The Failure Analysis And Improvement Of Lifted Cu Ball For RF PIN Diodes

Background: PIN diode is a diode with a wide,undoped intrinsic semiconductor region between a p-type semiconductor and an n-type semiconductor region.The p-type and n-type regions are typically heavily doped because they are used for ohmic contacts.The wide intrinsic region is in contrast to an ordinary p–n diode.The wide intrinsic region makes the PIN diode an inferior rectifier(one typical function of a diode),but it makes it suitable for attenuators,fast switches,photodetectors,and high voltage power electronics applications.Same as other semiconductor products,the Cu wire bonding started to be used on PIN diodes also.Anyhow after Cu wire bonding implemented on RF PIN diodes,it's wire bonding yield is significantly lower than other products and contributed most customer complaint,which brought big loss to company.The author performed very detail failure analysis and found the root cause.After that he cooperated with development department and worked out good solution,which is optimizing bond pad design of RF PIN diodes.Finally the sample built with new pad design passed all reliability testing,the problem was solved.The overall yield of RF PIN diodes improved ?2% after action implemented.As a hot topic on semiconductor backend industry,so many innovations and improvements have been implemented on Cu wire bonding,most of them focus on process parameter optimization or Cu wire material improvement.Based on the understanding of these actions,this article innovated new method to improve Cu wire bonding quality by optimizing bond pad design.This can be a reference for Cu wire technology innovation in future.