Manufacturing Flexible Circuits
The first step in flexible circuit fabrication is defining the circuit’s schematic and layout using PCB design software. This software can determine if there are any impedance or power delivery issues that may prevent the circuit from functioning properly and recommend changes to avoid these problems. The next step is to choose materials for the flexible circuits. A popular choice is polyimide, also known as Kapton, due to its superior temperature and electrical properties. Polyimide is not the only material used, however; polyester and PTFE are common alternatives.
Once the material is selected, the next step is to prepare it for the copper foil traces that will form the conductive components of the circuit. This preparation includes cleaning the substrate material and ensuring it is free of contaminants. The substrate can then be etched to create the desired pattern of conductive traces. This can be done through either a subtractive process, in which the solid areas of metal are removed to form the traces, or an additive process, in which the copper is deposited on the bare dielectric layer as needed.
Once the conductive tracks are formed, they are covered with a protective coating. This is often done with a gold or soft gold covering to prevent oxidation and corrosion during the assembly process. It can also be used to protect the tracks from chemicals and solvents that might damage them. Rigid stiffeners are sometimes added to the rigid sections to help support them during bending.
What Fabrication Techniques Are Used in Manufacturing Flexible Circuits?
In order to make the final product, the etched and plated flex circuit must be laminated into a panel with rigid sections of the same material. The layers of the flex circuit must then be aligned and registered with the layers of the rigid section to ensure accurate interconnections. The entire panel is then laminated together under controlled heat and pressure conditions to create a single, unified circuit.
Once the flex circuit is finished, it must be tested and verified to ensure that all of the components are connected correctly and that the circuit works as intended. Various test procedures can be performed to check for short and open circuits, signal strength and impedance matching, and thermal management considerations. A specialized automated test equipment (ATE) is often utilized to perform these tests, which can save significant time and money in the long run by eliminating manual testing steps that could lead to error.
Once all of the testing has been completed, the flex circuit is ready for assembly. The conductive pads are exposed by removing the cover lay, and component placement is performed using surface mount technology. The solder paste is applied to the conductive pads, and the assembled parts are placed on the board using a pick-and-place machine. Once the components are positioned on the board, they are heated, which causes the solder to adhere to the conductive pads and hold them in place.
