Optimization of lead free solder paste for robust process and reliable solder joint.

This paper will describe the process of lead free SnAgCu solder paste optimization to fulfil various industrial partners production constraints. A linear thermal profile which is highly recommended by solder paste manufacturers for lead free process cannot be applied to the full range of product. The challenge in IMS EFSOT program is to bring a solution with a robust solder paste formulation suitable for fine pitch printing, safe no clean flux in combination with a large soak zone in the reflow profile. A test vehicle has been designed by Philips, Thomson and AB Mikroelektronik which is representative for consumer applications and automotive applications. It contains a wide range of advanced components, such as: a.o. passives from 0201 to 0603, large heat sink packages, fine pitch BGAs. Further different pad designs and finishes, test patterns, various board materials and sizes are included. Once the printing and reflow performances of the solder paste have been validated with success, quality and reliability of solder joint were tested through visual control, X Ray and thermal cycling