Analyzing the Impact of Surface Treatment on Solder Joint Voids

The research presented in this article is a continuation of the previous publication, focusing on the relationships between the mechanical properties, IMC formation, and voids generation in the solder joints. Where the previous study addressed the mere mechanical resistivity of the soldered connections, the current work aims at a comprehensive understanding of the influence of the surface treatments, compositions of the solder alloy, and aging processes. Using a Design of Experiments methodology, 100 samples with varying surface treatments, solder materials, and aging exposure were investigated in terms of the influences of these factors on IMCs and voids formation and subsequent effects on the joints’ mechanical strength. The study focus on substantial influence of the surface roughness, regulated by different SiC grit sizes and electroplated nickel, on the IMC layer’s thickness, thereby, on the void formation. Moreover, thermal aging emerged as a crucial factor not only due to the direct enhancement of IMC thickness but also the increasing likelihood of Kirkendall voids occurring, especially at the Cu3Sn layer’s interface. Finally, the results indicated that voids bring negative implications for the mechanical integrity of the joint, especially those of size bigger than 30 µm. By combining the identified factors with the mechanical properties, the study reveals the intricate relationships involved and provides ideas for the enhanced reliability of the joints through optimization of the process parameters. In such a way, the present work emphasizes the necessity of the comprehensive approach to the solder joint enhancement, aiming to optimize the electronic assembling practices for higher durability and performance.

I. Introduction

Soldering represents the primary method of electrical and mechanical connection in electronics assembly. Numerous factors influence the quality of solder joints. A key concern for manufacturers is the solder's wettability. This can be caused by the oxidation of the soldered pad, this problem can be lowered by using flux. Oxidation can be mitigated through surface treatment and ensuring optimal shelf life. But this is not the ultimate solution, there is a lot more factors, that can cause instability or failure of the electronic assembly. Most of these issues were known even before the implementation of the RoHS directive, but the transition to lead-free solders has intensified the scrutiny on these concerns. This shift brought new challenges due to the different melting points, wetting properties, and mechanical characteristics of lead-free solders, demanding more rigorous control over soldering processes and material quality.