138°C
Sn42 / Bi58 Low-Melt Solder
A low-temperature eutectic solder alloy designed for specialized electronics rework and applications where reduced heat exposure is preferred.
Low Melt Solder Paste Product Guide
Precision Soldering at Lower Temperatures
Sn42 / Bi58 • 138°C Melting Point
Precision low-temperature solder paste engineered for professional electronics repair and rework.
Why Low-Melt Solder?
Lower Temperature. More Control.
Heat management is an important part of electronics repair. Excessive or prolonged heat can place unnecessary thermal stress on circuit boards, pads, connectors, and nearby components. PolarTronix Sn42/Bi58 solder melts at approximately 138°C, making it especially useful for controlled rework, component removal, and applications where reducing processing temperature is beneficial.
183°C
Sn63 / Pb37 Solder
A common eutectic tin-lead solder alloy used for general electronics soldering and board-level repair at a higher melting temperature.
Technical Note
Melting point is the temperature at which the solder alloy transitions to liquid. Actual hot-air, soldering iron, or reflow settings may be higher and will vary depending on PCB thermal mass, component size, airflow, equipment, and the repair process.
Ideal Applications
Designed for Controlled Electronics Rework.
PolarTronix Low Melt Solder Paste is designed for technicians who need greater control over heat during board-level repair and rework. Its 138°C melting point makes it especially useful in applications where reducing unnecessary thermal exposure is beneficial.
Component Removal
Lower-temperature solder can assist during component removal and rework by reducing the temperature required to reach a molten solder state, helping technicians work with greater control.
Heat-Sensitive Rework
Useful for repair procedures where limiting unnecessary thermal exposure to the PCB, solder pads, connectors, or nearby components is an important consideration.
Connectors & Ports
Well suited for controlled rework involving PCB-mounted connectors, ports, and other components with multiple solder joints where careful heat management is required.
Microsoldering & PCB Repair
A practical option for professional technicians performing detailed board-level repairs on smartphones, game consoles, laptops, tablets, and other modern electronics.
Professional Rework Material: Low-melt solder is a specialized material and should be selected according to the component, original solder alloy, operating conditions, and requirements of the repair.
Understanding the Alloy
What Makes Sn42/Bi58 Different?
PolarTronix Low Melt Solder Paste uses a eutectic Sn42/Bi58 alloy composed of 42% tin and 58% bismuth. This specific composition provides a defined melting point of approximately 138°C, making it well suited for specialized low-temperature electronics rework.
42%
Tin · Sn
58%
Bismuth · Bi
138°C
Melting Point
What Does “Eutectic” Mean?
A eutectic solder alloy transitions between solid and liquid at a defined temperature rather than softening gradually across a broad temperature range. For Sn42/Bi58, that transition occurs at approximately 138°C.
Why It Matters
The lower melting point allows technicians to perform certain soldering and rework procedures with reduced processing temperatures compared with many conventional electronics solder alloys.
Technical Note: The lower melting temperature of Sn42/Bi58 can be advantageous during controlled rework, but solder selection should always consider the original alloy, operating temperature, mechanical requirements, and intended use of the repaired assembly.
Technical Considerations
Low-Melt Solder Is a Specialized Material.
The lower melting temperature of Sn42/Bi58 can provide important advantages during certain electronics repair and rework procedures, but low-melt solder should not automatically be treated as a direct replacement for every conventional solder alloy.
Select the Alloy for the Application
Tin-bismuth solder alloys have different thermal and mechanical characteristics than conventional tin-lead and higher-temperature lead-free solder alloys. Before using Sn42/Bi58 as part of a permanent solder joint, consider the original solder alloy, operating temperature, mechanical requirements, and expected service conditions of the assembly.
01 / APPLICATION
Consider the End Use
Evaluate whether a low-temperature Sn42/Bi58 solder joint is appropriate for the device’s expected operating conditions and intended application.
02 / ALLOY COMPATIBILITY
Know the Existing Solder
Consider the original solder alloy already present on the assembly when selecting a material for repair, rework, or component replacement.
03 / APPLICATION CONTROL
Avoid Excessive Paste
Apply only the amount required for the soldering area. Controlled application can help reduce bridging, excess residue, and inconsistent solder joint formation.
04 / HEAT MANAGEMENT
Control the Process
Adjust temperature, airflow, heating time, and technique according to the PCB, component size, thermal mass, and equipment being used.
Professional Use: PolarTronix Low Melt Solder Paste is intended for controlled electronics soldering and rework. Proper material selection, surface preparation, application, and process control remain essential to achieving consistent results.
Related Products
Complete Your Rework Setup.
Pair Low Melt Solder Paste with complementary PolarTronix soldering, cleaning, and precision repair products designed for professional electronics technicians.
Solder Paste
Medium Melt Solder Paste
Sn63/Pb37 solder paste with a 183°C melting point for general electronics soldering and board-level repair.
View ProductSolder Wire
Low Melt Solder Wire
Sn42/Bi58 lead-free solder wire with a 138°C melting point for controlled low-temperature electronics rework.
View ProductSoldering Material
No-Clean Flux
Professional flux designed for electronics soldering, microsoldering, component work, and PCB rework.
View ProductSolder Wire
Medium Melt Solder Wire
Sn63/Pb37 solder wire with a 183°C melting point for general electronics repair and board-level soldering.
View ProductPrecision Cleaning
Nano Cleaning Brush
Ultra-fine precision cleaning brush designed for detailed PCB cleaning and delicate electronics repair work.
View ProductPrecision Tool
Ultra Fine Straight Tweezers
Fine-tip precision tweezers for controlled component handling, microsoldering, and detailed board-level work.
View ProductProduct Data
Technical Specifications.
Key product information for PolarTronix Low Melt Solder Paste, a lead-free Sn42/Bi58 solder paste designed around a 138°C melting-point alloy.
138°C
Melting Point
Sn42/Bi58
Alloy Composition
38 g
Net Weight
SP-101
Part Number
- Product Type
- Low Melt Solder Paste
- Part Number
- SP-101
- Alloy Composition
- Sn42 / Bi58 — 42% Tin (Sn) and 58% Bismuth (Bi)
- Melting Point
- 138°C / approximately 280°F
- Lead Content
- Lead-Free
- Net Weight
- 38 g
- Physical State
- Solid
Storage & Handling
Follow the product SDS and applicable workplace procedures when storing and handling Low Melt Solder Paste.
01 / TEMPERATURE
Keep Below 30°C
Store in a cool, ventilated location where the temperature does not exceed 30°C.
02 / CONTAINER
Keep Sealed
Keep the product container properly sealed when not in use.
03 / LIGHT
Avoid Direct Sunlight
Protect the product from direct sunlight during storage.
04 / STORAGE AREA
Cool & Ventilated
Store in an appropriately ventilated area and away from incompatible materials identified in the SDS.
Safety & Technical Information
Always review the current Safety Data Sheet before use. Product specifications describe the material and should not be interpreted as universal soldering, hot-air, or reflow equipment settings.
PolarTronix Soldering Materials
Built for Professional Repair.
PolarTronix Low Melt Solder Paste combines a lead-free Sn42/Bi58 alloy with a 138°C melting point for controlled low-temperature soldering and professional electronics rework.