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PurposeThe purpose of this paper is to investigate the effect of stand‐off height (SOH) on the microstructure and mechanical behaviour of the solder joints in high density interconnection.Design/methodology/approachCu/Sn/Cu solder joints with 100, 50, 20 and 10 μm SOH are prepared using a reflow process. The microstructures and compositions of solder joints are observed and analyzed by scanning electron microscopy. Tensile testing is carried out to investigate the mechanical properties of the solder joints.FindingsThe SOH has a significant effect on the microstructure and mechanical behaviour of Cu/Sn/Cu solder joints. The thickness of the intermetallic compound (IMC) decreases with the reducing SOH; however, their corresponding IMC proportion increases. Meanwhile, the Cu concentration in the solder bulk experiences a marked increase, and the dissolved Cu exists in the forms of a solid solution and Cu‐rich particles at the grain boundary. Because of the higher strain rate and more dissolved Cu in the solder bulk with the reducing SOH, the ultimate tensile strength of solder joints is enhanced. When the SOH reduces to 10 μm, there is only one grain in height in the bulk, and a fracture in the IMC layer occurs. According to the mass balance of substance, a model is established to semi‐quantitatively calculate the consumed Cu thickness, and it is found that the consumed Cu thickness decreases with the reducing SOH.Originality/valueThe paper offers insights into the microstructural and mechanical property changes of the solder joints with the reducing SOH.

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The further miniaturization of electronic devices brings the challenge to the electronic packaging, especially for 3D interconnection as the miscrostructure of the solder joint could be replaced by IMC fully without any solder bulk remain. In this paper, both FE modeling and experimental testing were applied to investigate the stress distribution and the fracture mode of the solder joint under tensile load by considering the effect of IMC type and portion. Then, the size dependency regarding the IMC properties on grain size, defects, and crystallographic orientation has been pointed out to help understanding the reliability of full IMC joints.