Electronic products universally rely on PCBs, making PCB market trends a key indicator of the electronics industry. As high-end, compact devices like mobile phones, laptops, and PDAs evolve, the demand for flexible PCBs (FPCs) continues to rise. PCB manufacturers are hastening the development of thinner, lighter, and denser FPCs. Let’s explore the various types of FPCs.

1. Single-layer FPC

This type features a single layer of chemically etched conductive patterns, with the conductive layer situated on the surface of a flexible insulating substrate made from rolled copper foil. The insulating substrate can consist of polyimide, polyethylene terephthalate, aramid cellulose ester, or polyvinyl chloride. Single-layer FPCs can be categorized into the following four sub-types:

1. Single-sided connection without covering


1. The wire pattern is situated on the insulating substrate, with no covering layer over the wire surface. Interconnection is achieved through soldering, welding, or pressure welding, a method commonly used in early telephone systems.

2. Single-sided connection with a covering layer

This type features an additional covering layer over the wire surface. The pads must remain exposed when applying the cover, although the end areas can be left uncovered. This is the most widely utilized single-sided flexible PCB, often found in automotive and electronic instruments.

3. Double-sided connection without a covering layer

The connection pads can interface on both the front and back of the wire. A via hole is created in the insulating substrate at the pad, which can be punched, etched, or formed using other mechanical methods at the desired location.

4. Double-sided connection with a covering layer

Unlike the previous type, this design includes a covering layer on the surface, equipped with via holes that allow terminations on both sides while maintaining the cover. It consists of two layers of insulating material and one layer of metal conductors.

Two, double-sided FPC

The double-sided FPC features conductive patterns etched on both sides of the insulating base film, enhancing wiring density per unit area. Metallized holes connect the patterns on both sides of the insulating material, creating conductive paths that support flexibility in design and use. The cover film safeguards both single and double-sided wires and marks component placement. Metallized holes and cover layers are optional, leading to fewer applications for this FPC type.

Three, multi-layer FPC

Multi-layer FPC consists of laminating three or more layers of single-sided or double-sided flexible circuits, creating metallized holes through drilling and electroplating to form conductive paths between layers. This eliminates the need for complex welding processes. Multilayer circuits offer significant advantages, including enhanced reliability, superior thermal conductivity, and improved assembly efficiency.

The benefits include lightweight base film and excellent electrical properties, such as low dielectric constants. Multi-layer flexible PCBs made from polyimide film are approximately one-third lighter than rigid epoxy glass cloth multi-layer PCBs, though they sacrifice some of the flexibility inherent in single-sided and double-sided designs. Most of these products do not require flexibility. Multi-layer FPC can be further categorized as follows:

1. Finished flexible insulating substrate

This type is produced on a flexible insulating substrate and is specified to remain flexible. The structure typically bonds the two-sided ends of multiple single-sided or double-sided microstrip flexible PCBs together while leaving the central sections unbonded, thus ensuring high flexibility. A thin, suitable coating, such as polyimide, is applied to the wire layer instead of a thicker laminated cover layer to maintain flexibility.

2. Finished soft insulating base material

This type is manufactured on a flexible insulating substrate and is designed to be flexible. Made from flexible insulating materials like polyimide film, this multilayer FPC is laminated to create a board that may lose some inherent flexibility after lamination.