Controlling Interfacial Reactions and Intermetallic Compound Growth at the Interface of a Lead-free Solder Joint with Layer-by-Layer Transferred Graphene

Abstract

The immoderate growth of intermetallic compounds (IMCs) formed at the interface of a solder metal and the substrate during soldering can degrade the mechanical properties and reliability of a solder joint in electronic packaging. Therefore, it is critical to control IMC growth at the solder joints between the solder and the substrate. In this study, we investigated the control of interfacial reactions and IMC growth by the layer-by-layer transfer of graphene during the reflow process at the interface between Sn−3.0Ag−0.5Cu (in wt %) lead-free solder and Cu. As the number of graphene layers transferred onto the surface of the Cu substrate increased, the thickness of the total IMC (Cu 6 Sn 5 and Cu 3 Sn) layer decreased. After 10 repetitions of the reflow process for 50 s above 217 °C, the melting temperature of Sn−3.0Ag−0.5Cu, with a peak temperature of 250 °C, the increase in thickness of the total IMC layer at the interface with multiple layers of graphene was decreased by more than 20% compared to that at the interface of bare Cu without graphene. Furthermore, the average diameter of the Cu 6 Sn 5 scallops at the interface with multiple layers of graphene was smaller than that at the interface without graphene. Despite 10 repetitions of the reflow process, the growth of Cu 3 Sn at the interface with multiple layers of graphene was suppressed by more than 20% compared with that at the interface without graphene. The multiple layers of graphene at the interface between the solder metal and the Cu substrate hindered the diffusion of Cu atoms from the Cu substrate and suppressed the reactions between Cu and Sn in the solder. Thus, the multiple layers of graphene transferred at the interface between dissimilar metals can control the interfacial reaction and IMC growth occurring at the joining interface.

Effect of Graphene Layers on Phenomena Occurring at Interface of Sn-Zn-Cu Solder and Cu Substrate

“…With increasing numbers of graphene layers, the contact angle of water on the copper surface gradually attains the value for water on the surface of graphite. In the most recent published work describing wetting of copper and copper covered by graphene with Sn-Ag-Cu (SAC) solder, 25 the authors describe the role of the graphene coating as a diffusion barrier, suggesting that the graphene layer should reduce copper diffusion from the substrate and thereby inhibit growth of the intermetallic layer. Cu atoms diffuse from the substrate through defects in the graphene coating.…”

Intermetallic compounds in 3D integrated circuits technology: a brief review

“…Likewise, thermal solid state aging causes a transformation from existing low-temperature Cu 6 Sn 5 IMCs to existing high-temperature Cu 3 Sn IMCs [ 11 ]. Ko et al [ 83 ] indicated that Cu 3 Sn arises largely from the consumption of Cu 6 Sn 5 , as in Equation ( 3 ): …”

Improvement in Thermomechanical Reliability of Low Cost Sn-Based BGA Interconnects by Cr Addition

“…Scanning electron microscopy (SEM; S-4700, Hitachi, Tokyo, Japan), together with energy dispersive X-ray spectroscopy (EDX; EDAX Genesis XM2 60, AMETEK, Mahwah, NJ, USA), was employed to characterize the IMC microstructure. For kinetic studies, the IMC thicknesses were measured from the SEM images of the metallographic cross-sections using the following image analysis procedure [7,8]: (1) an SEM image of each sample was obtained at the appropriate magnification; (2) the grayscale SEM image was enhanced using Adobe Photoshop (CS6, Adobe systems, San Jose, CA, USA, 2017) to identify the interfaces between the different layers; and (3) the mean thickness (H IMC ) of individual layers was calculated using the following equation:…”

“…A 1% reduction of Ag in a solder alloy results in at least a 15% reduction of the total solder cost. Currently, commercial imperatives to reduce costs have raised considerable interest in lowering the Ag content of SAC solder alloys to reduce the base alloy cost, especially in the context of decreasing profits in electronics manufacturing due to intense competition [7][8][9]. In this context, Ag-free solders, specifically the eutectic SC07 solder, has attracted much attention in automotive electronic applications because of the low cost and good drop reliability.…”