Single-layer FPC, double-layer FPC and multi-layer FPC in PCB manufacturing
Differences between single-layer FPC, double-layer FPC and multi-layer FPC
Multi-layer FPC
Multi-layer FPC is to stack three or more layers of single-sided or double-sided flexible circuits together, and make metallized holes through drilling, electroplating and other processes to achieve conductive paths between different layers, so no complex welding process is required. Multi-layer circuits have great functional differences in performance such as higher reliability, better thermal conductivity, and more convenient PCB assembly.
Advantages:
The base film is light in weight and has excellent electrical properties, such as low dielectric constant.
Multi-layer flexible PCB boards made of polyimide film are about 1/3 lighter than rigid epoxy glass cloth multi-layer PCB boards, but they lose the excellent flexibility of single-sided and double-sided flexible PCBs, and most of these applications do not require flexibility. Multi-layer FPC includes:
Flexible insulating substrate
This PCB is made on a flexible insulating substrate, and its finished product is specified as flexible. This structure usually bonds the two ends of many single-sided or double-sided microstrip flexible PCBs together, but does not bond the center part together, so it has high flexibility. A thin and suitable coating can be used on the conductor layer to provide high flexibility, such as polyimide, which can replace the thicker laminated cover layer.
Soft insulating substrate
Since the finished product can be flexed, this type of multi-layer FPC uses soft insulating materials such as polyimide film, which is pressed into a multi-layer board, and loses its inherent flexibility after lamination.
Double-sided FPC
The insulating base film of the double-sided FPC has etched conductive patterns on both sides, which increases the wiring density per unit area. The metallized holes connect the patterns on both sides of the insulating material to form a conductive path to meet the design and flexible applications. The cover film can well protect the single and double-sided wires and indicate the location of the components. Metallized holes and coatings can be selected according to requirements.
Single-layer FPC
FPC is a layer of chemically etched conductive patterns, and the conductive pattern layer on the surface of the flexible insulating substrate is rolled copper foil. Insulating substrates include polyimide, polyethylene terephthalate, aramid fiber ester and polyvinyl chloride, etc. More subdivisions include:
Single-sided connection with covering layer
Compared with single-sided connection without covering layer, the conductor surface has an extra covering layer, which is widely used in single-sided flexible PCBs, such as automotive instruments, electronic instruments, etc.
Single-sided connection without covering layer
The conductor pattern is on the insulating substrate, and there is no covering layer on the surface of the conductor. Its interconnection is achieved by soldering, fusion welding or pressure welding.
Double-sided connection with covering layer
The surface has a covering layer and access holes, which allows it to be terminated on both sides while retaining the covering layer. It consists of two layers of insulating material and a layer of metal conductor.
Double-sided connection without covering layer
The interface of the connecting pad is on the front and back sides of the conductor, and a hole is opened on the insulating substrate at the pad. It can be made at the required position of the insulating substrate by punching, etching or other mechanical methods.
Flexible printed circuit (FPC) is a high-reliability, excellent flexible printed circuit board made of polyimide or polyester film, with the advantages of high wiring density, light weight, thin thickness, and good bending performance.
FPC is divided into FPC single board, FPC double-sided board, FPC multi-layer board, etc. according to the number of layers. FPC single board is a relatively simple FPC flexible circuit board in the FPC flexible circuit board.
Single-sided FPC flexible circuit board has only one layer of conductive pattern formed by chemical etching, that is, rolled copper foil material. The insulating substrate can be polyimide, polyethylene terephthalate, aramid fiber ester, polyvinyl chloride and other materials, including:
Single-sided connection without covering layer
Single-sided connection with covering layer
Double-sided connection without covering layer
Double-sided connection with covering layer
Double-sided FPC flexible circuit board is made of conductive patterns by etching on both sides of the insulating base film, which increases the wiring density per unit area.
Metallized holes connect the patterns on both sides of the insulating material to form a conductive path to meet the design and flexibility. The cover film can protect single-sided and double-sided wires and indicate the location of components.
Multilayer FPC flexible circuit boards are three or more layers of single-sided or double-sided flexible circuits stacked together, and metallized holes are formed by drilling, electroplating, etc. to form conductive paths between different layers.
Multilayer FPC circuit boards have higher reliability, better thermal conductivity and more convenient assembly performance.