The Impact of Lead-Free Reflow Temperatures on the Moisture Sensitivity Performance of Plastic Surface Mount Packages

Environmental concerns continue to drive the demand for lead-free products int he electronics industry. Board assembly operations currently use near eutectic tin-lead solders to attach components to printed circuit boards. Lead-free solder alloys which have been identified as substitutes for tin-lead solders have melting points that are typically 30-40C higher. Therefore, peak reflow temperatures must be increased to ensure reliable board attachment. The increased reflow temperatures that are required for lead-free solders will impact the moisture sensitivity performance of plastic surface mount devices (SMDs). This paper presents the effect of lead-free simulated assembly on the moisture/reflow performance for conventional leadframe-based products (160MQFP and 144LQFP) and overmolded laminate-based products (27mm and 35mm PBGA and low profile fine pitch BGA). Moisture/reflow performance was assessed using C-mode Scanning Acoustic Microscopy (C-SAM) and cross-sectional failure analysis was performed to verify the location of the failing interface. The results indicate that the moisture sensitivity performance is generally degraded by at least one IPC/JEDEC level when the reflow temperature is increased to 260C. Performance analysis on one package type, a 160MQFP, revealed excessive die surface delamination even after reflow of "dry" packages at 260C. Improvements in materials and possibly package design will be needed for some package types to attain adequate moisture/reflow performance at the elevated temperatures required for lead-free assembly.