Dynamic Test
Mechanical test method used to evaluate the strength and fracture toughness of solder interconnects under rapid loading conditions. The high speed ball shear procedure involves a tool striking a solder ball at velocities significantly higher than traditional quasi-static testing. This method targets the strain-rate sensitivity of the intermetallic layer and the surrounding bulk solder.
It simulates drop-impact events more accurately than slow-speed shearing.
Brittle Sensitivity
Rapid displacement forces the fracture to occur within the weakest part of the joint, often revealing hidden embrittlement. Standard shear tests may allow for plastic deformation that masks a poor intermetallic bond, but high speed ball shear prevents this stress relaxation. Failure at the interface between the solder and the pad indicates a potential reliability issue with the plating or the reflow profile.
Analyzing the fracture surface helps determine if the crack propagated through the bulk solder or along the nickel or copper interface.
Operational Variable
Success in this test depends on the precise control of the tool height and the impact velocity during the measurement cycle. Modern testers can reach speeds of several meters per second to match the conditions of a handheld device hitting a hard floor. Data collected from these tests inform the selection of surface finishes such as ENIG or ENEPIG based on their resistance to interfacial cracking.
If the shear force drops significantly as speed increases, the assembly is deemed susceptible to brittle fracture. Impact performance is a critical metric for portable electronics.
