Thermo-Mechanical Reliability of Sintered-Silver Joint versus Lead-Free Solder for Attaching Large-Area Devices

This study mainly evaluated the thermo-mechanical reliability of lead-free packaging techniques for attaching large-area chip. With 3 MPa pressure, a low-temperature (<300 o C) sintering technique enabled by a nano-scale silver paste was developed for attaching 100 mm 2 silicon die. This new lead-free packaging technique for die-attachment was compared with soldering by vacuum reflow. Lead-free solder SAC305 and SN100C were selected and used in this work since they were widely used in electronic packaging industry. Inspection of as-prepared die-attachments by X-ray and optical microscopy (observation of cross-section) showed that the voids percentage in solder joint was less than 5% and no voids was observed at the scale of hundreds of micron in sintered silver joint. Then these die-attachment were thermal cycled with the temperature range from -40 o C to 125 o C. Deduction of curvature and residual stresses were found for both soldered and sintered die-attachment. After 800 cycles, the residual stresses in silicon-solder-copper sample already decreased to around 0. The SEM images of solder and silver joint after 800 thermal cycles showed that