Effect of reflow profile (RSP Vs RTP) On Su/3.8Ag/0.7Cu solder joint strength

Abstract

Reflow profile parameter with reducing soaking time demonstrated better solder joint performance in Lead-free BGA semiconductor packages. Hence, this paper studied the lead-free solder joint strength using two different reflow profiles: conventional ramp-soak-peak (RSP) and ramp to peak (RTP) for solder ball attachment. In this study, Sn/3.8Ag/0.7Cu solder balls were re flowed on solder pads with Ni/Au surface finish using these two reflow profiles in a seven zone forced convection oven. Ball shear testing along with failure mode analysis - ductile and brittle failure mode were used to assess solder joint performance at time zero, after multiple reflow and high temperature storage test (HTS). Intermetallic thickness was measured using Image Analyzer. Elemental analysis by EDX detected Cu-Sn phase at IMC peak and Cu-Ni-Sn phase presented at IMC interface. The overall result showed that RTP profile has higher and more consistent solder joint strength, thus giving lower standard deviation and higher Cpk, along with 100% ductile- failure mode and thinner IMC layer. RTP profile has been established as a benchmark of industry' standard. This profile has much shorter soak time during flux activation temperature at 130 °C to 170 °C to prevent flux dry-up and hence enable better flux activation during solder joint formation at peak temperature zone. This will enhance an even intermetallic growth and a stronger <£ more reliable solder joint. Copyright © 2006 IMAPS.