Below is the construction for a double layer flex circuit.
Double layer signifies that there are two layers of copper circuitry. In most cases, the two layers of copper are electrically connected by drilling small holes through the copper circuits and the separating dielectric, then plating the holes with copper to make a connection between them.
The slide show presents the artwork required for each layer of the circuit build.
The application for this double layer flex circuit is a keypad used on a hand held device. There are components assembled on the flex: a ZIF (zero insertion force) connector interface and LEDs (light emitting diodes).
Top Stiffener - Stiffeners are created to give flex circuits rigid areas where required. Stiffeners in most instances are made of printed circuit board, but can also be metal, ceramic and even additional layers of polyimide.
Top Silkscreen - The images will be printed onto the top of the finished circuit with indelible ink. This assists with component placement.
Top Coverlay - This is the top polyimide cover that adheres to the first layer of etched copper.
Layer 1 - This is the first layer of copper that PFC will etch.
Layer 2 - This is the second layer of copper to be etched. There will be a layer of dielectric material between the layers of copper.
Bottom Coverlay - The bottom coverlay is the polyimide dielectric material that covers the second layer of copper. The circuit is now encapsulated on top and bottom with polyimide.
Drill File - The drill file designates the location of the holes to be drilled in the circuit. The circuit layers (copper and coverlays) will be pressed together, drilled, then run through plating to put copper in the holes and make connections from the top copper layer to the bottom.
Outline - PFC’s flex are manufactured in 18”x12” or 18”x24” panels. We fit as many parts as possible on a panel then use a punch/die to cut the parts from the panel. This is the artwork for the tooling die to cut the part from the panel.
Completed Circuit - There are additional steps to making a circuit, such as plating, etching, pressing, electrical test, inspection and assembling that are not shown in the artwork slides.