Flexible printed circuit board introduction

Flexible printed circuit board introduction

Flexible Printed Circuit is referred to as FPC for a highly reliability and excellent deflection printing circuit board made of polytide or polyester film. It has the characteristics of high wiring density, light weight, thin thickness, and good bending.

Product introduction editor

Flexible circuit board (Flexible Printed Circuit, FPC), also known as soft circuit board and deflection circuit board, is very popular with excellent characteristics such as light quality, thin thickness, and free bending folding ... It mainly relies on artificial visual inspection, with high cost and low efficiency. With the rapid development of the electronics industry, the design of circuit board design has become more and more high -precision and high density. Traditional artificial testing methods can no longer meet production needs. FPC defect automation testing has become an inevitable trend of industrial development. [1]

Flexible circuit (FPC) is a technology developed by the United States to develop aerospace rocket technology in the 1970s. It is a high reliability, excellent deflection made by polycatis film or polytamine as a substrate material. The printing circuit is embedded in the circuit design on the bending light and thin plastic sheet to make a large amount of precision components in a narrow and limited space, thereby forming a bending deflection circuit. This kind of circuit can be bent at will, light and light weight, small volume, good heat dissipation, easy installation, breaking through traditional interconnect technology. In the structure of the flexible circuit, the material formed is an insulating film, conductor and adhesive.

Edit material editing

1. Insulation film

The insulation film forms the basic layer of the circuit, and the adhesive bonded the copper foil to the insulating layer. In multi -layer design, it is bonded with the inner layer. They are also used as protective coverage to separate circuits from dust and humidity, and can reduce the stress during the deflection, and copper foil forms a conductive layer.

In some flexible circuits, rigid components formed by aluminum or stainless steel are used. They can provide the stability of the size, providing physical support for the resettlement of components and wires, and release of stress. Adhesives bond the rigid components and flexible circuits together. In addition, there is also a material that is sometimes used in a flexible circuit. It is a bonding layer. It is formed formed by coating on both sides of the insulating film. The bonding layer provides environmental protection and electronic insulation functions, and can eliminate a layer of film, as well as multi -layer capabilities with less bonding layer.

There are many types of insulating film materials, but the most commonly used is polyimide and polyester materials. Nearly 80%of all flexible circuit manufacturers in the United States use polypelide film materials, and about 20%of the polyester film materials are used. Polybamine material has non -flammable, geometric size is stable, has a high resistance strength, and has the ability to withstand welding temperature. Polyester, also known as polyethylnetephthalate for short ), Its physical properties are similar to polyamide, have a lower dielectric constant, and the absorption of humidity is small, but it is not resistant to high temperature. The melting point of polyester is 250 ° C, and the glass conversion temperature (TG) is 80 ° C. This limits the use of them in applications that require a large number of end welding. In low temperature applications, they are rigid. Nevertheless, they are suitable for products such as calls such as telephones and other products that are not exposed in harsh environments. Polybamine insulation film is usually combined with polylide or acrylic adhesion. Polyester insulation material is generally combined with polyester adhesion. The advantages of combining the same characteristics of materials can have size stability after dry welding, or after multiple layer pressure circulation operations. Other important features in the adhesive are lower dielectric constants, higher insulation resistance values, high glass conversion temperature and low moisture absorption rate.

2. conductor

Copper foil is suitable for use in flexible circuits. It can use Electrogeposite short abbreviations: ED) or plating. The surface of the copper foil with electricity has shiny, while the surface of the processed on the other side is dull and lustrous. It is a soft material that can be made into many thickness and widths. The ectopic side of the ED copper foil is often improved after special treatment. Forging copper foil has the characteristics of hard smoothness in addition to being flexible, and it is suitable for applications in the occasion that requires dynamic deflection.

3. Adhesive

In addition to bonding the insulating film to the conductive material, the adhesive can also be used as a coverage layer as protective coating and coverage. The main difference between the two lies in the application method used. The coverage layer bonding and covering the insulated film is to form a circuit with a layer structure. The screen printing technology used in the coating of the adhesive. Not all overlapping layers contain adhesives. The overlapping layer without adhesives forms thinner circuits and greater softness. It has a better thermal conductivity compared to the stack structure based on adhesives. Because the thin structure characteristics of the flexible circuit of the non -adhesive interoperability and the thermal resistance of the adhesive is eliminated, it improves the thermal conductivity. Essence

Preparation Edit

During the production process, the problem of being scrapped and replenished in order to prevent too low or reduce the problem of excessive rates of drilling, pressure delay, and cutting in order to prevent too much short circuit. The best effect of the best effect is particularly important before giving birth.

Pre -treatment of pre -treatment, there are three aspects that need to be dealt with. These three aspects are completed by engineers. The first is the FPC board engineering evaluation, mainly to evaluate whether the customer’s FPC board can produce, whether the company's production capacity can meet the customer's board requirements and unit costs. The supply of raw materials, in the end, the engineer processes the engineering files of the customer's CAD structure, the Gerber line data, etc. to suitable The production department and various departments such as cultural control and procurement have entered the conventional production process.

Production process editing

Dual -panel system

Open → Drilling → PTH → Electroplating → Pre -processing → Dry Film → Pickup → Exposure → Graph Electroplating → Dalf Meeting → Putting Dry Film → Displaying Disposal → Etancular → During Mask → Surface Treatment → Paste the cover film → suppress → curing → nickel gold → printing characters → cutting → electrical test → final inspection → packaging → shipment

One -scale

Open → Drilling → Patching dry film → Division → Exposure → Evidence → Decoration → Surface treatment → Patch covering film → curing → surface treatment → sinking gold → printing character → electrical test → rushing → rushing Cut → final inspection → packaging → shipment

Characteristic editing

1. Short: The assembly time is short

All lines are configured. Save the connection work of excess row lines

2. Small: volume smaller than PCB

It can effectively reduce the volume of the product. Increase the convenience of carrying

3. Light: Light weight than PCB (hard board)

Can reduce the weight of the final product

4, thin: thickness than PCB

Can improve softness. Strengthen the assembly of three -degree space in the limited space

Basic Structure Edit

Copper Film (Copper Film)

Copper foil: Basically divided into two types: electrolytic copper and pressure delay copper. The common one is 1OZ 1/2oz and 1/3 OZ

Library film: The common thickness is 1mil and 1/2mil.

Plastic (follow -up): The thickness is determined according to customer requirements.

Cover Film

Cover film protection film: surface insulation. The common thickness is 1mil and 1/2mil.

Plastic (follow -up): The thickness is determined according to customer requirements.

Liyan paper: Avoid the follow -up agent to attach foreign objects before presking; easy to work.

Pi Stiffner Film

Reinforcement board: strengthen the mechanical strength of FPC, facilitate surface installation operations. The common thickness is 3mil to 9mil.

Plastic (follow -up): The thickness is determined according to customer requirements.

Divide paper: Avoid the follow -up agent to attach foreign objects before pressing.

EMI: Electromagnetic shielding film, protecting the inside line of the line board is not interfered by the outside world (strong electromagnetic area or vulnerable area).

Advantages and disadvantages

Advantages of flexible circuit board (FPC):

Flexible printing circuit board is a printing circuit made of flexible insulating substrate. It has the advantages that many hard print circuit boards do not have:

(1) You can be bent freely, row, and folding. You can arrange arbitrarily according to the space layout requirements, and move and teasele arbitrarily in three -dimensional space to achieve the integration of component assembly and wire connection;

(2) Using FPC can greatly reduce the volume and weight of electronic products, and apply the needs of electronic products to develop towards high density, miniaturization, and high reliability. Therefore, FPC has been widely used in the fields of aerospace, military, mobile communications, computer, computer peripherals, PDA, digital cameras and other fields or products;

(3) FPC also has the advantages of good heat dissipation and weldability, easy to install, and low comprehensive costs. The design of hard and hard combination also makes up for the slight insufficient in the bearing capacity of flexible substrates to a certain extent.

Disadvantages of flexible circuit board (FPC):

(1) High initial costs at one time: Because flexible PCB is designed and manufactured for special applications, the cost of the starting circuit design, wiring and photo bottom version is higher. Unless there is a special need to apply a soft PCB, it is usually not used when applying a small amount; it is best not to use it;

(2) The changes and repair of soft PCB are difficult: Once the flexible PCB is made, it must be changed from the bottom diagram or the compiled optical painting program, so it is not easy to change. Its surface covers a layer of protective film. It must be removed before repair, and it must be restored after repair. This is a difficult job;

(3) Size is limited: Soft PCB is usually made of intermittent method, so it is restricted by the size of the production equipment.

(4) Improper operation is easy to damage: Improper operation of the personnel is easy to cause damage to the soft circuit, and its tin welding and rework need to be trained. [3]

Development prospects `` ``

With the explosive growth of wearable devices, flexible display and smart devices, the demand for flexible circuit boards has increased significantly, the industry is becoming more and more widely used, and the local flexible circuit board industry has gradually entered the explosive period. In the context of the pursuit of light, thin, short, and small design, the ultra -thin and stretched flexible circuit board contains huge opportunities to promote further development of related equipment.