JPH06140554A - Outgoing lead of electronic component and joining method therefor - Google Patents

Abstract

PURPOSE:To manufacture a leading wire which is soldered by a thermocompression bonding method easily to perform soldering under the stabilized state and to provide the sufficient bonding strength. CONSTITUTION:A protruding part 3 is formed on a soldering surface 2 of a leading wire 1, which is soldered at a planer part. Thus, a solder layer is sufficiently secured even if the leading wire 1 is pushed and soldered by a thermocompression bonding method, and the powerful junction strength is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lead for external terminals of electronic parts. More specifically, the present invention relates to a lead-out lead of an electronic component in which the lead-out lead soldered by surface contact has improved soldering adhesive strength, and a joining method thereof.

[0002]

2. Description of the Related Art Conventionally, when a lead-out lead for an external terminal of an electronic component such as a semiconductor device is mounted on a printed circuit board by soldering, it is led out to a peripheral portion of a hybrid integrated circuit device (hereinafter referred to as a hybrid IC). For example, when the leads are soldered and led out of the resin,
In some cases, a method may be adopted in which the lead-out lead is formed from a lead frame or the like, and the flat portion thereof is brought into surface contact with a printed circuit board or the like and soldered. In that case, when soldering the leads of electronic parts such as semiconductor devices to the printed circuit board by solder reflow method such as applying solder paste, the leads may float or move (so-called “flapping”). Since it occurs, it is pressed down from above with a hot bar etc. and soldered by thermal pressure welding.

A method of soldering the extraction lead to the peripheral portion of the circuit board with the hybrid IC will be described with reference to FIG. FIG. 8 is a cross-sectional explanatory view of the soldering of the extraction lead.

First, a solder paste is applied to the surface of the electrode pad 32 provided on the peripheral portion of the surface of the circuit board 31, or the solder 33 is supplied by preliminary solder (such as solder plating or a previously applied solder layer). After that, the planar joint portion 35 at the end of the external terminal lead-out lead 34 is brought into contact. After that, in order to prevent the lead lead 34 for the external terminal from moving, the hot bar 37 is heated while being pressed against the lead lead 34 while the back surface of the circuit board 31 is supported by the contact plate 36. After the solder 33 has melted, heating is stopped to solidify the solder, and then the hot bar 37 is pulled out from the lead 34 for joining.

[0005]

When the solder 33 is melted and the solder reflow method is used to bring the electronic parts into contact with the printed circuit board or the like by the weight of the electronic parts for soldering, 0.2 between the soldering surface of the lead and the printed circuit board. ~ 0.3 mm
A solder layer of a certain degree is formed, and the soldering strength is maintained. However, in the case of lead-out leads that are soldered to the peripheral edge of the hybrid IC or fine-pitch leads,
If the lead-out lead 34 is not pressure-contacted with a sufficient pressure, the lead-out lead will move and cannot be fixed accurately. When strongly pressed, the solder 33 between the electrode pad 32 and the joint 35 is pushed away to the periphery of the joint 35, so that the thickness of the solder 33 on the lower surface of the joint 35 becomes extremely thin and the soldering There is a problem that the strength becomes weak. That is, as shown in page 66 of “Soldering Technology for Electronic Materials” by Isao Osawa (published by Kogyo Kogyo Kaisha, Ltd.), the soldering interval is 25
In the range of up to 150 μm, the larger the gap, the stronger the shear strength (an example of the shear strength for a typical copper soldering space is shown in FIG. 7).

On the other hand, Japanese Utility Model Publication No. 2-17854 and Japanese Utility Model Publication No. 2-79
No. 054 discloses that by forming a groove or hole in the soldering surface at the tip of the lead, or by making the soldering surface arcuate, the soldering area can be increased and the solder fillet can be secured to increase the adhesive strength. Means for doing so are disclosed. However, there is no disclosure of means for increasing the distance between the leads and the substrate, which is the subject of the present invention, to increase the adhesive strength of soldering by increasing the distance to a certain value or more. . By making the soldering surface of the lead arc-shaped in Japanese Utility Model Laid-Open No. 2-79054, the gap with the printed circuit board at the end becomes large, but the thickness is 0.1 to 0.2 mm and the width is 0.1 to 0.5 mm. It is difficult to make a constant interval of 0.02 mm or more with only a lead. Moreover, even if it were possible to form a concave groove on the back surface of the lead with a thickness of 0.1 to 0.2 mm and a width of 0.1 to 0.5 mm, or to form it in an arc shape, it would be extremely difficult for the work, and the number of steps would increase. However, there is a problem that it leads to cost increase.

Further, Japanese Patent Application Laid-Open No. 4-206890 discloses an example of soldering between a lead and a substrate through a spacer. This is to absorb the strain of stress due to the difference in thermal expansion between the lead and the conductor on the substrate.
In this example, as a result, the space between the leads and the soldering surface of the substrate is secured by the size of the spacer, and the soldering space by the size of the spacer is obtained. However, it is difficult to interpose a spacer in a small lead with a fine pitch such as a lead width of 0.1 to 0.5 mm and a lead interval of 0.2 to 0.8 mm. Even if the spacer is mixed in the solder paste, if the amount is increased, the gap is filled with the spacer and the amount of the solder becomes very small and the adhesive force is reduced, or the spacer protrudes from the lead and the space between the leads is reduced. It may cause poor contact. Also,
If the number of spacers is reduced, the leads do not become parallel and the quality becomes very unstable.

According to the present invention, such a problem is solved, a lead-out lead of an electronic component capable of sufficiently improving the soldering strength by sufficiently securing the soldering interval on the lower surface of the joint portion while stabilizing the external lead-out lead, and a lead thereof. The purpose is to provide a joining method.

[0009]

A lead-out lead for an electronic component according to the present invention is a lead-out lead for an external terminal of an electronic component, the tip of which is soldered to a circuit board by surface bonding.
A convex portion is provided on the soldering surface.

Further, in the flexible film substrate according to the present invention, one end side of the wiring pattern formed on the flexible film is connected to the electronic component chip or the terminal of the circuit wiring,
A flexible film substrate in which the other end side of the wiring pattern is soldered to an external substrate, and a convex portion is provided on a soldering surface of an end portion of the wiring pattern to be soldered, To do.

The method of joining the extraction leads of the present invention is as follows.
A joining method of thermocompression bonding an electrode pad formed on a circuit board and a lead lead provided in an electronic component, wherein a protrusion is provided on the crimping surface side of the lead lead, and solder is provided between the lead lead and the pad. The feature is that they are joined in a state of being interposed.

[0012]

According to the present invention, since the projection surface is formed on the soldering surface of the extraction lead at the joint with the electrode pad of the circuit board or the wiring electrode film, even if the extraction lead is pressed by a hot bar or the like. The distance between the soldering surface of the extraction lead and the bonding surface of the circuit board is maintained by the height of the convex portion. Therefore, the thickness of the solder layer formed in these gaps is always a certain amount regardless of the pressure acting on the joint, an optimum joint state is obtained, and as a result, the joint strength is improved. .

Further, when soldering the end portion of the wiring pattern of the flexible film substrate to a circuit board or the like, by providing a convex portion on the soldering surface of the end portion of the wiring pattern, it is possible to perform thermal pressure welding. Even in the soldering method, it is possible to reliably improve the bonding strength of the soldering surface.

[0014]

The present invention will be described below with reference to the drawings. FIG. 1 is a schematic structural view of a hybrid IC to which an embodiment of the extraction lead of the present invention is applied, FIG. 2 is an enlarged perspective view of an end portion of the extraction lead of FIG. 1, and FIG. FIG. 4 (a) shows a distribution of the bonding strength of the lead-out soldering according to this embodiment, and FIG. 4 (b) shows a distribution of the bonding strength of the lead-out according to the conventional structure. FIG. 5 is an enlarged perspective view of an essential part of another embodiment of the lead-out lead of the present invention. FIG. 6 is an enlarged perspective view of an essential part of a flexible film substrate to which another embodiment of the lead-out lead of the present invention is applied. It is a figure.

One embodiment of the extraction lead of the present invention is shown in FIGS.
3 shows. FIG. 1 shows a schematic structure of a hybrid IC, in which an electrode pad 7 is formed on a peripheral portion of a circuit board 5 on which an electronic component 6 is assembled, and a lead lead 1 is bonded to the electrode pad 7 by high temperature solder or the like. The periphery of the circuit board 5 is sealed with a resin 9 such as epoxy resin, and the other end of the lead lead 1 is led out from the resin 9. The lead-out lead 1 is formed of a lead frame, and when soldered to the circuit board 5, the other end side is connected to the frame and is cut and separated into each lead after being filled with resin. As shown in a partially enlarged perspective view of FIG. 2, a portion of the lead-out lead 1 which is soldered to the circuit board 5 at one end is formed with a convex portion 3 protruding toward the soldering surface 2 side. . Since the lead frame is thin with a thickness of 0.1 to 0.2 mm and is made of a soft metal plate such as phosphor bronze or iron, it is easy to hit a part of the mold when forming the lead frame. A concave portion 4 is formed on the upper surface and a convex portion 3 is formed on the lower surface. The height H of the convex portion 3 depends on the wall thickness of the lead, but is 25 to 50 μm for a lead having a thickness of 0.1 mm.
The degree is good. This is because if the height H becomes too large, inconvenience such as lead breakage may occur.

To solder the lead-out lead 1 to the electrode pad 7 of the circuit board 5, as shown in the partial sectional view of FIG. 7 parts and the soldering surface 2 of the extraction lead 1 are overlapped and sandwiched with a solder paste or a preliminary solder (hereinafter represented by solder paste) 8 therebetween. The hot bar 10 is heated by a built-in heater, and the lead wire 1 is pressed to heat the solder paste 8 for melting and soldering. At this time, since the convex portion 3 functions as a stopper, the height A of the convex portion 3 ensures the gap A between the soldering surface 2 and the electrode pad 7 even if the convex portion 3 is pressed against the hot bar. Therefore, the thickness of the solder layer formed in the gap A is always ensured to be a constant amount regardless of the pressure acting on the lead lead 1. When the heating is stopped after the solder paste 8 is melted, the joint portion 2 and the electrode pad 7 are soldered.

Next, the circuit board 5 and the electronic component 6 are entirely covered with a resin 9 so as to completely cover them, and a frame portion (not shown) connecting the leads 1 to each other is cut off to complete the manufacture of the hybrid IC. To do.

Next, FIG. 4 shows the joint strength of the lead lead shown in FIG. 2 in comparison with the joint strength obtained by the conventional method without providing a convex portion. In Figure 4, (a) shows the width of the lead wire is 0.5 mm, the thickness is 0.15 mm, and the height of the protrusion is 40 μm.
The data when the interval B (see FIG. 2) between the convex portions is 0.6 mm,
It is plotted at the load per one when it breaks. In addition, (b) is a lead of the same size when manufactured by the conventional method (the gap of the soldering surface is 3 to 10 μm).
similar data is shown. As is clear from FIG. 4, the bonding strength of the lead according to the present embodiment having a large gap A between the soldering surface 2 and the electrode pad 7 (that is, the height H of the convex portion 3) is larger than that of the conventional structure. Recognize.

The shape of the convex portion is not limited to the semi-cylindrical shape over the entire width of the lead-out lead described above, and as shown in FIG. 5, the convex portion having a hemispherical shape on the lower surface of the lead 10 is used. Even if 11 is formed, the same operation as in the above embodiment can be achieved. The convex portion 11 can also be formed by pressing with a protrusion from the upper side when punching from a thin plate into a lead frame (13 in the figure is a concave portion formed when the convex portion 11 is formed).

Further, as an application example of the lead-out lead 1, an application to a wiring pattern of a flexible film substrate will be described below.

When a flexible film substrate, such as TAB or FPC, on which an electrode wiring pattern is formed is used to connect an electronic component such as a semiconductor chip or a circuit wiring to another circuit wiring, a recent narrowing of the wiring pattern pitch is achieved. If the pitch is made finer to meet the above requirement, adjacent wirings are likely to be short-circuited, or contact failure due to floating of the leads is likely to occur. Therefore, a method of soldering while pressing with a hot bar or the like is being studied. However, also in this method, the soldering strength becomes a problem as in the above case.

As shown in FIG. 6, in the flexible film substrate 14, the wiring pattern 16 is radially formed on the flexible film 15 by a copper foil or the like, and the flexible film substrate 14 has, for example, an IC in a space at the center thereof. Chip 17 is placed and wiring pattern 16
Is connected to the terminal 18 of the IC chip 17 at one end thereof by, for example, a gold bump. The other end of the wiring pattern 16 is a surface to be soldered (wiring pattern in the figure).
16) is formed on the lower surface 16) and the preliminary solder 20 is supplied, the convex portion 19 is formed on the external circuit board 21 such as a printed circuit board.
It is adapted to be brought into contact with the terminal 22 of and soldered. As in the case of the hybrid IC described above, since the convex portion 19 acts as a stopper, even if the wiring pattern 16 and the terminal 22 are pressed and soldered with a hot bar or the like,
The gap is secured by the height of the convex portion 19. Therefore, the thickness of the solder layer formed in the gap is always kept constant regardless of the pressure acting on the wiring pattern 16, and the bonding strength can be improved. Further, it is possible to prevent a short circuit between adjacent leads, and it is possible to sufficiently cope with the narrowing of the pitch of the wiring pattern.

In the present embodiment, the wiring pattern 16 connected to the chip arranged in the center of the radially formed flexible film substrate is directly soldered to the external circuit substrate. Is not limited to this, and is, for example, a so-called mold TA obtained by molding a joint portion between an inner lead having a flexible film and a chip.
The same can be applied to a strip-shaped flexible film substrate for connecting the electrode groups on both sides, which is used for soldering the external leads of B and for connecting the display panel electrode portion of the liquid crystal display device to the drive circuit board. .

[0024]

According to the present invention, since the protrusions are formed on the soldering surface at the end of the lead-out lead, even when the soldering is performed by pressure contact with a hot bar or the like, the protrusions are not formed on the soldering surface. Spaces corresponding to the height can be formed, a sufficient solder layer can be secured, and the bonding strength of the extraction leads can be improved. Further, the convex portion can be formed by a simple press at the time of punching the lead frame, so that a soldering surface with good workability, low cost and high reliability can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic structural diagram of a hybrid IC to which an embodiment of a lead-out lead of the present invention is applied.

FIG. 2 is an enlarged perspective view of one end of the extraction lead shown in FIG.

3 is a cross-sectional explanatory view when soldering the lead-out lead of FIG. 1. FIG.

FIG. 4A is a diagram showing the distribution of the bonding strength of the extraction lead according to the present embodiment, and FIG. 4B is a diagram showing the distribution of the bonding strength of the extraction lead according to the conventional structure.

FIG. 5 is an enlarged perspective view of an essential part showing another embodiment of the extraction lead of the present invention.

FIG. 6 is an enlarged perspective view of an essential part of a flexible film substrate to which still another embodiment of the extraction lead of the present invention is applied.

FIG. 7 is a diagram showing an example of a relationship of shear strength with respect to a soldering surface distance of copper soldering.

FIG. 8 is an explanatory diagram showing a soldering state of a conventional lead-out lead.

[Explanation of symbols]

 1 lead-out lead 2 soldering surface 3 convex part 5 circuit board 7 electrode pad 8 solder paste 15 flexible film 16 wiring pattern 17 IC chip 21 external circuit board 22 terminal

Claims (3)

[Claims] 1. A lead-out lead for an external terminal of an electronic component, the tip of which is soldered in surface contact with a circuit board, wherein the lead-out lead for an electronic component is provided with a convex portion on the soldering surface. 2. A flexible structure in which one end of a wiring pattern formed on a flexible film is connected to an electronic component chip or a terminal of a circuit wiring, and the other end of the wiring pattern is soldered to an external circuit board. A flexible film substrate, which is a film substrate, wherein a convex portion is provided on a soldering surface of an end portion of the wiring pattern. 3. A joining method for thermocompression bonding an electrode pad formed on a circuit board and a lead lead provided in an electronic component, wherein a protrusion is provided on the crimping surface side of the lead lead, and the lead lead and the pad. A method for joining lead-out leads, characterized in that the joining is performed with a solder interposed between them.