HDI PCB - Rigid PCB

A rigid pcb is a support for electronic components that consists of an insulating substrate and a conductive layer with a rigid base material (e.g. glass fibre-reinforced epoxy resin) that provides structural robustness, high reliability and excellent immunity to interference. Rigid circuit boards ensure electrical connections and signal transmission by securing electronic components, wires and other connecting elements to a sturdy mechanical support platform.

Main characteristics of rigid pcb

High mechanical strength: Rigid pcb uses a robust substrate material that exhibits excellent mechanical strength,making them ideal for electronic products that require a high degree of stability.

Outstanding Thermal Stability: Rigid PCB maintains stable performance even in high-temperature environments, making them suitable for high-temperature operation of electronic devices.

Ease of assembly:the structural stability of rigid PCB facilitates the soldering and assembly process of electronic components,thus enhancing productivity.

Excellent electrical properties:the small spacing between the layers of wires in rigid PCB ensures fast signal transmission speeds, demonstrating their excellent electrical properties.

However, rigid circuit boards also have some shortcomings:

Lack of bendability:They cannot be bent or folded, which limits the flexibility of layout design to some extent.

Higher weight: Compared with flexible PCB, rigid PCB is usually more bulky.

Limited space utilisation:Rigid PCB may not be the best choice for applications that require compact space.

Thermal Expansion Hazards:Due to differences in the coefficient of thermal expansion of different materials, temperature changes can lead to potential problems.

Rigid PCB construction and manufacturing materials:

Substrate Layer: This is the substrate layer, which consists mainly of glass fibres. FR4 is the most commonly used substrate material, which gives the board the necessary rigidity and stiffness by virtue of the glass fibres. Although phenolic resins and epoxy resins can also be used as substrates, their performance is slightly inferior to that of FR4. However, both materials are more economical in terms of cost and have a characteristic bad odour. It is worth noting that phenolic resins have a low decomposition temperature, which may lead to delamination between layers if exposed to solder for a long time.

Copper Foil Layers:

At the top of the substrate layer, the copper foil is firmly affixed to the board with the aid of additional heat and adhesive. In conventional applications, copper is bonded to both sides of the board; however, for cost reasons, some lower-end electronic products may only use copper on one side of the board. The thickness of copper foil varies and is usually expressed in ounces per square foot.

Soldermask Level:

The soldermask layer sits on top of the copper foil, and its primary function is to form an insulating layer of protection on the surface of the copper foil, thus preventing other conductive materials from coming into direct contact with the copper foil and causing damage.

Silk-screen marking layer:

The silkscreen marking layer covers the soldermask and is used to print characters, symbols, and other information on the board so that the user can understand the layout of the board more clearly. White is the most commonly used colour for the silkscreen layer, but other colours such as grey, red, black, yellow, etc. are also available depending on the actual situation.

The core process for the production of rigid circuit board:

Design and Layout:The design and layout of the board is a fundamental and critical step before production begins. This includes the design of the circuit layout, the placement of components, and the determination of board size and form.

Substrate Selection:Selecting the right substrate material is a central part of the manufacturing process. Substrate materials need to have both excellent electrical insulation properties and sufficient mechanical strength, and common choices include FR-4,CEM series, and so on.

Copper Foil Lamination:As the core material of the conductive layer of the circuit board, copper foil is tightly bonded to the substrate material through the lamination process to form the conductive structure of the circuit board.

Drilling:Drilling is an important part of the manufacturing process, aiming to form through holes and blind holes on the circuit board.The accuracy of the drilled holes is directly related to the electrical connectivity and mechanical robustness of the board.

Photo-Etching:Etching removes excess copper layers to precisely pattern the circuitry. With photo-etching, the shape and size of the circuit pattern can be precisely regulated.

Electroplating:Electroplating is used to build up conductive layers and fill holes in a circuit board to improve its conductivity and mechanical strength.

Multilayer lamination:For multilayer boards,lamination is a key step in bonding the different layers of copper foil to the substrate material.The press-fit technique ensures precise alignment and strong bonding between the layers.

Surface finishing:Surface finishing techniques such as hot air surface levelling (HASL) and electroless nickel/impregnated gold (ENIG) are used to optimise the surface quality and solderability of the board.

Testing and calibration:At the end of the manufacturing process,the boards must be electrically tested and mechanically calibrated to ensure that they meet design requirements and performance specifications.

Quality Control:Strict quality control is essential throughout the manufacturing process.This includes the testing of raw materials,semi-finished and finished products, s well as the continuous monitoring and optimisation of production processes.

Rigid pcb is used in a wide range of applications,from household appliances and automotive electronics to aerospace,military equipment and medical electronics. Especially in the home appliance industry, with the wave of digitalisation, networking and intelligence, as well as the rise of the Internet of Vehicles,smart wearable devices and other emerging areas, the demand for rigid circuit boards has increased significantly.

The outlook for the rigid circuit board market is generally favourable, especially in electronic fields such as smartphones, tablet PCs, thin and light notebooks, and network communication devices. In addition, with the continuous breakthroughs in RF technology and wireless connectivity, the application prospects of rigid circuit boards will be even broader.

In the field of electronics, rigid pcb has become an important choice for manufacturing high-end electronic products due to their unique properties and wide range of applications. Looking ahead, the rigid circuit board market is expected to usher in a wider range of applications and development opportunities as information technology continues to advance.