Material Analysis of Lead Free Solder Deposited by Electrochemical Deposition

摘要

Lead-free solders have essentially replaced lead-tin solders for new microelectronicapplications. At the same time, many products are continuing to go through miniaturization, sothe behavior of the solder material is changing as a function of the connection size. As lead-tinsolder has been replaced by lead-free alloys, electrodeposited SnAg has become the standardsolder alloy used on wafers. Tin-based solders exhibit a complex material structure in thedeposit, as recrystallization occurs in the deposit, and as intermetallic compounds form.Understanding the complex nature of these materials is becoming increasingly important to theperformance of our electronic products. We have characterized ECD SnAg solder alloydeposits in terms of composition, grain size, phase, microstructure, and texture using EBSDanalysis. We will discuss the effects of modifying the process parameters on the microstructurewhich could implications on the performance of the solder bump as a chip-level interconnect.We have seen that the metals deposit as β-tin with finely dispersed intermetallic grains. Wehave also seen evidence of recrystallization of the deposit subsequent to deposition, althoughthe recrystallization behaviour is significantly different than the well-characterized copperrecrystallization. Finally, the metal at the interface below the solder reacts with Sn to formintermetallic compounds, the compositions of which are dependent on the materials present.The effects of the process parameters on the deposit properties are becoming increasinglyimportant to understand in order to control the properties of the interconnection, and how itchanges over its lifetime. We have characterized the incorporation of trace organic materials inthe deposit as a function of plating parameters. The deposition of SnAg from an MSA-basedplating bath is very different from the deposition of copper from a copper sulfate plating bath.We have noticed that the incorporation of organic additive materials, as well as the grain size,increases as the deposition rate is increased in the deposition of SnAg.