Effects of Au Bump Process Condition on the Interfacial Reaction and Mechanical Reliability of Non-cyanide Au Bump for Display Driver IC Bonding

The effects of annealing temperature and thermal cycle conditions on the adhesion characteristics of non-cyanide Si/sputter TiW/sputter Au/Au bump structure were systematically investigated using a shear test. No intermetallic compound was observed at the TiW/Au interface at all annealing temperatures, and voids formed between the TiW and Au bump interface at a temperature higher than 280 oC. In addition, the Au grains in the non-annealed and 250 oC specimens formed columnar grains, while equiaxed grains formed at temperatures higher than 280 oC. The measured shear strength of the non-annealed specimen was 44.58±3.60 MPa and it increased to 127.48±3.76 MPa at 250 oC. However, the shear strength decreased to 101.27±3.95 MPa at 280 oC and remained constant until 320 oC. The toughness also dramatically increased at 250 oC, then decreased at 280 oC, and remained constant until 320 oC. It is believed that the shear strength and toughness were increased because the inter-diffusion of the Au bump and the sputtered Au at 250 °C led to the formation of a single layer, causing delamination within the Au bump. However, the decrease in shear strength and toughness during annealing at 280 oC is believed to be due to the formation of voids between the sputtered TiW and Au bump, leading to delamination at the sputtered TiW/Au bump interface. Additionally, the shear strength of the specimen annealed at 250 °C was observed to remain at approximately 100 MPa even after 1000 cycles in the thermal cycling test, which is believed to be due to the absence of changes in the Au-grain structure.