DOES COPPER DISSOLUTION IMPACT THROUGH-HOLE SOLDER JOINT RELIABILITY?
Authors: Craig Hamilton, et al. Company: Celestica and IBM Corporation Date Published: 10/4/2009
Abstract: The process issues relating to high copper dissolution rates have been well documented within the industry. The copper dissolution rates of SAC305/405 plus many of the leading alternative lead-free wave alloys have been characterized and pin-through-hole rework process windows assessed. One remaining gap within the industry is the understanding of how copper dissolution or thinning of the through-hole barrel wall/knee locations impacts the thermal and mechanical reliability of a pin-through-hole joint. This paper provides a summary of previous work performed to study and characterize the copper dissolution rates of various Pb-free wave alloys, as well as attempts to assess the impact of high levels of copper dissolution on the thermal reliability of a 14 I/O PDIP connector. A total of five PDIP connectors were designed onto a test vehicle, each individually daisy chained using bottomside traces, for in-situ monitoring. A design of experiment was defined as an attempt to vary the level of plated copper remaining after simulating the rework of the five PDIP connectors. Each board was subjected to 0-100°C ATC for 6,000 cycles with in-situ monitoring to detect failures throughout testing using data loggers. The results from this work indicate reliability concerns when a severe degree of copper dissolution occurs and shows signs of reduced reliability due to thinning of the copper plating thickness at the knee location. In addition, mechanical and thermo-mechanical loading are key elements necessary to confirm the reliability of a pin-through-hole joint, this paper however, focuses on thermal fatigue reliability assessment. Lastly, this paper will highlight limitations of the copper plating measurement methodology used and suggests alternative non-destructive options to inspect for copper dissolution within manufacturing environments.