Solder Alloys Compared - Which One Fits Your Job?
The solder alloy you choose sets the melting point, wetting behaviour and long-term reliability of every joint. This guide compares the common alloys SAC305, SN100C, SnCu and leaded SnPb against the key criteria and helps you pick the right one for your application.
View solder and solder wireWhich solder alloys are common today?
Since the RoHS directive, lead-free alloys dominate electronics manufacturing. The most widespread is SAC305 (96.5 % Sn, 3.0 % Ag, 0.5 % Cu) with a melting range of about 217 to 220 °C. Alongside it sit silver-free options such as SN100C (Sn with ~0.7 % Cu, nickel-microalloyed) and plain SnCu.
The classic SnPb (63 % Sn, 37 % Pb) is eutectic, melts at exactly 183 °C and remains the technical benchmark for wetting and process stability. It is still permitted in aerospace, medical and military work under exemptions.
- SAC305: the standard for lead-free reflow and wave soldering, good reliability.
- SN100C: silver-free, cheaper, ideal for wave and selective soldering.
- SnCu (Sn99.3Cu0.7): the simplest lead-free base, higher melting point.
- SnPb (Sn63Pb37): eutectic, best wetting, allowed only under exemption.
How do melting point and wetting differ?
The melting point drives the thermal profile and the stress on components. Lead-free alloys sit roughly 30 to 40 °C higher than SnPb, calling for tip temperatures around 350 to 380 °C and putting more load on your tools.
For wetting, SnPb stays the yardstick: it flows fast and forms bright, concave fillets. SAC305 wets well but looks duller and grainier. Silver-free alloys wet a little more slowly and benefit from a more active flux and higher preheat.
Which alloy is the most reliable?
Reliability depends on mechanical and thermal load. SAC305 has high creep strength and survives many temperature cycles, but it is more sensitive to shock and drop. For shock- and vibration-loaded assemblies, low-silver alloys such as SAC0307 are often the better choice.
- Thermal cycling: SAC305 proves itself under repeated temperature swings.
- Mechanical shock: low-silver alloys (SAC0307) reduce brittle fracture.
- Wave soldering: SN100C causes less copper dissolution at the wave.
- Repair and hand soldering: SnPb stays the most forgiving where allowed.
Frequently asked questions
What exactly is SAC305?
SAC305 is a lead-free alloy of 96.5 % tin, 3.0 % silver and 0.5 % copper. It melts at about 217 to 220 °C and is the standard for lead-free reflow and wave soldering.
Why does lead-free solder wet worse than SnPb?
Lead-free alloys have higher surface tension and a higher melting point. With a more active flux, higher preheat and the correct tip temperature, wetting becomes practically equivalent.
Is SnPb still allowed?
In general electronics SnPb is banned by RoHS. For aerospace, medical, military and some exemptions it remains legal and is still used there for its process safety.
When is SN100C worth it over SAC305?
SN100C is silver-free, so it is cheaper and more price-stable. It shines in wave and selective soldering thanks to low copper dissolution and a calm wave, while SAC305 leads on reflow assemblies with high thermal cycling.
Looking for the right solder alloy?
We supply solder wire and paste in SAC305, SN100C, SnCu and leaded grades - with the matching flux core and a datasheet per IPC J-STD-006.
Standard-compliant
Alloys per IPC J-STD-006 with datasheet.
For every profile
Lead-free and leaded for reflow, wave and hand.
Best wetting
A matched flux core for every alloy.
Expert advice
Our specialists help you choose the alloy.