Choosing solder bars for wave soldering
Solder bars for wave soldering machines account for most of the consumables cost in the through-hole soldering process. Low-dross SAC and SnCu alloys help reduce solder loss, stabilize solder pot composition and limit defects such as bridging and insufficient joints.
This article compares common alloys and suggests ways to manage the solder pot to extend the interval between solder replacements.
Common alloys for lead-free wave soldering
Since the RoHS directive came into widespread use, most plants have switched to lead-free alloys. Each alloy has a different melting point, wettability and cost.
| Alloy | Melting point | Recommended pot temperature | Characteristics |
|---|---|---|---|
| SAC305 | 217–220°C | 255–265°C | Good wetting, durable joints, high cost |
| SAC0307 | 217–227°C | 260–270°C | Low silver, balanced cost |
| SnCu0.7 | 227°C | 265–275°C | Low cost, copper must be controlled |
| SnCuNi with micro-additives | 227°C | 260–270°C | Low dross, bright joint surface |
Why dross increases costs
The surface of the solder wave is constantly exposed to air, and the solder oxidizes to form a layer of dross. A single wave soldering machine can generate several kilograms of dross per shift. High-quality solder bars are thoroughly refined, enriched with anti-oxidation micro-additives and have low impurity content, which significantly reduces dross.
Measures to reduce dross at the machine
- Use nitrogen blanketing over the wave surface if the machine supports it.
- Keep the wave height stable and avoid an overly high wave that causes turbulence.
- Skim dross on a fixed schedule and do not let the dross layer build up.
- Turn off the wave pump during long line stoppages.
Controlling solder pot composition
During soldering, copper from component leads and pads gradually dissolves into the pot. When copper content exceeds about 1%, solder viscosity increases, causing bridging and grainy joints. Solder pot samples should be analyzed periodically every one to three months, and copper-free or low-copper solder bars should be added to bring the content back to the standard level.
Dross recovery
Skimmed dross still contains a large amount of tin metal. Instead of discarding it, plants can collect it separately by alloy type for recycling or exchange it for new solder bars, both reducing costs and meeting hazardous waste management requirements. Do not mix dross from leaded and lead-free alloys in the same container.
AMS supplies SAC and SnCu solder bars and offers solder pot sampling and analysis support for customers in industrial parks across northern Vietnam. Contact AMS Vietnam for advice on the right alloy for your wave soldering machine.
