https://uwaterloo.ca/centre-advanced-materials-joining/sites/ca.centre-advanced-materials-joining/files/uploads/files/hang_growth_behaviour.pdf

Growth behavior of Cu/Al intermetallic compounds and cracks in copper ball bonds during isothermal aging.

Behavior of aluminum oxide, intermetallics and voids in Cu-Al wire bonds

While the characterisation of intermetallic coverage and intermetallic phase (IP) growth in gold ball bonding on aluminium is quite well understood, there is relatively little literature concerning the morphology and growth of IP's between Cu balls bonded on aluminium pad metallisation The difference between Cu-Al IP growth compared with the well known Au-Al IP's has been studied mainly of larger wire diameter (35-50/spl mu/m) in the early 1980's Cu wire ball bonding has been established for many years mainly for high power devices at wire diameters /spl ges/ 38/spl mu/m and fine wire for discrete device applications However, there is now interest in fine pitch Cu wire ball bonding at smaller wire diameters of 25/spl mu/m and smaller for high pin count applications, driven mainly by cost reduction Development and optimisation of robust copper wire bonding processes for such applications requires an assessment of intermetallic coverage and Cu-Al intermetallic growth after isothermal aging This work describes the problems associated with coverage determination, some characteristics of Cu-Al and Au-Al intermetallic compounds and characterises the difference in the IP growth between Au-Al and Cu-Al The relative merits of gold and copper ballbonding are also briefly discussed

Characterisation of intermetallic growth in copper and gold ball bonds on aluminium metallization

https://dr.ntu.edu.sg/bitstream/10356/95669/1/20.%20A%20re-examination%20of%20the%20mechanism%20of%20thermosonic%20copper%20ball%20bonding%20on%20aluminium%20metallization%20pads.pdf

A re-examination of the mechanism of thermosonic copper ball bonding on aluminium metallization pads

Bond reliability under humid environment for coated copper wire and bare copper wire

Copper wire bonding is an alternative interconnection technology that serves as a viable, and cost saving alternative to gold wire bonding. Its excellent mechanical and electrical characteristics attract the high-speed, power management devices and fine-pitch applications. Copper wire bonding can be a potentially alternative interconnection technology along with flip chip interconnection. However, the growth of Cu/Al intermetallic compound (IMC) at the copper wire and aluminum interface can induce a mechanical failure and increase a potential contact resistance. In this study, the copper wire bonded chip samples were annealed at the temperature range from 150/spl deg/C to 300/spl deg/C for 2 to 250 h, respectively. The formation of Cu/Al IMC was observed and the activation energy of Cu/Al IMC growth was obtained from an Arrhenius plot (ln (growth rate) versus 1/T). The obtained activation energy was 26Kcal/mol and the behavior of IMC growth was very sensitive to the annealing temperature. To investigate the effects of IMC formation on the copper wire bondability on Al pad, ball shear tests were performed on annealed samples. For as-bonded samples, ball shear strength ranged from 240-260gf, and ball shear strength changed as a function of annealing times. For annealed samples, fracture mode changed from adhesive failure at Cu/Al interface to IMC layer or Cu wire itself. The IMC growth and the diffusion rate of aluminum and copper were closely related to failure mode changes. Micro-XRD was performed on fractured pads and balls to identify the phases of IMC and their effects on the ball bonding strength. From XRD results, it was confirmed that the major IMC was /spl gamma/-Cu/sub 9/Al/sub 4/ and it provided a strong bondability.

Sihyun Choe

Papers

Effects of Cu/Al intermetallic compound (IMC) on copper wire and aluminum pad bondability