Introduction to the Process of Connecting FPC (Flexible Printed Circuit) to Rigid PCB (Printed Circuit Board)

This article focuses solely on the soldering process between FPC and PCB. There are various methods for soldering flexible circuits, but overall, the main techniques can be summarized as follows:

1. Manual Soldering

Manual soldering of flexible circuits to PCBs is the most cost-effective method among all FPC soldering processes. In some cases, no fixtures are needed at all. However, it is also the least reliable in terms of soldering quality, as manual soldering often results in defects such as cold joints, weak joints, false soldering, and bridging short circuits.

To improve soldering yield, it is recommended to use a weight to press down on the flexible board during the soldering process and only remove it after completion. Additionally, it is advisable to include plated through holes (PTH) in the FPC’s gold fingers. This not only helps visually confirm soldering quality but also reduces the risk of solder bridging.

Manual soldering is not recommended for mass production.

2. HotBar Soldering

The principle of HotBar soldering is based on using a pulse current to flow through high-resistance metal materials such as molybdenum or titanium, generating Joule heat. This heat is then transferred to a thermode (heater tip), which melts the solder paste pre-applied to the PCB and connects it to the FPC.

HotBar soldering requires a HotBar machine and a carrier to hold the FPC in position on the PCB. As long as the FPC and PCB are well designed, this method can support mass production with stable yield rates.

3. Laser Soldering

Laser soldering uses laser energy converted into heat to achieve the soldering process. It is typically used when the laser can be directly targeted at the soldering area to provide localized heating.