Advanced No-Clean Solder Paste for SiP Applications

This paper reports the comparison of two solder pastes made using a no-clean flux platform and ultrafine SAC305 powders of Type 7 and Type 8+, made using Heraeus’ Welco® technology. The application tests were carried out using 008004 components, the smallest passives used in SiPs. For the paste with Type 7 powder, the application tests complete with 12 hrs, of stencil evaluation have been reported, whereas for the paste with Type 8+ powder, a preliminary work-life evaluation has been reported. Both pastes have been compared for the release performance using area ratios down to 0.35, with both circular and square stencil opening apertures. Cleaning evaluation was carried out with some of the commercially available cleaning agents to assess the compatibility of the flux residue. It has been demonstrated that the no-clean solder paste with Type 7 powder has excellent stencil work-life performance until 12 hrs. of printing, with voids after reflow being less than 10%. The paste with Type 8+ shows better release performance vis-à-vis Type 7, down to an area ratio of 0.35, for square stencil opening aperture. Results from cleaning evaluation show the leftover contamination can be fully removed. © 2021 IMAPS-International Microelectronics and Packaging Society. All rights reserved.