Introduction to the structure and function of PCB board

PCB substrates are composed of three main components: copper foil?layer, reinforcement material, and epoxy resin. With the advent of lead-free manufacturing processes, a fourth component, fillers, has been extensively incorporated into PCBs to enhance their heat resistance.

Introduction to PCB Substrate Structure and Functions

We can envision copper foil as the circulatory system, transporting vital signals to enable the PCB's functionality. The reinforcement material can be likened to the skeletal system, providing structural support and preventing the PCB from collapsing under pressure. Meanwhile, the epoxy resin can be compared to muscle tissue, forming the bulk of the PCB's composition.

Now, let's delve into the applications, characteristics, and considerations of these four types of PCB materials.

1. Copper Foil

Electric Circuits: Conductive pathways for electrical signals.

Signal Lines: Pathways for transmitting informational signals.

Vcc: Power layer, operating voltage. In the early days of electronics, the working voltage for many devices was set at 12V. With technological advancements and energy efficiency requirements, the operating voltage gradually decreased to 5V, 3V, and now even as low as 1V. Consequently, the demands on copper foil quality have increased accordingly.

GND (Grounding): Ground layer. Visualize Vcc as a water tower – when the faucet is opened, water (electrons) flows out due to water pressure (operating voltage). Electronic components function based on the movement of electrons. GND can be likened to a sewage system, channeling away all used or excess water, much like electron flow.

Heat Dissipation: Used for thermal management. Most electronic components generate heat as they consume energy. To prevent overheating and component failure, it's essential to design large areas of copper foil to rapidly dissipate heat into the surrounding air. Without proper heat dissipation, both humans and electronic components can experience adverse effects.

2.?Reinforcement

When selecting reinforcement materials for PCBs, it is essential to possess the following excellent characteristics. The majority of reinforcement materials used in PCBs are made from Glass Fiber (GF). On closer examination, the material of glass fiber resembles thin fishing line. Due to the following inherent advantages, glass fiber is commonly chosen as the fundamental material for PCBs.

High Stiffness: Possesses high rigidity, preventing PCB deformation.

Dimensional Stability: Exhibits good stability in dimensions.

Low CTE (Coefficient of Thermal Expansion): Has a low thermal expansion rate, preventing disconnection of internal PCB circuitry due to thermal changes.

Low Warpage: Demonstrates minimal deformation, meaning low board bending or warping.

3.?Resin Matrix

Traditional FR4 substrates mainly use epoxy, while LF (Lead Free) / HF (Halogen Free) substrates combine various resins and curing agents, leading to increased costs—about 20% for LF and approximately 45% for HF. HF substrates are more brittle and prone to cracking, with increased water absorption. Thick boards are susceptible to Conductive Anodic Filament (CAF), necessitating the use of woven or flattened fabrics and uniform impregnation reinforcement.

Good resin must possess the following characteristics:

Heat Resistance: Strong resistance to heat. It should withstand multiple heating and soldering cycles without delaminating or cracking.

Low Water Absorption: Minimal water absorption, as water absorption is a primary cause of PCB delamination.

Flame Retardance: Must be inherently flame retardant.

Peel Strength: High resistance to tearing or peeling forces.

High Tg (Glass Transition Temperature): Elevated glass transition point. High Tg materials generally exhibit reduced water absorption, and low water absorption is fundamental to preventing delamination, rather than solely relying on high Tg.

Toughness: Good resilience or toughness. Higher toughness leads to greater resistance to delamination. Toughness, also known as fracture energy, signifies a material's ability to withstand impacts and resist fracture.

Dielectric Properties: High dielectric characteristics, meaning effective insulation properties.

4.?Fillers System

In the earlier days of leaded soldering, temperatures were not excessively high, and the original PCB materials could withstand them. However, with the shift to lead-free soldering, temperatures increased, prompting the incorporation of fillers into PCB substrates to enhance their ability to withstand elevated temperatures.

Fillers should undergo coupling treatment to enhance dispersion and adhesion.

Heat Resistance: Excellent resistance to heat. A material is considered heat-resistant if it withstands multiple heating and soldering cycles without delamination.

Low Water Absorption: Minimal water absorption, as water absorption is a primary cause of PCB delamination.

Flame Retardance: Must inherently possess flame retardant properties.

High Stiffness: Exhibits elevated rigidity, preventing PCB deformation.

Low CTE (Coefficient of Thermal Expansion): Demonstrates a low thermal expansion rate, preventing disconnection of internal PCB circuitry due to thermal changes.

Dimensional Stability: Exhibits strong stability in dimensions.

Low Warpage: Displays minimal deformation, resulting in low board bending or warping.

Drill Processibility: Due to the high rigidity and toughness of fillers, drilling holes in PCBs becomes more challenging.

Heat Dissipation (due to high thermal conductivity): Used for thermal management.