Ribbon Bonding Failure Analysis And Process Optimization For Power Device Packagings

Al Ribbon Stitch as new soldering material,it has better electrical performance and lower cost than Au wire bonding and it provides comparable electrical performance to copper wire on a cost-effective basis.It has been more and more popularized and applied on power products in recent years.However,the reliability problems such as second ball lift issue always exist in the production process,the key point which restrict the quality of this process include technology and theory have very important practical significance and academic significance to promote the development of packaging technology.In this paper,a power device package A is taken as an example to systematically study for second bond lift issue and its improvement method.Firstly,the electrical performance of the failure samples were analyzed.It was found that the main failure cause of device A is second bond lift or root fracture.Then do non-destructive analysis such as visual inspection?X-ray?C-SACN and T-SACN for failure samples.It was found that there were delamination between bare copper L/F and compound at second bond through C-SACN.Through destructive analysis it was found bare copper L/F lead bonding area had contamination at second bond after de-cap and found there were organic contamination such as C,O,S element on L/F lead of EDX analysis.Combined with process investigation it was confirmed the possibility of organic contamination during DB and solder paste sintering process.Finally,a comparative test of shear stress between two groups of samples with flux contamination and without flux contamination was carried out and confirmed reduction of Al wire strength and delamination of second bonding area caused by flux contamination after solder paste sintering.In order to solve solder flux contamination after solder paste sintering,after evaluation,9288 solvent cleaning agent was selected for Ultrasonic cleaning of Al Ribbon Stitch products.The research shows that under the condition of frequency 80 KHZ,power 300 W and cleaning time of 5 minutes,there is no pin broken issue for flux contaminated units,the solder strength and data consistency of Al Ribbon Stitch contaminated by flux after Ultrasonic cleaning have been significantly improved and there is no delamination between bare copper L/F lead and compound,EDX analysis of leads after cleaning without contamination of C,O,S flux element.Do full assembly process verification at last,after introducing plasma cleaning technology with frequency of 80 KHZ and power of 500 W,the key process indexes of power products meet the design requirements,and the assembly yield is stable at 99.8%.