Soldering in Flexible Printed Circuit Board Assembly

Flexible Printed Circuit Board Assembly

Using soldering to connect components is an essential part of Flexible printed circuit board assembly. The same principles apply as when working with rigid PCBs, but there are additional factors to consider such as material handling and the flexibility of flex circuits.

Soldering is an incredibly versatile technique that can be used for almost any application, from joining metal parts to connecting electronic devices. The process involves molten solder being applied to the surfaces of two or more pieces of metal, forming a bond that carries current and protects the joints from corrosion. When properly executed, soldering is a cost-effective way to assemble PCBs and other electronic components.

Flex circuits can be connected with soldering, conductive epoxy adhesives, or anisotropic glues. The method chosen will depend on the materials of the unit to which the flexible printed circuit board is being attached, as well as the size and pitch of the contact pads on the flex. If the flex circuit will be subjected to repetitive bending, it is also necessary to use an anisotropic adhesive film that can withstand solder reflow temperatures and the stress of repeated bending.

Soldering in Flexible Printed Circuit Board Assembly

A flex PCB will require different processing conditions than a rigid one, due to the lack of fixed positioning. A positioning template with exposed positioning pins will be used to affix the flex circuit in place on the carrier board. Once the PCB has been positioned, it will be preheated and subjected to thermal profiling to ensure that the entire surface is adequately heated. This will prevent blistering and delamination of the flex circuit, as well as reduce the risk of soldering problems.

The temperature profiles used for reflowing rigid PCBs will usually be higher than a flex circuit can tolerate, and too much heat can cause damage to the substrate and components. It is therefore important to use proper fixturing, preheating and tooling to avoid damage during the reflow process. This can include mechanical clips or other holding methods, as well as a clean, well-lit workspace with plenty of space for inspection tools like microscopes and magnifiers.

When soldering a flex circuit, it is also vital to make sure that the soldering iron is set to the correct temperature. A low-temperature iron will not provide enough heat to melt the solder, and a high-temperature iron can cause oxidation of the copper pads. To get the best results, the optimum iron temperature is 315-370 degrees Celsius.

In addition to the right iron, it is important to use a flux pen during flex PCB soldering. Flux helps to clean the copper surfaces and enables a more effective transfer of molten solder. It also averts oxidation of the copper after heating, and it lowers the surface tension of the weld to help molten solder flow freely.

The last step in a flex PCB soldering operation is to clean off any residual flux. This is crucial, as residue could contaminate the finished product and prevent the joints from performing as expected. Using a high-quality no-clean flux will minimize the amount of cleanup required after the assembly is complete.