Analysis of Package Cracking During Reflow Soldering Process

Makoto Kitano, Asao Nishimura, Sueo Kawai, Kunihiko Nishi
1988 Reliability Physics Symposium  
Surface munt packages are heated up above solder melt ing temperature during reflow soldering process. If t h e p l a s t i c e n c a p s u l a n t h a s absorbed m o i s t u r e , package cracking may occur. In t h i s study, an evaluat i o n method of Lhe package cracking is developed by means of moisture diffusion analysis of p l a s t i c and deformation and s t r e s s analysis of packages. Introduct ion Recently p l a s t i c IC packages have been changing fran insertion types ( Fig. l (
more » ... n types ( Fig. l ( a ) ) t o surface mounted t y p e s ( F i g . l ( b ) ) . S u r f a c e mounted d e v i c e s (SMD) s o l d e r e d d i r e c t l y o n t o l a n d s on t h e s u r f a c e of a printed c i r c u i t board (PCB) reduce the s i z e , canplexity and c o s t s of PCBs and f a c i l i t a t e automation of PCB assembly [ 11. Reflow soldering such as vapor phase (VP) soldering or infrared (IR) soldering is used for soldering SElDs onto PCBs. During t h e process, packages are heated up above solder melting temperature. If the p l a s t i c encapsulant has absorbed moisture, package cracking may occur during reflow soldering a s shown in Fig. 2. Cracking must be prevented t o ,marantee t h e r e l i a b i l i t y of the mounted devices. Cracks are caused by vapor pressure generated inside the package causing excessive s t r e s s in the p l a s t i c [ 2 ] . The influence of package s t r u c t u r e on package cracking has been investigated experimentally and r a t e s of moisture absorption and d e s o r p t i o n of packages have been measured [ 3 ] . A q u a n t i t a t i v e explanation of the mechanism of t h i s phenomenon, however, h a s not been made, and a r'idical package design t o overcane t h i s problem is not w a i l a b l e a t present. The purpose of t h i s study i s t o develop a method t o explain the phenanenon quant itat iilely.
doi:10.1109/irps.1988.362205 fatcat:mu67bzsqgvbx7apt53hvgc32ha