Printed Circuit Board and Plated-Through Hole (PTH) Information


Xmultiple's Engineering Department

Printed Circuit Boards

A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board (PWB) or etched wiring board.

A PCB populated with electronic connectors and components is called a printed circuit assembly (PCA), printed circuit board assembly or PCB Assembly (PCBA). In informal use the term "PCB" is used both for bare and assembled boards, the context clarifying the meaning.

The vast majority of PCBs are manufactured with "1 ounce copper" on the outer layers. If there are inner layers, they are almost always manufactured with "1/2 ounce copper".

The thickness of the copper layer on the PCB affects the behaviour of the circuit. PCB copper thickness is usually measured in ounces per square foot, or frequently, just ounces. It can also be given in micrometres, inches or mils.

"Multi layer" printed circuit boards have trace layers inside the board. One way to make a 4-layer PCB is to use a two-sided copper-clad laminate, etch the circuitry on both sides, then laminate to the top and bottom prepreg and copper foil.

Design of Circuit and Design of PCB

The efficient laying out of traces on a PCB is a complex skill, and requires much patience. This task has been made vastly easier with the advent of readily available PCB layout software, but it is still challenging.

Electronics or electrical engineer design the circuit, and a layout specialist design the PCB. PCB design is a specialized skill. There are numerous techniques and standards used to design a PCB that is easy to manufacture and yet small and inexpensive.

Plated-Through Hole

For PTH (plated-through holes), additional steps of electroless deposition are done after the holes are drilled, then copper is electroplated to build up the thickness, the boards are screened, and plated with metal. The metal becomes the resist leaving the bare copper to be etched away.

The picture above is a Plated-Through Hole in an ten layer board. The amount of plating used in the hole depends on the number of layers in the printed circuit board, however only the least amount of metal is used for this process. Holes through a PCB are typically drilled with small-diameter drill bits made of solid coated tungsten carbide.


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