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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.

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Stress of encapsuant resin which acts on LSI chip was measured to evaluate passivation defects by a new method. It was cleared that the resin thermal stress gave damage to the LSI passivation film and aluminum corrosion took place by moisture penetrating through the film damage up to the metal surface in a humid atmosphere.The stress values obtained by the new method for various resins showed good correlation to the passivation defect densities. When a resin with half stress was applied, the defect density was halved.To improve the moisture resistance of plastic-encapsulated LSIs, the application of the low stress resin is supposed to be a good method.

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