Effect of Moisture on the Interfacial Adhesion of the Underfill/Solder Mask Interface

Abstract

Moisture poses a significant threat to the reliability of microelectronic assemblies and can be attributed as being the principal cause of many premature package failures. Of particular concern is characterizing the role of moisture with respect to the acceleration of the onset of package delamination. In this paper the effect of moisture on the interfacial fracture toughness of two no-flow underfill materials with a commercially available solder mask coated FR-4 board is experimentally determined. Bilayer specimens with prefabricated interface cracks are used in a four-point bend test to quantify the interfacial fracture toughness. Two groups of test specimens of varying underfill thickness were constructed. The first group was fully dried while the other was moisture preconditioned at 85°C/85%RH for 725 hours. The results of this study show that the interfacial toughness is significantly affected by the presence of moisture.