A Practical Approach for Low-Cost Hermetic Lid Sealing

Hermetic sealing of lids in ceramic microelectronic chip carriers is typically performed with eutectic solder in relatively large belt-style reflow furnaces. This process is characterized by 30 to 45-minute cycle times at temperatures above 350 C. An experimental study was undertaken with the goal of establishing a low-cost lid sealing method marked by a compact belt furnace with lower reflow temperature and lesser cycle time. This is particularly advantageous for GaAs devices which are limited to packaging process temperatures below 300 C. A series of instrumented test samples consisting of a representative die packaged in a HTCC leadless chip carrier (LCC) was prepared. Package lids were installed and sealed in a nitrogen environment with 80–20 Au-Sn lead-free solder under various cycle time and temperature conditions. Gross and fine leak testing confirmed hermeticity. Results indicate that practical sealing can be realized in the compact furnace apparatus with measurable reductions in temperature and cycle time. Seal performance is dependent upon package orientation, which suggests the process must be calibrated for unique package designs. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under Contract DE-AC04-94AL85000.