Effect of Isothermal Aging on Ball Shear Strength in BGA Joints with Sn-3.5Ag-0.75Cu Solder

Abstract

The ball shear strength of BGA solder joints during isothermal aging was studied with Sn-3.5Ag-0.75Cu solder on three different pads (Cu, electroless Ni-P/Cu, immersion Au/Ni-P/Cu) at temperature between 70 and 170 • C for times ranging from 1 to 100 days. The reliability of solder ball attachment was characterized by mechanical ball shear tests. As a whole, the shear strength of BGA joints decreased with increasing temperature and time. The shear strength for both the immersion Au/Ni-P/Cu and electroless Ni-P/Cu pads was consistently higher than that of the Cu pad for all isothermal aging conditions. The fracture surface showed various characteristics depending on aging temperature, time, and the types of BGA pad. The P-rich Ni layer formed at the interface between (Cu, Ni) 6 Sn 5 and Ni-P deposits layer after aging, but fracture at this interface was not the dominant site for immersion Au/Ni-P/Cu and electroless Ni-P/Cu pad.

Morphology of intermetallic compounds formed between lead-free Sn-Zn based solders and Cu substrates

“…[8][9][10][11][12] The brittle nature of the intermetallic compounds and the joining of two materials with dissimilar coefficient of thermal expansion cause degradation of interface integrity between substrates and solders. In the avionics and automotive applications, the reliability of solder joints extremely depends on the interfacial structure because the solder joint is subjected to thermal cycles and hightemperature circumstances up to 150°C.…”

Reliability of Solder Joint with Sn–Ag–Cu–Ni–Ge Lead-Free Alloy under Heat Exposure Conditions

“…1,2) Among lead-free solders, ternary Sn-Ag-Cu solders [3][4][5][6][7][8][9][10][11] are expected to be the substitute of a Sn-Pb eutectic solder, and have become wide spread in the manufacture of many electronic devices. However, the advanced lead-free solder, which has higher reliability than ternary Sn-Ag-Cu solders, is required to be used for various industry machines.…”

Interfacial Reaction and Mechanical Characterization of Eutectic Sn–Zn/ENIG Solder Joints during Reflow and Aging

“…It is known that at the Cu/solder interface, Sn (Zn for Sn-Zn solders) reacts rapidly with Cu to form the Cu-Sn (Cu-Zn for Sn-Zn solders) intermetallic compound (IMC), which weakens the solder joints, due to the brittle nature of this IMC. 10,15) Therefore, Ni is used as a diffusion barrier layer to prevent the rapid interfacial reaction between the solder and Cu layer in electronic devices. 7) Many studies have been performed on the interfacial reaction between Sn-Zn solders and the various surface finish layers (Cu, Au/Ni/Cu and electroless Nickel-immersion Gold [ENIG]) during reflow or aging.…”