The effect of underfill epoxy on warpage in flip-chip assemblies

Wenge Zhang, Derick Wu, Bingzhi Su, Saeed A. Hareb, Y. C. Lee, B. Pat Masterson

Research output: Contribution to journalArticlepeer-review

37 Citations (Scopus)


The thermally-induced warpage of both a real flip-chip thermosonically bonded assembly and a simulated tri-layered assembly was investigated. It was revealed the warpage of the assemblies was dominated by the forces applied by the underfill epoxy rather than the solder joints. The roles the underfill epoxy and solder joints played in causing warpage did not change even when the assembly had 196 solder joints under a 5.8 mm × 5.8 mm chip. Mechanical properties of epoxy depend on the curing and the glass transition temperatures, and these characteristic temperatures clearly divide the warpage levels into two distinctive regions. When the maximum temperature the assembly was exposed was less than the glass transition temperature (Tg), the warpage of the assembly was characterized by the curing temperature. When the maximum temperature the assembly was exposed to higher than Tg, the warpage was characterized by the Tg regardless of how high the temperature was. The distinctive deformation curves with sub-microns repeatability are reported for the first time. Depending upon the to different characteristic temperatures of an assembly, e.g., 80°C for curing and 130°C for Tg, the warpage and the Von Misses stress each could increase by as much as a factor of two. Such an increase could affect device reliability for RF packages and alignment for optoelectronic packages.

Original languageEnglish
Pages (from-to)323-328
Number of pages6
JournalIEEE Transactions on Components Packaging and Manufacturing Technology Part A
Issue number2
Publication statusPublished - Jun 1998


  • Flip-chip assembled
  • Packaging
  • Repeatibility
  • Underfill epoxy
  • Warpage

ASJC Scopus subject areas

  • General Engineering


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