With the flexible PCB production continues to increase and more than just the application and promotion of flexible PCB, PCB is now more common to say the inclusion of soft, rigid or flexible just say it is the layers of the PCB. Typically, the use made of soft PCB insulating substrate referred to as soft or flexible PCB, Rigid-flex PCB, said first compound of the flexible PCB. It is adapted to today's electronic products to high density and high reliability, small size, lightweight direction of development, but also to meet the strict economic requirements and competition in the market and technology needs.
In other countries, soft PCB in the early sixties has been widely used. China, then began in the sixties in the production and application. In recent years, as the global economic integration and open city to try to introduce technology to promote their use is growing constantly, some small and medium rigid PCB plant with soft targeting this opportunity to do a hard process, using existing equipment, tools for tooling and technology for improvement, transformation and adaptation to the production of soft flexible PCB PCB consumption growing needs. To further understand the PCB, flexible PCB technology here to make a study of the introduction.
I. Classification of the advantages and disadvantages of soft PCB
1. Classification of soft PCB
Flexible PCB is usually based on the structure of conductor layers and the following categories:
1.1 soft-sided PCB
Soft-sided PCB, only one layer of conductor, the surface can have a cover or not cover. Insulating base material used, with the application of the product varies. Insulation materials commonly used polyester, polyimide, PTFE, soft epoxy - glass cloth.
Soft-sided PCB can be further divided into the following four categories:
1) No cover side connection
Such soft wire graphics PCB insulating substrate, the conductor surface, no cover. Rigid single-sided PCB, as usual the same. These products are the most expensive one, often used in non-critical and have environmental applications. The interconnect is used for soldering, welding or bonding to achieve. It is commonly used in the early telephone.
2) single connected cover
Compared to the previous classes of such, only the surface of the wire according to customer requirements with a new layer coating. Required to cover the exposed pad, a simple region in the end is not covered. Precision may be required by the form of clearance hole. It is the most widely used single-sided flexible PCB, the most widely used in automotive instruments, electronic instrument widely used.
3) no cover-sided connection
Disk interface connecting such wires can be connected to the front and back. To do this, the pad insulating substrate at the hole to open a channel, the access holes in the insulating substrate of the desired location on the first punching, etching or other mechanical means made. It is used to install the element sides, the device and the need for soldering the occasion, access at the pad area without insulation substrate, such pad area is usually removed by chemical methods.
4) double-sided cover attached
Such differences with the former category is the surface layer of coating. However, there is access hole cover also allows the two sides can be terminated, and still maintain the cover. PCB is a kind of soft material and a layer of insulating layers made of metal conductors. Be used in devices need to cover each other and the surrounding insulation, and its also insulated from each other, at the end they need the positive and negative situations are connected.
1.2 soft-sided PCB
Soft-sided PCB, with two conductors. The application of these double-sided PCB and advantages of soft-sided flexible PCB with the same, the main advantage is to increase the wiring density per unit area. It may be there, and there are no holes, no cover is divided into: a no holes, no cover layer; b no holes, there are cover layer; c have holes, no cover layer ; d with through holes, a cover layer. No double-sided flexible PCB cover fewer applications.
1.3 The multi-layer flexible PCB
Multilayer PCB Flexible PCB, such as rigid as multi-layer, multi-layer laminate technology, can be made into multi-layer flexible PCB. The simplest multi-layer flexible PCB is covered on both sides in the single-sided PCB with two layers of copper shield and the formation of three flexible PCB. This three-tier flexible PCB in the electrical characteristics equivalent to coaxial cable or shielded wires. The most common multi-layer PCB structure is the four-story structure, soft, with holes to achieve the interconnection between layers, the middle layer is generally the power and ground planes.
The advantages of multi-layer FPC substrate film has excellent light and electrical properties, such as low dielectric constant. Substrate with a polyimide film layers made of soft PCB, epoxy glass cloth than the rigid multi-layerPCB board light weight of about 1 / 3, but it lost its single-sided, double-sided PCB excellent soft The flexible, most of these products are not required to be flexible in.
Multi-layer flexible PCB can be further divided into the following types: