Mechanical Stress
Force applied to a solder joint at high velocity or large displacement amplitudes measures the resilience of the interconnection under extreme mechanical loading. High strain shear testing evaluates the strength of the bond between the component lead and the printed circuit board pad. It reveals the ductility of the solder alloy and the integrity of the intermetallic layer.
Industrial standards for portable electronics often specify these tests to simulate dropping or impact events.
Failure Mode
Testing equipment drives a shear tool into the side of a component at speeds exceeding 100 millimeters per second. During high strain shear, the energy absorbed by the joint is calculated from the force-displacement curve. Brittle fractures at the interface indicate poor plating or excessive intermetallic growth.
Ductile failures within the bulk solder are generally preferred as they show better energy dissipation. The transition from ductile to brittle behavior often occurs as the strain rate increases. Real-time data capture identifies the exact moment the metal lattice begins to fail.
Temperature Dependency
Reliability data from these tests informs the selection of solder alloys and surface finishes like ENIG or OSP. High strain shear results vary significantly with the age of the joint and the number of reflow cycles. Boards intended for aerospace or automotive environments must withstand these forces without catastrophic failure.
Testing stops when the component is completely detached from the substrate.
