The Lower Cost, Better Performing SAC305 Alternative You’ve Been Looking For
This article explores REL61’s place in the evolution of lead-free solder, the unique advantages of its bismuth-enhanced formulation, and its performance compared to widely used alternatives like SAC305. Additionally, we’ll address its ideal use cases, limitations, and its availability as a versatile, global solution.
REL61 in the Evolution of Lead-Free Alloys
Ever since environmental regulations and industry standards began phasing out traditional leaded solders, manufacturers have sought alternatives that combine reliability, cost-effectiveness, and ease of use. In the first generation of the lead-free transition, SAC305 emerged as a top contender. Though it remains popular to this day, it is not without its drawbacks including cost, thermal fatigue, and other performance issues.
Enter REL61: AIM Solder’s third-generation lead-free alloy, designed to outperform its predecessors while meeting the diverse needs of modern manufacturing. REL61 is a low-silver SAC-based alloy containing a small percentage of bismuth.
Understanding the Role of Bismuth
Although bismuth offers notable benefits, its adoption as a solder constituent was initially limited. When bismuth and lead combine, they form a very low melting and brittle eutectic. Hence, if there was any lead in a process or in components, bismuth simply could not be used.
Today, however, completely lead-free processes have become the norm in many facilities, putting bismuth back into consideration as a prospective element.
Some people may be familiar with bismuth as a common element in low-temperature solder alloys. In this space, it has gained an unfortunate reputation for brittleness. But while it is true that as a main constituent in low-temperature solders, bismuth does contribute to brittleness, these concerns do not apply when it is used as a minor additive in high-reliability solder formulations.
In fact, in small percentages, typically around 1–6%, bismuth actually enhances solder performance rather than detracting from it. At these low concentrations, bismuth instead acts to refine the alloy’s microstructure, improving properties like strength, thermal stability, and even fatigue resistance.
This is why REL61, with its SAC+Bi composition, tends to outperform traditional SAC305 and other low/no-silver alternatives across most metrics. Even better, because of its low silver content, it costs 10-20% less than SAC305.
Comparing REL61 with Other Lead-Free Alloys
REL61 was specifically designed as a low-cost SAC305 alternative that still delivered on performance. But the end result was that it actually outperformed SAC305 and many other 1st and 2nd generation alloys.
The graph below shows how REL61 compares in tensile strength to other alloys. Not only does it start out strong when first cast, but it doesn’t lose strength after aging like the other alloys tested.
The reason for the thermal fatigue resistance can be traced back to microstructure. The following image shows that, as cast, both SAC305 and REL61 look similar. But after aging at 150C for a day, the difference is quite striking. SAC305 forms large scale structures that contribute to failure, while REL61 does not.
Just a few of the additional benefits of REL61 over SAC305 and similar alloys include:
- Improved hardness: REL61 is almost twice as hard as SAC305
- Improved thermal cycling performance: REL61 performs 1-1.5x better than SAC305 on thermal cycle tests
- Improved thermal shock performance: After 1500 cycles, 40% of SAC305 joints had failed, compared to 0% of REL61 joints. After 3000 cycles, 80% of SAC305 had failed, compared to 40% of REL61 joints.
- Improved hole fill in selective and wave applications: Many studies have shown better hole fill and consistency with REL61.
- Less dross: In an internal study comparing dross generation of several alloys, REL61 outperformed SAC305, SN100C and other low/no-silver alloys.
What REL61 Is and Isn’t
What REL61 Is
- A Cost-Effective SAC305 Alternative: REL61 represents a next-generation solution for manufacturers seeking a cost-effective and high-performing alternative to SAC305.
- Well-Performing: REL61 outperforms SAC305 and many other low/no-silver alloys.
- Versatile: REL61 is phosphorous-free, ensuring compatibility with selective soldering processes and offering exceptional performance in bar, wire, and paste forms.
- Lead-Free Compatible: REL61 is compatible with most elements in lead-free environments, including SAC alloys, nickel finishes, and trace germanium.
What REL61 Is Not
Despite its many strengths, REL61 is not without limitations:
- Not Compatible with Leaded Alloys: For mixed environments where leaded solder may be present, SAC305 remains a better choice. Using REL61 in such environments can lead to brittle joints due to incompatibilities with lead.
- Not High Reliability: While REL61 outperforms SAC305 and similar alloys in many metrics, it is not classified as a high-reliability alloy. For applications demanding the utmost reliability, such as aerospace or automotive, AIM Solder recommends its high-reliability REL22 alloy as the ideal solution.
Applications and Availability
REL61’s exceptional properties make it suitable for a wide range of applications, including:
- Selective Soldering: Its phosphorous-free formulation minimizes nozzle clogging and ensures consistent performance.
- Wave Soldering: Minimal dross formation, lower pot temperature requirements, and excellent wetting make REL61 ideal for high-volume production.
- Surface Mount Technology (SMT): REL61 in paste form delivers reliable results for SMT assemblies, ensuring high-quality joints and efficient processing.
- Robotic and Hand Soldering: REL61 is also available in both solid and flux-cored wire of different flux percentages for robotic and hand soldering applications.
Global Availability
AIM Solder’s global manufacturing network ensures consistent supply and support for REL61. With production facilities and distribution partners worldwide, customers can rely on AIM to meet their demands, regardless of location. AIM’s commitment to quality, combined with its technical support team, ensures seamless integration of REL61 into any production line.
Hundreds of manufacturers around the globe have already adopted REL61 with outstanding results, highlighting its effectiveness and versatility across industries.
Conclusion
Choosing REL61 for your soldering needs provides the perfect balance of performance, cost, and innovation. To learn more or request a quote, contact AIM Solder today.
