Identification of new mechanism of epoxy underfill void formation in electronic packages

Abstract

This paper presents an understanding of a new mechanism of void formation in an epoxy-amine underfill system resulting only from interaction of the underfill with a decomposition product of residual chip attach flux formed during package assembly. This is possible since flux residues have been known to sometimes be retained between the die and substrate even after the deflux process. Differential Scanning Calorimetry (DSC) was used extensively to study the thermal properties of both flux and underfill and to simulate the heating processes that these materials undergo at assembly. Thermal Gravimetric Analysis (TGA) was used to confirm the mechanism. This study does not make any attempt to explain the other effects contributed by equipment, bump pitch, filler size or any mechanical aspect on the voiding process. [

Synchronous curable deoxidizing capability of epoxy–anhydride adhesive: Deoxidation quantification via spectroscopic analysis

“…Electrical interconnections are achieved with a deoxidizing agent (fluxing agent), which also causes solder joint failure due to the mismatch of the coefficients of thermal expansion (CTE) between the chip and the circuit board. An additional capillary underfill process has been employed to relieve thermal fatigue and enhance mechanical integrity . Recently, bump pitch and gap have become increasingly fine and narrow, resulting in the restriction of the capillary underfill process and the need for an additional vacuum process and thus causing vexatious multi‐step processing .…”