FlexiblePCBsupplierchina learned that，almost all the FPC manufacturing processes so far have been processed by the subtractive method (etching method).Usually, a copper clad board is used as a starting material, a resist layer is formed by photolithography, and the unnecessary part of the copper surface is etched and removed to form a circuit conductor.Due to problems such as undercutting, the etching method has limitations in the processing of fine circuits.

Based on the processing difficulties of the subtractive method or the difficulty in maintaining high-yield micro-circuits, the semi-additive method is considered to be an effective method, and various semi-additive methods have been proposed.Examples of micro-circuit processing using the semi-additive method.The semi-additive process uses polyimide film as a starting material.First, a liquid polyimide resin is cast (coated) on a suitable carrier to form a polyimide film.

Semi-additive method FPC

Next, a sputtering method is used to form a seeding layer on the polyimide base film, and then a resist pattern of the reverse pattern of the circuit is formed on the seeding layer by photolithography, which is called a plating resistant layer.The blank part is electroplated to form a conductor circuit.Then remove the resist layer and unnecessary seeding layer to form the first layer of circuits.Coating photosensitive polyimide resin on the first layer of circuit, using photolithography to form holes, protective layer or insulating layer for the second layer of circuit layer, and then sputtering on it to form a seeding layer, as the second The base conductive layer of a two-layer circuit.Repeat the above process to form a multilayer circuit.

PCBmanufacturer learned that，using this semi-additive method, ultra-fine circuits with a pitch of 5um and a via hole of 10um can be processed.The key to making ultra-fine circuits using the semi-additive method is the performance of the photosensitive polyimide resin used as the insulating layer.