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www.us-tech.com


March 2026


The Move to Silver-Free Solder is Well Underway


By Keith Sweatman, Senior Technical Advisor, Nihon Superior


Superior Co. Ltd, Tetsuro Nishimura, has ob- served that a distinguishing feature of the year has been the move away from silver-con- taining solder alloys. In his own company he has seen significant growth in the sales of Nihon Superior’s flagship silver-free, lead- free solders, SN100C and SN100CV as elec- tronics manufacturers realize that they are not getting value from the premium they are paying for the 3-4% silver alloys they have been using. Nishimura is expecting this trend to accelerate as the silver price rises to a lev- el that reflects its value as a “critical materi- al” in the rapidly developing technologies on which the global economy increasingly relies.


I


An Inevitable Trend Nishimura has always seen this


trend to zero silver as inevitable. Since the very early days of the changeover to lead-free solders, he has been an advo- cate for silver-free solders. Even at the time of implementation of the EU RoHS Directive on July 1, 2006, the cost of sil- ver was a serious concern for an indus- try that had gotten used to relying on a solder in which the relatively expensive tin was diluted by more than a third by cheap lead. The increase in cost result- ing from the increase in the tin content to more than 95% was a challenge even before the cost premium added by the addition of 3-4% silver. Nishimura responded to that challenge


with the development of an alloy, that, in- stead of being based on the tin-silver-copper eutectic, is based on the tin-copper eutectic, with a precisely controlled addition of nickel that brought the performance of the alloy, in terms of soldering processes and the appear- ance of the resulting solder fillets, up to the standards the industry had come to expect from the tin-37% lead alloy that had been the benchmark. That alloy, SN100C, delivered a solder that satisfied the RoHS requirements without compromising performance in solder- ing processes, the appearance of the solder joint and, importantly, reliability in service. The iNEMI Alternative Alloy Project con- firmed that SN100C outperformed or at least matched the performance of tin-37% lead in even the most severe accelerated thermal cy- cling regimes.


n his review of developments during 2025, solder alloy innovator and president of leading solder manufacturer, Nihon


Why Silver? In the late 1990s, when the electronics


manufacturing industry first became aware of moves in the U.S. and Europe to remove toxic ingredients such as lead from the sol- ders on which they relied, the understanding of the performance of solder in soldering processes and their reliability in service was less advanced than it is now after 30 years of intensive study and practical experience. The 183°C melting point of the tin-37%


lead alloy was considered to be the most im- portant property for a lead-free replacement to match. Because of its proven non-toxicity and its unique ability to react with and wet the copper- and iron-based substrates joint substrates, the starting point had to be tin. However, the 232°C melting point of pure tin was considered too high for electronic assem-


highlighted but the trade-off was a 3°C in- crease in the liquidus temperature, which means that solidification occurs over a tem- perature range, 217 to 220°C rather than at a single eutectic point but consequences were judged as acceptable and the tin-3.0% silver- 0.5% copper was endorsed by what was then the IPC (now Global Electronics Association) as, “the lead-free solder alloy of choice for the electronics industry.”


Silver’s Reliability Bonus? In the evaluation of lead-free solder alloy


alternatives by industry consortia it was found that solder joints based on the tin-sil- ver-copper eutectic had a longer life in ther- mal cycling, one of the recognized methods of evaluating the reliability of electronic assem- blies. It seemed that replacing lead with sil- ver had yielded a bonus of a significant increase in reliability. Microstructural studies revealed that the increase in the time to failure in thermal cycling could be attributed to the strengthen-


As silver prices rise and its role as a critical material grows, its use in solder alloys becomes increasingly difficult to justify.


SN100CV solder paste.


bly. And the mechanical properties of pure tin are constrained by its body-centered tetragonal crystal structure which has limit- ed slip planes available for accommodating the stress to which solder joints are subjected in service. An obvious first addition was copper and


there is a tin-0.7% copper eutectic with a melting point of 227°C, Given the constraints imposed by the RoHS Directive the next addi- tion considered was silver and there is a tin- 3.8 silver-0.7 copper eutectic with a melting point of 217°C. With no other non-toxic additions that


could significantly reduce the melting point further, the tin-silver-copper eutectic was widely endorsed as the best RoHS-compliant solder alloy for electronics assembly. Patent issues prompted the introduction of a tin-sil- ver-copper alloy with only 3% silver. The cost benefit of the lower silver content was also


ing effects of fine, closely-spaced parti- cles of the intermetallic compound, Ag3Sn, which formed in the tin phase during the solidification of the tin-sil-


ver-copper eutectic phase. The early rounds of the iNEMI Alter -


native Alloys project appeared to confirm the benefit of silver in a solder formulation. The Characteristic Life, which, in the Weibull analysis is the measure of reliability, showed an almost linear relationship with the silver content of the solder. However, that first round of testing was done with a thermal cycle of –40 to 125°C and 10-minute dwells at each temper- ature. When, in subsequent tests the dwell time was increased to more realistic levels, 30 minutes and 60 minutes and to higher peak temperatures, the benefit of the silver declined to the point that there was little difference be- tween the characteristic life of silver-contain- ing and silver-free solder alloys. Studies at Auburn University found a


similar decline in the strength of silver-con- taining solder alloys even if there was a delay Continued on next page


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