JPH0832213A - Coverlay film bonding method and production of flexible printed board - Google Patents

Abstract

PURPOSE:To obtain a method for bonding a coverlay film and a method for producing a flexible printed board with quite low fail rate. CONSTITUTION:In the method for bonding a coverlay film 2 in a flexible printed board to the board base by means of a hot press, the coverlay film 2 is hot pressed through a buffer including a polyethylene sheet 5 and a sheet 6 for preventing the polyethylene sheet 5 from spreading.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cover lay film bonding method and a flexible printed circuit board manufacturing method, and more particularly to a cover lay film bonding method and a flexible printed circuit board manufacturing method having a hot pressing step.

[0002]

2. Description of the Related Art Conventionally, various methods for manufacturing a flexible printed circuit board have been proposed, and one example thereof will be described below.

FIG. 4 is an explanatory view showing an example of the structure of a conventional stacking buffer section covering a circuit pattern of a flexible printed circuit board, and FIG. 5 shows heat and pressure after stacking the stacking buffer section. It is sectional drawing which showed the state added.

In the conventional flexible printed circuit board, as shown in FIG. 4, both sides of the circuit pattern 1 are covered with a coverlay film 2, and the coverlay film 2 is further covered.
The heat-resistant release film 3, the polypropylene sheet 4, the polyethylene sheet 5, the polyethylene terephthalate 7, the stainless steel plate 8 and the chip balls 9 are covered in this order with a laminated buffer portion. The polyethylene sheet 5,
There is also known an example in which elastic force of a rubber sheet or the like is used instead of polyethylene terephthalate 7.

This conventional flexible printed circuit board is
After stacking the stack buffer section on the substrate, the chip ball 9
From outside (see FIG. 5), heat (160-
200 ° C.) and pressure (20-40 kgf / cm 2) are applied. That is, as shown in FIG. 6, the heat is increased to the set value at once, and the pressure is increased to the set value at the same time or with a slight delay.

[0006]

However, in the structure of the laminated buffer portion in the above-mentioned conventional flexible printed circuit board, the polyethylene of the polyethylene sheet 5 melted by the heat of the hot press device is then removed by the pressure of the hot press device. The stainless steel plate expands in the direction of the arrow shown in FIG. 5 in a plane, and the stainless steel plate also expands in the direction of the arrow shown in FIG. 5 due to thermal expansion. At this time, since the polyethylene terephthalate 7 and the stainless steel plate 8 have small surface frictional resistance and pressure easily escapes in the lateral direction, diffusion of the polyethylene cannot be suppressed. If polyethylene is excessively diffused, the pressure is less likely to be transmitted downward, and the pressure applied to the cover lay film 2 and the adhesive layer 11 is reduced. Therefore, bubbles 12 may be generated between the circuit patterns 1 on the substrate 10 or the through holes may be insufficiently filled.

Further, there is a possibility that the dimension may be extended due to the diffusion of polyethylene and the thermal expansion of the stainless steel plate.

Further, in the conventional method for controlling heat and pressure of the hot press in the method for manufacturing a flexible printed circuit board, the heat is raised to the set value at once, and is raised to the set value at the same time or with a slight delay. The adhesive layer 11 of the lay film 2 melts and begins to cure before the space between the circuit patterns 1 on the substrate 10 is filled, and as described above, bubbles 12 are generated between the circuit patterns 1 or through holes are formed. The embedding may be insufficient.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a cover lay film bonding method and a flexible printed circuit board manufacturing method having an extremely low defect rate.

[0010]

In order to achieve the above object, a coverlay film bonding method according to the present invention is a coverlay film bonding for heating and pressing a coverlay film in a flexible printed circuit board to a substrate base. The method is characterized in that the coverlay film is heated and pressed through a cushioning material containing at least a polyethylene sheet and a polyethylene diffusion preventing sheet for suppressing diffusion of the polyethylene sheet.

In order to achieve the above object, the first method for manufacturing a flexible printed circuit board according to the present invention is the method for manufacturing a flexible printed circuit board, wherein a cover lay film is adhered onto a circuit board having a circuit pattern. A heat-resistant release film, a polypropylene sheet, a polyethylene sheet, and a polyethylene diffusion-preventing sheet are laminated on the lay film, and a cushioning material is placed on the lay film. A predetermined temperature and pressure are applied to the cushioning material to cover the cover layer. It is characterized in that the film is adhered to the substrate base.

In order to achieve the above object, a second method for manufacturing a flexible printed circuit board according to the present invention is the method for manufacturing a flexible printed circuit board, wherein a cover lay film is adhered onto a circuit board having a circuit pattern. A heat-resistant release film, a polypropylene sheet, a polyethylene sheet, and a polyethylene diffusion-preventing sheet are laminated on the lay film, and a cushioning material that suppresses the diffusion of polyethylene is placed in this order. Hold at a certain first temperature for a predetermined time, and then keep a sufficient first pressure to allow polyethylene to enter into a narrow space between circuits, and the adhesive melts while keeping the first pressure. The adhesive layer is heated to and held at a second temperature for melting for a predetermined period of time between the circuits, and then the above-mentioned second Under pressure of, characterized by bonding the cover lay film on the substrate base by holding raised to a third temperature to cure the adhesive layer.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an explanatory view for explaining a method for manufacturing a flexible printed circuit board which is an embodiment of the present invention.
The structural example of the lamination | stacking buffer part which covers the circuit pattern of this flexible printed circuit board is shown. FIG. 2 is a cross-sectional view showing a state in which heat and pressure are applied after stacking the stack buffer section.

As shown in FIGS. 1 and 2, the flexible printed circuit board in this embodiment has a circuit pattern 1,
On both sides of the flexible printed circuit board composed of the coverlay film 2, a laminated cushioning material composed of a heat resistant release film 3, a polypropylene sheet 4, a polyethylene sheet 5 and a polyethylene diffusion prevention sheet 6 is laminated. As shown in FIG. 2, the circuit pattern 1 is arranged on the substrate 10, and the adhesive 11 is applied to the surface of the coverlay film 2 facing the circuit pattern 1.

The polyethylene diffusion prevention sheet 6 is made of a material having a large surface friction resistance, and is made of a chip ball in this embodiment.

The flexible printed circuit board having such a structure is heat-pressed by using a heat press device from outside the polyethylene diffusion preventing sheet 6 at a timing shown in FIG. 3 and at a pressure (20 to 40 kgf). / Cm
2) Add and.

The polyethylene of the polyethylene sheet 5 is melted by the applied heat, but the melted polyethylene is suppressed from being diffused by the polyethylene diffusion preventing sheet 6. That is, the melted polyethylene permeates the polyethylene diffusion preventing sheet 6, whereby the surface resistance is increased and the diffusion of polyethylene is suppressed. Further, diffusion is also suppressed by the polypropylene sheet 4 that contracts due to heat. Therefore, the polyethylene sheet 5 can sufficiently enter between the circuit patterns 1 and transmit a sufficient pressure to the adhesive 11 applied to the lower surface of the coverlay film 2.

Further, in this embodiment, as shown in FIG.
The timing of melting the polyethylene of the polyethylene sheet 5 to transmit pressure between the circuit patterns 1, the timing of melting the adhesive 11 to fill the space between the circuit patterns 1 and the timing of curing are set to different predetermined times. , Controlling the applied heat and pressure. As a result, the adhesive 11 is sufficiently filled between the circuit patterns 1.

Specifically, as shown in FIG. 3, by holding a temporary temperature at the polyethylene melting temperature (A),
The polyethylene sheet 5 is completely melted, and then pressure is applied to allow the polyethylene to enter into a narrow space such as between the circuit patterns 1 so that the pressure is sufficiently transmitted.

Next, the temperature is raised to the adhesive melting temperature (B), and the adhesive 11 is melted to allow it to enter a narrow space such as between the circuit patterns 1. Then raise to the adhesive curing temperature,
The adhesive 11 is cured.

As described above, according to the present embodiment, by disposing the polyethylene diffusion preventing sheet as the laminated cushioning material, the polyethylene melted by heat is prevented from laterally diffusing and a sufficient pressure is applied between the circuits. It is possible to convey.

Further, according to the present embodiment, by controlling the heat and pressure of the hot press device, the adhesive sufficiently enters into a narrow space such as between the circuits to prevent bubbles between the circuits and to prevent defective filling of the through holes. Can be prevented.

Although the flexible printed circuit board tends to expand its dimensions after hot pressing due to the diffusion of polyethylene, in this embodiment, the expansion of dimensions is also suppressed by suppressing the diffusion of polyethylene.

In the present embodiment, the chip balls are used as the polyethylene diffusion preventing sheet 6, but the polyethylene ball is not limited to this and may be any one that increases the frictional resistance of the surface.

As described above, according to the present embodiment, the control of the heat and pressure of the device is optimized by the structure of the cheaper cushioning material, so that bubbles between circuits and defective filling of through holes do not occur. Further, the amount of dimensional change can be further suppressed by suppressing the diffusion of polyethylene.

[0027]

As described above, according to the present invention, it is possible to provide a cover lay film bonding method and a flexible printed circuit board manufacturing method having a very low defect rate.

[Brief description of drawings]

FIG. 1 is an explanatory diagram illustrating a method for manufacturing a flexible printed circuit board that is an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a state in which heat and pressure are applied after stacking a stacking buffer portion that covers a circuit pattern of a flexible printed circuit board in the above embodiment.

FIG. 3 is a timing chart showing heat and pressure applied to the flexible printed circuit board in the above embodiment.

FIG. 4 is an explanatory diagram showing a configuration example of a stacking buffer section that covers a circuit pattern of a conventional flexible printed circuit board.

FIG. 5 is a cross-sectional view showing a state in which heat and pressure are applied after stacking a stacking buffer portion covering a circuit pattern of a flexible printed circuit board in the conventional example.

FIG. 6 is a timing chart showing heat and pressure applied to the flexible printed circuit board in the conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Circuit pattern 2 ... Coverlay film 3 ... Heat-resistant release film 4 ... Polypropylene sheet 5 ... Polyethylene sheet 6 ... Polyethylene diffusion prevention sheet 10 ... Substrate 11 ... Adhesive

Claims (3)

[Claims] 1. A coverlay film bonding method for heating and pressure bonding a coverlay film in a flexible printed circuit board to a substrate base, the buffer including at least a polyethylene sheet and a polyethylene diffusion preventing sheet for suppressing diffusion of the polyethylene sheet. A coverlay film bonding method, characterized in that a coverlay film is heated and pressed through a material. 2. A method for manufacturing a flexible printed circuit board, which comprises bonding a coverlay film onto a substrate having a circuit pattern, wherein a heat-resistant release film, polypropylene sheet, polyethylene sheet, polyethylene diffusion prevention sheet is provided on the coverlay film. Place the cushioning material stacked in the order of,
A method for manufacturing a flexible printed circuit board, characterized in that the cover lay film is adhered to a substrate base by applying a predetermined temperature and pressure to the buffer material. 3. A method for manufacturing a flexible printed circuit board, wherein a coverlay film is adhered onto a substrate having a circuit pattern, wherein a heat-resistant release film, polypropylene sheet, polyethylene sheet, polyethylene diffusion prevention sheet is provided on the coverlay film. A cushioning material that suppresses the diffusion of polyethylene laminated in this order is placed, and this cushioning material is held at a first temperature, which is the polyethylene melting temperature, for a predetermined time,
After that, the first pressure sufficient to allow polyethylene to enter the narrow space between the circuits is further maintained, and the adhesive layer is formed for a predetermined time while the adhesive melts and enters the circuit while maintaining the first pressure. Raise and hold the second temperature to melt,
Thereafter, further under the first pressure, the cover layer film is adhered to the substrate base by raising and holding the adhesive layer at a third temperature for curing, and the cover layer film is adhered to the substrate base. Production method.