Effect of Au-Sn IMCs’ formation and morphologies on shear properties of laser reflowed micro-solder joints

Abstract

Purpose – The purpose of this paper is to investigate the effect of typical morphologies of Au-Sn IMCs (intermetallic compounds) at the interfaces of solder and pads on shear properties of laser reflowed micro-solder joints. Design/methodology/approach – Sn-2.0Ag-0.75Cu-3.0Bi (SnAgCuBi) solder balls (120 μm in diameter), pads with 0.1, 0.5, 0.9 or 4.0 μm thickness of Au surface finish, and different laser input energies were utilized to fabricate micro-solder joints with Au-Sn IMCs having different typical morphologies. The joints were performed by a shear test through a DAGE bond test system. Fracture surfaces of the joints were analyzed by scanning electron microscopy and energy-dispersive X-ray spectrometry to identify fracture modes and locations. Findings – Morphologies of Au-Sn IMCs would affect shear properties of the joints remarkably. When needle-like AuSn4 IMCs formed at the interfaces of solder and pads, almost entire surfaces presented the manner of ductile fracture. Moreover, shear forces of this kind of solder joints were higher than those of joints without Au-Sn IMCs or with a nearly continuous/continuous Au-Sn IMCs layer. The reason was that the shear performance of the solder joints with needle-like AuSn4 IMCs was enhanced by an interlocking effect between solder and needle-like AuSn4 IMCs. As a nearly continuous or continuous Au-Sn IMCs layer formed, the fracture surfaces presented more character of brittle than ductile fracture. However, if an Au layer still remained under Au-Sn IMCs, the shear performance of the joints would be enhanced. Originality/value – The results in this study can be used to optimize microstructures and shear properties of laser reflowed micro-solder joints.

TEM observation of interfacial compounds of SnAgCu/ENIG solder bump after laser soldering and subsequent hot air reflows

“…However, no Au-Sn IMCs were detected at the interface of SAC305/Ni-P plating. In our previous reports, the needle-like AuSn 4 IMCs usually formed at the interfaces of solder and pads during laser soldering [5,6,10]. But in this study the Au layer was far thinner than that in our previous reports with relatively longer laser heating time, the ultrathin Au layer has sufficient time to dissolve into the molten solder.…”

“…The Electroless Ni-P/Immersion Au (ENIG) finish is widely used as a surface treatment on Cu pad for its advantages of good solderability, low-cost, and antioxidation [7][8][9]. During soldering process, SnAgCu solder and ENIG/Cu pad react with each other and form various intermetallic compounds (IMCs) like, [6,9,10] and hot air reflow [8,[11][12][13] have been extensively studied, respectively. However, the evolution of interfacial microstructures of SnAgCu/ENIG after hybrid and multiple reflows seems not sufficient.…”

Microstructure Evolution and Shear Strength of the Cu/Au80Sn20/Cu Solder Joints with Multiple Reflow Temperatures

“…Macdonald [5] and K. Bobzin [6] showed the high adaptability of the Au-based solder in bonding wafer-level packages (WLP) and chip-scale packages (CSP). Among them, the Au80Sn20 eutectic solder shows the advantages of high strength, excellent creep and fatigue resistance and the possibility of flux free soldering, resulting in its wide application in the field of the high-power electronic devices and optoelectronic packaging [7][8][9]. Considering that Cu is often applied as the substrate material, Cu/Au80Sn20 is a common preamble interconnection solder joint in electronic packaging.…”

Experimental and Statistical Study of the Fracture Mechanism of Sn96.5Ag3Cu0.5 Solder Joints via Ball Shear Test

“…Due to human health and environmental concerns the use of lead-free solder materials, especially Sn-based solder alloys, have been widely used in interconnecting structures in the microelectronic packaging industry [ 1 , 2 , 3 , 4 , 5 ]. However, Sn-based materials exhibit obvious viscoplasticity at room temperature due to their low melting point, such that room temperature can be considered a ‘high’ temperature [ 6 ].…”