Moisture sensitivity of thin small outline packages

The kinetics of moisture absorption and desorption under different temperature and humidity conditions in a TSOP (thin small outline package) was found to be different than in conventional thick SMT (surface mount technology) packages. TSOP absorbs and loses moisture quickly, because the plastic thickness in TSOP is roughly one-third of that in thick packages. Even under severe preconditioning no package cracking was observed. It is believed that the thinness of the package and the interlocking effect of dimples on the die paddle are the key factors leading to this behavior. Increased amounts of plastic (below the die paddle) are known to give additional mechanical strength and protection. However, the reliability performance of TSOPs in this investigation suggests that thin profile inherently provides smaller shear force and less propensity for delamination