Lifted Wedge Bond or Wedge Lifting

Lifted Wedge Bond

Figure 1. An Al wedge bond that has lifted off the bond pad

Figure 1 shows a SEM photo of an aluminum (Al) wedge bond that has lifted off its aluminum bond pad.

Close inspection of this lifted wedge bond seems to indicate that it has a material attached to it that is not aluminum. It is very likely that this material is the barrier metal under the aluminum bond pad. This barrier metal 'isolates' the aluminum bond pad from the silicon substrate, since silicon atoms tend to interdiffuse with aluminum atoms and subsequently appear on the surface of the aluminum bond pad as silicon nodules.

In this case, the barrier metal most likely lifted off the silicon substrate along with the aluminum bond pad layer (which is on top of it) and the wedge bond itself (which is on top of the Al bond pad). This seems to indicate that the root cause of the wedge bond lifting is not poor adhesion of the wedge bond to the bond pad, but poor adhesion of the barrier metal to the silicon substrate.

Whether the material on the wedge bond came from the barrier metal or not can easily be confirmed by EDX Analysis.