What Are the Different Types of PCBs?
Types of PCBs
The complexity of today’s electronics requires circuit boards to be able to carry an incredible number of small components with advanced microchips and multiple electrical interfaces. It would be impractical to manually connect all of these with wires, so the copper connections are deposited directly onto insulating substrates through a manufacturing process called PCB etching. There are various types of PCBs to suit a variety of different applications, but they are generally classified according to how they are constructed and the type of conductor material that is used.
The first step in classifying a pcb is to determine the type of substrate. These are the insulating materials that hold the conductive layers. Rigid substrates are typically created from glass-reinforced epoxy laminates such as FR-4, which is commonly seen in PCBs for consumer and industrial electronics products, like calculators, time clocks, radios, cellular phones and solid state drives. Flexible PCBs, on the other hand, are constructed from thin, flexible materials such as polyimide or polyester, which can bend and twist without damaging the conductive traces. Flex and rigid-flex PCBs are popular in wearable electronics, medical devices and aerospace systems, as they can be bent to conform to specific product shapes and withstand vibration.
Next, the conductive layers are added. The most common are single-sided and double-sided, with a layer of conductive metal such as copper applied to both the substrate and one side of the board. Holes drilled through the substrate and the conductor layer allow the circuits on one side of the board to connect to those on the other, and the entire substrate is covered with a solder mask to prevent oxidation and contamination.
What Are the Different Types of PCBs?
More advanced PCBs feature more than two conductive layers, which are often combined to form multi-layer circuit boards (MLCs). This type of construction is usually employed in high-end applications, such as satellites and data servers. In addition to having a larger capacity for more complex circuitry, the additional layers also help ensure that the copper is distributed evenly throughout the circuit board.
Other PCBs are characterized by their substrate material, fabrication method or the way in which the actual conductor pattern is imaged on the surface. Surface mount PCBs are less common, but can be a good choice for a number of applications. This is because they don’t require the use of soldered wires to connect individual components, and instead rely on small leads that are soldered directly to the substrate.
Finally, High-Density Interconnect (HDI) circuit boards are designed to accommodate the increasing demands of modern electronic devices by using smaller traces and vias. The lower trace widths and spacings allow for increased component density, while the smaller via diameters help reduce the overall board size. The surfaces of these boards are often coated with special finishes such as hot air solder leveling (HASL), electroless nickel immersion gold (ENIG) or organic solderability preservative (OSP), which improve durability and aid in assembly and troubleshooting.