Script – Reflow Soldering
During the Pick & Place operation, components are glued to the board by the solder paste.
A reliable connection is made during the reflow soldering process. The solder paste melts during this process and cools down again to create a good solder joint.
We use Ersa Hotflow ovens. These are long convection ovens with many heating zones that together create a soldering cycle.
Each heating zone of the oven has a regulated temperature set to the solder profiles for the assembly process.
Multiple segments help to get an optimised heat transfer and minimum temperature differences between different points on the PCBA.
Solder profiles need to be optimised for each individual assembly job.
The solder profile is influenced by the number of layers in the PCB, the copper distribution on the board, the number and size of components. Overheating components can damage them.
Reflow solder profiles usually have four stages, preheat, thermal soak, reflow and cooling.
The aim of the preheating stage is to accumulate heat smoothly in the board and the components.
The Temperature gradient is important because too quick changes of temperature can cause damage to components.
During the thermal soak the flux is activated to reduce oxidation of pads and leads of components and improve wetting.
In the third section the solder paste is melted and the process reaches its maximum temperature.
This maximum temperature must remain under the maximum allowed temperature of the components.
The component that has the lowest maximum temperature allowance will define the maximum temperature.
The processed board is cooling down in the last zones of the reflow oven, the solder alloy solidifies and makes the solder joints.
Reflow profiles or processes that are not well optimised can lead to poor or non-wetting, damaged components or cold soldering.
After soldering the boards are inspected in detail.