Soft solders have been used for many years, with solder alloy technology remaining relatively unchanged until the 1900s. Tin-Lead (SnPB) solder has been the default joining material in electronics since the first circuits were created. The low melting temperatures, eutectic structure and relatively low cost made the Tin-Lead solder a natural fit for electronics.
However, legislation was adopted in the 1980s and 1990s to minimize the use of lead in all electronics. This resulted in a move to Tin-Silver-Copper (SAC) and other less expensive solders that do not include silver, leading to the latest generation of solders that are being marketed as high reliability. Are these high reliability solders proven to perform better than their Pb-free SAC solder counterparts in all use environments? Should they be used in all applications? This post takes a look at why high reliability solders are being developed and their actual reliability.
SAC Solders and the Rise of High Reliability Solders
SAC solders are the most common Pb-free solder alloys used in today’s electronic applications, with SAC305 as the clear favorite. Although popular, SAC305 should not be used in applications that go above 125°C. SAC305 is also more susceptible than softer solders to brittle fracture of the intermetallic layer during mechanical shock events. This can be problematic, as an increasing number of applications experience hotter operating temperatures and mechanical shock loads. These factors, coupled with the volatile price of silver and insufficient mechanical performance of SAC305 solders in mobile phone applications, led to the marketing of several low- or no-silver solder alloys including SN100C, SAC0307, SAC105, SAC125Ni.
Innolot Solder Example
In the early 2000s a European consortium focused on creating a solder with increased creep resistance. Increasing the creep resistance should reduce the amount of energy dissipated by the solder joint at every thermal cycle and increase the fatigue life of the joint. After almost 15 years in the market (patented in 2003), the Innolot solder has seen relatively low market penetration. Initial test data indicated a great promise for temperature cycling performance, but the data has been inconsistent. The current market interest for high reliability solders is being driven by LED lighting and automotive applications. These applications either have a high cycle count, high temperatures or both. Innolot may have a brighter future as these applications continue to grow, as the increasing complexity of electronics and niche applications offer more opportunities for custom joining technologies.
The Power of a Comprehensive Approach
When it’s all said and done, high reliability solders have the potential to produce very impressive results, but that doesn’t mean they are necessarily a good fit for all applications, or that they are guaranteed to always provide a vast improvement in expected device lifetime compared to SAC solders. Solder fatigue prediction should be comprised of more than just testing; it requires a comprehensive understanding of material behaviors in order to create more robust, accurate predictions and a confident decision to integrate high reliability solders into an application.
To find out more about how you can help ensure reliable solder joints in your electronic devices, download our free webinar, System Level Effects on Solder Joint Reliability.