EVALUATION OF HIGH RELIABILITY REWORKABLE EDGE BOND ADHESIVES FOR BGA APPLICATIONS

摘要

Reworkable edge bond adhesives are finding increasing utility in high reliability and harsh environment applications. The ASICs and FPGAs often used in these systems typically require designs incorporating large BGAs or ceramic BGAs. For these high reliability and harsh environment applications, these packages typically require underfill to achieve the needed thermal cycle, mechanical shock and vibration reliability. Moreover, these applications often incorporate high dollar value printed circuit boards (on the order of thousands or tens of thousands of dollars per PCB) hence the need to rework these assemblies and maintain the integrity of the PCB and high dollar value BGAs. This ftirther complicates the underfill requirements with a reworkablity component. Reworkable underfills introduce a number of process issues that can result in significant variability in reliability performance. In contrast, edge bond adhesives provide a high reliability solution with substantial benefits over underfills. This paper presents a study of new high performance reworkable edge bond materials designed to improve the reliability of large area BGAs and ceramic BGAs assemblies while maintaining good reworkablity. Four reworkable edge bond materials (commercially available) were studied. Test vehicles included 12mm BGAs with plans to expand the study to include ceramic BGAs and large area BGAs. Process development was also conducted on the edge bond process to determine optimum process conditions. For edge bond processing, establishing an edge bond that maximizes bond area without encapsulating the solder balls is key to achieving high reliability. The reliability testing protocol used included board level thermal cycling (-40 to 125 °C) and random vibration testing (3 G, 10-1000 Hz).