Soldering Temperature Guide: Melting Points for Every Alloy

The soldering temperature you set is not the solder’s melting point — it’s typically about 100 °C higher, because the iron or oven has to heat the copper pad and component lead, not just the solder sitting on top. Eutectic leaded solder (Sn63Pb37) melts at 183 °C, but you hand-solder it around 320–360 °C. Lead-free SAC305 melts at 217 °C and wants 350–380 °C. This guide gives you the melting point of every common solder alloy in one chart, the right iron, reflow, and wave temperatures for each, and the solidus, liquidus, and pasty-range distinctions that trip people up. Set it wrong and you get cold joints, lifted pads, or a tip that oxidizes in minutes.

Key Takeaways

• Soldering temperature is not the melting point: set the iron roughly 100 °C above the alloy’s liquidus to overcome the heat sink of the pad and lead.
• Leaded Sn63Pb37 melts at 183 °C (eutectic); lead-free SAC305 melts at 217–220 °C — about 35 °C higher, needing a hotter iron and reflow peak.
• Hand-soldering iron: ~320–360 °C for leaded, ~350–380 °C for lead-free; never above 400 °C, which cooks pads and components and kills tip life.
• Reflow peak runs 20–50 °C above liquidus (≈240 °C leaded, 245–250 °C lead-free); wave-solder pots run 250–290 °C.
• A lower melting point isn’t automatically safer — Sn42Bi58 (138 °C) is brittle and forms a catastrophic 96 °C phase with any lead contamination.

What Is Soldering Temperature? Melting Point vs. Soldering Temperature

Soldering temperature is the temperature you actually run the process at — the iron tip setting, the reflow peak, the wave pot. The melting point is a property of the alloy: the temperature at which the solder turns liquid. The two are not the same, and the gap between them is where most bad joints come from.

Here’s the distinction that trips people up. When the iron touches a joint, it doesn’t only melt the solder — it has to pour heat into the copper pad and the component lead, both of which start at room temperature and act as heat sinks. If you set the iron at the solder’s melting point, the moment it contacts that thermal mass the tip temperature collapses below liquidus and the solder never flows. So you run the iron well above the melt point — a common rule of thumb is melting point plus about 100 °C — to carry a reserve of heat that brings the joint to liquidus in a second or two. That’s why a 183 °C alloy gets a 320–360 °C iron.

Two more things to keep in mind. The iron’s display is not the joint temperature — thermal drop through the tip, an oxidized tip, or a big ground plane pulling heat away all mean the metal sees less than the number on the station. And hotter is not better: above roughly 400 °C you damage pads and heat-sensitive parts, and you oxidize the tip fast. The acceptance requirements for the finished joint, regardless of temperature, are defined by J-STD-001, the industry standard for soldered electrical and electronic assemblies.

Solder Alloy Melting Point Chart

This is the table to bookmark. It covers the alloys you’ll actually encounter — leaded, low-temperature, and high-temperature — with melting points verified against alloy datasheets. The lead-free alloys all sit roughly 30–45 °C above their leaded counterparts, which is the single biggest reason the switch to RoHS made soldering harder.

Alloy	Composition	Melting point	Type	Typical use
Sn63Pb37	63 Sn / 37 Pb	183 °C (eutectic)	Leaded	General leaded SMT/THT, rework
Sn60Pb40	60 Sn / 40 Pb	183–190 °C	Leaded	Hand soldering, general purpose
Sn62Pb36Ag2	62 Sn / 36 Pb / 2 Ag	179 °C (eutectic)	Leaded + silver	Silver-bearing pads, fine work
SAC305	96.5 Sn / 3.0 Ag / 0.5 Cu	217–220 °C	Lead-free	Default commercial lead-free
SAC405	95.5 Sn / 4.0 Ag / 0.5 Cu	217–224 °C	Lead-free	Automotive, higher fatigue life
Sn96.5Ag3.5	96.5 Sn / 3.5 Ag	221 °C (eutectic)	Lead-free	High-reliability, no copper
Sn99.3Cu0.7	99.3 Sn / 0.7 Cu	227 °C (eutectic)	Lead-free	Budget, wave soldering
Sn42Bi58	42 Sn / 58 Bi	138 °C (eutectic)	Low-temp	Heat-sensitive parts, step soldering
In52Sn48	52 In / 48 Sn	118 °C (eutectic)	Low-temp	Ultra-low-temp, glass/ceramic
Sn10Pb88Ag2	10 Sn / 88 Pb / 2 Ag	~268–290 °C	High-temp	Die attach, CBGA, hot environments

How to Read the Chart: Solidus, Liquidus & the Pasty Range

Most solders don’t melt at a single temperature. They have a solidus — the highest temperature at which the alloy is fully solid — and a liquidus — the lowest temperature at which it’s fully liquid and will wet a pad. Between the two is the pasty range, where the solder is slushy and won’t flow. Sn60Pb40 has a narrow 5–7 °C pasty range, but a low-tin 40/60 alloy spans about 51 °C of mush. A eutectic alloy is the exception: its solidus and liquidus are identical, so it snaps from solid to liquid at one temperature. Sn63Pb37 (183 °C), Sn99.3Cu0.7 (227 °C), and Sn42Bi58 (138 °C) are all eutectic — and that instant freeze on cooling is exactly why eutectic alloys produce fewer disturbed joints than their non-eutectic cousins.

Soldering Temperature by Method: Hand, Reflow & Wave

The same alloy gets a different temperature depending on how you’re soldering it. Hand soldering uses a single hot tip; reflow uses a controlled oven profile that only touches peak for 30–60 seconds; wave soldering drags the board across a molten bath. These are working ranges — confirm against your alloy and paste datasheet.

Method	Leaded (Sn-Pb)	Lead-free (SAC)	Notes
Hand soldering (iron tip)	320–360 °C	350–380 °C	~100 °C above liquidus; never above 400 °C
Reflow peak	~235–245 °C	240–250 °C	20–50 °C above liquidus; 30–60 s at peak
Wave solder pot	250–270 °C	260–290 °C	Through-hole; molten bath temperature
Hot air rework	300–400 °C (air)	320–400 °C (air)	Air cools before reaching the joint

Within hand soldering, the right tip temperature also depends on the thermal mass of what you’re heating. A bare 0402 pad needs far less than a pad tied to a ground plane, and flex circuits lift pads if you run them hot.

Task / component	Leaded iron	Lead-free iron
Through-hole (0.5–1.0 mm holes)	320–350 °C	350–380 °C
SMD chip terminals	300–330 °C	320–360 °C
Fine pitch (< 0.5 mm)	280–310 °C	300–340 °C
Large ground plane	360–380 °C	380–420 °C
Flex circuit	~280–300 °C	280–310 °C

How to Set Soldering Temperature: Best Practices & Common Mistakes

A client once sent us a board specified only as ‘lead-free’ on the BOM — no alloy named. A previous contract manufacturer had built it with Sn99.3Cu0.7 instead of SAC305 to shave cost. The joints looked fine and passed functional test, but SnCu carries roughly 30% lower fatigue life than SAC305, and the boards began failing in 0–100 °C thermal cycling in the field. Naming the alloy explicitly would have prevented the whole thing. Most temperature problems are like that — avoidable with a few habits.

1. Set the iron about 100 °C above the alloy’s liquidus. That’s the thermal reserve that brings the joint to melting in 1–2 seconds. Setting it at the melting point guarantees cold joints.
2. Don’t chase heat with temperature. If solder isn’t flowing in 2–3 seconds, the problem is usually a worn or oxidized tip, not a low setting. Lead-free oxidizes tips four to five times faster than leaded, so cranking the dial just kills the tip quicker.
3. Stay under 400 °C and limit dwell to 1–2 seconds. Above that you risk lifted pads, delaminated LEDs, and boiled electrolytic capacitors. Use a fine tip and the low end of the range on small parts.
4. Preheat thick or copper-heavy boards. Bringing the board to around 100 °C with a preheat plate lets a normal iron temperature work on a heavy ground plane instead of forcing you to overheat the tip.
5. Name the exact alloy in the BOM — not just ‘lead-free.’ ‘Lead-free’ could be SAC305, SAC405, or SnCu, and they differ in temperature and fatigue life. Specify the alloy on the BOM and assembly drawing so nothing is left to assumption.
6. Watch lead contamination with bismuth solder. Sn42Bi58 forms a low-melting 96 °C phase with lead. If any lead is present — a HASL finish, a leaded component termination — a 138 °C low-temp joint can fail at normal operating temperature.
7. Verify the tip with a thermometer. Station displays drift, and cheap stations are only ±15 °C accurate at best. Check the actual tip temperature periodically and trust solder flow behavior over the number on the dial.

Frequently Asked Questions About Soldering Temperature

What temperature should I solder at?

For hand soldering, set the iron to roughly 320–360 °C for leaded solder and 350–380 °C for lead-free — about 100 °C above the alloy’s melting point. Drop to the lower end for small SMD parts and raise it for ground planes, but never exceed 400 °C.

What is the melting point of solder?

It depends on the alloy. Eutectic leaded solder (Sn63Pb37) melts at 183 °C, the most common lead-free alloy (SAC305) melts at 217–220 °C, tin-copper (SnCu) at 227 °C, and low-temperature tin-bismuth (Sn42Bi58) at just 138 °C. Indium alloys go lower still.

Why is soldering temperature higher than the melting point?

Because the iron has to heat the copper pad and component lead, not just the solder — and both start cold and pull heat away. Running the iron about 100 °C above the melting point gives it a thermal reserve so the joint reaches liquidus quickly without the tip dropping below the melt point.

What temperature does lead-free solder melt at?

The standard lead-free alloy SAC305 (tin-silver-copper) melts at 217–220 °C, about 35 °C higher than leaded solder. Tin-copper (Sn99.3Cu0.7) melts a bit higher at 227 °C. Lead-free needs a hotter iron and reflow peak, and it wets less easily than leaded solder.

Can you solder at too high a temperature?

Yes. Above roughly 400 °C you risk lifting pads, delaminating LEDs, vaporizing electrolytic-capacitor electrolyte, and warping the board. High temperatures also oxidize the iron tip rapidly — especially with lead-free solder — so the tip stops wetting and has to be replaced sooner.

What is the difference between solidus and liquidus?

Solidus is the highest temperature at which an alloy is completely solid; liquidus is the lowest temperature at which it’s completely liquid and able to wet a pad. Between them lies the pasty range, where the solder is slushy. Eutectic alloys have identical solidus and liquidus — one melting point.

What temperature is reflow soldering?

Reflow uses a profile, not a single setting, with the peak landing 20–50 °C above the alloy’s liquidus — about 235–245 °C for leaded and 240–250 °C for lead-free SAC305. The board only sits at peak for 30–60 seconds to form the joint without overheating components.

Is leaded or lead-free solder better?

It’s a trade-off. Leaded solder melts lower, wets better, and is more forgiving to hand-solder, but it’s banned for most commercial products under RoHS. Lead-free is required for sale in regulated markets and avoids lead toxicity, at the cost of higher temperatures and trickier soldering.

Get the Soldering Temperature Right for Your Build

Pick the alloy for your application, set the iron about 100 °C above its liquidus, keep the peak in range, and name the exact alloy on your BOM — get those right and the soldering temperature stops being a source of cold joints and field failures. If you’d rather hand it off, send your Gerber and BOM and we’ll select the alloy and run the right temperature profile on a J-STD-001 line as part of a DFM review.