Microstructural evolution and cracking of Pb-free ball grid array assemblies under thermal cycling

Wei Wang, Zhongguang Wang, Aiping Xian, Jianku Shang

Research output: Contribution to journalArticlepeer-review


Two kinds of CBGA (ceramic ball grid array) assemblies were made by reflow soldering process using two different Pb-free solders. Microstructural evolution and cracks induced by thermal cycling in CBGA assemblies were examined by scanning electron microscopy (SEM) and finite element method (FEM). Before thermal cycling, intermetallic compounds (IMCs) Cu6Sn5 and Ag3Sn were observed at the solder interface between Cu and Ag metallizations, respectively. After thermal cycling, another IMC Cu3Sn was observed near the Cu pad in both two assemblies and the layers of Cu6Sn5 and Ag3Sn became thicker. As a result of thermal cycling, cyclic stress and strain were accumulated in the solder joint leading to fatigue cracking. Both experiments and FEM revealed that cracks preferred to initiate at the corner of each solder joint. Multi-modes of the crack propagation were found in the two assemblies. Based on Coffin-Manson equation, the thermal fatigue life was calculated and the predicted life showed good agreement with the experimental results.

Original languageEnglish (US)
Pages (from-to)85-91
Number of pages7
JournalJournal of Materials Science and Technology
Issue number1
StatePublished - Jan 2007


  • Assembly
  • CBGA
  • Cracking
  • FEM
  • Thermal cycling

ASJC Scopus subject areas

  • Ceramics and Composites
  • Mechanics of Materials
  • Mechanical Engineering
  • Polymers and Plastics
  • Metals and Alloys
  • Materials Chemistry

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