Meaning
Mechanical force capacity required to detach minute metallic interconnect bumps from chip pads defines structural integrity in advanced packaging. Evaluating microbump shear strength measures the maximum lateral load a microbump array element withstands prior to mechanical fracture or pad detachment. Test results reflect the quality of Under Bump Metallurgy adhesion and intermetallic compound formation.
High shear strength values verify that interconnects will endure mechanical stresses imposed during underfilling and operational thermal cycling.
Testing Protocol
Precision micro-shear testing tools position a hardened tool tip at a controlled standoff height above the substrate surface. To measure microbump shear strength accurately, the shear tool advances against the bump flank at a fixed speed, recording peak force at fracture. Standardized test protocols require precise alignment to prevent tool dragging against passivation layers during data collection.
Failure Mode
Post-test microscopic inspection categorizes fractures into intermetallic brittle cleavage or pad lift from the silicon die. Ductile failure within the bulk solder material confirms optimal interfacial bonding and correct metallurgy formation during reflow processing.
Pad Integrity
Inadequate surface preparation or defective barrier plating reduces shear resistance, causing premature separation at lower applied loads. Minimum acceptable shear force thresholds are established by international electronics standards to ensure long-term assembly reliability.
