アンダーフィルの物性値の適正化によるはんだ接合部の信頼性向上

概要

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The recent trend in electronics device towards bonding large chips to PCB boards by means of solder joint and intermingling with many others assistant materials, such as selectable underfills. This means a larger differential thermal expansion and deformation mismatch between the board, the chip and others assistant materials. To reduce the thermal stresses and strains at solder joints, a lot of underfills have been developed and customarily added to fill the deformation between the chip and the PCB board. In this research, firstly, we show presence of local mismatch of thermal deformation between solder and alloy connector. Secondly, we discuss the effects of the underfill on the reduction of solder joint stresses and strains with deformation mismatch of thermal expansion based on a finite element analysis. This procedure has typically at least moderated the thermal stress at solder joint by a factor of 3, as compared to lower CTE (Coeff. of Thermal Expansion) of underfill. Finally, we probe a method to minimize the deformation mismatch of solder joint by means of optimizing properties (Youngs Modulus, Poissons Ratio and CTE) of the underfill to reduce stresses and strains at solder joints. The optimum method presented here can effectively improve the reliability of solder joint of electronics package by optimizing the properties of underfills, and the method is useful to select or develop underfill materials.