Reliability Evaluation of Intense Pulsed Light Flip-Chip Bonding with Various Surface Finishes

초록

In this study, the effect of surface finish on the bonding reliability of flip-chip solder joints was systematically investigated by comparing intense pulsed light (IPL) bonding with conventional reflow processes. Three surface finishes (organic solderability preservative (OSP), electroless nickel immersion gold (ENIG), and electroless nickel electroless palladium immersion gold (ENEPIG)) were evaluated. Cross-sectional SEM analysis revealed that IPL bonding produced significantly thinner intermetallic compound (IMC) layers across all surface finishes compared to conventional reflow, attributed to the ultra-short thermal exposure inherent to the IPL process. Notably, the Ni₃P sublayer clearly observed at the Ni-based interfaces in reflow samples was barely detectable in the IPL-bonded samples, indicating that the Ni barrier structure is well preserved under IPL conditions. Reflow samples exhibited similar peak shear forces regardless of surface finish (5.5–5.8 Kg), whereas IPL-bonded samples achieved 9.1 Kg (ENIG), 8.1 Kg (ENEPIG), and 6.9 Kg (OSP). Failure mode analysis revealed that IPL-bonded ENIG and ENEPIG samples exhibited pad lift as the dominant failure mode (53% and 67%), in contrast to the IMC interface fracture typically observed in reflow samples. This shift indicates that IPL bonding produces sufficiently strong solder joint interfaces that the Cu pad–substrate adhesion becomes the weakest link in the joint structure, highlighting the potential of IPL bonding for advanced semiconductor packaging.

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