Voids in Solder
Multi Chip Module (MCM) Direct Bond Copper Defects - Application Note 1066
Sample & Method
This rectifier has three ceramic substrates solder bonded to a copper base. The image was generated at 50 MHz by focusing through the copper base to the copper base/ceramic substrate interface.
The black areas observed in the substrate regions (multi-colored areas) are large and small voids in the solder. Since heat dissipation is critical in rectifiers, the reduction in heat-sink efficiency by these voids is significant.