush so that unnecessary adhesion can be removed. The board surface is treated by other means, and then the filler 5 is hardened by heating or UV irradiation means. Surface smoothing treatment can also be performed during this hardening treatment step.

Next, as shown in FIG. 3 (3), an electrolytic plating process is carried out to continuously apply a common electrolytic plating layer 6 to an appropriate thickness on the exposed outer surfaces of both conductive foils 2 and 3 and the filler 5. This ensures continuity between the conductive filler 5 and both conductive foils 2.3. Since this plating layer 6 does not require thickening treatment for conventional electroless through-hole plating, it can be formed as thinly as possible on the plane area between the outer surface of the filler 5 and both conductive foils 2 and 3. It is something.

Next, depending on the shape and density of the circuit wiring pattern to be formed, a film-like or liquid photosensitive resin (not shown) is deposited on the plating layer 6, and if a liquid photosensitive resin is used, a coating process is performed. After that, let it dry. Further, in the case of a film-like photosensitive resin, the release paper is appropriately removed before exposure. After this process, exposure and
After the development process, an etching process and patterning process are performed to remove unnecessary photosensitive resin, resulting in a circuit wiring pattern 7° having the required conductive parts as shown in FIG. 1 (4). You can get 8. Each of these steps can be performed continuously, making it easier to manage the steps and realizing a highly reliable double-sided conductive structure of a flexible circuit board with high efficiency.

"Effects of the Invention" Since the present invention has the above-described configuration, through-holes can be continuously formed all at once using a simple punch press without performing the conventional through-hole drilling process for through-hole plating using an NC drill. Therefore, it is easy to make the process continuous by using a long laminate. Therefore, it is possible to reduce the causes of non-adherence such as hand stains and dust, which are problems when handling short lengths as in the past, and it is also possible to reduce pre-treatment for each transition to the next process.

In addition, since the present invention does not require electroless plating, there is no need to adopt a structure in which the electrolytic plating layer is thickened.
It is sufficient to provide an electrolytic plating layer as thin as possible to complement the electrical connection between the conductive filler for the through hole and the conductive foil on both sides, so it is possible to simplify the plating process and reduce the cost. Formation of circuit wiring patterns can be easily achieved. As described above, the present invention has the advantage that a double-sided flexible circuit board with high conductivity reliability can be manufactured at low cost with suitable mass productivity while promoting process continuity.

[Brief explanation of the drawing]

Fig. 1 (11 to (4)) shows a conceptual process diagram for implementing the double-sided conductive structure of the flexible circuit board according to the present invention, and Fig. 2 shows the process diagram of the conductive filler forming the conductive part. A diagram illustrating an example of a filling method. Figure 3 is an explanatory diagram of a state in which a through hole is drilled using an NC drill using a conventional method. Figures 4, 5 @, and 6 are double-sided conduction using conventional through hole plating. Explanatory diagrams for each process order to explain the means,
FIGS. 8 and 9 are diagrams for explaining the problems of the conventional through-hole plating conduction structure. 1: Flexible insulating base material 2.3: Conductive foil 4: Through hole 5: Conductive filler 6: Electrolytic plating layer 7.8: Circuit wiring pattern Applicant Nippon Mectron Co., Ltd. Figure 1 Figure 2 Figure 3 Figure 4 '55 Figure 6 Figure 7 Figure 8 Procedure? 1. Indication of the case Japanese Patent Application No. 61-311645 2. Name of the invention Double-sided conductive structure and method for flexible circuit board 3. Relationship with the case of the person making the amendment Address of the patent applicant Tokyo 1-12-15 Shiba Daimon, Miyakominato-ku Name: Nippon Mectron Co., Ltd. 4, Agent: 300-122, (029g) 74-
23516, Subject of amendment Brief description of drawings in the specification (Contents of amendment) (1) Changed “Fig. 8 and 9” to “Fig. 7 and 9” in the third line from the bottom of page 11 of the specification. Figure 8 is corrected. that's all

Claims (2)

[Claims] (1) In a flexible circuit board having a required circuit wiring pattern on both sides of a flexible insulating base material and having conductive parts at required locations on the front and back sides of the circuit wiring pattern, the conductive part is
1. A double-sided conductive structure for a flexible circuit board, comprising a conductive filling member and an electrolytic plating layer provided on the outer surface of the conductive filling member and on both the front and back circuit wiring pattern surfaces. (2) Through-holes are sequentially punched at required locations in a sheet-like laminate in which conductive foil is uniformly bonded to both sides of a flexible insulating base material, and these through-holes are conductive. A flexible circuit board characterized in that, after being sequentially filled with a filler, electrolytic plating is applied to the outer surfaces of the conductive filler and both of the conductive foils, and then subjected to a process of forming a required circuit wiring pattern. double-sided conduction method.