Improving Non-Stick on Bond Pad Using High Pre-US (Ultrasonic) Power in Hydroxyl Coated Material

In wire bonding process, one of the key factors to have a good bonding quality is the cleanliness of the bonding surfaces whether it is bonding pad (Die) or lead (leadframe). Foreign particles, contaminations, discolorations on bonding surfaces are common causes of non-sticking of ball bond. Improving material handling procedures, cleanroom procedures, additional line processes, improvement in process controls, process parameter optimizations, etc. are some of the preventions and improvement actions being carried out by semiconductor companies to minimize or eliminate such bonding surface conditions. In this paper, improvement of Non-Sticking On Pad (NSOP) caused by impurities or contaminations formed after ArH₂ plasma cleaning process will be shown. It is detected in the impacted bonding pad surface a thick layer of “O” underneath the “C” layer when undergo depth profiling using X-ray Photoelectron Spectroscopy (XPS) surface analysis. Wirebond 1^st bond parameter have been optimized to break through these “O” layer which is believed to be a film of hydroxyl (-OH) where one hydrogen atom combined to one oxygen atom formed after the ArH₂ plasma cleaning process. The wirebond parameter (pre-US power) used in this non-sticking on bond pad improvement is not new in the wirebond equipment available today in the market. But with its function, ball bonding was able to break through the thick “O” layer and good bonding is achieved.