THE EFFECT OF UNDERFILL EPOXY ON WARPAGE IN FLIP-CHIP ASSEMBLIES

The thermally-induced warpage of both a real dip-chip thermosonically bonded assembly and a simulated tri-layered assembly was investigated. It was revealed the warpage of the assemblies was dominated by the fo rces 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 x 5.8 mm chip, Mechanical properties of epoxy depend on the curi ng and the glass transition temperatures, and these characteristic tem peratures clearly divide the warpage levels into two distinctive regio ns. When the maximum temperature the assembly was exposed was less tha n the glass transition temperature (T-g), the warpage of the assembly was characterized by the curing temperature. When the maximum temperat ure the assembly was exposed to higher than T-g, the warpage was chara cterized by the T-g regardless of how high the temperature was. The di stinctive deformation curves with sub-microns repeatability are report ed for the first time. Depending upon the to different characteristic temperatures of an assembly, e.g., 80 degrees C for curing and 130 deg rees C for T-g, the warpage and the Von Misses stress each could incre ase by as much as a factor of two. Such an increase could affect devic e reliability for RF packages and alignment for optoelectronic package s.