Improved Bond reliability through the use of Auxiliary Wires (Security Bumps and Stand-Off Stitch)

Whether the need is due to poorly bondable materials, non-flat bonding surfaces, odd packaging situations, or just the need for high reliability; the integrity of a wire bond interconnect can usually be greatly improved through the proper use of Auxiliary Wires. Auxiliary Wires are defined as Security Wires, Security Bumps, or Stand-Off Stitch (aka Stitch on Bump). The old stand-by Security Wire has been an asset for several decades, however, this is being replaced by Security Bumps which require a smaller second bond termination area. Further, Stand-Off Stitch (SOS) has many more applications and also has many side benefits that could be incorporated into a circuit design for better wire strength properties, fewer interconnects (die to die bonding), and lower loops. Stand-Off Stitch bonding involves the placement of a ball bump at one end of the wire interconnect, then placing a wire with another ball at the other end of the interconnect and stitching off the wire on the previous placed ball bump. This results in a near homogeneous stitch bond interconnect to the bump with an inherent improvement in stitch bond pull strength. Another use for SOS is Reverse Bonding (Stitch bond on bump on die bond pad) often resulting in a lower loop profile than standard forward wire loop and the loop is stronger because the wire hasn't been work annealed above the ball (in the Heat Affected Zone). A major impediment to the implementation of SOS is the retraining of visual inspectors and the approval of quality departments.