关键词: 电子封装, Sn-Pb钎料, Cu核微焊点, 液-固界面反应, 金属间化合物

Abstract: Cu-cored micro solder joints exhibited superior electrical conductivity, thermal conductivity, and mechanical properties compared to traditional Sn-based micro solder joints, enabling effective control for the height of the solder joints. This paper initially investigated the electrodeposition process of Sn-Pb alloys and fabricated Cu-cored solder balls (Cu@Sn-Pb and Cu@Ni@Sn-Pb) through electroplating. And then the Cu/Cu@Ni@Sn-Pb/Cu and Cu/Cu@Sn-Pb/Cu solder joints were prepared to investigate the liquid-solid interfacial reactions during reflow at 250 ℃ and to further explore the shear fracture mechanism. The results indicated that the composition of the Sn-Pb coating was influenced by the concentration of the Pb²⁺, methanesulfonic acid concentration, current density, and electroplating solution temperature, among which the concentration of the Pb²⁺ was the most significant factor. The optimal plating results were achieved with the electroplating solution temperature at 25 ℃ and the current density as 1~2 A/dm². After reflow, Cu/Cu@Sn-Pb/Cu solder joints formed scallop Cu₆Sn₅ intermetallic compounds (IMC) and thin laminar Cu₃Sn IMC on both sides of the Sn-Pb/Cu-core and Sn-Pb/Cu-substrate interface. In contrast, Cu/Cu@Ni@Sn-Pb/Cu solder joints developed scallop (Cu,Ni)₆Sn₅ IMC on the Sn-Pb/Ni/Cu-core side and columnar (Cu,Ni)₆Sn₅ IMC on the Sn-Pb/Cu-substrate side after reflow, with the growth of Cu₃Sn IMC being suppressed. The thickness of (Cu,Ni)₆Sn₅ IMC on the Sn-Pb/Cu-substrate side was significantly superior to that on the Sn-Pb/Ni/Cu-core side. Shear test results revealed that the shear strength of Cu/Cu@Ni@Sn-Pb/Cu solder joints and Cu/Cu @Sn-Pb/Cu solder joints was respectively 55.2 MPa and 47.9 MPa and the solder joint strength was increased by 15.5% after reflow for 1 min.

Key words: electronic packaging, Sn-Pb solder, Cu-cored micro solder joints, liquid-solid interfacial reaction, intermetallic compound