A Study on Novel Low Temperature Soldering Process using Vapor phase

The packaging is a core technology in various integrated semiconductor systems, and interconnection is the key element of the packaging in providing monolithic-like performance. As the process temperature is increasing owing to the RoHS policies on major materials, there is an increasing need to address issues about degradation on quality and performance. It is essential to develop low-temperature processes that can guarantee reliability and mass production quality by limiting overheating. In this paper, a new low temperature soldering process, which utilized energy generated during vapor condensation, has been demonstrated to control temperature without overheating in the semiconductor packaging processes. The vapor phase soldering(VPS) process can control temperature to around the boiling point by taking advantage of the energy generated during vapor condensation. Actual test of introducing VPS into um-mm pitch processes including surface mount technology(SMT), flip chip mount(FCM), and solder ball attach(SBA) were carried out. Interconnection quality including joint gap and IMC growth was confirmed to be equivalent level of that of conventional convection reflow process. The slip phenomenon, misalignment of the soldering target with bump pad, occurred during the test of SBA and FCM process. The slip phenomenon was analyzed to be occurred by various forces applied on soldering target during the phase change of the soldering process. Solutions including adding weight or airflow were introduced to solve the slip phenomenon. The proposed method was verified by additional experiment in FCM process resulting that yield has improved significantly from 5% to 100% by controlling gravity and resistance, and simulations for FCM and SBA process had conducted for defining the relationship between applied forces during the VPS process with or without additional force applied.