Sn-Ag Based Solders Bonded to Ni-P/Au Plating: Effects of Interfacial Structure on Joint Strength

Abstract

This study investigates interfacial reaction and joint strength of Sn-Ag and Sn-Ag-Cu solder balls bonded to electroless Ni-P plating with various thicknesses of Au coating (50, 250 and 500 nm). For the Sn-Ag solder joints, a P-rich layer formed after reflow-soldering at the joint interface, regardless of thickness of the Au coating. However, for the Sn-Ag-Cu solder joints, a P-rich layer formed at the joint interface only in those samples with Au coating of 250 and 500 nm. Fractures were found to occur at the interface, and the joint strength degraded at Au thickness of >250 nm for both the Sn-Ag and Sn-Ag-Cu solder joints. An Au thickness of 50 nm resulted in the best joint strength.

Reactivity between Sn–Ag Solder and Au/Ni–Co Plating to Form Intermetallic Phases

“…However, due to the barrier effect of this layer against the diffusion of Ni to solder, formation of intermetallic compound at inside of Sn-Ag solder was not occur as such even if holding time of peak temperature was extended. 4,5) While, in this Ni/Sn-Ag/Au/Ni-20Co joint, much intermetallic compounds were formed and the amount of the heat of melting decreased. The microstructure of specimen in the case of heating until 553 K was similar to that in the case of holding at 513 K for 1:8 Â 10 3 s, moreover, the endothermic peak decreased in the case of heating at Exo.…”

Microstructure, creep properties, and failure mechanism of SnAgCu solder joints

“…Studies of failure mechanisms in other kinds of tests, like pull or shear tests, have shown that the failure mechanism is strongly dependent on the test method, the geometry of the solder joint, and the temperature. [9][10][11][12][13][14][15] In general, the fracture behavior can be sorted out to occur either as a ductile fracture in the bulk solder, as a brittle fracture along the intermetallic layer, or as a combination of these two fracture modes. In the shear test, the fracture usually occurs in the bulk solder, but thermal aging may cause the fracture to occur in a more brittle manner in joints on Cu.…”

Interfacial Microstructure and Joint Strength of Sn-Ag and Sn-Ag-Cu Lead Free Solders Reflowed on Cu/Ni-P/Au Metallization

“…However, the reaction between solders and Cu/Ni-P/Au metallization causes some problems in the reliability of solder joints. It has been reported that a brittle intermetallic compound layer and/or P-rich layer formed at the interface between solder and Ni-P plating resulted in degradation of the joint properties [4][5][6][7][8]. Moreover, a thick Au coating may cause degradation in the joint reliability [9][10].…”