Reliability study of surface mount printed circuit board assemblies with lead-free solder joints

Purpose - The purpose of this paper is to evaluate the lead-free solder joint reliability of a variety of surface mount components assembled onto printed circuit boards (PCBs) under a number of different tests. Design/methodology/approach - Lead-free solder with a composition of Sn96.5-Ag3.0-Cu0.5 was used in a surface mount reflow process. Different types of surface mount dummy components with a daisy chain, such as CBGAs, BGAs, PLCCs, CSPs, and QFNs, were assembled onto PCBs. Both the mechanical and thermo-mechanical reliability of the solder joints were evaluated by several tests. The experiments included package shear, package pull, three-point bending and accelerated thermal cycling testing for 2,000 cycles. The packages were examined by X-ray and C-SAM before the reliability tests were carried out. The maximum load and the corresponding load-displacement curve were recorded, in the mechanical test. Findings - The results from the mechanical tests show the major failure mode is on the copper pad. Weibull analysis shows that the characteristic lives of most packages are between 1,100 and 2,400 cycles. For the CBGA, the characteristic life of 96 cycles is relatively short, due to the serious CTE mismatch. Cross-section inspection shows failures occur at the solder joint. Copper pad failure is also observed. Originality/value - This paper provides both the mechanical and thermal-mechanical reliability of lead-free solder joints. The experimental data are very useful in the lead-free SMT industries.