Novel Residue-Free High-Lead Solder Paste for Power Discrete

In most semiconductor industries, there are multiple different types of solder pastes which are utilized for power discrete die-attach applications. The flux in the solder paste plays a critical role to remove the oxides from the interconnect surfaces. However, most of the fluxes in the solder pastes leave residue on the substrates after reflow, which not only can influence the next process, such as wire bonding, but can also cause electrical and mechanical connection problems that impact long-term reliability performance. As a result, the cleaning process is essential for almost all types of pastes. The industry is searching for a no cleaning resolution. Soldering with gaseous activation has been investigated for decades; however, most of the studies are well established in the field of preform or solder bump soldering and not in solder paste. In this paper, a novel, near zero residue, high-lead solder paste “F” for semiconductor die-attach applications was developed and reflowed under formic acid vapor in a nitrogen atmosphere. It provides a novel assembly process for power discrete, which can eliminate the cleaning process. The paste also showed good workability and solderability.