Solder-grade tin is refined tin specifically selected and controlled for solder alloy production. Unlike standalone tin grades (A, B, C), solder-grade tin is defined by its alloy system—most commonly tin-lead (Sn-Pb)—to achieve predictable melting, excellent wetting, mechanical reliability, and long-term electrical performance.
Common Sn-Pb Solder Compositions
| Solder Grade | Tin (%) | Lead (%) | Melting Range (°C) | Characteristics |
|---|---|---|---|---|
| Sn63-Pb37 | 63 | 37 | 183 (Eutectic) | Best wetting, no plastic range |
| Sn60-Pb40 | 60 | 40 | 183 – 188 | General electronics solder |
| Sn50-Pb50 | 50 | 50 | 183 – 215 | Higher strength, higher temp |
| Sn40-Pb60 | 40 | 60 | 183 – 238 | Plumbing, heavy joints |
| Sn30-Pb70 | 30 | 70 | 183 – 255 | High-temperature solder |
✔ Sn63-Pb37 is eutectic with a sharp melting point
✔ Higher lead content increases strength and melting temperature
Tin Purity Used in Solder-Grade Tin
| Application | Tin Purity Typically Used |
|---|---|
| High-reliability electronics | 99.95 – 99.99% Sn |
| Commercial electronics | 99.90 – 99.95% Sn |
| Industrial / plumbing solder | 99.85 – 99.90% Sn |
| Heavy-duty solders | ≥ 99.80% Sn |
Mechanical Properties (Typical Sn63-Pb37)
| Property | Typical Value |
|---|---|
| Tensile Strength | 40 – 50 MPa |
| Shear Strength | 25 – 40 MPa |
| Elongation | 40 – 60% |
| Hardness | ~15 – 18 HB |
| Fatigue Resistance | Excellent |
| Creep Resistance | Good |
Physical Properties
| Property | Behavior |
|---|---|
| Melting Point | 183 °C (Eutectic) |
| Electrical Conductivity | Good |
| Thermal Conductivity | Moderate |
| Density | ~8.4 g/cm³ |
| Surface Tension | Low (excellent wetting) |
Metallurgical Behavior
Sn-Pb solders form a fine eutectic microstructure that provides excellent mechanical reliability and fatigue life. Lead acts as a stress reliever and suppresses tin whisker growth, making these alloys exceptionally stable over long service periods.
Key Characteristics
✔ Excellent wettability and flow
✔ Predictable melting behavior
✔ Minimal shrinkage
✔ High joint reliability
✔ Tin whisker suppression
❌ Contains lead (regulated in many regions)
Refining & Processing Requirements
Tin used for solder applications must be low in bismuth, antimony, and arsenic, free from oxides and inclusions, and consistently refined.
Typical processing includes electrolytic tin refining, controlled alloying with lead, inert-atmosphere melting, and precision wire or bar casting.
Available Forms
Solder wire (flux-cored / solid)
Solder bars & ingots
Solder paste
Preforms
Applications
Electronics
PCB assembly, aerospace electronics, automotive ECUs
Industrial & Mechanical
Plumbing, heat exchangers, sheet-metal joining
High-Reliability Systems
Military, aerospace, medical electronics (exempt uses)
Advantages
✔ Best-in-class reliability
✔ Low melting temperature
✔ Excellent fatigue life
✔ Proven performance over decades
Limitations & Regulations
❌ Lead toxicity
❌ Restricted by RoHS / REACH
✔ Permitted in aerospace, defense, medical, and safety-critical systems
Sn-Pb vs Lead-Free Solders
| Feature | Sn-Pb | Lead-Free (Sn-Ag-Cu) |
|---|---|---|
| Melting Point | Lower | Higher |
| Reliability | Excellent | Good |
| Whisker Risk | Low | Higher |
| Cost | Lower | Higher |
| Regulatory | Restricted | Compliant |
Why Choose Solder-Grade Tin (Sn-Pb)?
Choose Sn-Pb solder-grade tin when reliability, fatigue resistance, whisker suppression, and long-term joint stability are critical and regulatory exemptions apply.
Engineering Insight:
Sn-Pb remains the global benchmark for solder performance.