One doesn’t have to be a computer geek to know what printed circuit boards are, what they do and how they are used. However, as it an essential part of any electronic gadget, including the much-revered laptops, tablets and mobile phones, it may be important to know and understand how these boards make them work and how to fix any bugs that could affect the way consumers use their devices.
First off, a PCB holds and connects various components that make devices work.This is done using various features on copper sheets that are laminated on a substrate that is non- conductive. These include conductive tracks and pads. There are several types of printed circuit board classified based on the number of layers they have. The one-sided printed circuit board has only one copper layer while the double-sided type has two copper layers.
The multi-layered board has both an inner and an outer layer which allow for higher component density.The conductors on the different layers of printed circuit boards are connected with visa which are plated-through holes. Simply put, a PCB is like the electronic version of a lasagne with alternating layers of different materials to come up with a single, useful object. The materials usedin the layers are silkscreen, solder mask, copper and substrate.
The Layers Revealed
The substrate or the lowest layer, is usually made of fibre glass. This gives the PCB its rigid feel and thickness. There are also PCBs that are made from highly-flexible temperature plastic, epoxies, or phenolics. These, however, lack the durability of fiberglass and may break down faster. Phenolics give off a distinctly bad smell when being soldered and usually delaminate, smoke, and burn when the soldering iron is held too long. This is because of their low thermal decomposition temperature.
The next layer, which is copper, is added to the board using heat and adhesive. In manufacturing a double-sided printed circuit board, copper is applied to both sides of the substrate. There can be as many as 16 copper layers or just one, which is very common in low-quality gadgets. The thickness can also vary and is measured by ounces per square foot.
High-powered PCBs usually have 2 to 3 ounce copper while most PCBs will usually have only 1 ounce per square foot. The solder mask layer is the layer on top of the copper foil. This is the distinctive green colour you usually associate with PCBs. It basically insulates the copper from other metal, solder, or conductive pieces. It also prevents solder jumpers because it helps the user solder on the correct places. It can be any colour, however, and not just limited to green.
On top of the solder mask goes the white silkscreen layer. This adds letters, numbers and symbols to the PCB to allow for easier assembly and understanding of the board. It is also used to label the function of each pin or LED.
Coming to Terms with the PCB
Getting to know the PCB means learning all the common terms that come with it. Among the most heard-of include the following:
Annular ring—the copper ring around a plated-through hole.
DRC—also known as the design rule check, it helps ensure there are no errors in the PCB design. This includes traces that don’t touch, too-skinny traces, or traces that have too- small holes.
Drill hit—places where holes should be drilled on the design or where holes are actually drilled. One of the most common manufacturing issues concerns inaccurate drill hits caused by dull bits.
Finger—these are the exposed metal pads used to create a connection between two circuit boards.
Designing Your Own PCB
It is inevitable that you get bugs even in the most simple design for your own printed circuit board but that can’t be helped. These bugs can be the types that go bang to the ones that cause intermittent glitches and fixes can range from a five-minute job to months. Not everyone can design a PCB. Anyone who wants to attempt to do so should be familiar with design and experimentation. He should also have an effective design-for-test strategy in place to avoid costly rework. Finding a CAD package that is easy to use and capable, looking into what other people have done and constant practice will ensure you come up with a design successful enough to sell and make you money.