JPH0346397A - Manufacture of flexible printed wiring board - Google Patents

Abstract

PURPOSE:To acquire a single-sided flexible printed wiring board having through- holes effectively at a low cost by using two single-sided copper-clad flexible films and by applying conventional manufacture process of double-sided flexible printed wiring board. CONSTITUTION:A process starts with acceptance of a single-sided copper-clad flexible film 11 which is formed by applying a copper foil 2 to one side of an insulating film 1 which uses a polyimide film as a base. Through a process to bond insulating film sides 1 of the single-sided copper-clad flexible film 11 each other to acquire a structure similar to a double-sided copper-clad flexible film, through-holes are formed. Then, a through-hole plating process is carried out and a process to separate the bonded insulating films 1 is executed. Two single-sided flexible printed wiring boards with through-hole function can be acquired simultaneously.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing flexible printed wiring boards used in various electronic devices.

BACKGROUND OF THE INVENTION Flexible printed wiring boards are widely used for the purpose of increasing packaging density and improving reliability based on the trend toward thinner, lighter weight, and more compact electronic devices. In particular, when electrical connections are made by placing the conductive lands of a flexible printed wiring board and a rigid printed wiring board facing each other, or for the purpose of mounting electronic components, reinforcement is applied to the lands that have component insertion holes on the flexible printed wiring board. In order to improve connection reliability when bonding hard boards for use with other devices, many double-sided flexible printed wiring boards with through holes are used.

A conventional method for manufacturing a flexible printed wiring board will be described below.

FIG. 6 schematically shows the manufacturing process of a conventional flexible printed wiring board. On both sides of an insulating film 1 based on a polyimide film with a thickness of 25 μm,
The process starts with step A in which a double-sided copper-clad flexible film 3 with a thickness of <2.2' is inserted into the holder. Next, in order to form the through-hole hole 4, after going through the hole drilling process B using a processing method such as normal drilling or press punching using a mold, electroless plating 5 is applied to about 0.1
The through-hole hole 4 becomes electrically conductive through step C of forming the entire surface with a thickness of ~5 μm. Next, by performing electroplating 5' through an electroplating process to form through holes 6, the thickness of the copper on both sides becomes approximately 35 μm (<2.2'), and the thickness of the copper plating in the through holes 4 is as follows. The thickness is approximately 18 μm including electroless plating. In order to obtain the conductive pattern 8 and to protect the through hole 6 from etching, a step E is passed in which etching resist films 7 and 7' are formed. Next, a necessary conductor pattern 8 is formed through etching and etching resist film stripping step F. Further, through step G of drilling only the conductor lands 9, 9' where soldering etc. are to be carried out, and thermocompression bonding of the coverlay 10 and 10' with B stage adhesive, the process is carried out by press punching with a mold, etc. The external shape processing step H is applied to produce a finished product.

FIG. 7 shows an example of a flexible printed wiring board formed through the above manufacturing process.

FIG. 7(a) is a top view, (b) is a sectional view along line A-A',
(C) shows a bottom view. In this double-sided flexible printed wiring board, the conductor pattern 8 connecting the conductor lands 9 exists only on one side as shown in FIG. 7(a), and on the opposite side as shown in FIG. 7(C). teeth,
Only the conductor land 9° is provided independently. The conductor land 9 and the conductor land 9 on the opposite side are through holes 6
Therefore, conduction is established.

Problems to be Solved by the Invention A flexible printed wiring board with such a configuration has a great function when circuits are formed on both sides, but for example, as shown in FIG. However, there is only a conductor land 9'', and this conductor land 9'' is irrational because it exists only to form the through hole 6 with the conductor land 9 on the opposite side. In other words, although the conductor pattern on one side is sufficient for the function, the necessity to use the double-sided copper-clad flexible film 3 has resulted in the inconvenience of increased material costs. In addition, since the manufacturing process required a double-sided flexible printed wiring board process, the number of man-hours increased and the work was complicated.

In order to solve these problems, the present invention aims to easily provide a flexible printed wiring board having a through-hole function using a single-sided copper-clad flexible film.

Means for Solving the Problem In order to solve this problem, the present invention goes through a step of bonding the insulating film surfaces of a single-sided copper-clad flexible film to each other to form a structure similar to that of a double-sided copper-clad flexible film, and then through-hole holes are formed. This is a manufacturing method in which the steps of forming, through-hole plating, and further separating the bonded insulating films are sequentially performed.

Effect By adopting the manufacturing method with the above configuration, two relatively inexpensive single-sided copper-clad flexible films are used, and 1. By utilizing the existing manufacturing process of double-sided flexible printed wiring boards, through-holes are formed. To provide a single-sided flexible printed wiring board at low cost and efficiently.

EXAMPLE An example of the present invention will be described below with reference to the drawings. FIG. 1 shows a method for manufacturing a flexible printed wiring board according to a first embodiment of the present invention.

In addition, in FIG. 1, the same steps as the conventional manufacturing method,
Identical parts will be explained using the same symbols and numbers.

The process starts with step A in which a single-sided copper-clad flexible film 11 is received, in which a copper foil 2 with a thickness of 18 μm is attached to one side of an insulating film 1 based on a polyimide film with a thickness of 25 μm. Next, the two single-sided copper-clad flexible films 11 are bonded together on their insulating film surfaces (2). Of course, the same method can be applied by bending one single-sided copper-clad flexible film 11 and bonding it so that the insulating film surfaces face each other. Here, a solvent-soluble type acrylic thermoplastic adhesive sheet 12 is used as the adhesive, and a heat roller is used to connect between the insulating films 1 of the single-sided copper-clad flexible film 11, that is, between the 25 μm thick polyimide films. Linear pressure 1k
g/cm laminated and glued. The resulting double-sided copper-clad flexible film is subjected to step B in which through holes 4 are formed by ordinary drilling or press punching using a die. Electroless plating 5 is applied to a thickness of approximately 0.1 to 5μ to ensure conduction within the through-hole hole 4.
The through hole 13 is formed through process C, which is applied to the entire surface with a thickness of m.
form. Next, a process J is performed in which this double-sided copper-clad flexible film is separated into single-sided copper-clad flexible films 14 before bonding. Here, since the acrylic thermoplastic adhesive sheet 12 has a core material, the adhesive sheet can be easily separated from the surface of the insulating film 1.

If the adhesive portion remains on the surface of the insulating film 1, it can be easily removed by using a solvent such as thinner. Although the adhesive here is of a solvent-soluble type, for example, if it is an alkali-soluble type, the adhesive can be reliably removed by performing alkaline cleaning.

In order to form the necessary conductor pattern 15 on the single-sided copper-clad flexible film 14 in which the through holes 13 have been formed, an etching resist film 16° 16° is applied, followed by an etching and etching resist film peeling step. Through F, a necessary conductor pattern 15 is formed. Furthermore, only the conductor land 9 part to be soldered etc. is drilled, and the cover lay 1 is attached with B stage adhesive.
A finished product 17 is obtained through a process G of thermocompression bonding 0 and an external shaping process H such as press punching using a mold.

As described above, according to this embodiment, the single-sided copper-clad flexible film 11 is used, the insulating films 1 are bonded together, and after going through the same process as the manufacturing process of the double-sided flexible printed wiring board, the insulating films 1 are bonded together. By separating, a single-sided flexible printed wiring board 17 with through holes can be obtained.

Furthermore, as an application example of the flexible printed wiring board obtained by the manufacturing method of the present invention, as shown in FIGS. 2a and 2b, for example, a double-sided copper through-hole printed wiring board 1
When attempting to obtain a composite printed wiring board by making the through holes 19 of 8 and the through holes 21 of the flexible printed wiring board 20 face each other and bonding them with a thermosetting adhesive 22, the copper through hole printed wiring board on both sides is used. The distance 23 between the conductor land provided with 18 through holes 19 and the edge portion of the through hole 21 of the flexible printed wiring board 20 is important. This is because, needless to say, it is advantageous to have a smaller distance 1123 as the step when performing cream solder printing as a post-process and attempting to obtain electrical continuity by solder connection through a solder reflow process. Of course, the thickness of the thermosetting adhesive 22 is the minimum required, but if a double-sided flexible printed wiring board is used, conductor lands and coverlay thickness are added to the surface in contact with the thermosetting adhesive 22. Considering this, using the single-sided flexible printed wiring board 20 with through holes according to the present invention is very effective in terms of connection reliability.

Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 3 shows a method for manufacturing a flexible printed wiring board according to a second embodiment of the present invention.

The process starts with step A, in which a single-sided copper-clad flexible film 11 is received, in which a steel foil 2 of 18 μm in thickness is attached to one side of an insulating film 1 based on a polyimide film of 25 μm in thickness. The next step is bonding the insulating film surfaces of the two single-sided copper-clad flexible films E1 together, Step B of forming through-hole holes 4, Step C1 of applying electroless plating 5, and bonding the single-sided copper through bonding. Up to step J of separating the flexible printed wiring boards 14,
This step is similar to the step shown in FIG. 1 of the first embodiment. Next, electroplating 5 is performed, and the thickness of the copper foil 2 is about 35 μm, and the thickness of the copper plating on the through-hole hole 4, including the plating in the electroless plating step C, is about 18 μm. This is to form through holes 24 by performing an electroplating process on the approximately 1 to 5 μm formed by electroless plating 5, taking into consideration the conductivity reliability of the through holes. . After this step, in the same manner as in the first embodiment, in order to form the necessary conductor pattern 15, there is a step E of applying an etching resist film 16, 16', an etching and etching resist film peeling step F, and a step F of bonding the coverlay 10. A finished product 25 is obtained through a step G of forming the finished product and a step H of processing the external shape.

As described above, according to this embodiment, the single-sided flexible film 1 is used, the insulating films 1 are adhered to each other, the same process as the double-sided flexible printed wiring board is performed, and then the electroless plating process C1 insulating film 1 A single-sided flexible printed wiring board 25 having highly reliable through-holes 24 can be obtained through a process of separating and electroplating.

Next, a third embodiment of the present invention will be described with reference to the drawings. FIG. 4 shows a method for manufacturing a flexible printed wiring board according to a third embodiment of the present invention.

In the figure, the process of inserting the substrate, bonding process I for single-sided flexible boards, through-hole forming process B, and electroless plating process C is the same as in the first and second embodiments. . In this example, the thickness of the copper foil 2 is approximately 3
The thickness of the copper plating on the through hole 26 is approximately 18 μm, and the process is similar to that for forming the through hole in a normal double-sided flexible printed wiring board. After that, a step E of applying an etching resist film 16 on both sides at corresponding positions in order to form the necessary conductor patterns 15 on both sides;
Etching and etching resist film peeling process F, single-sided copper-clad flexible printed wiring board 2 where adhesion was performed
7. Go through step J to separate the comrades. In this process, the two single-sided copper-clad flexible printed wiring boards 27 are tightly adhered to each other due to the approximately 18 μm copper plating in the through holes 26, so a relatively strong force is required to separate them. .

Further, the edge cross section 28 of the separated through hole 26 has irregularities. From now on, the first
．． As in the second embodiment, a finished product 25 is obtained through a coverlay adhesion process G and an external shape processing process H.

As described above, according to this embodiment, a fine uneven surface can be formed on the edge section 28 of the through hole 26 of the separated single-sided flexible printed wiring board 27. As an example of application, if a composite printed wiring board is constructed of a double-sided copper through-hole printed wiring board 18 and a single-sided flexible printed wiring board 20 having through-holes 21, as shown in FIG. Since the edge cross section 28 of the through hole 26 of the wiring board 27 forms a finely uneven surface, it is possible to provide a highly reliable mechanical and electrical connection even in solder connection due to the so-called chisel effect. .

Next, a fourth embodiment of the present invention will be described with reference to the drawings. FIG. 5 shows a method for manufacturing a flexible printed wiring board according to a fourth embodiment of the present invention.

In the same figure, the board holder is placed in a step A, the single-sided flexible board is bonded and laminated (■), the through-hole is formed, and the hole is formed in a step B.
Electroless plating step C1 Electroplating step D, etching resist film forming step E, etching. The same steps as in the third embodiment are performed up to the etching resist film stripping step F.

Thereafter, in this embodiment, the single-sided copper-clad flexible printed wiring boards 27 are left bonded to each other in the coverlay bonding step G.
, a step H of external processing, and finally a step J of separating into single-sided copper-clad flexible printed wiring boards 25 to produce a finished product. The coverlay adhesion process G uses a thermoforming press in stages at a temperature of 160 to 180°C and a pressure of 10 kg/
It is a process with very low productivity, as it involves heating and pressurizing for 20 to 60 minutes at cj to 40ks/cd, and then cooling and pressurizing for about 10 to 30 minutes. In addition, external shape processing and process H are generally punched out using one press using a mold or blade, and there is no continuous process flow, so products tend to stagnate between processes and become unusable. It was in an efficient state.

Therefore, it is reasonable to perform the production process for two sheets at the same time, from the coverlay adhesion process G to the external shape processing process H, and this will lead to a reduction in the number of work steps.

In the first embodiment, the step J of dividing into single-sided flakes was carried out after the electroless plating step C, but after the etching and etching resist film peeling step F, or after the coverlay adhesion step G, the outer shape It may be after processing and process H.

Also in the third embodiment, the step J of dividing into single-sided flexible sheets was carried out after the etching and etching resist film peeling step F, but it was similarly carried out after the electroplating step or in the coverlay adhesion step G i&. Needless to say, it is possible. The insulation film 1 has a thickness of 25
Although the explanation has been made regarding a polyimide film having a thickness of .mu.m, the same applies to other polyester films, and a thin glass cloth epoxy resin laminate having a thickness of 0.1 to 0.5 mm may also be used.

Effects of the Invention As described above, the present invention provides a double-sided copper-clad flexible film by bonding a single-sided copper-clad flexible film in which a conductive foil is formed on one side of an insulating film base so that the insulating films face each other. A single-sided flexible printed wiring with through-holes is obtained by sequentially performing the process of forming a through-hole, the through-hole plating process, and the process of dividing the bonded insulating film. There is no need to use an expensive double-sided flexible printed wiring board like in the past, and it can be used in the same way as existing double-sided flexible printed wiring boards by using two inexpensive single-sided copper-clad flexible films. By going through the manufacturing process, two single-sided flexible printed wiring boards with a through-hole function can be obtained at the same time.

[Brief explanation of drawings]

FIG. 1 was obtained using a flexible film according to the first embodiment of the present invention. A perspective view and a sectional view of main parts showing an example of a flexible printed wiring board, FIG. 3, and a large sectional view FIG. 7(a)
, (b), and (c) are a top view, an AA' sectional view, and a bottom view showing an example of a conventional flexible printed wiring board. 1... Insulating film, 2... Conductive foil, 11... Single-sided copper-clad flexible film, 4
...Through hole hole, 5...Electroless plating, 13.24.26...Through hole, 1
2...Adhesive, 15...Conductor pattern.

Claims (4)

[Claims] (1) A process of adhering a single-sided copper-clad flexible film with a conductive foil formed on one side of the insulating film so that the insulating film side without the conductive foil is facing each other, a process of drilling a through hole, and a process of forming a through hole. A method for manufacturing a flexible printed wiring board, comprising sequentially passing through a step of plating and a step of separating an adhered insulating film. (2) The method for manufacturing a flexible printed wiring board according to claim 1, further comprising a step of forming a pattern after the step of separating the bonded insulating film. (3) The method for manufacturing a flexible printed wiring board according to claim 1, further comprising a step of forming a pattern and a step of separating the bonded insulating film after the step of performing through-hole plating. . (4) The flexible device according to claim 1, further comprising, after the step of through-hole plating, a step of forming a pattern, a step of performing external processing, and a step of separating the bonded insulating film. A method for manufacturing printed wiring boards.