What Is a Rigid PCB?
A rigid PCB (printed circuit board) is a type of circuit board characterized by its inflexibility.
PCBs are insulating boards featuring wiring on the surface or internally, essential for mounting electronic components to create electronic circuits.
PCBs are generally categorized into rigid PCBs, made of stiff materials, and flexible PCBs, made of thin, pliable materials. Rigid PCBs are the most commonly used type.
Rigid PCBs come in various forms, including single-sided (wiring on one side), double-sided (wiring on both sides), multi-layer (several layers of substrates), and high-density interconnect (HDI) or build-up PCBs, allowing for high-density wiring.
Uses of Rigid PCBs
Rigid PCBs, known for their high strength, find widespread use across various applications due to their excellent electrical characteristics. They are essential in devices like medical equipment, automobiles, aircraft, ships, industrial equipment, PCs, consumer electronics, office automation equipment, IT devices, IC cards, digital cameras, and motherboards. Their ability to integrate numerous components in a small area using double-sided or multi-layer boards is a significant advantage.
Principle of Rigid PCBs
Rigid PCBs consist of a substrate made from materials like glass cloth or paper, impregnated with resins such as epoxy, phenol, Teflon, or BT. They also include prepreg (semi-cured resin) and are laminated with copper foil using a high-temperature, high-pressure press.
These boards are manufactured from copper-clad laminates, with circuit patterns formed from copper foil and solder-resist ink to protect the board’s surface.
Other Information on Rigid PCBs
Types of Printed Circuit Boards
PCBs vary based on the base material and resin in the copper-clad laminate, including paper phenolic, paper epoxy, glass composite, glass epoxy, silicon, and BT substrates. Rigid PCBs also encompass metal-based and ceramic substrates made solely of aluminum or ceramics, without resin.
Flame retardancy and heat resistance of PCBs are typically classified by the FR (flame retardant) grade.
1. Paper Phenolic Substrates
Made by impregnating paper with thermosetting phenolic resin, paper phenolic substrates like Bakelite are economical but have low solder heat resistance and flame retardancy. They absorb water easily, complicating plating processes. Classified into FR-1 and FR-2 grades, they differ in insulation properties. Through-hole processing allows for conductivity between the front and back sides.
2. Paper Epoxy Substrates
These substrates, made by impregnating paper with thermosetting epoxy resin, are categorized as FR-3. They have better water resistance, soldering heat resistance, and electrical properties than paper phenolic substrates.
3. Glass Epoxy Substrates
Glass epoxy substrates are prominent in PCBs, made by impregnating glass cloth with epoxy resin for enhanced flame resistance. They offer high chemical resistance and allow circuit formation on both sides through through-hole processing.
4. Glass Composite Substrates
Constructed from glass cloth and non-woven fabrics, glass composite substrates are often used as cost-effective alternatives to glass epoxy substrates.
5. Metal Base Substrates
Metal base substrates use metals like copper or aluminum for their base, coated with epoxy resin and laminated with copper foil, aiming for efficient heat dissipation. The cost increases with the base metal’s thickness.
6. Ceramic Substrates
Similar to metal-based substrates in their heat dissipation properties, ceramic substrates use materials like silica or silicon nitride as their base. They have a superior thermal expansion coefficient compared to metal-based substrates.