Thermal Oxidation Study on Lead‐free Solders of Sn‐Ag‐Cu and Sn‐Ag‐Cu‐Ge

Abstract

Heat treatment experiments were carried out in SX-12-10 electric furnace. The experimental conditions are as follows: a. 450°C × 15 min (holding time) with cooling in the furnace (FC); b. 500°C × 15 min (holding time) with cooling in air (AC); c. 550°C × 15 min (holding time) with cooling in water (WC). The measurements of the linear recovery behavior of the Ti-Ni alloy springs involved the below steps. Firstly, Ti-Ni alloy springs were pre-drawn and unloaded at ambient temperature. Secondly, the springs were located on the selfmanufactured equipment (see Fig. 8) which is made for recovery behavior, then heated by water bathing with 2°C/min from the room temperature. Lastly, the experimental data such as temperature and displacement were collected and handled by computer aided measurement system, meanwhile, the results and the corresponding R-T (Recovery degree -Temperature) curves were obtained.The rare-earth sources in the thermochemical treatment were CeO 2 with 99.9 % purity and SmH 3 with 99.95 % purity, which were available from Jiangxi Provincial Rare-Earth Institute. Ceriuming experiment was carried out in SXZ-4-10 electric furnace, while samariuming experiment in ZKL-3 vacuum furnace. The measurements of recovery behavior was the same as above. The fracture surfaces of TiNi SMA springs were observed by the Quanta 200 scanning electronic microscopy (SEM). The composition of samples was measured by the Oxford 6650 energy spectrometer.

XPS Analysis of Oxide Films on Lead-Free Solders with Trace Additions of Germanium and Gallium

“…Lead-free solders sometimes display a yellow discoloration, particularly during the reflow process, and previous surface studies of this phenomenon on Sn-Ag-Cu solders have been reported [5][6][7]. In an X-ray Photoelectron Spectroscopy (XPS) study of a Sn-3.0Ag-0.5Cu solder alloy [5], a yellow discoloration of the usual metallic sheen was observed after five reflows. The thickness of the yellow oxide was determined to be 20 nm.…”

“…The addition of 500 ppm (0.05 wt.%) Ge allowed the metallic sheen on the sample surface to be retained, with an oxide thickness of 10 nm. Ge was not detectable on the surface by XPS after one reflow, but was observed in LMM Auger peaks after five reflows, indicating that Ge had become concentrated within the oxide layer during successive reflows [5]. The authors proposed that a thin layer of GeO x formed within the oxide film protecting the Sn-Ag-Cu-Ge alloy from further oxidation.…”

Effect of Heat Treatment and Thermochemical Treatment on Linear Recovery Property of TiNi Shape Memory Alloy

“…To the best of my knowledge, there are hardly any reports on the linear recovery effect of SMA. [1][2][3][4] The present researches focus on the recovery properties of TiNi SMA spring and improvements of the linear recovery effect through heat treatment and rare-earth thermochemical treatment.Linear recovery behavior of shape memory alloy (SMA): For a one-way shape memory effect, if it is deformed in Martensitic state, it will recover when heated, and the recovery quantity depends on temperature. Besides, the recovery proportion of SMA could be defined as the function of temperature.…”

“…To the best of my knowledge, there are hardly any reports on the linear recovery effect of SMA. [1][2][3][4] The present researches focus on the recovery properties of TiNi SMA spring and improvements of the linear recovery effect through heat treatment and rare-earth thermochemical treatment.…”