Micromechanics of void growth and coalescence - Vapor pressure induced failure in thin film and multilayer structures

Abstract

<P>THIS WORK INVESTIGATES VAPOR PRESSURE DRIVEN VOID GROWTH AND COALESCENCE IN TWO TYPES OF MULTILAYER STRUCTURES: I) BIMATERIAL INTERFACE AND II) ADHESIVE JOINT. IT AIMS TO PROVIDE SOME INSIGHTS INTO THE MOISTURE-INDUCED FAILURE A?? A??POPCORNINGA?? IN IC PACKAGING. INCOMPATIBILITY IN MATERIAL PROPERTIES NATURALLY INDUCES A PREDOMINANTLY MODE II LOADING ON INTERFACES. WHEN VAPOR PRESSURE IS SUPERPOSED ON MODE II DOMINANT LOADING, THE BEHAVIOR OF INTERFACE FAILURE IS NOT WELL-UNDERSTOOD TO DATE. PRESENT WORK ADDRESSES THIS KEY ISSUE.</P><P>OUR RESULTS SHOW THAT: I) IN BIMATERIAL INTERFACE, VAPOR PRESSURE CAUSES SEVERAL-FOLD REDUCTION IN THE INTERFACE FRACTURE TOUGHNESS WHEN THE LOADING IS MODE II DOMINANT; II) IN ADHESIVE JOINT, THE PRESENCE OF VAPOR PRESSURE AT A HIGHLY POROUS INTERFACE CAN NEGATE ANY POSSIBLE TOUGHENING CAUSED BY LARGE FILM THICKNESS OR HIGH MODE MIXITY. WITHOUT ASSUMING ANY PRE-EXISTING CRACK, PRESENT WORK PROPOSES AN APPROACH TO MODEL INITIATION OF INTERFACE DEBOND