A Brief Guide To Printed Circuit Boards

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Paul Eisle invented the first PCB in 1936. However, it became popular only in the 1950s when the US military started using the technology in bomb detonators. Today, PCB Circuit Boards are an integral part of almost all equipment, like cars, mobile phones, computers and more.

How Is A Printed Circuit Board Manufactured?

To make a custom PCB, first the electronic diagram of the required circuit is prepared using Computer Aided Design (CAD) software. After that the PCB prototype is developed using Computer Aided Manufacturing Software technology.

The common materials used for manufacturing PCBs are: FR4, FR4 High Temperature, Polyimide, GeTek, Rogers, Arlon, Nelco, Alumina, Ceramic, Bakelite, FR1, CEM1, and CEM5. The size and thickness of the board depends upon the requirements of the circuit. The substrate is coated with a layer of copper. Then, using photosensitive coating, the circuit diagram is printed on the board. The undesired copper is etched out from the board to form copper "tracks", called traces. This process is known as Photoengraving. There are two other common methods used for developing ...
... connecting traces. PCB milling is a mechanical system where undesired copper is removed with CNC machines. Another process is Silk-Screen printing, where special ink that is etch-resistant is used to cover the areas where the copper traces have to be made.

Once the board is ready with copper traces, holes are drilled into the board to assemble leaded electrical and electronic components. For drilling, special Tungsten Carbide drill bits or laser is used. The holes made are filled with hollow rivets or coated through using an electroplating process, thus forming an electrical connection among the various layers. The next step is coating of the entire board, except holes and pads, with masking material. Materials commonly used for this purpose are: lead solder, lead free solder, OSP (Entek), deep/hard gold (electrolytic nickel gold), immersion gold (electroless nickel gold - ENIG), wire bondable gold (99.99% pure gold), immersion silver,
flash gold, immersion tin (white tin), carbon ink, and SN 100CL, an alloy of tin, copper, and nickel. The last step is screen-printing, where the legend and text are printed on the PCB.

Testing Of PCB

Before assembly of components or delivery of Printed Circuit Boards, the board should be tested to find any possible "shorts" and "opens" that could lead to a non-functioning board. A "short" indicates the existence of an undesired connection and an "open" indicates that two points that should have been connected are unconnected. All such errors should be fixed before PCB assembly. It is important to note that not all PCB Manufacturing shops test the boards before shipping, it is sometimes considered an added cost but a vital one to provide a fully functioning board before adding components.

PCB Assembly

Once the board is ready, components are assembled and added to the surface as per the circuit diagram. Some of the common assembly techniques used are surface-mount construction and through-hole construction. Sometimes, a combination of these two techniques is also used for assembly.

Types of Printed Circuit Boards

Single Sided Board

This is the least complex of the Printed Circuit Boards, since there is only a single layer of substrate. All electrical parts and components are fixed on one side and copper traces are on the other side.

Double Sided Board

This is the most common type of board, where parts and components are attached to both sides of the substrate. In such cases, double-sided PCBs that have connecting traces on both the sides are used. Double-sided Printed Circuit Boards usually use through-hole construction for assembly of components.

Multi Layered Board

Multi layered PCB consists of several layers of substrate separated by insulation. Most common multilayer boards are: four layers, six layers, eight layers, and 10 layers. However, the total number of layers that can be manufactured can exceed over 42 layers. These types of boards are used in extremely complex electronic circuits.

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