Measurement of interface toughness as a function of temperature, moisture concentration and mode mixity

Abstract

This paper describes a bulge test method of measuring the toughness of the pad-encapsulant interface. The specimen employed was an actual square PQFP package fabricated without the die. A circular delaminated region was created at the pad-encapsulant interface and a hole drilled through the top layer of the encapsulant and through the pad. With the PQFP suitably supported, a shaft was then pushed through the hole and onto the bottom plastic layer until the initial delamination is extended. An interaction integral method was employed to compute the fracture toughness of the interface from the maximum failure load measured. The effect of humidity and temperature on interface toughness was determined by conducting the tests for specimens under various levels of moisture preconditioning and various temperatures. The interface toughness was found to decrease with increase in temperature and moisture concentration. The interface toughness was also measured by the standard three-point bending test. From the data obtained, an expression for the toughness of the pad-encapsulant interface was obtained as a function of temperature, moisture concentration and mode-mixity. The effect of dimples on the pad on the interface toughness was also measured.