Laser Bond Header

This invention relates to headers for semiconductor devices, and more particularly to a header having a ground post laser bonded to a lead frame ground lead.

Power transistors carry large currents, and to provide for this current, multiple ground leads are connected from the semiconductor chip to a mounting base on the lead frame. Often this mounting base serves also as a heat sink. To accommodate the current flow from the mounting base to a ground lead on the lead frame, multiple wires are needed. Any faulty bonding or breaking of any of these wires presents problems in that the remaining wires may not have sufficient current handle carrying capacity to adequately handle current through the semiconductor. An alternate method is to mechanically join the leads and the heat sink. However this connection is unreliable because it can become open during thermal cycling.

The invention is to a lead frame that has a single ground post on the semiconductor chip mounting base. This ground post may be extruded from the metal of the base, or may be a post securely mechanically and electrically attached to the mounting tab. The ground lead of the lead frame is placed over the ground post and then bonded there with a laser beam fusing the metal of the ground post with the metal of the lead frame ground lead.

The technical advance represented by the invention as well as the objects thereof will become apparent from the following description of a preferred embodiment of the invention when considered in conjunction with the accompanying drawings, and the novel features set forth in the appended claims.

FIG. 1 shows multiple ground connections according to the prior art;

FIG. 2 is a side view of FIG. 1;

FIG. 3 show the ground post of the present invention;

FIG. 4 is a side view of FIG. 3;

FIG. 5 is an example of a ground post and ground lead;

FIG. 6 shows the header ground lead on the ground post; and

FIG. 7 is a cross-sectional view of the ground post

FIG. 1 illustrates a prior art device showing a header base 10 having a semiconductor chip 11 mounted thereon. Header 10 includes a plurality of leads 12, one of which 13 is the ground lead for the device. Semiconductor chip 11 is connected to the header base tab by a plurality of leads indicated at 14 and 15. The header base is then connected to ground lead 13 by multiple wires 16. The ground bonds formed by wires 14, 15 and 16 are required because the current handling capacity of a single wire is not sufficient. In order to use a single bonder to bond the other leads 18 to the semiconductor chip, the multiple wires are used for the ground lead.

FIG. 2 is a side view showing the wire bond between header lead 13 and the connection wires 16.

FIG. 3 shows a header and semiconductor chip mounted thereon according to the present invention. Header 20 has a semiconductor chip 21 mounted thereon and interconnected to header leads 22 with bond wires 27. There are a plurality of bond wires 24 and 25 providing ground wires from semiconductor chip 21 to header 20. To connected the ground connection of header 20, a post 28 is provided on header 20, and header lead 23 has an end 26 that has a central opening 29 that is placed down over post 28. After placing header lead 26 over post 28, then post 28 and header lead 26 are bonded together by, for example, a laser fusing process where both the metal of post 28 and lead end 26 are fused together. The fusing of the metal makes a better and sturdier connection since a solder connection is subject to corrosion or a bad solder connection and mechanical connections can flex open and are subject to thermal damage. Post 28 and lead end 26 may be, for example, copper, or may have a low temperature material plated thereon to provide a fusible material.

FIG. 4 is a side view, in part, of FIG. 3, showing the side of the header 20, semiconductor chip 21, and header lead end 26 over post 28.

Post 28 may be a separate post that is secured to header 20, or may be a portion of header 20 extruded to form the post. The ground post 28 and ground lead 23 are illustrated in FIG. 5 with the ground lead positioned above the ground post.

FIG. 6 shows the ground lead 23 on the ground post 28 and laser bonded at 30.

FIG. 7 is a cross-sectional view of the extruded post 28 with ground lead 23 mounted around ground post 28.