Structural characterisation and properties of lead-free solders on different surface roughness of copper substrate

Ong, Chien Chung (2016) Structural characterisation and properties of lead-free solders on different surface roughness of copper substrate. Project Report. Universiti Teknikal Malaysia Melaka, Melaka, Malaysia. (Submitted)

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Abstract

The lead-free solders have been introduced to overcome the problem caused by the lead-based solders. This research will focus on the bond reliability of the lead-free solder on the copper (Cu) substrate with different surface roughness. The bond reliability strongly relies on the chemical bonding from the formation of the intermetallic compounds (IMC) between the solder and substrate. The materials used were solders wires with 2 different compositions, which were 96.5Sn-3.0Ag-0.5Cu (SAC305) and 95.5Sn-3.8Ag-0.7Cu (SAC387) and Cu substrates with coarse and fine surfaces prepared by grinding process. The primary objective is to deposit SAC305 and SAC387 on Cu substrates with different surface roughness. After soldering the SAC alloys on the substrates, the samples were left in the furnace at different ageing time. The samples were then put under the optical microscope and scanning electron microscope (SEM) to study the morphology. The hardness values were obtained from the solder joint using the micro Vickers hardness test. The IMC characterization was done using the X-ray diffractometer (XRD) to obtain the composition at the solder joint. From the result, the ageing duration has increased the IMC formation. Ageing for 3 hours at 125ºC give the most optimum hardness for both solders and surfaces. The Cu6Sn5, Cu3Sn and Ag3Sn IMC were found present in the samples. SAC387 showed more spheroid-shaped and long Cu6Sn5 IMC due to higher solder density. SAC387 was also harder than SAC305 due to the high Ag3Sn content. Lastly, it has been founded that the coarse substrates can be harder than the fine surface with proper ageing duration for the solder to wet onto the surface of the substrate.

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