Run a leaded soldering profile on a lead-free board and the joint will look fine right up until it fails in the field — because the solder never fully melted. Solder melting point is the single number that determines whether an iron, wave pot, or reflow oven actually forms a sound joint, and it changes depending on the alloy. This guide breaks down exactly what temperature each common solder alloy melts at, why it matters, and how to set your process around it.
Takeway
- Leaded solder (63/37 Sn/Pb) melts at a sharp 183°C (361°F); lead-free SAC305 melts across 217°C–220°C (423°F–428°F) — a roughly 35–37°C gap.
- Eutectic alloys like 63/37 transition solid-to-liquid at one exact temperature with no pasty phase; near-eutectic alloys like SAC305 melt across a narrow range.
- Iron tip temperatures run 315°C–370°C for leaded solder and 370°C–400°C for lead-free — using the wrong profile causes open circuits or overheated components.
- Never mix leaded and lead-free solder on the same joint; it creates unpredictable alloy ratios and weaker mechanical properties.
- Reflow oven preheat, soak, and reflow zones must be built around the specific alloy’s solidus and liquidus values, not a generic profile.
What Is Solder Melting Point?
Solder melting point refers to the specific temperature, or temperature range, at which a solder alloy transitions from solid to liquid, enabling it to wet and bond component leads to PCB pads during soldering, wave soldering, or reflow assembly. Solder is not a single pure metal but an engineered alloy — most commonly tin-based — and its melting behavior is defined by two key values: the solidus temperature, where melting begins, and the liquidus temperature, where the alloy becomes fully molten.
Eutectic alloys, such as classic 63/37 tin-lead solder, transition sharply at a single temperature with no intermediate pasty phase, while near-eutectic alloys like SAC305 melt across a narrow range. The two dominant families used in PCB assembly are leaded solder (63/37 Sn/Pb), which melts at 183°C (361°F), and lead-free SAC305 (Sn96.5/Ag3.0/Cu0.5), which melts at approximately 217°C to 220°C (423°F to 428°F).
Solder melting point governs iron tip temperature, wave pot temperature, and reflow oven profile settings across electronics manufacturing, rework, and repair.
Why Does the Melting Point Change Between Alloys?
Solder melting point is the foundational parameter around which every soldering process is built. It solves the basic joining problem in PCB assembly: creating a metallurgical bond between a component lead and a copper pad without melting the base materials themselves.
Because solder is an alloy rather than a pure element, its melting behavior follows the eutectic principle. Combining tin and lead in the right ratio produces a mixture that melts at a temperature lower than either metal alone. Pure tin melts at 232°C and pure lead at 327°C — yet their 63/37 eutectic blend melts at a single sharp point of 183°C, well below either parent metal.
Functionally, the melting point sets the floor for every downstream process temperature. A soldering iron tip, wave solder pot, or reflow oven peak must run comfortably above the alloy’s liquidus point to ensure full wetting, but not so far above it that components, laminate, or nearby joints suffer thermal stress. Leaded solder is soldered at iron tip temperatures of around 315°C to 370°C, and lead-free SAC305 requires higher tip temperatures, adjusted reflow profiles, and greater attention to thermal stress on components — typically 370°C to 400°C for hand soldering and reflow peaks of 260°C or higher.
This matters for reliability because a thermal profile tuned for one alloy family fails outright with the other: a profile built for 183°C eutectic solder will not fully melt SAC305, resulting in open circuits and defective assemblies, while running a leaded profile at lead-free temperatures overheats components designed for the gentler leaded process. Getting the melting point and resulting thermal profile right is one of the most critical steps in surface mount assembly, directly determining joint strength, wetting quality, and long-term reliability.
Key Features and Advantages
| Feature | Description | Benefit |
| Eutectic transition (63/37 Sn/Pb) | Sharp solid-to-liquid change at 183°C with no pasty range | Predictable, fast solidification and clean joint formation |
| Near-eutectic transition (SAC305) | Solidus 217°C, liquidus 220°C, narrow melting window | Reliable joints with a well-defined process window |
| Alloy composition control | Precise Sn/Ag/Cu or Sn/Pb ratios per IPC/JEDEC standards | Consistent, repeatable melting point across batches |
| RoHS/REACH compliance | Lead-free alloys formulated to environmental standards | Enables sale into regulated markets requiring lead-free assembly |
| Cross-process compatibility | Available in wire, bar, and paste formats | Same alloy usable in hand, wave, selective, and SMT reflow |
| Dross-control technology | Additives that reduce drossing and improve flow | Cleaner wave pots and fewer bridging/icicling defects |
Technical Specifications
| Parameter | Value/Range |
| Leaded solder (63/37 Sn/Pb) melting point | Eutectic, 183°C (361°F) |
| Leaded solder (60/40 Sn/Pb) melting range | Approx. 183°C–190°C (361°F–374°F) |
| SAC305 (Sn96.5/Ag3.0/Cu0.5) melting point | Solidus 217°C / Liquidus 220°C (423°F/428°F) |
| Sn100C / SN100 (tin-copper) melting point | Approx. 227°C (440°F) |
| Sn3.5Ag (tin-silver) melting point | Approx. 221°C (430°F) |
| Tin-bismuth low-temp alloys | As low as 138°C, with brittleness trade-offs |
| Recommended iron tip temp — leaded | 315°C–370°C |
| Recommended iron tip temp — lead-free | 370°C–400°C |
| Wave solder pot temp (SAC305) | 255°C–265°C (491°F–509°F) |
| Selective soldering pot temp (SAC305) | 280°C–320°C (536°F–608°F) |
| Standards/compliance | IPC, JEDEC, RoHS, REACH |
Customization & Product Options
Alloy family: leaded (Sn/Pb) for legacy/military exemptions, or lead-free (SAC305, SAC405, Sn100C) for RoHS-compliant assembly
Format: solder wire (with flux core options), solder bar/ingot for wave pots, or solder paste for SMT stencil printing
Wire diameter: commonly 0.3mm–1.6mm for hand soldering wire
Flux type and percentage: no-clean, water-soluble, or rosin flux cores at varying flux-to-metal ratios
Trace element additions: bismuth for wetting/fatigue resistance, nickel (as in SN100C) for enhanced wetting and reduced copper dissolution
Packaging: spools, bars, notch bars, or cartridges sized for production volume
Where Does Melting Point Matter Most in Assembly?
Hand soldering and rework: technicians select iron tip temperature based on the alloy’s melting point, using leaded solder for legacy board repair and SAC305 for lead-free rework
Wave and selective soldering: through-hole assembly lines set solder pot temperatures 35–100°C above the alloy’s liquidus point to ensure full pad and lead wetting
SMT reflow assembly: reflow oven profiles are built around the paste alloy’s solidus/liquidus values to define preheat, soak, reflow, and cooling zones
Automotive electronics: SAC305 and automotive-certified variants are used where higher thermal cycling and vibration demand robust, well-characterized joint reliability
Consumer electronics manufacturing: lead-free SAC alloys dominate due to RoHS restrictions on lead content in consumer goods
Repair and legacy equipment servicing: leaded 63/37 solder remains standard for repairing older boards or equipment exempt from RoHS requirements
Manufacturing Capability
Solder alloy suppliers typically offer technical data sheets specifying exact solidus/liquidus values, chemical composition tolerances (e.g., Sn 96.0–97.0%, Ag 3.0%, Cu 0.5% per JSTD-006C), and shelf-life data — commonly around seven years for lead-free bar stock under proper storage. Quality control generally includes composition verification, dross and oxide testing, and process validation such as wetting balance testing.
Storage requirements typically call for dry, non-corrosive environments between 10°C and 40°C (50°F–104°F) to preserve alloy integrity. Suppliers commonly provide solder bath analysis services to monitor copper pickup in wave pots, since copper levels above roughly 0.95% can raise the bath’s liquidus temperature and require compensating adjustments.
Leaded vs. Lead-Free vs. Low-Temperature Solder
| Attribute | Leaded Solder (63/37 Sn/Pb) | SAC305 (Lead-Free) | Tin-Bismuth (Low-Temp) |
| Melting point | 183°C eutectic (361°F) | 217–220°C (423–428°F) | As low as 138°C |
| Melting behavior | Sharp eutectic transition | Narrow near-eutectic range | Low-temperature eutectic |
| Iron tip temperature | 315°C–370°C | 370°C–400°C | Lower, reduced thermal stress |
| Joint appearance | Bright, shiny | Duller, grainier (normal) | Bright, low-stress joints |
| RoHS compliance | Non-compliant (restricted) | Compliant | Compliant |
| Best use case | Legacy repair, exempted applications | Standard consumer/automotive lead-free assembly | Heat-sensitive components, but more brittle |
Frequently Asked Questions
What is the melting point of leaded solder versus lead-free solder?
Leaded solder (63/37 Sn/Pb) melts at 183°C (361°F), while the most common lead-free solder (SAC305) melts at approximately 217°C to 220°C (423°F to 428°F). That roughly 35–37°C gap is the reason leaded and lead-free processes use different iron temperatures, wave pot settings, and reflow profiles — treating them as interchangeable is the most common cause of cold joints and open circuits in mixed-process shops.
Can leaded and lead-free solder be mixed on the same joint?
No — mixing leaded and lead-free solder on the same joint can create unpredictable alloy compositions with unreliable melting ranges and weakened mechanical properties, so alloy families should not be combined during rework. If a board’s history is unknown, technicians should remove existing solder fully before applying a different alloy family rather than topping up over it.
Why does lead-free solder require higher soldering temperatures?
Because SAC305 and similar alloys have a higher liquidus point than eutectic leaded solder, the iron tip, wave pot, or reflow oven must run 30–45°C higher to fully melt the alloy and achieve proper wetting. Running lead-free solder at leaded-process temperatures typically produces dull, grainy, or incompletely wetted joints even when the solder appears to flow.
Does solder alloy meet RoHS and industry standards?
Lead-free alloys such as SAC305 comply with RoHS and other lead-free standards and are typically manufactured to IPC, JEDEC, and REACH specifications for electronic assembly. Composition tolerances — for example Sn 96.0–97.0%, Ag 3.0%, Cu 0.5% under JSTD-006C — are documented on the supplier’s technical data sheet and should be confirmed before qualifying an alloy for a regulated product line.
How does melting point affect reflow oven profile design?
The alloy’s solidus and liquidus temperatures define the preheat, soak, and reflow zones of the profile; a profile built for one alloy’s melting point will not correctly reflow a different alloy, risking open circuits or component damage. Reflow peak temperature is typically set 20–40°C above the paste’s liquidus point, with time-above-liquidus controlled tightly enough to ensure wetting without overheating nearby components.
Find What You Need on LCSC
LCSC stocks a wide range of solder wire, bar, and paste — leaded and lead-free, including SAC305, Sn100C, and low-temperature tin-bismuth alloys — sourced from trusted manufacturers with full technical data sheets available. Datasheets, RoHS/REACH certification, and real-time stock levels are visible before you order, so engineering and procurement teams can qualify an alloy and place a purchase order in one session. Browse LCSC’s solder and soldering materials category to compare alloys side by side and check availability before you buy.
