Influence of Flux and Related Factors on Intermetallic Layer Growth within SAC305 Solder Joints.

Karel Dušek,Balázs Illés,Attila Géczy,Adam Petráč,Petr Veselý,David Bušek,Oliver Krammer

doi:10.3390/ma14247909

Abstract

Flux contained in solder paste significantly affects the process of solder joint creation during reflow soldering, including the creation of an intermetallic layer (IML). This work investigates the dependence of intermetallic layer thickness on ROL0/ROL1 flux classification, glossy or matt solder mask, and OSP/HASL/ENIG soldering pad surface finish. Two original SAC305 solder pastes differing only in the used flux were chosen for the experiment. The influence of multiple reflows was also observed. The intermetallic layer thicknesses were obtained by the image analysis of micro-section images. The flux type proved to have a significant impact on the intermetallic layer thickness. The solder paste with ROL1 caused an increase in IML thickness by up to 40% in comparison to an identical paste with ROL0 flux. Furthermore, doubling the roughness of the solder mask has increased the resulting IML thickness by 37% at HASL surface finish and by an average of 22%.

Highlights

Soldering technology is a predominant technique for joining electronic components on the printed circuit board (PCB)
One of the main topics was to study the effect of the solder mask type on the intermetallic layer (IML) thickness
It is apparent that the flux type and its amount in the joint during the reflow have a significant influence on the IML growth

Summary

Introduction

Soldering technology is a predominant technique for joining electronic components on the printed circuit board (PCB). The tin-based solders with the help of fluxes are used for joining metal parts. The soldering process is a complex one, where a combination of flux, temperature, and materials all have a decisive influence on the resulting joint. Flux reduces the oxides present on the metal surfaces and prepares the conditions for good wetting by solder. The formation of the intermetallic layer (IML) is inevitable and begins when the solder starts to wet the substrate.

Methods

Discussion

Conclusion