Board Level Reliability of Components with Matte Tin Lead Finish

摘要

Manufacturers, suppliers, and industry consortia have all been working towards a common acceptable drop-in solution for the standard eutectic tin lead. SnAgCu alloys are now expected to be the leading choice by the electronics industry. For instance, NEMI has recommended Sn3.9Ag0.6Cu as an industry standard for lead-free solder paste, with Sn0.7Cu for wave soldering. Similarly, SnAgCu alloys were also recommended for array packages. Unfortunately, there has been no recommendation for a lead-free finish for leaded packages, although these packages still constitute the largest portion of the worldwide semiconductor production. The IC suppliers had to struggle to evaluate the various lead-free finish options available (e.g., NiPd, SnBi, SnCu, SnAg, and matte Sn), and assess the resulting impact of the transition on their manufacturing logistics. Benchmarking indicated that two finishes have emerged to be leading contenders from such evaluation, namely, matte Sn and NiPd (1,2). For a company to transition from tin lead to lead-free involves resolving a number of technical and logistics issues. This has been documented earlier for National Semiconductor (3). This paper will report on the solder joint reliability of matte Sn used as a finish for leaded packages. Package selection, PCB design, solder wettability, selection of reflow profiles, and effect of reflow temperature will also be discussed. The data showed the following: · NiAu boards exhibited better wetting characteristics than did OSP boards. · SnAgCu paste showed equal wetting onto SnPb and Sn components. · No significant difference was seen between standard and linear reflow profiles in terms of wettability of SnPb and lead-free solder pastes. · The 230°C profile did not completely reflow the lead-free solder pastes, although this did not translate directly to a weakening of the solder joints. · Matte Sn components showed comparable board level reliability to that of SnPb..