PCBs, also known as Printed Circuit Boards are widely used in elected circuits. PCBs are used to provide the mechanical foundation on which the circuit is built. Generally, all circuits are printed circuit boards and used in quantities of millions.
The technology surrounding the manufacture of PCBs is evolving rapidly. For example, innovation and advanced technology has allowed the track size to be decreased. Similarly, in order to increase connectivity, the number of layers in the board is increased. Many companies are launching new designs to allow smaller SMT devices to be handled efficiently and other processes can become functional in a relatively short time.
The PCB manufacturing process can be done in several ways keeping in view a number of factors. Though these factors may differ from process to process, the basic procedure is similar for every PCB manufacture.
The Parts of a PCB
Printed Circuit Boards can be made out of multitudinous substances. However, the most common type of PCB is made out of a glass fibre based board called FR4. The reason for its popularity is because of its ability to provide a reasonable degree of stability under different temperatures and does not break down badly. It is also super affordable making it all more purchasable. There are other cheaper materials available as well for PCBs in low cost commercial products. If you are rooting for high performance radio frequency designs where the dielectric constant of the substrate is important and requires low level of loss, then PTFE based PCBs can come in handy albeit they are difficult to handle.
If someone wants to build a PCB with tracks for the components, the first thing you should get is a copper clad board. This consists of the substrate material, generally FR4, with copper plating on both sides of the board. In addition to this, this copper plating is laced with a thin layer of copper sheet attached to the board. This bonding is good for FR4. However, the nature of PTFE might make the job laborious and this may cause a problem in the functioning of PTFE printed circuit boards.
Standard PCB Manufacturing Process
With your required PCB board, the next step is to proceed towards the required tracks on the board and to remove the board unwanted copper. The manufacturing process starts off using a chemical erosion process. Usually, ferric chloride is used as an etch for PCB.
It is very important to gain the correction sequence of the tracks. For this purpose, a photographic process is used. The copper on the bare PCB is covered with a thin film of photoresist. The details of the track cannot be seen through naked eye. It is exposed to light through a photographic film or photo mask. There is one more reason behind this exposure. In this way, it is transferred to the photo-resist. After this step, the photo-resist is put in a developer so that those areas of the board where tracks are needed are covered in the resist.
Thereafter, we proceed with placing the PCB into the ferric chloride to corrode the areas where we don’t need copper or track. It is very important to know the concentration of the ferric chloride and the thickness of the copper on the board. The next step is to place it into the etch for an appropriate period of time. Remember, if the PCB is placed in the etch for too long, you may lose some definition as the ferric chloride may undercut the photo-resist.
Most PCB boards are manufactured by means of photographic process but other methods are also used. One of these methods consists of using a highly specialized accurate milling machine. The machine. This machine efficiently removed copper in those areas where it is not needed. The process is automated and generated from files driven by the printed circuit board design software. This type of PCB is most suitable where very small quantities of PCB prototypes quantities are needed and may not be ideal for large quantities.
Print etch resistant inks is another method used for a PCB prototype. The print etch resistant inks onto the PCB making use of the silk screening process.
Manufacturing Multilayer Printed Circuit Board
In some instances, you may require increased connectivity which might not be possible using just two sides of the PCB. The need usually rises when dense microprocessors and other similar boards are being designed. That is why multilayer printed circuit boards are used.
Although the manufacture of multilayer printed circuit boards is almost the same as for single layer boards, the process demands a greater degree of calculation, accuracy and manufacturing process control.
The boards are relatively thinner designed for each layer and then assembled together to make the overall PCB. With the increasing number of layers, individual boards become thinner to prevent the PCB from becoming too thick. To clean the bond, the bonding material is heated. If large multilayer PCBs are not designed correctly, they may have a prominent wrap.
PCBs Holes and Vias
To connect different layers together at different points, holes also known as vias are needed. These are also required to allow leaded components to be placed on the PCB.
The inner surface of the hole has copper lining so that they can electrically and easily connect the layers of the board. These plated holes are made through a special process of plating. In this way, the layers of the board stay connected.
The next stage is drilling which is achieved using numerically controlled drilling machines. The less the number of different sizes of holes, the lower the cost of PCB manufacture.
Some holes are required to be placed only in the centre of the board in order to have the inner layers of the board to be connected.
All in all, PCB manufacturing requires specific tools, materials and optimum temperature conditions. These factors vary according to the type of PCB you wish to manufacture.
We hope this study guide has helped you to get the gist of what PCB manufacturing process is.