Importance of the power devices

Green house gas emission is a big issue in terms of global environmental protection. To achieve carbon neutral society, transition to a renewable energy and electric vehicles (EV) is promoted. In these approaches, using electric power efficiently is the crucial key. With this global trend, power devices are drawing attention as a key technology in reducing environmental burden because it can significantly contribute to more efficient conversion of the electricity.

Issues relating to redox vacuum reflow

Power device solder joint is required to be as low void as possible. To meet this requirement, redox vacuum reflow using solder preform has been a predominant method. However, this process has been associated with issues:

・Material cost is high
・Flexible size adjustment is
・Requires fastener jig to hold the component

By using solder paste instead of solder preform, both cost reduction through material and process can be achieved.

New suggestion for redox vacuum reflow

Issues associated with conventional solder paste

Conventional solder paste which contains resin/ rosin slumps during reflow as the heat softens it. This makes the space among the solder powder smaller and unevaporated constituents fills the space. As a result, reduction gas (formic acid gas) cannot enter deep into the solder, which fails to fully reduce the oxidation and deteriorates the solder wetting.

Solution

New technology to be compatible with redox vacuum reflow (patented technology: Preheat evaporation method)

・Newly developed flux constituents links solder powders during preheat
・The links maintain space among printed solder powders
・Formic acid can enter the printed solder powders and reduce oxidations

Cost Reduction

・Material cost can be approximately 50% lower than solder preform
・No need for a die to produce solder preform (punching) reduces initial die making cost upon design change
・Printing solder paste allows solder to be provided uniformly at once. Automated process can reduce solder feed process time
・Some of the production process needed to use solder preform or conventional solder paste, such as fastening and releasing jig for solder preform and cleaning flux residue, can be reduced.