What is a Printed Circuit Board?
A Printed Circuit Board or PCB is essentially a board that connects electronic components. It is the basic building block of any electronic design and has developed over the years into a very sophisticated component. In 1925, Charles Dukas of the US, created and patented a way of electroplating an electrical path onto an insulated surface. The Printed Circuit Board was born, opening the door to smaller, simpler and less cumbersome designs.
Paul Eisler, an Austrian refugee to Britain in 1936, is considered the real founder of the PCB. He developed and patented a number of applications that eventually grabbed the attention of US military. The rest, as they say, is history.
PCBs have moved from 1 layer boards to the 20 + layer boards found in your smartphone. They have interconnecting layers that allow the overall size to be reduced – think of mobile phones in the 80s versus the smart phones of today.
To describe how a PCB is created, we’ve taken a standard 2 Layer or Double Sided PCB. Using DesignSpark PCB Software to design your PCB, Gerber and NcDrill files are created. Each Gerber file represents a component necessary for PCB Manufacture including the copper layers, soldermask and silkscreen data, the PCB outline and the solder paste data for producing a laser stencil for assembly. The NcDrill file defines the location and size of each hole on the PCB both PTH (pin through hole) and NPTH (non pin through hole).
The double sided PCB is made of epoxy glass (FR4) with copper foil on both sides of the epoxy glass. This is generally bought pre-prepared from suppliers. The FR4 material is fibreglass and gives the board its rigidity. To create multilayered PCBs combinations of the pre-made material are pressed together with other layers or non-copper clad FR4 (Prepreg) used to isolate the copper layers from each other.
In the PCB design stage, using the DesignSpark software, a drill or DRL file is created. This is the drill file containing the information used to drill the necessary holes.
At this point there is no electrical connection between the layers. The hole walls need to layered with copper. As the walls are non-conductive, a layer of copper is deposited chemically over the hole walls. This process, known as electroplating, is repeated until the copper thickness reached is optimum for connectivity, typically 25um.
The board is covered with photo-resist. This is a soft, photo-sensitive material. The copper film is placed over the board, aligned with the drills and the board is exposed to UV light. The unexposed areas of resist are removed by passing the boards through a developer solution leaving the copper track\pad pattern visible on the board.
The next step is the deposit a coating over the exposed copper, this coating protects the copper on vias, component holes and traces from being removed during the etching stage.
The photo-resist is stripped (chemically), from the board. It is now time to remove all the copper chemically. The chemical will only remove the copper and not the copper protected by the coating. Now the coating is removed, exposing all the traces and component pads, vias, etc. This is the fundamental PCB circuitry.
A layer of soldermask is added to both sides. It is generally green, although other colours are common. Using a similar process to the photo-resist, the areas for soldering are exposed.
The soldermask insulates the copper and will only create a contact where it is exposed. It also acts as a protector against oxidation & corrosion of the copper. The soldermask layers will include clearances around traces, vias, etc.
To identify the PCB, often developers like to add print to the PCB. This silk-screen will be added at this stage using epoxy ink. Typically, this is white, although many coloured options are available.
A layer of gold, silver or solder on the copper pads will be applied to all component pads, vias, etc., giving the expected finish for the customer. This improves the solderability and protects these surfaces from oxidation. This is the final surface finish.
At Mint Tek Circuits we use a global panel of proven PCB manufacturers to get the best technology, at the best price, in the best time. We work closely with the DesignSpark community to create a simple supply chain for design engineers. Experience our online PCB Quote Calculator for yourself.
CommentsAdd a comment
April 25, 2016 09:33
To date myself, I attended a lecture by Paul Eisler while in my second year at college. He didn't 'sell' the idea very well to some students who had not met it before. Before 1939, GEC made a radio that used copper (maybe phosphor-bronze) strips riveted to a board instead of printing. After Eisler came Sargrove, who printed most of the components, with resistive inks and other techniques, to make a simple radio. That technique didn't survive, but it made what was almost a big IC.