Ambient temperature ultrasonic bonding of Si-dice using Sn-3.5wt.%Ag

Jung Mo Kim, Jae Pil Jung, Y. Norman Zhou, Jong Young Kim

Research output: Contribution to journalArticlepeer-review

18 Scopus citations


Ultrasonic bonding of Si-dice to type FR-4 printed circuit boards (PCB) with Sn-3.5wt.%Ag solder at ambient temperature was investigated. The under-bump metallization (UBM) on the Si-dice comprised Cu/Ni/Al from top to bottom with thicknesses of 0.4 μm, 0.4 μm, and 0.3 μm, respectively. The pads on the PCBs consisted of Au/Ni/Cu with thicknesses of 0.05/5/18 μm, sequentially from top to bottom. Solder was supplied as Sn-3.5wt.%Ag foil rolled to 100 μm thickness, and inserted in the joints. The ultrasonic bonding time was varied from 0.5 s to 3.0 s, and the ultrasonic power was 1400 W. The experimental results showed that reliable joints could be produced between the Si-dice and the PCBs with Sn-3.5wt.%Ag solder. The joint breaking force of "Si-die/solder/FR-4" increased with bonding times up to 2.5 s with a maximum value of 65 N. A bonding time of 3.0 s proved to be excessive, and resulted in cracks along the intermetallic compound between the UBM and solder, which caused a decrease in the bond strength. The intermetallic compound produced by ultrasonic bonding between the UBM and solder was confirmed to be (Cu, Ni)6Sn5.

Original languageEnglish
Pages (from-to)324-330
Number of pages7
JournalJournal of Electronic Materials
Issue number3
StatePublished - Mar 2008


  • Intermetallic compound
  • Joint reliability
  • Lead free solder
  • Sn-3.5wt.%Ag
  • Ultrasonic bonding


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