Meaning
Catastrophic failure mechanism occurs directly at the boundary between different material phases in a solder joint or bond. Appearance of an interfacial cleavage fracture typically shows a smooth and mirror-like surface indicating little plastic deformation before the final separation. This type of failure results from excessive brittleness at the connection point.
Stress Concentration
External forces apply tension to the rigid interface where mismatched thermal expansion coefficients create localized weak points. The arrival of an interfacial cleavage fracture often signals that the intermetallic layer has grown too thick or has developed internal voids during the assembly process. Voids act as initiation sites for high-speed cracks.
Failure Analysis
Cross-sectional imaging confirms whether the separation happened cleanly between the bulk solder and the under-bump metallization. High occurrence rates of interfacial cleavage fracture indicate a need for revising the surface finish or adjusting the reflow oven cooling rate. Examining the chemistry of the fracture surface reveals if contaminants were present.
Process Optimization
Mitigation efforts focus on limiting the time at liquid temperatures to keep intermetallic growth within stable ranges. Lowering the overall hardness of the soldering alloy can also prevent the rigid buildup that leads to an interfacial cleavage fracture over long deployment cycles. Precise control of temperature helps maintain a flexible bond.
