What temperature does solder melt at? A practical chart
Solder melts between 95°C and 327°C depending on the alloy. The alloy most electronics work uses, 63% tin / 37% lead (Sn63/Pb37), melts at 183°C (361°F) — and that single number is the anchor for almost every reflow profile and soldering iron setting you’ll ever set. Lead-free SAC305 (Sn96.5/Ag3.0/Cu0.5) melts at 217°C (423°F), about 34°C higher, which is why lead-free processing requires hotter ovens and hotter irons.
If you remember nothing else: pick your alloy first, then set your iron or oven 30–60°C above its melting point for a wire/iron joint, or 20–40°C above for a reflow profile.
By Michael Torres, Senior Process Engineer
Michael Torres is a Senior Process Engineer at WellCircuits with 12 years of experience in SMT process development, reflow profiling, and BGA assembly. He holds IPC-A-610 and IPC-7711/7721 certifications.
Table of contents
- Solder melting point chart (quick reference)
- What “melting point” actually means
- SnPb alloys: 60/40 vs 63/37 vs 50/50
- Lead-free alloys: SAC305, SN100C, and low-silver alternatives
- Specialty low-melt alloys (BiSn, indium-bearing)
- Melting point vs working temperature — the trap
- Reflow profile peak temperature
- How PCB surface finish shifts your effective window
- Lessons from the WellCircuits production line
- How WellCircuits handles this for your build
- Frequently asked questions
- Conclusion
TL;DR
- Sn63/Pb37 (eutectic tin-lead) melts at 183°C (361°F). It is the single most common electronics solder and the benchmark every other alloy is compared against.
- SAC305, the dominant lead-free alloy, melts at 217°C (423°F) — about 34°C higher than Sn63/Pb37.
- 60/40 tin-lead is not eutectic; it pastes between 183°C and 190°C before going fully liquid. Use 63/37 if you need a sharp melting transition.
- Solder paste does not have a single “melting point.” It has a melting range determined by the powder’s alloy and the flux activation window.
- “Working temperature” on a soldering iron is typically 300–380°C — well above the alloy’s melting point. The gap is intentional and required.
Solder melting point chart (quick reference)
| Alloy | Composition | Melting point (°C) | Melting point (°F) | Eutectic? | Typical use |
|---|---|---|---|---|---|
| Sn63 / Pb37 | 63% Sn, 37% Pb | 183 | 361 | Yes | Through-hole, SMT, rework (leaded) |
| Sn60 / Pb40 | 60% Sn, 40% Pb | 183–190 (paste range) | 361–374 | No | General electronics, plumbing |
| Sn50 / Pb50 | 50% Sn, 50% Pb | 183–215 | 361–419 | No | High-temp step soldering, older assemblies |
| SAC305 | Sn96.5 / Ag3.0 / Cu0.5 | 217 | 423 | Yes (near-) | Lead-free SMT reflow (most common) |
| SAC405 | Sn95.5 / Ag4.0 / Cu0.5 | 217–220 | 423–428 | No | Lead-free, slightly better wetting |
| SN100C | Sn / Cu / Ni + Ge | 227 | 441 | Near-eutectic | Lead-free wave soldering |
| BiSn (58/42) | 58% Bi, 42% Sn | 138 | 280 | Yes | Low-temp assembly, fire-risk applications |
| Indium-bearing | Sn / In / Ag | ~118–140 | ~244–284 | Varies | Step soldering, cryogenic seals |
| Pure tin | 100% Sn | 232 | 450 | No (single element) | Whisker-prone; rarely used alone |
| Pure lead | 100% Pb | 327 | 621 | No | High-temp solder, radiation shielding |
For most board-level work today you are choosing between two rows: Sn63/Pb37 (183°C) if your build is leaded and you don’t need RoHS, or SAC305 (217°C) if it has to be lead-free.
What “melting point” actually means
A pure metal has a single melting point — the temperature at which solid becomes liquid. Pure tin at 232°C, pure lead at 327°C, pure bismuth at 271°C. One number, one transition.
A solder alloy is a mixture. It almost always has a range over which it goes from solid to fully liquid, not a single sharp transition. The exception is a eutectic alloy, where the mixture melts at one temperature the way a pure metal does. Sn63/Pb37 is eutectic — 183°C and it goes liquid in an instant. SAC305 is near-eutectic — it has a narrow melting range (217°C to 220°C depending on the source) but it is not perfectly sharp.
For a non-eutectic alloy like 60/40 (60% tin, 40% lead), the alloy starts to soften around 183°C as the tin-rich phase melts first, then it pastes through a range, and it is fully liquid around 190°C. That paste stage matters in practice: if you try to reflow 60/40 at exactly 183°C you’ll get grainy, unreliable joints because you never reached full liquidation.
SnPb alloys: 60/40 vs 63/37 vs 50/50
Three tin-lead alloys still show up on shelves and in older equipment:
- 63/37 (Sn63/Pb37) — the eutectic alloy. Melts cleanly at 183°C. Use this for any rework, prototyping, or hand soldering where you want predictable results. Our SMT line prefers 63/37 for through-hole rework because the sharp transition means the joint goes liquid and wets fast — no paste stage to manage.
- 60/40 (Sn60/Pb40) — close to eutectic but not quite. Pastes from 183°C to 190°C. Still sold widely. Slightly cheaper than 63/37 historically, but the price gap has narrowed enough that 63/37 is almost always the right pick.
- 50/50 (Sn50/Pb50) — pastes from 183°C all the way to 215°C. Used for step soldering (soldering a component on top of an existing joint without re-melting it). Also used in some plumbing.
According to ESolder’s solder alloy reference chart, 63/37 is the recommended alloy whenever the application can tolerate lead and the goal is a sharp, repeatable joint.
Lead-free alloys: SAC305, SN100C, and low-silver alternatives
RoHS compliance (in effect for most consumer electronics sold in the EU since 2006) drove the industry to lead-free. The dominant replacement is the SAC family — tin-silver-copper.
- SAC305 (Sn96.5/Ag3.0/Cu0.5) — 217°C melting point. The default lead-free alloy for SMT reflow. Used by roughly 70–80% of lead-free contract assemblers, per industry surveys.
- SAC405 (Sn95.5/Ag4.0/Cu0.5) — 217–220°C. Slightly better wetting than SAC305 because of the higher silver, but more expensive.
- SN100C (Sn / Cu / Ni + Ge) — 227°C. A lead-free wave soldering alloy developed by Nihon Superior. Common in through-hole lead-free lines.
- Low-silver SAC alternatives (SAC0307, SAC105) — 217–227°C. Cheaper than SAC305. Used where the thermal and mechanical benefits of silver aren’t required.
Lead-free costs you two things at the alloy level: higher process temperature (more energy, more warpage risk on large boards) and higher silver cost when silver content is non-trivial. SAC305 is roughly 2–3× the price per kilogram of Sn63/Pb37, mostly because of the silver.
Specialty low-melt alloys (BiSn, indium-bearing)
Some applications need a melting point lower than tin-lead:
- BiSn (58% Bi, 42% Sn) — melts at 138°C. Common in temperature-sensitive assemblies and fire-protection devices where a solder joint must fail at a known temperature.
- Indium-bearing alloys (In / Sn / Ag) — melt between roughly 118°C and 140°C depending on composition. Used in cryogenic sealing and in step-soldering where a low-melt layer is applied last.
- Wood’s metal and similar field’s-metal-class alloys — melt below 100°C. Used in prototyping, model making, and some safety devices. Not for permanent electronics joints.
The trade-off with bismuth is brittleness. A BiSn joint is more brittle than a SnPb joint at the same geometry, and it does not tolerate thermal cycling as well. It also has a peculiar failure mode we’ll come back to in the lessons section.
Melting point vs working temperature — the trap
This is the single most common point of confusion in hand soldering. Melting point is the temperature at which the alloy becomes fully liquid. Working temperature is the temperature of the soldering iron tip, which has to be considerably higher because:
- The tip loses heat to the joint the instant it touches the pad and lead.
- You need a margin so the joint reaches full liquidation even with thermal mass from a large pad or a ground plane.
- You need to keep the joint above liquidus long enough for wetting and fillet formation.
A good rule of thumb for leaded hand soldering (Sn63/Pb37):
- Idle tip: 315–345°C (600–655°F)
- Small joints (0402, 0603): 315–330°C
- Larger joints (through-hole, large pads): 340–370°C
For lead-free (SAC305), bump everything up by 30–40°C:
- Idle tip: 345–380°C
- Small joints: 345–365°C
- Larger joints: 370–400°C
Going higher than 400°C on a lead-free joint is usually a sign something else is wrong — too much thermal mass, a dirty pad, or an iron that’s too small for the joint. Turn it down before you burn the board.
Reflow profile peak temperature
For SMT reflow ovens, the alloy melting point is the bottom of your process window, not the top. The peak temperature of your reflow profile should be roughly 20–40°C above the alloy’s liquidus, with a time-above-liquidus (TAL) of 30–90 seconds.
Typical lead-free SAC305 profile:
- Preheat: 150–200°C, ramp 1–3°C/s
- Soak (flux activation): 150–200°C for 60–120 s
- Ramp to peak: up to 235–250°C peak
- Time above liquidus (217°C): 30–90 s
- Cool down: ≤ -3°C/s
Typical Sn63/Pb37 profile:
- Peak: 205–220°C
- Time above liquidus (183°C): 30–90 s
The peak has to clear liquidus with enough margin to handle oven-to-oven variation, board thermal mass, and thermocouple placement error. According to IPC J-STD-020, moisture-sensitive components also need a controlled ramp rate to avoid “popcorn” damage during reflow — independent of the alloy.
The bigger error we see on the production line isn’t an alloy choice. It’s running a SAC305 profile on a Sn63/Pb37 board (or vice versa). The thermocouple says “good profile,” the solder says otherwise, and the BGA joints crack during thermal cycling because the intermetallic layer grew wrong.
How PCB surface finish shifts your effective window
The alloy melting point sets the floor. The surface finish on the PCB sets how easily the alloy wets and how forgiving your profile is. Two finishes worth understanding:
- ENIG (Electroless Nickel Immersion Gold) — the most common lead-free-friendly finish. The thin gold layer dissolves into the solder on first reflow and exposes nickel, which the tin in your solder bonds to. Good wetting, but exposure to multiple reflow cycles can cause “black pad” nickel failure.
- OSP (Organic Solderability Preservative) — a thin organic coating over bare copper. Cheaper than ENIG but more sensitive to storage conditions and multiple reflow cycles. The window for OSP can be tighter than the alloy melting range suggests, especially on a double-sided reflow build.
The point: don’t pick your iron temp or oven profile from the alloy melting point alone. Account for the finish, the board thickness, and how many times this board will see reflow. We add a 5–10°C margin to peak temperature on every ENIG-heavy lead-free build.
Lessons from the WellCircuits production line
Three things we have seen go wrong in real manufacturing that don’t show up in any alloy chart.
1. Bismuth-bearing paste at a SnPb profile. A customer sent a board with a BiSn low-melt paste intended for a step-soldered subassembly. Our line ran it on the Sn63/Pb37 profile as a default. The BiSn reflowed fine, but the existing SnPb joints underneath never reached liquidus — the joint sat in a Bi-rich liquid phase that ate the lead out of the existing fillet. Every previously-good joint failed pull test. We now ask about paste alloy on every NPI, not just the BOM.
2. SAC305 profile on a SnPb board. The inverse mistake. SAC305 needs a peak around 240–250°C to get 60–90 s above liquidus. Run that profile on a Sn63/Pb37 board and you push the joint well past its ideal thermal exposure — grain growth in the intermetallic layer, and the joint becomes brittle. We caught this on first article X-section once. We now check paste type before pulling a profile from the library.
3. Head-in-pillow on BGAs from a too-cool profile. BGA balls don’t collapse properly when peak temperature is below the alloy’s liquidus plus a 15–20°C margin. The BGA appears to have reflowed (resembles a soldered joint on X-ray) but the ball and the paste never fully coalesced. The result looks fine on the line and fails on thermal cycle. The fix is almost always: profile it. Don’t trust the oven’s recipe.
All three of these are “above melting point” failures. The alloy had reached liquidus. It just wasn’t liquidus plus margin.
How WellCircuits handles this for your build
Every board that comes through our line gets a reflow profile verified before the first production panel runs. If you’re sending us a build with an unusual alloy (BiSn, indium, step-soldered subassemblies), flag it on the travelers — we’ll profile specifically for that paste, not from a library.
We run SAC305 by default for lead-free builds and Sn63/Pb37 for leaded. If you need something else, we can source SN100C for wave soldering or low-silver SAC for cost-sensitive runs.
Working on a build with tight thermal margins or an unusual solder alloy? Send us your paste spec and we’ll profile it before production.
Frequently asked questions
What is the melting point of solder?
The most common electronics solder, 63% tin / 37% lead (Sn63/Pb37), melts at 183°C (361°F). The dominant lead-free alloy, SAC305, melts at 217°C (423°F). Most other solder alloys fall between 138°C (BiSn) and 327°C (pure lead).
What temperature does lead-free solder melt at?
SAC305 melts at 217°C. Other lead-free alloys fall in the 217–227°C range (SAC405, SN100C, low-silver SAC). Specialty lead-free alloys like BiSn melt as low as 138°C but are used for specific low-temperature or step-soldering applications, not general SMT.
Is 60/40 solder eutectic?
No. 60/40 tin-lead is not eutectic. It pastes between 183°C and 190°C, with the tin-rich phase melting first and the lead-rich phase melting last. 63/37 is the eutectic tin-lead alloy and melts sharply at 183°C.
What is the difference between melting point and softening point?
Melting point (or liquidus) is the temperature at which the alloy is fully liquid. Softening point (or solidus) is the temperature at which it starts to melt. For a eutectic alloy these are the same. For non-eutectic alloys, the alloy is partially liquid between solidus and liquidus, which is the “pasty range.” Solder paste has a related but different “softening point” tied to the flux activation temperature, which is usually 30–50°C below the alloy liquidus.
What soldering iron temperature should I use for lead-free solder?
Set the iron tip to 345–380°C (655–715°F) for lead-free SAC305 hand soldering. Larger joints (through-hole, big pads) need the higher end of that range, around 370–400°C. Going above 400°C usually means you have a thermal mass or wetting problem worth diagnosing, not a temperature problem.
What is the lowest melting point solder?
Field’s metal (Bi / Sn / Pb / Cd in various ratios) melts as low as 62°C. Wood’s metal melts at about 70°C. For electronics work, the lowest-melting practical alloy is BiSn (58/42) at 138°C, used where the joint must fail at a known temperature or where step soldering requires a low-melt layer last.
Why does lead-free solder melt at a higher temperature?
Lead-free SAC305 contains tin, silver, and copper. The silver and copper raise the alloy’s melting point relative to tin-lead, which contains lead — a metal that lowers the melting point of tin dramatically. SAC305’s 217°C is roughly 34°C higher than Sn63/Pb37’s 183°C, which is why lead-free reflow ovens and irons run hotter.
Conclusion
Solder melting point is one number per alloy, but using it correctly takes a little more: account for the pasty range on non-eutectic alloys, the surface finish on your board, and the margin your iron or oven needs above liquidus. Sn63/Pb37 at 183°C and SAC305 at 217°C cover the vast majority of electronics work today. Everything else is a specialty case with its own profile.
If you’re specing a build and aren’t sure which alloy or profile fits your thermal and reliability targets, send us your paste spec and stack-up. We profile before we run, and we have caught more than one design that looked fine on paper and would have failed first thermal cycle.
Need a reflow profile for an unusual alloy or a tight thermal window? Talk to WellCircuits’ process engineering team
Published for WellCircuits — Professional PCB Manufacturing and Assembly
