Development and Characterization of Sn99Ag0.3Cu0.7 -(ZrO2/CuO/TiO2) Nano-Composite Solder Alloys

The “lead-free” change in the soldering technology caused the widespread application of the SnAgCu (SAC) solder alloys. The so-called low Ag content ones, like Sn99Ag0.3Cu0.7 (SAC0307) and Sn98.5Ag1Cu0.5 (SAC105), are more and more popular recently due to their good price and thermo-mechanical properties. The most novel solution to further improve the solder alloys‘ properties is adding nano-sized ceramic reinforcement particles into the solder alloys. This procedure results in, nano-composite‘’ solder joints. A wide range of ceramic nano-particles (NPs) was already tested, like Fe
2
O
3
, TiO
2
, Si
3
Ni
4
, ZrO
2,
Al
2
O
3,
SiC, La
2
O
3
, etc. The reinforcement particles improve the solder joints' mechanical properties (shear force, yield strength, microhardness, etc.), with some Kelvin of increase in the liquidus-temperature of the alloy. It is generally accepted that mechanical improvement is caused by dispersion-strengthening mechanisms. The ceramic nano-particles are not soluble in the Sn, so they incorporate at the intermetallic (Cu
6
Sn
5
, CU
3
Sn, and Ag3Sn) grains and at the Sn grain boundaries, where they enhance heterogeneous nucleation. This effect suppresses the grain growth (all phases) and decreases dislocation motions. In the present study, the effect of three oxide ceramics (TiO
2
, ZrO
2
, and CuO) as reinforcements in 0.25wt% weight fraction was investigated on the quality and reliability of the composite SAC0307 solder alloy. The primary particle size of NPs was between 20–100nm. The NPs were mixed into the solder paste. Standard spread tests of the different alloys were done on FR4 laminates covered by Cu foil and imm-Ag surface finishing over on it. Solder joints were prepared from the alloys and 0603 chip resistors by convectional surface mounting technology on FR4-based printed circuit boards with imm-Ag surface finish. The shear strength of the chip resistors was measured. The solder joints were loaded with 4000 hours 85°C/85RH% climatic test to investigate their corrosion resistance. The results showed that NPs slightly decreased the wettability of nano-composite solder alloys. The shear strength of the composite joints generally increased, which proved that the second phase dispersion strengthening mechanism worked. However, the NPs have different effects on the corrosion resistance of the composite alloys. A former study proved that TiO2 could increase corrosion resistance [13]. Now it was observed that ZrO
2
did not change it, and CuO decreased it considerably. In correlation with corrosion resistance, the different composite alloys produced different amounts of Sn whiskers during the corrosive climate test.