Putting through hole components through an SMT process
Schurter in Switzerland has developed a technique to allow large components that have had to use a through-hole solder process on a printed circuit board to instead use the same surface mount process as the rest of the board.
Large components such as capacitors and fuse holders traditionally have to use through hole technology (THT) to get the necessary mechanical support. However THT requires a separate soldering process to the surface mount technology process (SMT) to avoid putting more stress on the board, which then means two separate runs through an oven.
The double soldering process poses an additional risk from its practical implementation. The THT components are usually inserted after the reflow soldering process for SMT and manual placement of the components for the second soldering cycle in the wave bath involves a massively increased risk of incorrect placement.
To avoid these problems, there are several approaches. The simplest is to prevent them from occurring altogether. In other words, use only SMT or only THT components, then a single soldering process is always sufficient.
However, this is often not possible in practice due to the technical properties that the end product to be soldered should have.
The Through Hole Reflow (THR) developed by Schurter uses components that are specially designed for automated assembly and high thermal stress in the reflow oven.
During the assembly process, a paste is first printed in the vias for the THT pins, and then the component is pushed through the solder paste.
As the paste melts in the reflow oven, the liquid solder retracts into the vias due to wetting and capillary forces, forming a clean solder joint.
The company used THR for circuit protection on a PCB that can be automatically assembled Installing a fuse holder on the SMT board, which can also be soldered right away in the reflow process.
Schurter’s glow wire resistant, OGN open fuse holder is designed for 5×20 fuses of various rated currents and tripping characteristics. It can also be easily converted into a closed fuse holder by means of a cover.
The company has now developed a THR version that is fully compatible with the THT version and enables one soldering process.