Effects of PCB Substrate Surface Finish and Flux on Solderability of Lead-Free SAC305 Alloy

A. Siewiorek,Z. Adamek,N. Sobczak,Z. Huber,A. Kudyba,J. Wojewoda-Budka,M. Homa

doi:10.1007/s11665-013-0492-4

Abstract

The solderability of the SAC305 alloy in contact with printed circuit boards (PCB) having different surface finishes was examined using the wetting balance method. The study was performed at a temperature of 260 °C on three types of PCBs covered with (1) hot air solder leveling (HASL LF), (2) electroless nickel immersion gold (ENIG), and (3) organic surface protectant (OSP), organic finish, all on Cu substrates and two types of fluxes (EF2202 and RF800). The results showed that the PCB substrate surface finish has a strong effect on the value of both the wetting time t 0 and the contact angle θ. The shortest wetting time was noted for the OSP finish (t 0 = 0.6 s with EF2202 flux and t 0 = 0.98 s with RF800 flux), while the ENIG finish showed the longest wetting time (t 0 = 1.36 s with EF2202 flux and t 0 = 1.55 s with RF800 flux). The θ values calculated from the wetting balance tests were as follows: the lowest θ of 45° was formed on HASL LF (EF2202 flux), the highest θ of 63° was noted on the OSP finish, while on the ENIG finish, it was 58° (EF2202 flux). After the solderability tests, the interface characterization of cross-sectional samples was performed by means of scanning electron microscopy coupled with energy dispersive spectroscopy.

Highlights

The SAC305 (SnAg3.0Cu0.5, wt.%) alloy belongs to the SAC family of Pb-free solders recommended for the joining of various components in electronic devices, in printed circuit boards (PCB)
Typical acquired wetting balance curves that represent the change of measured force (Fr) versus time (t) and characterize the dynamic wetting behavior of the SAC305 solder on PCB substrates with different surface finishes are shown in Fig. 1 and 2 for RF800 and EF2202 flux, respectively
The wetting balance measurements of solderability of the SAC305 alloy in contact with PCB having three different surface finishes (HASL LF, electroless nickel immersion gold (ENIG), and organic surface protectant (OSP)) on Cu substrates and using two types of fluxes (EF2202 and RF800) are evidenced as follows: [1] The type of surface finish has a strong effect on the solderability with SAC305, measured in terms of both wetting force Fr and wetting time t0

Summary

Introduction

The SAC305 (SnAg3.0Cu0.5, wt.%) alloy belongs to the SAC family of Pb-free solders recommended for the joining of various components in electronic devices, in printed circuit boards (PCB). The typical thickness of HASL LF is 1.3-35 lm The benefits of this kind of PBS finish are low cost coupled with good shelf life and excellent solderability, while its disadvantages are non-uniformity of the coating, low thermal shock resistance, and the formation of brittle IMCs at the interface during both processing and solder jointsÕ operation. The influence of the type of flux and PCB surface finish (HASL LF, ENIG, OSP) on the solderability of SAC305 alloy with selected PCBs was investigated. It was accomplished using the wetting balance method, which allows the direct measurements of the wetting force and wetting time and indirect determination of the contact angle values (Ref 16 - 18)

Materials and Testing

Results and Discussion

Conclusions