Evaluating silver paste strength for die bonding during the reflow soldering process is important, as silver paste fracturing is one of the main causes of package failure. First, we assumed that the fracturing was caused by thermal stress and vapor pressure at the interface between the resin and the copper lead frame. Next, we measured the silver paste fracture strength using a three-point bending test and a bonded specimen with silver paste. Finally, we predicted the occurrence of silver paste fracturing by calculating the silver paste stress during reflow soldering process and comparing it with the measured fracture strength. Results obtained in strength evaluation analysis were consistent with those obtained in package reflow tests, indicating that this method can be used to predict the occurrence of silver paste fracturing.

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We developed a novel method to estjmate 止e strain di 面 bution of a small area such as so亘 der joints based the combination ofan electromotive force methOd and finite element analysis ( FEA ) ． This meth (xi estimates a strain dis な ibutjon by analyzing a ten) perature change whlch is generated by elastic a皿 d plastic deforrnations ， In this paper ． we applied this rneth ( X1 to a solderjoint subjected to enforced tensile displacemen し The diameter and the thickness ofthe solderjoint are 500 and 200 μ m r 卿 tively As a re 甜 lt ， calculated temperatUre increase was corTesponded to measured one ． ［ ［ herefere ， the strain distribution in a small solderjoint can be estimated by electromotive force and FEA ．

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