JPH01183192A - Flexible printed wiring board and manufacture thereof - Google Patents

Abstract

PURPOSE:To place a high density circuit by forming a height difference on a plated layer covering the surface of a metal foil provided on the base film of a conductor layer. CONSTITUTION:A plated layer 5 made of electrolytic copper is formed on the part of a metal foil 1 for forming a circuit pattern to provide a conductor layer 6A made of the foil 1, and a conductor layer 6B covering the surface of the foil 1 with the layer 5, and a height difference with the surface of an insulating film 3 as a reference is formed on these surfaces. Thus, by utilizing the height difference provided on the conductor layer, a circuit element or jumper wire or the like is provided to be superposed in a three-dimensional manner, components disposed on the lower part of the conductor layer is held at the high part of the conductor layer, and adjacent low conductor layers are isolated therebetween by the high conductor layer to prevent a bridge at the time of soldering from occurring.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a flexible printed wiring board, and particularly to a flexible printed wiring board suitable for mounting various electronic circuits having high-density integrated circuits.

"Prior Art" Generally, flexible printed wiring boards (hereinafter abbreviated as FPC) use a laminate (hereinafter abbreviated as CCL) made by bonding metal foil to the entire surface of a visible base film with an adhesive. , a predetermined circuit pattern is formed by etching the conductor layer.

By etching the above CCL, the 10th
As shown in the figure, a metal foil 1 constituting a two-dimensional circuit pattern is used as an FPC fixed on a base film 3A with an adhesive layer 2. Then, as shown in FIG. 11, the etched wiring board is coated with metal foil 1.
By laminating a coverlay film (hereinafter abbreviated as CL) 3B on the surface of the adhesive layer 2 or by providing a coating film using a cover coat material, the area to be electrically connected to the outside. The metal foil 1 is protected by being coated except for the metal foil 1.

In addition, in the above-mentioned FPC, there are locations where electrical continuity should be established with the outside, or locations where electrical continuity between each conductive layer should be established when multiple conductor layers are provided one after the other.
For example, for conductors that become lands, connector connections, etc.
Plating treatment with copper, nickel, aluminum, etc. is performed as necessary to form a plating metal layer 4, in which case,
A masking material is provided in areas where plating is not required, or the CL or coating film is used in place of the masking material.

``Problems to be Solved by the Invention'' By the way, the circuits mounted on the FPCs having the above structure tend to become more complex in order to further improve their performance, and along with this, there is a demand for higher density circuits. Therefore, it is possible to increase the density within a two-dimensional plane by making the circuit pattern finer, but there is a natural limit to finer circuit patterns, and with finer circuit patterns, higher precision is required for the etching process or plating process. As a result, various factors tend to increase costs, such as a decrease in production efficiency or a decrease in manufacturing yield due to the occurrence of defective products.

The present invention was proposed in view of the above circumstances, and an object of the present invention is to obtain an FPC on which high-density circuits can be mounted.

1 "Means for Solving the Problem" In order to achieve the above object, the first invention provides a flexible base film in which a circuit is formed by selectively providing a conductor layer on the surface of a flexible base film. In the printed wiring board, a flexible printed wiring board is constructed by providing height differences in the plating layer covering the surface of the metal foil provided on the surface of the base film of the conductor layer, and the second invention provides a flexible printed wiring board. The method for manufacturing a flexible printed wiring board according to the first invention is comprised of a step of forming a circuit with metal foil on the surface of a base film having The third invention includes a step of forming a circuit using a metal foil having selective height differences on the surface of a flexible base film, and a step of forming a circuit on the surface of the formed metal foil almost uniformly. The method for manufacturing a flexible printed wiring board according to the first aspect of the invention includes the step of applying plating to a certain thickness.

"Function" According to the configuration of the first invention, circuit elements or jumper wires, etc. can be provided three-dimensionally overlapping each other by utilizing the height difference provided in the conductor layer, or the lower part of the conductor layer can be stacked three-dimensionally. It is possible to prevent the occurrence of bridging during soldering by holding components placed in the upper part of the conductor layer at a higher part of the conductor layer, and by separating adjacent lower conductor layers by the higher conductor layer.

Further, according to the second and third inventions, an F having the above-mentioned characteristics is provided.
PCs can be manufactured.

"Embodiment" Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the figure, parts common to the conventional example are given the same reference numerals to simplify the explanation.

1 and 2 show a first embodiment of the present invention.

This FPC is constructed in the same manner as the conventional example shown in FIG. 10, and by providing a plating layer 5 made of electrolytic copper on a part of the metal foil 1 constituting the circuit pattern, a conductor layer 6A made of the metal foil 1 itself is formed. , a conductor layer 6B formed by covering the surface of the metal foil 1 with a plating layer 5 is provided, and a height difference is created between these surfaces with respect to the surface of the insulating film 3.

When manufacturing an FPC with the above configuration, first, a laminate (CC
A predetermined circuit pattern is formed by the usual method of etching the surface of L), then a plating mask is applied to the surface of the metal foil 1 other than the part where the plating layer 5 is to be provided, and then electrolytic copper plating is applied. As shown in FIG. 1, a low conductor layer 6A made of the metal foil 1 itself and a high conductor layer 6B made by covering the surface of the metal foil 1 with a plating layer 5 are formed. The surfaces of the conductor layers 6A and 6B, which are formed with a difference in height as described above, are put into use after being vapor-deposited or plated with metals such as nickel, aluminum, and solder, depending on the purpose of use. Ru. In addition, in the drawings of the embodiments, a metal layer deposited or plated on the surfaces of the conductor layers 6A and 6B, and a protective layer such as a coverlay film that covers the surfaces of the conductor layers 6A and 6B are not shown. Omitted.

In the FPC constructed in this way, as shown in FIG. 2, the high conductor layers 6B and 6B provided on both sides of the low conductor layer 6A are made of metal such as copper, aluminum, or gold. It is possible to electrically connect with the conductor wire 7, and the conductor wire 7 does not come into contact with the lower conductor layer 6A, so in conventional FPC, circuit conductors are provided on both the front and back surfaces of the board, or jumper wires are installed. It is possible to realize a so-called cross-over path, that is, a circuit in which patterns intersect so that when a plan view is drawn, the circuit conductors appear to intersect.

Next, FIG. 3 shows a second embodiment of the present invention, in which the FPC of this embodiment is produced by selectively masking the surface of a metal foil etched in a predetermined pattern on a laminated board (CCL). By plating or etching, conductor layers 8, 8 each having a height difference are provided.

In this second embodiment, the lead wires 9a of the flat package component 9 are connected to the conductor layers 8, 8, respectively, and the chip component (having the lead wires) is placed on the low conductor layer 6A between the conductor layers 8, 8. By providing the component (not included) 10, the upper circuit consisting of the flat package component 9,
The lower circuit consisting of the chip component 10 can be arranged three-dimensionally. Further, the flat package component 9
Since the lead wires 9a are arranged in a so-called raised state on the conductor layers 8, 8, they can straddle the chip components 10 without making the lead wires 9a particularly long. It becomes possible to apply flat package parts with the same specifications (that is, with short legs for the lower circuit) to both, increasing versatility. In addition, in FIG. 3, an F is shown in which the flat package component 9 is mounted only in the high component circuit without the chip component 10 in the lower circuit.
A PC is also possible.

Next, FIG. 4 shows a third embodiment of the present invention, in which a "valley" is formed by providing a height difference in the conductor layer 8A.
The structure is such that the chip component 10 is placed in the area.

In this way, by holding the chip component 10 in the "valley" portion created by giving the conductor layer 8A a height difference, the chip component 10 can be temporarily positioned at the previous stage of soldering. Therefore, automatic soldering is carried out on the production line after applying paste-like solder.The reflow process (a process in which the solder is heated and melted) is carried out on a production line, where the chip standing phenomenon (chip movement due to surface tension when the solder melts) occurs. It is possible to prevent this phenomenon.

Next, FIG. 5 shows a fourth embodiment of the present invention, in which heights are provided so as to frame the periphery of the conductor layer 8B.

If the periphery of the conductor layer 8b is edged to match the outer shape of the leads 9a in this way, it is possible to ensure that the solder melted by the solder reflow process or the like does not straddle the adjacent leads 9a and 9B and form a so-called bridge. It can be prevented.

Furthermore, as in the fifth embodiment shown in FIG. 6, by using a conductor layer 8B having a high current portion 11A with a large cross-sectional area and a low-current portion 11B with a small cross-sectional area, it is possible to Thus, a circuit pattern having a current capacity corresponding to the current flowing through the circuit can be realized.

In the first to fifth embodiments, the magnitude of the height difference to be provided in the conductor layer varies depending on the purpose, but each predetermined function can be achieved by a height difference of at least about 50 μm.

Furthermore, in each of the above embodiments, the conductor layer has a structure in which height differences are created by adjusting the thickness of the plating layer provided on the surface of the metal foil having a uniform thickness. Instead of this method, the height difference may be provided by the following method.

First, as shown in FIG. 7, adhesive layers 21 are provided on the entire surface of the base film 20, and the adhesive layers 21
Metal foil (generally copper foil) with a thickness of 200 μm or less
22 and applying masking (etching resist) to a predetermined area of this metal foil 22, a primary etching remaining area 23 is provided, and when the primary etching is applied to this area, as shown in FIG. , primary etching remaining area 2
Parts other than 3 are dissolved. Next, when the second etching remaining area indicated by reference numeral 24 in FIG. is dissolved. Furthermore, by providing a metal layer of nickel, aluminum, solder, etc. with a substantially uniform thickness on the surface of the remaining metal foil 22 by vapor deposition, plating, etc. as necessary,
As shown in FIG. 9, a low conductor layer 8D, a high conductor layer 8E
, conductor layers 8F having height differences are formed.

"Modification Example J a. Vapor deposition,
After a nickel layer is provided by a method such as plating, the surface of the nickel layer may be plated with gold to a thickness of 2 μm or less to improve the corrosion resistance of the substrate.

b. An FPC with a pattern having a height difference has the same function regardless of whether it is manufactured by adjusting the plating metal to create the height difference or by adjusting the amount of etching. You can.

C. The circuit pattern to be provided on the base film or the height difference of the conductor layer is not limited to the above embodiments.

d. Of course, the present invention can also be applied to the case where conductor layers are provided on the front and back sides of the base film.

"Effects of the Invention" As is clear from the above explanation, according to the present invention, it is possible to obtain an FPC in which the conductor layer provided on the surface has a difference in height. Effects can be obtained.

(a) At the point where the circuit patterns intersect, it is possible to create a height difference between the conductors that are about to intersect with each other, thereby creating a three-dimensional space between them. A so-called crossover circuit can be realized.

(b) chip components that are mounted directly on the substrate;
When a lead wire or a flat package component with legs is to be arranged in a vertically overlapping state, there is no need to use a flat package component with exceptionally long legs that would straddle the chip component. , can be easily realized using flat package parts with regular legs.

(c) Placing the chip components between high conductor layers allows the components to be held at a point before soldering, thus reducing component misalignment during processes such as solder reflow. It never occurs.

(d) When the points to be soldered are crowded, if each soldering point is set at the position of a low conductive layer, and this soldering point is surrounded by a high conductive layer, the soldering will be easier. It is possible to prevent short circuits between the leads due to bridging of the leads, thereby increasing the degree of two-dimensional integration of the circuit pattern.

(e) Due to the synergistic effect of the above effects, it is possible to realize an FPC with a higher degree of integration.

[Brief explanation of the drawing]

1 and 2 show a first embodiment of the present invention. FIG. 1 is a cross-sectional view of the RPC, FIG. 2 is a cross-sectional view of the RPC connected by a conductor wire, and FIG. A sectional view of the second embodiment, FIG. 4 is a sectional view of the third embodiment of the present invention, and FIG.
The figure is a perspective view of the fourth embodiment of the present invention, FIG. 6 is a perspective view of the fifth embodiment of the present invention, and FIGS. 7 to 9 are, respectively,
10 and 11 are cross-sectional views showing an example of the RPC manufacturing method according to the present invention in the order of steps, respectively.
FIG. 3 is a cross-sectional view showing one conventional example in the order of strokes. 1...Metal foil, 2...Adhesive, 3...
...Base film, 6A, 6B, 8, 8A8~F
...conductor layer.

Claims (1)

[Scope of Claims] 1. In a flexible printed wiring board in which a circuit is formed by selectively providing a conductor layer on the surface of a flexible base film, the conductor layer (6A, 6B)
A flexible printed wiring board characterized in that a metal foil (1) fixed to a surface of a base film (3) is provided with a height difference based on the surface of the base film. 2 Consists of a step of forming a circuit with metal foil (1) on the surface of a flexible base film (3), and a step of applying plating (5) of different thickness to the surface of the formed metal foil. A method for manufacturing a flexible printed wiring board according to claim 1. 3 The process of forming a circuit using metal foil (1) with selective height differences on the surface of a flexible base film (3), and forming a circuit with a substantially uniform thickness on the surface of the formed metal foil. 2. The method for manufacturing a flexible printed wiring board according to claim 1, further comprising the step of applying plating (5).