Power QFN Second Bond Lift And Improvement Study

Power quad flat no-lead(PQFN)package is mixing signal technology combine generally circuit,CMOS circuit and high power circuit based on Quad flat no-lead(QFN)design.PQFN was developed to meet the high power dissipation requirements of automotive,industrial and commercial applications.Possible failure modes are power die crack,wafer damage by Al wire bonding,Au ball lift issue,Au second bond lift issue,etc.In semiconductor assembly,ball lift and second bond lift are general problem after the reliability.A lot of papers introduce the ball bond issue in the domestic and oversea,while the second bond issue is less.More factors including packging material,processing environment,processing condition and their intercatoin can impact the second bond issue,which come to the quality critical for assembly device after the reliability.And the analysis method and theory study for the second bond are very important to the semiconductor assembly development and academic study.This paper studys the second bond issue based on PQFN SOBA product.This paper firstly executes electrical analysis for PQFN SOBA device that the device failed second bondopen on customer apply board level.Based on the result of electrical analysis,Au second bondlift issue was found.Then failure analysis showed that it can be caused by the delamination and contamination at second bondarea.This paper focus on the delamination and contamination study and explore the root cause and improvement method of Au second bondlift issue by FEA(Finite Element Analysis)and modern instrumental analysis.In our research,the delamination between compound and lead frame is introduced from mechanism analysis.FEA for unit and PCB modeling is established the correlation between the delamiantion and second bondlift issue based on SOBA device.Meanwhile,SIMS,XPS,AES and FTIR analyze the composition of second bondarea of the failed unit including raw materials(tape and compound)of SOBA device.Finally,PDMS(PolyDiMethylSiloxane)was detected from the tape and experiment results guarantee it can cause the delmaination and contaminatoin.In this study,Series of actions to improve and enhance the second bondintegrity of SOBA device were introduced including Tape change from A to B,adding plasma cleaning,second bondposition changing based on the FEA result and security loop application on down bond.After all,the whole study result reveals that second bondperformance on SOBA device is more robust and passed the reliability test.It furhter improve the reliability level and theory study for semiconductor assembly technology and can be applied universally.