Abstract
For assembly of MEMS by use of soldering, the metallization
on the MEMS and the soldering process must be selected carefully to ensure long-term reliable joints. A range of combinations of adhesion metal layers and solders were tested in this work. The target was to find a metallization system for the MEMS without layers of pure Cu or Ni due to risks related to cross-contamination. All combinations were apparently strong and no degradation was measurable after thermal storage simulating more than 10 years of operation at 25 °C. However,the cross sections showed clear differences in microstructure as well as changes in morphology after thermal aging, which could potentially result in differences in reliability and joint quality. Both a first hypothesis related to NiCr outperforming TiW as adhesion layer, and a second hypothesis related to Au-richer systems to be less reliable than their counterparts with less Au, were confirmed from the fracture surfaces where
differences were clear. A targeted cohesive fracture mode was
achieved both in the as-bonded state and after thermal aging
for a combination with limited amounts of Au and with NiCr
used as adhesion layer on the MEMS.
on the MEMS and the soldering process must be selected carefully to ensure long-term reliable joints. A range of combinations of adhesion metal layers and solders were tested in this work. The target was to find a metallization system for the MEMS without layers of pure Cu or Ni due to risks related to cross-contamination. All combinations were apparently strong and no degradation was measurable after thermal storage simulating more than 10 years of operation at 25 °C. However,the cross sections showed clear differences in microstructure as well as changes in morphology after thermal aging, which could potentially result in differences in reliability and joint quality. Both a first hypothesis related to NiCr outperforming TiW as adhesion layer, and a second hypothesis related to Au-richer systems to be less reliable than their counterparts with less Au, were confirmed from the fracture surfaces where
differences were clear. A targeted cohesive fracture mode was
achieved both in the as-bonded state and after thermal aging
for a combination with limited amounts of Au and with NiCr
used as adhesion layer on the MEMS.