WO2003009658A1

WO2003009658A1 - Method for singulating flexible circuit

Info

Publication number: WO2003009658A1
Application number: PCT/TR2001/000030
Authority: WO
Inventors: Bülent TASKELI
Original assignee: Aselsan Elektronik Sanayi ve Ticaret AS
Current assignee: Aselsan Elektronik Sanayi ve Ticaret AS
Priority date: 2001-07-16
Filing date: 2001-07-16
Publication date: 2003-01-30
Anticipated expiration: 2004-01-16

Abstract

Singulation method according to the present invention is based on the mechanical resistance difference between conductor layer (1), insulating material (2) and the base material (3) patterns. The conductor peel band (5) is created along the edges of the flexible circuit (4) on both side of base material. Flexible circuit (4) is separated from the panel by lifting the start point (6) and pulling the conductor peel band (5) till the end along the edges of the circuit (4).

Description

METHOD FOR SINGTJ ATING FLEXIBLE CIRCUIT

TECHNICAL FIELD

The present invention relates to a method of singulating flexible circuits.

BACKGROUND OF THE INVENTION

Singulating of flexible circuits is always a problem for PCB manufactures. There are several methods for singulating flexible circuit. The main methods are vector based cutting and punching methods.

Vector based cutting methods such as routers, lasers and water-jet cutters are all need to a computer program. A main advantage of those methods is that a number of panels can be cut at a time. They also do not need for special tooling to wait. But, edge quality may suffer in most cases and special scaling or re- offsetting should be performed to compensate the material shrinkage. Despite these efforts, results may not be always satisfactory.

Punching methods are the reversing the vector based cutting methods. They are relatively expensive and preparation time can be very long. Depending on the type of die, they may need to resharpen again. But they create perfectly clean edges and registration is relatively better.

In the view of the problems in the prior art described above, an object of this present invention is to provide a singulating method capable of separating the flexible circuit from the panel without using soft and hard tooling requirements.

Another object of the present invention is to provide a singulating method, wherein the edges of the separated flexible circuit are perfect. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of copper pattern in accordance with the present invention.

FIG. 2 is a cross-sectional view of panel before singulating flexible circuit in accordance with the present invention.

FIG. 3 is a cross- sectional view of panel after singulating flexible circuit in accordance with the present invention.

The present invention shall be generally described with reference to FIGS. 1-3. With the description as provided below, it should be readily apparent to one skilled in the art that the various processes and structures described with references to the Figures may be used in various combination and configurations. Further, it should be apparent that the scaling in the Figures does not represent precise dimensions of the various elements illustrated therein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Singulation method according to the present invention is based on the mechanical resistance difference between conductor layer (1), insulating material (2) and the base material (3) patterns.

Both sides 1 oz. conductor layer (1), e.g. copper clad, 1-2 mils thick polimide film as base material (3) and photoimageable 1-3 mils thick dry-film coverlay are used as insulating material (2) in the present invention. Liquid photoimageable coverlay may also be used as insulating material.

During the pre-production CAM work, edges of the flexible circuit (4) are drawn with 40 mils thick copper peel band (5) and expanded 21 mils outside, leaving 1 mil gap between sidewalls of the copper peel band (5) and final cutting edge of the flexible circuit (4).

In order to ease the start point lifting, special copper pattern (6) is put as shown on Figure 1. This start point pattern (6) is connected to copper peel band (5) and helps to start peeling action. To be comfortable, it should be large enough to hold and lift with fingers.

Any corner may be chosen as the start point pattern (6). Preferably, the comer where the start and end sides are perpendicular to each other is the best one. There should be approximately 4 mils of gap (7) "between start and end points lines to mark the correct path while peeling.

Start point pattern (6) is separated from the panel by means of 3 row-holes during drilling operation. Diameters of the holes (8) may be approximately 40 mils. Preferably closest one used in flexible circuit (4). This makes the start point pattern (6) lifting easy.

Complete pattern including start point (6) and copper peel band (5) pattern then copied to the copper pattern layers of flexible circuit (4). Before this, any residual items should be removed.

Same pattern is applied to the coverlays (2) on both sides with one exception. Coverlay patterns should be 4 mils larger than the original pattern. This corresponds to 44 mil. wide coverlay peel band area. Result is 2 mils gap between coverlay pattern and master copper peel band pattern. The center of the 2 mils gap area is exactly the final cutting edge of the flexible circuit.

At the end of the production, the copper peel band (5), along the edges of the flexible circuit (4) is easily created. Both sides of the band are free of coverlay

(2). At the sidewalls of the copper peel band (5), there is 2 mils wide copperless base polimide film (3) area with no coverlay (2) on both sides. Thickness of this area is same with the base polimide film thickness. This area is mechanically less resistant relative to both copper peel band (5) and circuit pattern (4).

Almost all kind of plating options are convenient for the method according to the present invention. But, care must be taken if HASL process is to be applied. HASL is very harsh process for flexible circuits. Due to flexibility of the panel, it is not easy to centralise the panel between air knives. Therefore, uniform solder deposition is almost impossible everywhere on the panel. During the method of present invention, thick solder areas on the copper peel band, may often inhibit continuous peeling action and may cause to break. "

To prevent this problem, copper peel band area may also covered with coverlays. But, care must be taken not to cover the 2 mil gap area with coverlays.

Several advantages may also be provided by the present invention. For example, perfect flexible circuit edges and +/- 25 microns dimension tolerances thereof, is available through the use of the present invention. Moreover, no soft or hard tooling is required and very simple to apply and cut compared to other operations. Moreover, the method according to present invention is specially ideal for edge connector applications. Since the distance of the edge connector pattern and the edge of the circuit pattern is defined by the same pattern generation method, there is absolutely no alignment risk.

The method for singulating flexible circuit according to the present invention is relatively best in advantages and disadvantages compared to the other methods. Unique disadvantage is in compatibility with high volume production speed. The method according to the present invention can not compete with punching methods due to speed. But in most cases, depending on the flexible circuitry shape, it can compete with vector based cutting methods. Although the invention is illustrated and described with reference to all the specific features described in connection with the preferred embodiments, it is to be understood that changes to certain features which do not alter the overall function and concept of the invention may be made without departing from the spirit and scope of the invention, as defined in the claims.

Claims

1. A method of singulating flexible circuit board comprising the steps of:

(a) coating an insulating layer therein after the conductor layer on the base material is imaged and etched to form circuit patterns wherein an uncoated conductor peel band is created along the edges of the circuit on both side of base material;

(b) forming a start point pattern wherein it is connected to copper peel band and helps to start pulling action;

(c) separating start point pattern from the panel by means of row-holes during drilling operation;

(d) singulating the flexible circuit by lifting the start point, and pulling the conductor peel band till the end along the edges of the circuit.

2. The method of claim 1, wherein a gap is formed between the start and end point lines to mark the correct path while pulling the conductor peel band.

3. The method of claim 1, wherein the insulating layer is photoimageable coverlay material.

4. The method of claim 1 , wherein the base material is polimide film.

5. The method of claim 1 , wherein the conductor layers are copper layers.