JP2570381B2 - IC chip mounting structure on flexible printed circuit board - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a technology for directly mounting an IC chip on a flexible printed circuit board.

(Prior Art) Mounting an IC chip directly on a flexible printed circuit board is widely used because of the following advantages.
First, the circuit configuration can be reduced in size as compared with mounting the packaged IC. Second, when the packaged IC is used, the connection between the IC and the package lead in the package and The connection between the package lead and the connection pattern on the printed circuit board is required at two locations. However, if the IC chip is directly mounted, there is no connection point equivalent to the connection between the package lead and the connection pattern, and the number of connection points is reduced. By doing so, the reliability of the circuit is improved. For this reason, IC chips are mounted directly on flexible printed circuit boards.
The technology of attaching the IC chip to the printed circuit board and connecting the circuit is the same as the connection between the IC chip and the package lead in the packaged IC, and the wire bonding method is used.

FIG. 4 shows a general structure when an IC chip is directly mounted on a flexible printed circuit board. 1 is a base film of a flexible printed circuit board, 2 is a cover film covering a conductor foil constituting a printed circuit, and 3 is a conductor foil of a printed circuit pattern. Reference numeral 4 denotes an IC chip bonded to a die pattern of a conductive foil, and reference numeral 5 denotes a bonding wire connecting between the IC chip and a bonding pattern portion of a circuit pattern of the conductive foil, and a bonding pad on the IC chip and a flexible printed board. Each of the upper bonding patterns is connected by a thermal ultrasonic bonding method or the like. In order to perform this wire bonding, the cover film 2 is removed from the die pattern portion and the bonding pattern portion of the flexible printed circuit board to which the IC chip is adhered, and the conductive foil is exposed. Therefore, the cover film removed portion of the IC chip and the flexible printed board is covered with the sealing resin 6. The problem with this structure is the surface occupied by the sealing resin 6. As described above, mounting the IC chip directly on the flexible substrate is intended to reduce the area occupied by the IC portion, to reduce the size of the entire circuit, and to facilitate the integration of the flexible printed substrate into various devices such as a camera. It is. In this case, if the area occupied by the above-mentioned sealing resin is large, the IC mounting density on the printed circuit board is correspondingly reduced and the flexibility of the flexible printed circuit board is also killed at the sealing resin portion, so that Flexibility of the substrate as a whole is reduced. The area occupied by the sealing resin is an area obtained by adding a margin to the area of the cover film removed portion for mounting the IC chip on the flexible printed circuit board. On the other hand, it is preferable that the area of the cover film removing portion is large from the viewpoint of workability when the IC chip is wire-bonded to the flexible printed board. If this area is large, that is, if the exposed area of the bonding pattern of the printed circuit is large, the position and size of the cover film removal part will vary, the relative position of the bonding pattern and the IC chip will vary, and the error in the operation of the bonding machine. Is easy to absorb. For this reason, the cover film removal portion has conventionally been considerably widened without any particular standard.

FIG. 5 shows a conventional example of a mounting structure of an IC including a light receiving element on a flexible printed circuit board. As in the example of FIG.
The IC chip 4 is adhered on the die pattern, connected to the bonding pattern of the printed circuit by the wire 5,
A frame 7 is adhered around the IC chip, and a transparent resin is injected into the frame to seal around the IC chip. In this case, the frame 7 is bonded to the portion of the flexible printed circuit board from which the cover film has been removed. Therefore, the area of the portion where the cover film is removed must be large enough to extend outside the outer periphery of the frame 7, and an exposed portion of the conductive foil 3 is formed on the outer periphery of the frame 7. In order to prevent moisture in this portion, a sealing resin must be applied to the outer periphery of the frame 7. If the size of the portion where the cover film is removed is made smaller than the inner size of the frame 7, the frame 7 will be adhered on the cover film, and there is no need to apply a sealing resin on the outer periphery. Then, as described above, since the cover film removing portion is made considerably large from the viewpoint of workability of wire bonding, the frame 7 is located further outside, and the IC sealing structure is further enlarged.

(Problems to be Solved by the Invention) The present invention seeks to minimize the area occupied by a sealing resin or a sealing structure on a flexible printed board when the IC chip is directly mounted on the board. Things.

(Means for solving the problem) When mounting an IC chip on a flexible printed circuit board by wire bonding, the length of the exposed portion of the bonding pattern of the flexible printed circuit board is 2 mm.
The dimensions of the portion where the cover film was removed were set as follows, and in this exposed portion, the portion having a tip length of 0.4 mm or more was defined as a linear portion extending in the direction in which the bonding wire was pulled out from the IC chip. Further, in the above configuration, when a frame is further bonded around the IC chip and a sealing resin is injected into the frame, the frame is bonded to the cover film.

(Operation) As a result of analyzing the work of mounting an IC chip on a flexible printed circuit board by wire bonding,
In the bonding pattern on the printed circuit board, the part where the wire for IC chip connection is bonded must have a linear part of 0.4 mm or more in the direction in which the wire extends, and the length of the exposed part excluding the cover film is up to 2 mm It became clear that there was enough. Here, the above-mentioned linear portion will be described with reference to FIG. 3. In FIG. 3, reference numeral 4 denotes an IC chip, and hatched 3d denotes a bonding pattern.
As shown in the drawing, the bonding wire 5 is connected to the IC chip. For example, in the bonding pattern at the upper left corner of the drawing, the tip is a straight line extending in the direction in which the bonding wire 5 extends. Is the above-mentioned straight line portion, and the bonding pattern in the middle of the right is a straight line in the direction of the bonding wire in the whole bonding pattern. In this case, the above-mentioned straight line portion is indistinguishable from the other portions of the bonding pattern. It still exists. And this straight line part
The linear section of 0.4 mm or more is necessary to absorb the variation in the amount of movement of the wire bonding machine and to reduce the distance between the wire and the bonding pattern by crushing and spreading the wire when it is bonded. This is because the connection is ensured, so that an area enough to accommodate this spread is required on the bonding pattern side. Next, the length of the exposed part of the bonding pattern
It is sufficient that 2 mm is sufficient as described above, in addition to the 0.4 mm necessary for ensuring the reliability of wire bonding, the conductor pattern length due to the dripping of the conductor pattern edge in the etching for forming the conductor pattern Of the cover film is about 0.1 mm, and the cover film is pasted on the printed circuit board by removing the window from the part where the IC chip is mounted.
About 0.3mm is necessary, and the adhesive that sticks out of the above window is about 0.3mm, so when all these are put together, it becomes 0.4 + 0.1 + 0.3 + 0.3 = 1.1mm, and the wire bonding is secure. In order to secure the length of the bonding pattern linear portion of 0.4 mm for ensuring the performance, it is sufficient that the nominal length of the exposed portion of the bonding pattern is 1.1 mm. In the present invention, the maximum length of the exposed portion is set to 2 mm by giving a considerable margin to this 1.1 mm. This way,
Cover film slippage 0.3mm and adhesive protrusion 0.3
mm, the exposed portion is shortened by 0.6 mm, and even if the bonding pattern is shortened by 0.1 mm due to etching, the length of the exposed portion of the bonding pattern is 1.3 mm
Thus, the length is too long to obtain the certainty of wire bonding.

When bonding the frame on the cover film, the inside dimensions of the frame need only be slightly larger than the dimensions of the removed portion of the cover film.

FIG. 1 shows an IC chip mounting portion of a flexible printed circuit board according to an embodiment of the present invention. In this figure, D is a die pattern on which an IC chip is bonded. B is the bonding pattern, and the inside of the rectangular frame line C is the cover film removed portion. In this example, the dimensions of x shown in the figure are nominally 1.
Each bonding pattern B is a straight line extending in the wire drawing direction from each bonding pad of the IC chip in the portion where the cover film is removed, and the shortest is 1.1 mm. (Nominal), the longest one is the pattern in the upper left corner in the figure and the length is about 1.5mm (nominal)
It is.

2 and 3 show an embodiment in which an IC chip 4 including a light receiving element is directly mounted on a flexible printed circuit board.
Is a base film of a flexible printed circuit board, 2 is a cover film, the inside of the square shown by C in FIG. 3 is a cover film removed portion, and 3 is a conductor foil. IC chip 4
Is bonded onto a die pattern 3d of a conductive foil with an adhesive 8, and the wire 5 is connected to the bonding pattern 3b. Reference numeral 7 denotes a frame which is positioned on the outer periphery of the cover film removed portion C, is adhered to the cover film 2 by an adhesive 9, and a transparent resin 10 for sealing is injected inside, and an inward step 11 is formed.
A smooth transparent resin plate 12 is fitted on the upper surface, and is adhered to the transparent resin 10. In this embodiment, the protruding length X of the bonding pattern 3b into the portion where the cover film is removed is 1.1 to 1.5 mm.

(Effects) According to the present invention, the result of analyzing the work of directly mounting an IC chip on a flexible printed circuit board shows that the length of the exposed portion of the IC bonding pattern on the flexible printed circuit board is set to a range of at least 0.4 and a maximum of 2 mm by wire bonding. It has been found that it is the most preferable in order to ensure the reliability of the bonding pattern and to minimize the length of the exposed portion of the bonding pattern as much as possible, and the area occupied by the sealing resin according to the present invention is as small as possible. In addition, the reliability of the circuit is not reduced at all. Also, since the exposed length of the bonding pattern is not unnecessarily large, the frame can be bonded onto the cover film even in a structure in which the frame is provided and the sealing resin is injected. , And the trouble of applying a sealing resin to the outer periphery to secure moisture proof can be saved.

[Brief description of the drawings]

FIG. 1 is a plan view of a mounting portion of a flexible printed circuit board according to one embodiment of the present invention, FIG. 2 is a vertical sectional side view of a main part of another embodiment of the present invention, FIG. Is a vertical sectional side view of a main part of a conventional example, and FIG. 5 is a vertical sectional side view of a main part of another conventional example. D: Die pattern on flexible printed circuit board, B
... bonding pattern, C ... outer periphery of cover film removed portion, 1 ... base film of flexible printed circuit board, 2 ... cover film, 3 ...
Similarly, conductive foil, 4 IC chip, 5 bonding wire, 6 sealing resin, 7 frame, 8, 9 adhesive, 1
0 ... Transparent resin.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Kiyoshi Seijiji 2-30 Azuchicho, Higashi-ku, Osaka-shi, Osaka Inside Osaka International Building Minolta Camera Co., Ltd. (56) References JP-A-62-179732 (JP, A) JP-A-61-271848 (JP, A) JP-A-56-129738 (JP, U)

Claims (2)

(57) [Claims] 1. A flexible printed circuit board on which an IC chip is mounted, a bonding pattern extending from a printed circuit pattern is arranged around a region where the IC chip is mounted, and a bonding pad of the IC chip is bonded to the bonding pattern. An IC chip mounting structure on a flexible printed circuit board connected by wires, comprising a cover film that covers a part other than the IC chip mounting section on the flexible printed circuit board, wherein the cover film on the flexible printed circuit board is removed. The cover film removed portion is formed so that the length of the exposed portion of the bonding pattern exposed to the IC chip mounting portion is 2 mm or less, and the portion to which the bonding wire is connected in the exposed portion of the bonding pattern is formed. Same As a straight line portion extending in the drawing direction of the loading wire, IC chip mounting structure of the length of that portion to the flexible printed circuit board, characterized in that not less than 0.4 mm. 2. A flexible printed circuit board according to claim 1, wherein a frame is bonded to an outer periphery of a portion where the cover film is removed in an IC chip mounting portion of the flexible printed circuit board, and a sealing resin is injected into the frame. IC chip mounting structure on printed circuit board.