Meaning
Volumetric measurement comparing air pockets to the total space occupied by a joint defines the internal porosity of a connection. Quality engineers monitor the void volume fraction to ensure that the internal structure of a connection is solid enough to carry the required electrical and thermal loads. High levels of internal gassing during the soldering process can leave behind bubbles that reduce the effective cross sectional area of the joint.
Measurement Technique
Calculating this value usually involves using high resolution X-ray imaging and software that can segment the voids from the surrounding metal. The software determines the area of each void in a two dimensional top down view and then estimates the void volume fraction based on the known thickness of the joint. For more critical applications, computed tomography provides a full three dimensional model of the voids.
This level of detail allows the factory to see if the air pockets are concentrated at the interface or spread throughout the bulk of the solder. Modern systems in Shenzhen assembly plants automate this calculation to ensure every batch is inspected without slowing down the line.
Performance Consequence
Large voids can block the path of heat moving away from a high power semiconductor, leading to overheating and premature failure. When the void volume fraction is too high, the mechanical strength of the joint is also compromised because there is less metal to resist cracking. Small, distributed voids are often considered acceptable, but a single large void that covers more than twenty five percent of the pad area is typically a cause for rejection.
Engineers use these measurements to tune the temperature profile of the reflow oven to allow gases to escape before the solder solidifies.
Quality Standard
Criteria for the maximum allowed percentage of internal empty space are defined in documents such as IPC-A-610. These standards are widely adopted by Chinese manufacturers to ensure their products meet global expectations for reliability. Consistently meeting these standards is necessary for maintaining the status of an approved supplier in the international electronics market.
