Kirkendall Void Formation Mechanisms at Lead Free Copper Interface Boundaries
Suppressing Kirkendall voiding demands controlling substrate copper electroplating additives and microalloying solders to balance diffusion rates.
Ball Shear Test
Meaning
Mechanical destructive testing of microelectronic interconnects evaluates the integrity of solder bumps or gold balls on semiconductor substrates. Performing a ball shear test involves applying a parallel force via a shear ram to a specific ball until the joint separates. This procedure determines the maximum force required to cause shear failure in ball grid array packages or wire bonds.
It identifies weakness in the intermetallic compound layer that forms between the solder and the metal pads.
Stress Evaluation
Characterization of the mechanical joint under high-speed loading reveals the failure modes. A ball shear test measures the energy absorption and maximum load of the interconnect. Low-speed testing shows plastic deformation of the solder, whereas high-speed testing exposes brittle fracture at the interface.
This provides data to optimize reflow oven temperatures and pad metallurgy.
Procedural Execution
Positioning the shear tool at a precise height above the substrate is necessary for repeatable results. Standardized procedures for the ball shear test require a shear height of less than ten percent of the ball height to avoid rolling or tipping. Calibration of the equipment and alignment of the tool tip prevent gouging of the substrate.
Automation of the test reduces human error and increases throughput in production audits, allowing operators to scan large arrays of interconnects in a single run.
Quality Threshold
Adherence to industrial specifications like those from the Joint Electron Device Engineering Council determines acceptance. The ball shear test must show a minimum force limit based on ball diameter. Solder ball compositions with lead-free alloys require different limits than traditional leaded alloys.
Passing the test ensures the microchip can withstand the physical forces of shipping and thermal expansion.