Low-Temperature Solder Paste (Sn42Bi58)

As a leading solution in low‑temperature soldering, Low‑Temperature Solder Paste (Sn42Bi58) combines a high‑reliability flux system with fine spherical Sn42/Bi58 alloy powder. This advanced Solder Paste is engineered to deliver exceptional printability, minimal residue, and robust electrical performance, making it an ideal choice for heat‑sensitive assemblies and high‑density interconnects. Its eutectic composition ensures a sharp melting point at 138 °C, enabling energy‑efficient reflow and protecting temperature‑critical components.

Solder Paste Composition

The Solder Paste formulation of Low‑Temperature Solder Paste (Sn42Bi58) consists of a eutectic Sn42/Bi58 alloy powder and a specially developed flux system. According to the technical datasheet:

• Alloy composition: Tin 41.5–42.5%, Bismuth 57.5–58.5% – eutectic point at 138 °C (both liquidus and solidus).
• Flux content: 10.0 ± 1.0 wt%, with halogen content < 0.05 wt%.
• Flux composition (wt%):

1. Hydrogenated Rosin: 45–48%
2. Straight‑chain C9–C12 Aliphatic Alcohol: 20–22%
3. Cyclical C12–C16 Ester: 9–15%
4. Polymerized Fatty Oil: 4–6%
5. Dicarboxylic Acid Activator: 4–8%
6. Organic Amine C8–C10: 2–3%
7. Antioxidant/Corrosion Inhibitor: 2–3%

This low‑ionic flux system ensures that Low‑Temperature Solder Paste (Sn42Bi58) leaves minimal, non‑conductive residues after reflow, eliminating the need for post‑soldering cleaning while maintaining high surface insulation resistance (SIR) – a hallmark of a reliable Solder Paste for no‑clean processes.

Printing Performance & Process Stability

Designed for both conventional and fine‑pitch applications, this Solder Paste features a particle size distribution of 25–45 μm (between Type 3 and Type 4), enabling excellent release from additive‑process stencils.

Recommended printing parameters (Table 3 from TDS):

Key advantages for production:

• Minimal viscosity change during continuous printing, ensuring consistent deposit volume – a critical factor for high‑yield Solder Paste applications.
• Non‑hydrophilic nature allows stable operation even at up to 80 % RH without compromising performance.
• Stencil life exceeds 8 hours, supporting high‑volume SMT lines with this robust Solder Paste.

Flux Reliability & Electrical Performance

The flux system in Low‑Temperature Solder Paste (Sn42Bi58) employs a low‑ionic activator, passing stringent tests without causing corrosion or electromigration. This makes it suitable for applications where post‑reflow cleaning is impractical, reinforcing its status as a premium no‑clean Solder Paste.

These results confirm that Low‑Temperature Solder Paste (Sn42Bi58) delivers high reliability even in humid or high‑voltage environments, meeting the demanding requirements of modern consumer, automotive, and industrial electronics – a true testament to the quality of this Solder Paste.

Low‑Temperature SnBi Alloy Advantages

As a lead‑free Solder Paste (Pb < 0.001 %), Low‑Temperature Solder Paste (Sn42Bi58) fully complies with RoHS directives. Compared to conventional SAC (SnAgCu) alloys, the Sn42/Bi58 eutectic alloy offers:

• Melting point 138 °C – approximately 80 °C lower than SAC, protecting temperature‑sensitive components and substrates, while reducing energy consumption.
• Mechanical properties:

1. Tensile strength: 55 MPa (25 °C) / 28 MPa (100 °C)      
2.  Elongation: 13 % (25 °C) / 18 % (100 °C)           
3. Coefficient of thermal expansion: 13.4 × 10⁻⁶/°C

• Excellent creep resistance and thermal fatigue performance, verified in LED lighting, automotive sensors, and high‑frequency RF modules.

This low‑temperature profile also reduces thermal stress on PCBs, contributing to higher assembly yields – a key benefit that makes this Solder Paste the preferred choice for heat‑sensitive designs.

Reflow Profile & Process Guidelines

To achieve optimal wetting and minimize voiding or solder balling, the following reflow profile is recommended for Low‑Temperature Solder Paste (Sn42Bi58):

Note: The actual profile should be optimized based on board mass, component density, and oven type.

Handling guidelines for this Solder Paste:

• Thawing: Allow 4–6 hours at 25 °C before opening the container to prevent moisture absorption.
• Mixing: Use automatic Solder Paste mixer for 2–5 minutes (sealed) or manual stirring for 3–6 minutes until uniform viscosity is restored (180 ± 20 Pa·s).
• Printing‑to‑placement window: Complete component placement within 3–6 hours after printing to avoid surface drying.
• Storage: Sealed at 0–10 °C, < 75 % RH; shelf life 180 days from date of manufacture.

Application Scenarios & Supply Capacity

Low‑Temperature Solder Paste (Sn42Bi58) has been successfully deployed in mass production across multiple sectors:

• Consumer Electronics: TWS earbuds, smartwatches, and portable devices – benefiting from low‑temperature assembly and fine‑pitch capability of this Solder Paste.
• LED Lighting: COB modules and automotive interior lighting – where thermal management and reliability are critical.
• Automotive Electronics: Battery management systems (BMS), in‑vehicle sensors, and infotainment – requiring high SIR and vibration resistance.

With over 30 active customers and a monthly production capacity exceeding 2 tons, this Solder Paste is readily available with 72‑hour delivery to support continuous SMT line operations. Our technical team provides on‑site process support to ensure seamless integration of Low‑Temperature Solder Paste (Sn42Bi58) into your existing production workflow.

Safety & Handling Compliance

• Contains no regulated hazardous substances (Japan Industrial Safety and Health Act).
• Free from organic solvents subject to poisoning prevention regulations.
• In case of skin contact, clean immediately with ethanol‑soaked cotton, then wash with soap and water.
• Adequate ventilation is recommended during reflow to minimize fume exposure.