Preheating for soldering and rework: why and how do I preheat the board?
Preheating brings the whole board evenly to a moderate temperature before the iron or hot air is applied. This lowers the temperature gradient, avoids thermal shock and helps large ground planes and multilayer boards reach soldering temperature. It is especially important for lead-free solder and BGA rework.
View preheatersWhy should I preheat the board?
Preheating brings the whole assembly evenly to a moderate temperature before the actual soldering heat is applied. This reduces the temperature gradient between the joint and the cold surroundings and so avoids thermal shock, which can damage components, pads and the board itself.
What preheater types are there?
Two designs are mainly used for preheating: infrared (IR) preheaters radiate the heat onto the board from below, hot plates transfer it through direct contact. Both bring the assembly to a moderate level that lies below the reflow peak.
| Preheater type | Principle | Use |
|---|---|---|
| Infrared (IR) | radiant heat from below onto the board | large area, no contact, also populated undersides |
| Hot plate | heat transfer through direct contact | small to medium boards with a flat underside |
| Hot air preheat | preheated air stream from below | flexible, often combined in rework stations |
In practice the preheater is combined with the tool for the actual joint: the preheater holds the board at base temperature while the iron or hot air adds the final heat locally. More on this under Hot air rework.
How do I preheat correctly?
The preheat temperature is typically 100 to 150 °C, well below the peak temperature of the reflow. The board is brought evenly to this level and held there, then the iron or hot air adds the remaining heat up to soldering temperature.
- Preheat to 100‑150 °C, below the reflow peak - the assembly should be warm, not soldered.
- Large ground planes and multilayer boards benefit most because they draw away a lot of heat.
- Lead-free solders and BGA rework need preheating against thermal shock and for even melting.
- Combine preheating with hot air: base temperature from below, local soldering heat from above.
Why lead-free solders need higher temperatures and thus more preheating is explained under Lead-free soldering.
Frequently asked questions
What temperature do I preheat to?
Typically 100 to 150 °C, well below the peak temperature of the reflow. The board should be evenly warm so the iron or hot air only has to add the remaining heat up to soldering temperature.
When is preheating especially important?
For large ground planes, multilayer boards, lead-free solder and BGA rework. There a lot of heat is drawn away and the higher soldering temperatures carry a greater risk of thermal shock and delamination.
Infrared or hot plate - which is better?
Infrared heats without contact and over a large area, even with populated undersides. Hot plates transfer the heat through direct contact and suit small to medium boards with a flat underside. Both are combined with an iron or hot air.
Preheaters for gentle soldering and rework
IR preheaters, hot plates and rework stations - ESD-safe and from a single source.
ESD-safe
Preheaters for the ESD workstation.
Reviewed
Content reviewed by soldering specialists.
Accessories
Preheaters, nozzles and flux in stock.
Expert advice
Personal advice on rework.