Soldering

Wave or reflow soldering is used for the fully-automatic or semi-automatic soldering of components to circuit boards and flat modules.

In wave soldering, after the circuit board has been assembled, it is heated and then passed over a solder wave. In this process, hot fluid solder is pumped through a gap (chip and delta wave) or, for example, through holes in a perforated plate (Wörthmann wave). The component’s solder pins take up the solder, which results in a perfect solder connection after the solder has cooled.

In reflow soldering, soldering paste is applied under pressure to the circuit board. As the applied solder has adhesive properties, the circuit board can be assembled without any further fixation, and can then pass through the furnace. After a pre-heating phase, the solder is heated to fusion temperature during the soldering phase. At this temperature, the solder becomes liquid, and this creates a bond between the component and circuit board. The result is a fault-free solder connection after the solder has cooled.

The soldering process consists of the following four main phases:

1. Preparation
In the wave soldering process, first the components are mounted on the circuit board. In reflow soldering, by contrast, first the soldering paste is applied, and then the components are mounted.

2. Preheating
During this phase, the assembled circuit boards are brought to a preheat temperature – there are different processes for this purpose. The preheating method prevents deformation of the circuit board or its components and other damage.

3. Soldering
In wave soldering, the preheated circuit board passes over a solder wave. In reflow soldering, the entire circuit board is heated to the soldering temperature. The soldering time must be carefully selected to ensure that there is no damage to the circuit board or its heat-sensitive components.

4. Cooling
The circuit board components should be cooled under supervision immediately after soldering. This minimises thermal stress on the circuit board and its components.

In download area there are examples of soldering temperature profiles for various soldering processes used with through-hole products, based on EN 61760-1 for SMD products. The actual soldering process depends on various factors, including PCB design, solder paste used, number, type and size of the components used. This means that the profiles illustrated can only be seen as recommendations. It is not possible to make generally binding statements about the various processes, PCBs and components. Any decision about the profile which ensures your best soldering result must be taken on a case-by-case basis. The aim is to carry out work at the lower maximum load for the components used, so in general the maximum temperatures used are lower than those shown in the soldering profiles.