Abstract
In order to present the multiple reflow process during electronic packaging, the influence of the different short-time reheating temperatures on the microstructure and shear strength of the Cu/Au80Sn20/Cu solder joints was studied and discussed. The results showed that high-quality Cu/Au80Sn20/Cu solder joints were obtained with 30 °C for 3 min. The joints were mainly composed of the ζ-(Au,Cu)5Sn intermetallic compound (IMC) with an average thickness of 8 μm between Cu and solder matrix, and (ζ-(Au,Cu)5Sn +δ-(Au,Cu)Sn) eutectic structure in the solder matrix. With an increase in the multiple reflow temperature from 180 °C to 250 °C, the microstructure of the joint interface showed little change due to the barrier effect of the formed ζ IMC layer and the limitation of short-time reheating on the element diffusion. The eutectic structures in the solder matrix were coarsened and transformed from lamellar to the bulk morphology. The shear strength of the as-welded joint reached 31.5 MPa. The joint shear strength decreased slightly with reheating temperatures lower than 200 °C, while it decreased significantly (by about 10%) with reheating temperatures above 250 °C compared to the as-welded joint. The shear strength of the joints was determined by the brittle solder matrix, showing that the joint strength decreased with the coarsening of the δ phase in the eutectic structure.
Highlights
Miniaturization of electronic products promotes the development of ultra large scale (ULSI) and super large scale (SLSI) integrated circuits, which require a higher packaging density [1,2]
The results showed that the AuSn2 and (Cu,Au)6 Sn5 layers formed at the interface gradually disappeared and the interface configuration transformed from AuSn/AuSn2 /(Cu,Au)6 Sn5 /Cu3 Sn layers to AuSn/Cu3 Sn layers
A few pores existed in the solder matrix, tempera matrix, which were attributed the air during the welding
Summary
Miniaturization of electronic products promotes the development of ultra large scale (ULSI) and super large scale (SLSI) integrated circuits, which require a higher packaging density [1,2]. 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]. The current research, involving Cu-Au80Sn20 joining, mainly focuses on the effect of aging on the microstructure and properties of the solder under service conditions. Reheating temperature and time have significant effects on the microstructure and properties of the solder joints. There are few reports on the effect of subsequent short-time reheating (soldering) cycles, from subsequent solder processes, on the microstructure and properties of first high-temperature solder joints. To simulate the effects of different subsequent low-temperature soldering on the microstructure and properties of previous high-temperature solder joints, the Cu substrate was soldered with Au80Sn20 solder in an air furnace. The microstructure evolution and shear properties of the joints were analyzed to investigate the effect of the secondary thermal cycle on the Cu/Au80Sn20/Cu as-welded joints
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