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Method for solder doping to improve Imax performance in high-current flip-chip packages

IP.com Disclosure Number: IPCOM000144774D
Publication Date: 2007-Jan-06
Document File: 2 page(s) / 44K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for solder doping to improve maximum current draw (Imax) performance in high-current flip-chip packages. Benefits include improved functionality, improved reliability, and improved ease of implementation.

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Method for solder doping to improve Imax performance in high-current flip-chip packages

Disclosed is a method for solder doping to improve maximum current draw (Imax) performance in high-current flip-chip packages. Benefits include improved functionality, improved reliability, and improved ease of implementation.

Background

      Electron migration can cause the failure of flip-chip solder joints. The failure increases with bump crowding and increased current. The conventional solution is to use copper (Cu) column-style bumps.

      Conventional solder is tin-silver (Sn-Ag) or eutectic Sn-Ag-Cu (SAC).

Description

      The disclosed method is solder doping to improve Imax performance in high-current flip-chip packages. A metallic element is added at <1wt.% to conventional solder. The elements used include the following:

•     Iron (Fe)

•     Cobalt (Co)

•     Zinc (Zn)

•     Nickel (Ni)

•     Germanium (Ge)

      The doping does not change the melting point of the solder significantly.

      The disclosed method changes the intermetallic compound (IMC) structure at the solder/Cu interface (solder joint). For example, when Zn is added, the Cu3Sn phase is suppressed. Because faster Cu diffusion occurs with Cu6Sn5 than with Cu3Sn, the flux divergence at the Sn-to-Cu6Sn5 interface is reduced due to the increased Cu availability. The additional Cu reduces Cu dissolution...