The Effect of Solder Paste Reflow Conditions on Surface Insulation Resistance
Authors: Karen Tellefsen and Mitch Holtzer Company: Alpha Date Published: 9/28/2014
Abstract: Three different reflow temperature vs. time profiles, a 1.5°C/s ramp to 230°C, a 1.5 °C/s ramp to 252°C and a 90 s soak at 175°C with a 230°C peak, were used to reflow three lead-free solder pastes in both air and nitrogen atmospheres. Fourier transform infrared spectra of the reflowed flux residues shows how reflow profile conditions and atmosphere affects the decrease of a peak around 1700 cm-1 and the appearance and increase of another peak at 1600 cm-1. The 1700 cm-1 is smaller for flux residues that were reflowed under hotter conditions and for those that were reflowed in air. The peak at 1600 cm-1 is larger for residues exposed to hotter reflow profiles in air, but is hardly present for residues reflowed in nitrogen. The affect of these reflow conditions on surface insulation resistance (SIR) per IPC-TM-650 Method 220.127.116.11 at 40°C 90% RH and 12V bias has been studied. This measurement shows that hotter reflow conditions result in higher SIR values for two of the pastes, as would be expected, but has a smaller affect on the third paste.
Solder paste, flux residue, IR spectroscopy, SIR, Electrical reliability