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48 SMT007 MAGAZINE I DECEMBER 2025 tronics industry has adopted solder pastes based on tin (Sn), silver (Ag), and copper (Cu)—SAC alloys⁵—valued for their robust mechanical and thermal properties. However, these alloys require high reflow temperatures between 240–250°C, and have several inherent drawbacks: 1. High energy consumption: Achieving and maintaining high process temperatures increases operating costs and carbon foot- print. 2. Equipment wear: Elevated temperatures accelerate wear and tear on reflow ovens and soldering machines, increasing the need for maintenance. 3. Thermal stress on components: High ther- mal stress can cause degradation of compo- nents and substrates, leading to warping and premature aging. In particular, a lower peak temperature in the reflow process (below 200°C) significantly reduces thermal stress, pre- venting defects and increasing reliability, a crucial advantage, for example, in "package-on- package" (PoP) applications. Initially, LTS alloys were pri- marily studied for assembly with heat-sensitive components. Early studies focused on two metals known for their low melting points: • Bismuth (Bi): The Sn42-Bi58 alloy melts at 138°C, but bismuth experts recognize it for its brittleness. It tends to fracture rather than deform, limiting its electronics applications. Developers introduced formulations such as Sn-Bi-Ag (e.g., 42Sn-57.6Bi-0.4Ag) to further improve the properties and enhance fatigue resistance. • Indium (In): The Sn52-In48 formulation melts at 118°C and exhibits greater ductility than bismuth alloys. However, its main disad- vantage is the extremely high and unstable market cost of indium⁶. As these limitations of binary LTS alloys became clear, researchers turned to multicomponent alloys to achieve a balanced solution. These multicom- ponent solders exhibit enhanced mechanical prop- erties, improved wetting behavior, and improved thermal fatigue resistance. This stage marked a shift from simply accommodating heat-sensitive components to designing alloys for broader reli- ability and manufacturability across diverse elec- tronics applications. Energy Consumption and Environmental Impact The adoption of LTS technology offers significant advantages in terms of reducing energy consump- tion and costs in soldering processes. Decreas- ing the reflow temperature from 250°C to 190°C or 175°C can generate energy savings of more than 30% per production run. Such energy reductions directly translate into substantially lower CO 2 emissions, making a signif- icant contribution to sustainability goals. Addition- ally, low temperatures enhance the long-term reli- ability of products by reducing thermal stress on components and substrates. This also enables the use of PCB laminates with lower glass transition temperatures (Tg), which offer additional material cost savings. A simple calculation on a single soldering system indicates the following: Engineers adapt the setting temperatures for SAC-based alloy paste because its melting point exceeds 220°C. In the preheating phase (above 180°C), and in the peak phase (above 250°C), a power of more than 20 kWh and CO 2 emissions of more than 42 kg of CO₂e are consumed. On the other hand, the use of OM565 paste with a melt- ing point at 146°C allows much lower tempera- tures: 140°C in the preheating phase, and a peak at 175°C, which translates into a power of just over 14 kWh and a CO₂e impact of 29 kg. From a lifecycle perspective, the cumulative energy savings over millions of units are enor- mous. For manufacturers that produce thousands of boards per day, this can translate into annual savings of several megawatt-hours (MWh), signifi- cantly reducing their environmental impact. D a n i e l e Pe ri c o