Time-of-Flight Mass Spectroscopic Studies of Non-Stick on Pad Issues in Wire Bonding

Traditional Non-Stick on Pad (NSOP) analysis was typically carried out with X-ray photoelectron spectroscopy (XPS) surface analysis to find out any suspect contamination on the pad that may cause the non-stick issue. However, there are cases, in which their XPS analysis on the NSOP bond pad shows no difference in elemental composition when comparing to a good unit. In this paper, the time-of-flight secondary ion mass spectrometry (TOF-SIMS) that has the sensitivity in ppm level much higher than the XPS sensitivity which is usually at 0.1% was used instead for the NSOP analysis. The results revealed there is indeed a very thin organic contamination on top surface of the affected pad when comparing to a good unit. After searching through their process materials and verified with TOF-SIMS test, the contamination was pinpointed to be possibly from the polyethylene glycol originated from the sawing surfactant.