Numerical Metric
The ratio of the total surface area of internal cavities to the total surface area of a solder joint quantifies the density and completeness of the connection. Standard inspection routines utilize the void area percentage to evaluate the structural integrity of surface-mount solder joints. This metric measures the presence of gas pockets that can compromise the mechanical and thermal performance of the assembly.
Measurement Method
Non-destructive x-ray imaging determines this value by measuring the density differences between the metal alloy and the empty cavities. Automated inspection algorithms calculate the void area percentage by dividing the total pixel area of identified voids by the total pixel area of the solder joint. This calculation is performed for every ball on ball-grid array packages to ensure no individual joint exceeds acceptable limits.
In contrast, manual inspection relies on visual estimations of the x-ray images, which introduces operator variability that can affect the consistency of the results.
Reliability Threshold
Electronics standards establish maximum limits for these internal cavities to prevent premature joint failure. When the void area percentage exceeds twenty-five percent, the joint becomes susceptible to fatigue cracking under mechanical stress. Corrective action involves adjusting the reflow oven temperature profile to improve flux outgassing.
