The present invention relates to a wire bonding method for making connection between a die electrode pad and an external lead and more particularly to a method for forming low wire loop during wire bonding.
In wire bonding, when, in order to bond a wire at a second bonding point, a capillary is moved to slightly above the second bonding point, excess wire hangs down from the lower end of the capillary, and a wire shape develops in which a hanging down part is formed. This hanging down part causes a repulsion to occur, when the wire is bonded at the second bonding point, so as to swell upward, resulting in that the straightness of the wire loop deteriorates. Japanese Patent Application Laid-Open Disclosure Nos. (1992) 4-370941 (Japanese Patent No. 3049515) and 2000-82717 disclose wire bonding methods for preventing wire loop from swelling at the time that bonding is made to the second bonding point.
In the method of Japanese Patent Application Laid-Open Disclosure (1992) No. 4-370941 (Japanese Patent No. 3049515), after connecting a wire to a first bonding point, the capillary is positioned slightly above the second bonding point and slightly on the first bonding point side, and then the capillary is descended diagonally in the direction of the second bonding point, thus bonding the wire at the second bonding point. In other words, in the method of Japanese Patent Application Laid-Open Disclosure (1992) No. 4-370941, by way of causing the capillary to descend diagonally, the hanging down part that hangs down from the lower end of the capillary is absorbed.
In the method disclosed in Japanese Patent Application Laid-Open Disclosure (2000) No. 2000-82717, after the wire is connected to a first bonding point, the capillary is lowered slightly from a second bonding point to the first bonding point side so that the capillary presses the hanging down part hanging down from the lower end of the capillary against a horizontal surface, then the capillary is moved to above the second bonding point and then is caused to descend, thus bonding the wire at the second bonding point. In other words, in the method of Japanese Patent Application Laid-Open Disclosure (2000) No. 2000-82717, the wire hanging down from the lower end of the capillary is pressed against a horizontal surface prior to bonding at the second bonding point; as a result, swelling of the wire loop at the time of bonding to the second bonding point is prevented.
Though not directly related to the problems the present invention would resolve, Japanese Patent Application Laid-Open Disclosure (1997) No. 9-51011 hereinafter “JP'51011,” the disclosure of which is herein incorporated by reference, discloses a wire bonding method in which the height of the wire loop from the first bonding point is formed low, of this specification. In this method, in other words, a ball is formed at the tip end of the wire, and this ball is pressure-bonded to a die electrode pad to form a pressure-bonded ball, and then, after performing loop control for moving the capillary to ascend or moving it horizontally, or the like, the wire is pressure-bonded on the pressure-bonded ball to form a wire bonding part. According to JP'51011, by way of performing bonding to the first bonding point, the wire loop height from the first bonding point can be low. For more information on low height loop at the first bonding point, see JP'51011 which is incorporated herein by reference
Even if the capillary is caused to descend diagonally prior to bonding to a second bonding point as disclosed in Japanese Patent Application Laid-Open Disclosure (1992) No. 4-370941 (Japanese Patent No. 3049515), the hanging down part of the wire at the lower end of the capillary, though it is less than that in the conventional method of bonding to a second bonding point, still remains nevertheless. Accordingly, the repulsion caused by plastic deformation of the hanging down part in the wire at the time of bonding at the second bonding point is not avoidable, and swelling occurs in the slanted part of the wire loop.
When the hanging down part is pressed against a horizontal surface, as in the method disclosed in Japanese Patent Application Laid-Open Disclosure (2000) No. 2000-82717, such a banging down part disperses in the interior of the capillary and in the slanted part of the wire loop, causing those respective portions to get loosened. When the capillary ascends to a certain height in the next step, the wire that was loose inside the capillary will be pushed back downward and come out at the lower end of the capillary. Since the wire that came out at the lower end of the capillary at the next bonding to the second bonding point is pressed against the second bonding point, similar to Japanese Patent Application Laid-Open Disclosure (1992) No. 4-370941 repulsion caused by plastic deformation in the wire occurs, and swelling does occur in the slanted part of the wire loop though the amount thereof is smaller than with the conventional method of bonding to the second bonding point.
Accordingly, the object of the present invention is to provide a wire bonding method in which wire loop is prevented from swelling, thus improving the wire loop straightness.
The above object is accomplished by a set of unique steps of the present invention for a wire bonding method for connecting a wire, which passes through a capillary, between an electrode pad that is a first bonding point and an external lead that is a second bonding point with a use of the capillary; and in the present invention,
The above object is accomplished by another set of unique steps of the present invention for a wire bonding method for connecting a wire, which passes through a capillary, between an electrode pad that is a first bonding point and an external lead that is a second bonding point with a use of the capillary; and in the present invention,
As seen from the above, in the present invention, the capillary is, after the bonding at the first bonding point, moved in a direction away from the first bonding point, thus pulling the wire connected to the first bonding point and making it a linear wire portion, and then this linear wire portion is cut (separated) from the wire at the thin part. Thus, with this step, a spring-up part is formed in the wire bonded to the first bonding point and is then pulled and cut at the thin part to make a one-side supported linear wire portion, and the end of this one-side supported linear wire portion is pressed by the capillary and bonded to the external lead, wherefore wire loop straightness is enhanced.
a) through 1(c) show the steps of the wire bonding method according to the first embodiment of the present invention;
a) through 2(c) show the steps continuing from
a) and 3(b) show the steps continuing from
a) through 4(c) show the steps of the wire bonding method according to the second embodiment of the present invention;
a) through 5(c) show the steps continuing from
a) and 6(b) show the steps continuing from
A first embodiment of the wire bonding method of the present invention will be described with reference to
On a lead frame 2 on which an external lead 1 is formed, a die 4 having thereon an electrode pad 3 is formed is mounted. As seen from
First of all, bonding is performed at the first bonding point A (first bonding) shown in
In other words, as seen from
Next, the clamper 6 attains its open condition, the capillary 5 (and the clamper 6) descends after moving above the first bonding point A, and the ball 14 is bonded to the first bonding point A, and then, as seen from
Then, after performing loop control for moving the capillary 5 (and the clamper 6) so as to ascend or moving it horizontally, or the like, the wire 10 is pressure-bonded on the pressure-bonded ball 11 to form the wire bonding part 12.
After that, the capillary 5 (and the clamper 6) is moved so that the capillary 5 is positioned slightly above the second bonding point B of the external lead 1. In this case, a hanging down part 15 of the wire resulting from the excess wire 10 hanging down from the lower end of the capillary 5 is formed.
Next, as shown in
Next, the clamper 6 closes and, as shown in
Then, as shown in
Next, as shown in
In the next step (second bonding) shown in
Then, the clamper 6 opens as shown in
As seen from the above, in the steps shown in
A second embodiment of the wire bonding method of the present invention will be described with reference to
In the above-described first embodiment, after the step shown in
After the step shown in
Then, the clamper 6 next opens as shown in
Next, with the clamper 6 attaining its open condition, and the capillary 5 (and the clamper 6) is moved back in the direction toward the first bonding point A and to above the end 19 of the linear wire portion 18.
Then, as shown in the step (second bonding) of
Next, as shown in
In this second embodiment of the present invention as well, since the end 19 of the one-side supported linear wire portion 18 is bonded to the second bonding point B, wire loop straightness is enhanced as in the above-described first embodiment. In this second embodiment, moreover, since the pressure-bonded ball 27 is formed in the end 19 bonded to the second bonding point B, the thickness of the bonding to the second bonding point B is thick (or thicker than in the first embodiment), and the strength at the second bonding point B is enhanced.
In the embodiments described above, the bonding to the first bonding point A is performed in accordance with the method disclosed in JP'51011 which is incorporated herein by reference; however, the present invention is not limited to use this method, and any ordinary bonding method can be used in the present invention. However, with the bonding method of JP'51011 which is incorporated herein by reference, it is possible to keep the rise from the first bonding point A low, which is preferable.
Number | Date | Country | Kind |
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2005-328291 | Nov 2005 | JP | national |
Number | Name | Date | Kind |
---|---|---|---|
6173885 | Takahashi et al. | Jan 2001 | B1 |
6270000 | Nishiura | Aug 2001 | B1 |
20030019098 | Wildner | Jan 2003 | A1 |
Number | Date | Country |
---|---|---|
4-370942 | Dec 1992 | JP |
9-51011 | Feb 1997 | JP |
2000-82717 | Mar 2000 | JP |
Number | Date | Country | |
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20070108256 A1 | May 2007 | US |