Contents
What is PCB Substrate?
PCB substrate, also known as the base material or core, is the foundation upon which a printed circuit board is built. It serves as the insulating and supporting structure for the conductive layers and components of the PCB.
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What Is the Role of the Substrate in a PCB?
The substrate in a PCB serves as the foundation, providing mechanical support and electrical insulation between layers to prevent short circuits. It also plays a critical role in thermal management by dissipating heat, while influencing the board's electrical, mechanical, and thermal properties.
What Are the Common Types of PCB Substrates?
Common PCB substrates include FR-4 for general use, FR-2 for low-cost electronics, Polyimide for high-temperature applications, PTFE for RF/microwave use, Ceramic for high-power, and Aluminum for heat dissipation.
| Type of PCB Substrate | Composition/Properties | Common Usage |
|---|---|---|
| FR-4 (Flame Retardant 4) | Fiberglass-reinforced epoxy laminate. Good electrical insulation, flame retardant, relatively low cost. | General-purpose PCBs |
| FR-2 (Flame Retardant 2) | Paper-phenolic resin. Lower cost, less durable than FR-4. | Simple, low-cost electronics |
| Polyimide | Excellent thermal stability, high flexibility. | High-temperature applications, flexible PCBs |
| PTFE (Polytetrafluoroethylene) | Also known as Teflon. Excellent high-frequency performance, low dielectric constant. | RF and microwave applications |
| Ceramic | Excellent thermal conductivity, high dimensional stability. | High-power and high-temperature applications |
| Aluminum | Excellent thermal conductivity, good for heat dissipation. | LED lighting, power supplies |
What Are the Key Properties of PCB Substrates?
Key properties of PCB substrates include electrical factors like dielectric constant, thermal stability, mechanical strength, and chemical resistance for durability and performance.
| Category | Key Properties |
|---|---|
| Electrical Properties | Dielectric constant (Dk), Dissipation factor (Df), Insulation resistance |
| Thermal Properties | Glass transition temperature (Tg), Coefficient of thermal expansion (CTE), Thermal conductivity |
| Mechanical Properties | Flexural strength, Dimensional stability, Moisture absorption |
| Chemical Properties | Resistance to chemicals and solvents, Flammability rating |
How to Choose PCB Substrate Materials
You have the choice of picking from three different PCB types:
Rigid
Flexible
Flex-rigid
The primary goal is to pick a board that will be perfect for your product. Many people aim for compact size and shape but forget about performance.
Polyimide film can be a smart choice as it is versatile and can fit into different categories like black, white, and transparent. It also ensures a low thermal expansion coefficient while maintaining adequate resistance to heat.
On the other hand, Mylar substrate is very elastic and has excellent resistance to environmental factors. On top of that, it is relatively affordable, which is why many users consider it.
Flexible PCBs have to strive to achieve the same level of performance in terms of frequency and speed as standard PCBs. Advanced polyimide substrate and polytetrafluoroethylene are smart choices for flexible boards.
You can find flexible boards in many industries, including medicine, smartphone, and the gadget industry. That is why the market has been implementing multi-layer boards that are flexible and extra thin (0.2-0.4mm).
At this point, you can expect flexible boards to secure a speed of up to 5Gbps, but you will need to use a low Dk/Df substrate material. It is also smart to use conductors with over 100μm of thickness as that will help handle the amounts of current and power.
Image 5: A close-up look at the printed circuit board
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