Improved High Speed, Low Loss Materials for Lead-Free Assembly Compatibility

摘要

Environmental regulations such as the Reduction of Hazardous Substances (RoHS) act are forcing the elimination of lead (Pb) from electronic equipment. Lead-free solders currently being used and developed for printed circuit assembly require higher processing temperatures that can degrade the base materials commonly used in printed circuits, resulting in decreased long-term reliability. The higher temperatures also result in greater amounts of Z-axis thermal expansion in the printed circuit board. This increased thermal expansion results in greater stress on plated through holes in the printed circuit board which also negatively impacts long-term reliability. Following a brief discussion of the lead-free solder materials and processes, this paper will review several base material properties that are critical to specify when transitioning to lead-free assembly. These properties include the glass transition temperature, coefficients of thermal expansion, decomposition temperature, and times to delamination. This paper will then compare the properties of a new low Dk, low Df material with an existing low Dk, low Df material in widespread use.