SAC305, SAC0307 or 99SnCuNiGe (SN100C equivalent): which lead-free alloy for wave and selective soldering
In bath processes, wave and selective soldering, the solder pot holds tens or hundreds of kilos of alloy and must be topped up continuously: the choice of alloy weighs on costs more than in any other process. This guide compares the three most widely used lead-free alloys and explains when each one is the right choice.
Dickmann Srl · updated
The three alloys compared
The differences are qualitative and refer to the alloys in general; results on the line depend on the machine, boards, flux and bath management.
| Characteristic | SAC305 | SAC0307 | 99SnCuNiGe (SN100C equiv.) |
|---|---|---|---|
| Composition | Sn96.5/Ag3/Cu0.5 | Sn99/Ag0.3/Cu0.7 | Sn/Cu0.7/Ni0.05/Ge |
| Silver | 3 % | 0.3 % | 0 % |
| Melting | 217–220 °C | 217–227 °C | 227 °C (eutectic) |
| Alloy cost | High | Medium-low | Low |
| Dross formation | Medium | Medium | Reduced |
| Copper erosion | Higher | Higher | Reduced |
| Joint appearance | Matte | Matte | Bright |
| Typical use in baths | When the specification calls for it | Wave, selective, HASL at lower cost | Wave, selective, silver-free HASL |
When to choose SAC305
SAC305 is the standard of lead-free electronics and the reference alloy for SMT reflow. In wave and selective baths it is used mainly when the customer prescribes it in the specification, or when the same alloy is wanted in all the board's processes. It contains 3 % silver, so it is the most expensive of the three.
When to choose SAC0307
SAC0307 contains one tenth of the silver of SAC305 and costs less, while maintaining good wettability in bath processes. In return it has a wider melting range (217–227 °C), requires a few degrees more in the solder pot and has somewhat lower mechanical strength and thermal fatigue resistance: it is suitable for THT components and non-critical boards produced in high volumes.
When to choose 99SnCuNiGe
99SnCuNiGe is the Dickmann alloy equivalent to SN100C®: tin-copper with small additions of nickel and germanium, without silver. Nickel reduces copper erosion of pads and leads and gives bright joints; germanium limits oxidation of the bath and therefore dross. It is eutectic at 227 °C: in baths it runs a few degrees above SAC305.
SN100C® is a registered trademark of Nihon Superior Co., Ltd. 99SnCuNiGe is a Dickmann alloy with an equivalent composition.
Changing alloy in the solder pot
Alloys must not be mixed: topping up a SAC305 bath with 99SnCuNiGe changes its composition and melting range. To change alloy, the solder pot must be emptied or diluted and the new bath checked by analysis. Dickmann analyses customers' baths on a sample of at least 250 grams: see our analysis services. The alloys are available as wave soldering bars and as solid wire for selective soldering.