Assessment of potential solder candidates for high temperature applications

Multi-Chip module (MCM) technology is a specialized electronic packaging technology recently gaining momentum due to the miniaturization drive in the microelectronics industry. The step soldering approach is being employed in the MCM technology. This method is used to solder various levels of the package with different solders of different melting temperatures. High Pb containing alloys where the lead levels can be above 85% by weight, is one of the solders currently being used in this technology. Responding to market pressure i.e. need for green electronic products there is now an increasing pressure to eliminate lead containing materials despite the fact that materials for high Pb containing alloys are currently not affected by any legislations. A tentative assessment was carried out to determine the potential solder candidates for high temperature applications based on the solidification criterion, phases predicted in the bulk solder and the thermodynamic stability of chlorides. These promising solder candidates were precisely produced using the hot stage microscope and its respective anodic and cathodic polarization curves were investigated using a micro-electrochemical set up. The corrosion surface morphology and also the corrosion products were analyzed using SEM. Focus in particular has been given to the property of corrosion resistance since corrosion resistance is a major issue for lead-free solder alloys. The electric field experienced by the solders during usage further complicates the corrosion problems. Although the cost of corrosion in the electronic sector could not be estimated, it has been suggested that a significant part of all electronic system failures are caused by corrosion. Thus, the determined potential solder candidates were classified based on its property of corrosion resistance.