Quality Procedure
Standardized mechanical evaluation used to measure the bond strength between a solder ball and its corresponding pad on a ball grid array package or a printed circuit board. The solder ball shear test involves a motorized tool that pushes against the side of a solder ball until it detaches from the surface. This test is a fundamental part of the qualification process for new solder alloys and surface finishes.
It provides a numerical value for the peak force required to break the interconnect.
Shear Parameter
Accuracy of the measurement depends on the height of the shear tool above the substrate and the speed at which it moves. If the tool is too high, it creates a bending moment that can artificially lower the recorded force. During the solder ball shear test, the displacement of the tool is monitored to ensure a constant strain rate throughout the process.
The resulting data allow for a comparison between different reflow profiles or plating thicknesses to identify the optimal assembly conditions.
Evaluation Criterion
Inspection of the fracture site after the test determines if the failure occurred in the bulk solder, the intermetallic interface, the substrate or the pad metallization. Ductile failures within the bulk solder are generally preferred because they indicate a strong interfacial bond. If the solder ball shear test results in a brittle separation at the pad, it may signal contamination or a brittle intermetallic layer.
This information is used to troubleshoot manufacturing defects and improve the long-term reliability of high-density electronic packages. Peak force and failure mode are both essential for process control.
