Meaning
Quantitative measure of microscopic cavities aligned along a single geometric plane within a material interface provides an assessment of bond quality. High planar void density indicates a weakness in the solder joint that can lead to electrical failure. These voids usually form during the heating process when gasses are trapped or when the plating chemistry is out of balance.
Spatial Distribution
Locations of the gaps tend to cluster at the interface between the nickel and the solder. When measuring planar void density, an inspector looks for the percentage of the total area occupied by these empty spaces.
Inspection Metric
Non-destructive testing using x-ray imaging allows for the visualization of the internal structure without breaking the part. A planar void density exceeding twenty percent of the interface area is often grounds for immediate rejection in aerospace and automotive applications. This calculation relies on automated image analysis to sum the area of all detectable voids within a specific horizontal cross section of the joint.
Joint Failure
Mechanical stress concentrates around the edges of each void and facilitates the growth of cracks. A low planar void density ensures that the thermal and electrical paths remain clear and that the component can withstand repeated cycles of heating and cooling.
