Assembly and solder joint reliability of plastic ball grid array with lead-free versus lead-tin interconnect

Many governments, particularly in Japan and Europe, have proposed laws reducing or eliminating the use of lead (Pb) and other toxic substances in products in an effort to decrease landfill pollution and ground water contamination. Thus, there exists a need for lead-free components in order to comply with government standards and to meet market demands for “green” products. As the semiconductor industry moves towards environmentally friendly components, it is important that their assembly and reliability be well characterized. This paper will describe experiments performed to determine the interconnect reliability of a peripherally leaded 1.0 mm pitch, 324 PBGA with lead-free (tin-silver) versus conventional (tin-lead-silver) solder balls. Assembly was performed with lead-free versus eutectic solder paste. Two different PBGA substrate manufacturers were evaluated and the test boards used had an immersion gold over electroless nickel surface finish. The assembled boards were thermal cycled in both -40 to 125 and -50 to 150°C until >50% failure to compare lifetime of the lead-based and lead-free material. Solder joint failures were detected with continuous in-situ electrical monitoring and most were then verified with dye penetrant. Additionally, solder ball shear testing versus 125 and 150°C bake out to 1,008 hrs was performed on lead and no-lead parts using one of the two substrate suppliers. Ball shear as a function of number of reflows was also performed. Scanning electron microscopy (SEM) was used to analyze the elemental content and intermetallic thickness of both ball sheared and board-level cycled parts. The data from the aforementioned experiments suggests that the lead-free 324 PBGA packages are at least as reliable as the lead containing ones