Influence of reflow soldering profiles on creation of IMC at the interface of SnBi/Cu

Abstract

The paper describes the effect of the solder profile on the formation of an intermetallic layer in the solder composition of 57.6% Bi-42% Sn-0.4% Ag. Soldered joints were made by soldering of chip resistors of 1206 size with different soldering reflow profiles. Solder pads on the PCB are made of copper therefore they mainly make Cu 6 Sn 5 IMC. This layer has an effect on the mechanical strength of the soldered joint. Samples are measured by using the shear strength test. The thickness of the IMC layer is measured by Confocal Laser Scanning Microscope. IMC layer thickness grows with greater delivered energy into the joint during soldering.

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

“…The type of flux influenced the IML thickness even more significantly. The change of flux type (from ROL0 to ROL1) increased the thickness by up to 40%, which could negatively influence the mechanical properties of the solder joint [23]. The materials and their parameters (flux, surface finishes, solder alloy, solder mask, etc.)…”

“…An increase in IML thickness has also been observed after increasing the reflow temperature (peak temperature), increasing the reflow time (time above liquidus) [21] or the number of reflow cycles. A parameter known as a heating factor (defined as the integral of the measured temperature over the dwell time above liquidus) has been used in several studies [22][23][24] to quantitatively describe the effect of the heating process (effect of the combination of temperature and time during reflow soldering) on the resulting thicknesses of intermetallic layers. However, the heating factor does not always play the decisive role, since it describes only the reflow phase of the soldering process.…”