Analysis of Package Cracking During Reflow Soldering Process
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 (
... 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.