Modeling, design and demonstration of low-temperature, low-pressure and high-throughput thermocompression bonding of copper interconnections without solders Conference

Shahane, N, McCann, S, Ramos, G et al. (2015). Modeling, design and demonstration of low-temperature, low-pressure and high-throughput thermocompression bonding of copper interconnections without solders . 2015-July 1859-1865. 10.1109/ECTC.2015.7159853

cited authors

  • Shahane, N; McCann, S; Ramos, G; Killian, A; Taylor, R; Sundaram, V; Raj, PM; Smet, V; Tummala, R

abstract

  • High-throughput assembly technologies to form Copper (Cu) interconnections without solders at below 200°C, and pitch below 40μm has been a major challenge in the semiconductor industry. A unique solution has been demonstrated by Georgia Institute of Technology to overcome this grand challenge. This technology utilizes thermocompression bonding to form copper interconnections with process tolerances to accommodate non-coplanarities of bumps and warpage of the substrate, without solders. The bonding pressure applied for thermocompression was 365MPa, to enable Cu bump collapse by 3μm. As thermocompression bonders are generally force-limited to 400N, such high bonding pressures may hinder scalability of this technology to fine pitches with higher I/O densities. This paper addresses this manufacturability challenge with the novel Electroless Palladium Autocatalytic Gold (EPAG) surface finish instead of the standard Electroless Nickel Immersion Gold (ENIG) or Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG) finish, previously used to prevent Cu oxidation for bonding load reduction down to 120MPa. Finite element modeling was carried out to understand the bonding mechanism and deformation behavior of Cu bumps and pads. Compensation of non-coplanarities and warpage by collapse of the Cu bumps was found to be the prevalent limiting factor for pressure reduction. New interconnection material and structure innovations were studied for their deformation behavior as a function of the applied pressure in thermocompression. The EPAG surface finish enables a 3X reduction in bonding pressure, by the elimination of Ni, and redistribute plastic deformation more equally between bumps and pads. The proposed innovations thus address both manufacturability and scalability of copper interconnections to 20μm pitch, while maintaining compatibility with current production-level thermocompression tools and processes.

publication date

  • July 15, 2015

Digital Object Identifier (DOI)

International Standard Book Number (ISBN) 13

start page

  • 1859

end page

  • 1865

volume

  • 2015-July