LEAD-FREE BGA PAD DESIGN: A COMPARITIVE STUDY OF THE AFFECT OF PAD DIMENSIONS ON THE ATTACHMENT OF AREA ARRAY PACKAGES UTILIZING LEAD-FREE SOLDER PROCESSES AND VARIOUS PASTE PRINT METHODS
Author: Ray Cirimele Company: Best, Inc. Date Published: 1/17/2006
Pan Pacific Symposium
Abstract: The use of the Area Array Package and in particular, Ball Grid Array (BGA) technology in the electronics industry continues to increase due to the fact that this package type allows for a greater I/O count in a smaller area while maintaining a pitch that allows for ease of manufacture. The original assembly process, and to a large extent the rework process for BGA devices utilizing tin/lead solder materials, has proven to be fairly trouble-free. Environmental and legislative concerns are forcing many manufacturing facilities to transition to lead-free materials and processes. As the circuit density on the printed circuit boards (PCBs) continues to increase, there are two choices for how to accomplish this and the associated BGA escape routing. One of the choices is to increase the signal routing on the topside of BGA land patterns. Once conductor widths and spaces have been minimized, reduction of the pad diameters of the BGA land patterns to accommodate the additional signal routing will be necessary. The other alternative is to increase the signal routing on internal layers. As BGA land pattern diameters vary, this may have some effect on the long-term reliability of the BGA solder joints. Most of our data on the reliability of land pattern design is based on the use of tin/lead solder. It is now common knowledge that lead-free solder will exhibit reduced wetting when compared to traditional tin/lead solders. As more and more assemblies are transitioned to lead-free materials, it is important to understand what impact the variables of pad diameter and wetting will have on the reliability of these lead-free assemblies. This paper will review the results of thermal cycling of BGA samples that were processed with lead-free materials utilizing different solder paste print methods, and different BGA land pattern diameters.