SN100C Achieves 20 Years of Reliable Service

The implementation of the European Union’s RoHS Directive mandated the use of Pb-free solders in the electronics industry by July 2006; however, five years before, Japan’s appliance recycling WEEE (waste electronic and electrical equipment) regulation for home electrical goods, air conditioner, refrigerator, freezer, TV, washing machine, clothes dryer was implemented in 2001. A new category of waste type, a category that includes precious metals as well as such toxic substances as lead (Pb) and polybrominated biphenyls (PBBs) was included in the WEEE regulation. For the solution to replacing Sn-Pb solder, the industry looked to lead-free alloys of which the SnCu system seemed reasonable. However, the SnCu did not perform as expected as a eutectic solder so the industry started to research improvements to the challenge to turn SnCu into a user-friendly solder.

In 1998, Tetsuro Nishimura, Nihon Superior’s Technical Manager, in partnership with the Audio Video Division of the Panasonic Corp. investigated extensively the cause of the poor performance of SnCu.  He identified nucleation of the second phase of the eutectic Cu₆Sn₅ as the problem. A nickel (Ni) addition at a trace level (0.05%) was discovered as the most effective method of enhancing the performance as a solder. During solidification, Ni works by facilitating the nucleation of the intermetallic Cu₆Sn₅, making it possible to solidify as a eutectic like Sn-Pb solder. With the microalloying of Ni to SnCu, SN100C was born. During the development, a germanium (Ge) addition also was identified as the most effective way of controlling the oxidation that generates dross.

Figure 1a. SnCu Figure 1b. SN100C

Nishimura was awarded Best Inventor by SMT Today Magazine during the 2015 SMTA International Conference & Exhibition in recognition throughout the electronics industry as the inventor of SN100C and the pioneer of micro-alloyed solders. The Best Inventor Award recognizes an individual or team whose innovation/s have not only addressed a need and solved a problem but also have been used to drive improved efficiency, productivity and performance within the electronics manufacturing industry.

Nishimura stated, “The small amount of Ni is like the effect of salt in a food dish. A small amount has no taste, so no effect, but and a large amount of salt overpowers the dish, making it not taste good. A good dish requires the right amount of salt just as SN100C has the right amount of nickel. On the other hand, Ge is similar to pepper in which it gives a good taste, but the amount may be varied.”

The first commercial use in mass production for the newly developed SN100C solder was in 1999 for a Panasonic VCR. Since then SN100C has been widely accepted and has gained the reputation as a reliable solder. The reliability of SN100C has been proven in a wide range of electronics assembly products, from appliances to industrial to automotive to aerospace. The alloy delivers a silver-free stable microstructure that can accommodate the long-term and impact strains to which a solder joint can be subjected. The eutectic character of the SN100C alloy and the associated high fluidity provides faster wetting and increased spreadability over SAC305, which is beneficial in wave soldering and hand soldering applications as well as in reflow. 

Solder is used to connect electrical components to printed circuit boards to make functioning electronic devices. Recently, there has been a significant increase in interest in eco-friendly hybrid and/or electric vehicles that can be exposed to extreme temperatures during service. Therefore, resistance of a solder joint to thermal fatigue is an important characteristic.

Figure 2 is an example of the reliability provided by the highly reliable, low-cost silver-free SN100C. From the cross-sections below, it is clear in thermal cycling there are significant differences between the SN100C and the Sn-3.8Ag-0.7Cu alloy. Cracks started to appear in the latter alloy after 2000 cycles with compete failure at by 4000 cycles. In the joints made with SN100C, there was no significant cracking until 4000 cycles. The conclusion is that SN100C has excellent resistance to thermal fatigue.

Figure 2. Cycling test showing SN100C’s reliability compared to the Sn-3.8Ag-0.7Cu alloy

Nihon Superior has been a leader in soldering and brazing materials since it was founded in 1966 by Toshiro Nishimura and continues its tradition of developing lead-free joining materials with improvements in reliability, thermally stable joining, and lead-free die attach. Toshiro’s son, Tetsuro now runs the company and Toshiro’s grandson, Takatoshi, also is involved, making Nihon Superior a third-generation family-owned business (Figure 3). The company continues to develop highly reliable products and is committed to earning its customers’ highest level of trust by taking full responsibility for every product delivered to them and remains ready to meet their rising demands for diversification, increasingly sophisticated technologies, and environmental protection. 

Figure 3. Three generations of the Nishimura family (L to R): Grandson Takatoshi, Founder Toshiro and CEO Tetsuro

It is becoming increasingly apparent that the simple ternary SAC305 alloy cannot deliver everything that the electronics industry requires in a solder in terms of cost and performance. The cost of the 3-4 percent Ag required to get the 217°C solidus temperature was one of the main reasons for choosing the Sn-Ag-Cu eutectic that has prompted the industry to reduce the Ag content to as low as 0.1 percent Ag or to use Sn-Cu based alloys with no Ag. Nihon Superior has now developed SN100CV that meets or exceeds the strength of SAC305 although it is silver-free. The new SN100CV alloy gains its strength from solute atoms in the tin matrix of the joint unlike silver-containing alloys that derive their strength from a dispersion of fine particles of eutectic Ag₃Sn. The Bi addition enables thermally stable solder joints even after thermal cycling.

Another product the company has developed is the Alconano Silver Sintering Paste, which is based on a patented technology that makes it possible to effectively join most metals as well as Si and SiC at low sintering temperatures, in nitrogen if necessary, without the nitrous or sulfurous residues that are the byproducts of the sintering of some other nano-silver pastes. The highly active surface of the nano-silver particles and the consequent strong capillary forces make it possible to achieve strong bonds with high electrical and thermal conductivity at low temperatures without the need for external pressure.

Conclusion

Twenty years ago, when SN100C was invented, it was considered to be a reliable and stable alternative to Sn-Pb solders. Two decades later, SN100C’s reputation has grown even stronger as it has evolved to meet new industry challenges. Moving into the future, the company will continue its mission of developing new products while staying committed to its customers. 

For more information, contact Keith Howell, Technical Director, at Nihon Superior USA LLC., 1395 Hawk Island Dr., Osage Beach, MO 65065, E-MAIL: k.howell@nihonsuperior.co.jp  Web site: www.nihonsuperior.com.