What Are the Electrical Properties of Printed Circuit Assemblys?
Electrical Properties of Printed Circuit Assemblys
A printed circuit assembly, or PCB, is the backbone for all electronic devices, providing critical mechanical support and electrical connections. Those connections are established by copper traces etched into the outer layers of a laminated sandwich structure of conductive and insulating materials. When a device is built using these boards, they can be fixed to them with components that are soldered into place using a technique called wave or selective soldering to both electrically and mechanically attach them to the board. The materials that go into a PCB assembly have many different properties that play important roles in its functionality and performance.
A primary consideration when selecting a printed circuit assembly material is its dielectric constant. This measure of a substrate’s ability to absorb and transmit electricity has an impact on signal speed and the amount of heat that is dissipated by the components attached to the board. Modern dielectric materials used in the manufacture of circuit boards usually have a dielectric constant in the range of 2.5 to 4.5.
Another important property of a PCB material is its volume resistivity, or how much it hinders the flow of electric charges. A high level of bulk resistivity can make it more difficult to route conductive traces across the board, and can have an impact on the required trace thickness for a 50 Ohm impedance. PCB materials with low bulk resistance can help designers reduce the thickness of traces and achieve better signal integrity, lower electromagnetic interference (EMI), and greater routing density on the board.
What Are the Electrical Properties of Printed Circuit Assemblys?
Depending on the design of a circuit board, it may require either through-hole or surface mount technology to accommodate components with wire leads. Through-hole components have a standardized connector that attaches to the board using solder, while surface mount components are soldered to pads on the conductive layers. Through-hole components must be soldered using a process known as “wave” or “selective” soldering to ensure the correct positioning and bonding of each component to the board.
When designing a printed circuit board, it is also important to account for thermal effects caused by the components and the copper traces. This can be done through careful placement of the components and by adding heat sinks to allow excess heat to be dissipated. In addition, the PCB material should have a thermal conductivity that is suitable for the intended application.
A final important property of a PCB material is the silkscreen layer, which allows the manufacturer to write labels and component identifiers on the surface of the circuit board. This helps during the assembly and troubleshooting process. Most silkscreens are white, but other colors like red and yellow may be used to denote important areas of the circuit board. A typical silkscreen will be coated with hot air solder leveling (HASL) or electroless nickel immersion gold (ENIG) to protect the copper and improve its solderability. This protective coating is a key aspect in ensuring that the printed circuit assembly performs at the expected level.