Design for BGA Lead-Free Solder Joint Reliability

Abstract

ABSTRACT There are three trends within the electronic industry that are driving the need for greater solder joint reliability for BGA components. Improvements to current BGA design practices may be needed to meet new product reliability requirements. One industry trend that is pushing BGA solder joint reliability to its limits is the fact that as more and more functionality is being added to components that requires an increase in the number of connections to the circuit board. Higher ball count requirements are driving an increase in component size as well as a reduction in the array pitch. This means that the size of the solder joint is getting smaller and spread over a greater distance. The result of this is that the solder joint now has to withstand increased stress by a smaller solder joint. The number of mobile products being manufactured has been increasing steadily over the past years and the stress these products are subjected to during their life is very different than a more traditional product such as a desk top computer. Mobile phones, MP3 and laptop computers must all withstand shock from being transported and dropped multiple times during the period they are in service. To assure the solder joint meets these new requirements additional shock testing above and beyond the traditional thermal cycling that has been traditionally used to assure product reliability is required. The industry is undergoing one of the largest changes in its history and that is the transition to lead free solders. Though lead free solder is stronger and has demonstrated improved reliability for low stress applications the opposite is true under higher stress conditions. Lead free solders have a lower modulus of elasticity making them more susceptible to fracture. As previously stated industry trends seem to be moving in the direction of putting more stress on the solder joint. In many cases lead free solder has resulted in a loss of reliability margin for BGA components especially those in the finer pitch realm. This paper addresses what constitutes solder joint reliability and what can be done to assure that the product design is going to maximize solder joint reliability.