PCB Basics:

NEED:

If we connect different electronics components directly with wire or their leads, we have to face a lot of problems like, loose connection, problems in troubleshooting, low reliability, low durability, etc. Also, if we try to move it from one place to other, we may lose the connections due to no physical support. The only solution to avoid all these problems is “PCB”.

Image of a PCB Layout

Fig. 1: Image of a PCB Layout

PCB:

PCB stands for “Printed circuit board”. In this, wire connections are printed as copper tracks. It can provide physical support to the circuit, thereby avoiding loose connections. Besides, the testing and troubleshooting of the circuit also become simple. We can keep the size of circuit in such a way that it can be accommodated at the desired place. Nowadays very complex circuits, like motherboards, are also designed as PCBs by engineers.

History:

If we look into the history of PCB’s, their initial phase was referred as “printed wire”. 1^st patents for “printed wire” were issued in 1900’s, but the PCB’s came into use after 2^nd world war. Charles Ducas from United States submitted a patent application for a method of creating an electrical path directly on the insulated surface by printing through a stencil, in the year 1925. But in 1943, Dr. Paul Eisler was credited for making the first operational printed circuit board. It was used as a replacement to the bulky Radio tube wiring.

PCB layers:

The simple printed circuit board contains copper tracks only on one side of its surface. These kinds of boards are called “One Layer” printed circuit boards. The most common PCBs are 2 layer PCBs, which contain copper tracks on both sides of its surface. More than two layers PCBs are also possible to design; those are called multi-layer PCBs containing 8 or more layers.

In multilayer PCBs, alternating insulated, and conductive layers are laminated together under high temperature and pressure. This process ensures that air isn’t trapped between layers, and conductors are completely encapsulated by resin. The range of the material combination is extensive from basic epoxy glass to exotic ceramic or Teflon materials. Multilayer PCB manufacturing needs a specialized hydraulic press with heated plates.

Advantages of multilayer PCBs:

1. Increased in flexibility.

2. Considerable saving on apace.

3. High assembly density.

4. Reduces overall weight.

5. Reduces interconnection wiring harnesses.

Applications of multilayer PCBs:

1. Where cross-talk levels are critical, multilayer PCBs are very useful.

2. While the weight and space are the considerable, multilayer PCBs are especially valuable.

3. In Aerospace PCBs.

4. Computer motherboard and mobile boards manufacturing.

5. Satellite systems.

6. X-ray equipment.

7. Medical electronics. Etc.

Terminology:

*S.No*	*Term*	*Meaning*
1	Mil	Thousandth part of the inch (1 mil = 0.001 inch = 25.4 microns)
2	Thou	Thousandth part of the inch and equivalent to “mil”
3	mm	Thousandth part of the meter (millimeter)
4	ESD	Electrostatic discharge caused by static electricity
5	Trace	A path made of copper on PCB. It is same as a wire used to connect components.
6	Via	It is a hole with copper inside, it can provide electrical connection between trace on one layer to trace on another layer.
7	Pad	Pads are conductive surfaces to solder SMD devices.
8	Annular Ring	It is the area on the pad that surrounds the via.
9	Silk screen	Markings of component names and values and outlines on a PCB. It will help in easy assembly and debugging.
10	Solder mask	It is applied to the whole board except pads, and it is a substance that solder won’t stick to.
11	Surface finish	A layer on the top of the pads to prevent copper layer from the oxidation
12	Gerber file	The file which is in the Gerber format and it can tell to manufacturer entire PCB information. Like dimensions, layouts etc.
13	Through hole components	These are Components which have leads like normal resistors. These components leads are soldered on other side of the board.
14	Surface mount devices	These are components without leads, which can be soldered simply on pads instead of through holes.
15	Panelizing	Manufacturers will create a huge PCB with identical boards on it, and often cut into individual boards. This process is called panelizing.
16	PCBA	Printed circuit board Assembly is soldering components on PCB.
17	FR-4 substrate	Most commonly used material for creating PCBs
18	CAM	Computer Aided manufacturing
19	CAM files	These are data files used directly in PCB manufacturing. Examples: Gerber file, NC drills file, fab and assembly drawings, etc
20	Capture	Extract the information automatically by using software.
21	Components library	Representation of the components as deculs, and used by the CAD software.
22	Connection	Also called “pin pair”, it is the connection between two points.
23	Decal	A graphic representation of the component.
24	BOM	Stands for “Bill of materials”, it gives you the list of components on the PCB. With this we can cross check the components we forgot by mistake.
25	Foot print	Collection of pads and outline which makes an individual component.
26	Blind via	Via used between top layer and internal layer.
27	Buried via	Via between internal layers.
28	Through hole via	Via between top and bottom layers.

Software tools and procedure:

In market, many PCB designing software are available like ORCAD, Eagle CAD, ALTIUM, ULTIBOARD, etc.But these all are paid software. Alternatively, we can use open source software like KICAD, Free PCB, etc. WEB versions software are also available, like PCBWEB designer.

In any software, the procedure to design PCB is very much similar, but options, components, libraries, quality and Auto routers are different.

The basic procedure is:

Step 1: Creating schematic.

In this, we have to select the components, make their connections and give values to components.

Step 2: Switch to the board and modify the Board.

After creating the schematic, switch to the board. As an output, we will get components with perfect dimensions and connections. Place these components properly as per size, shape, dimension and requirements of PCB (placing components is our choice). Place the holes with suitable drill dimensions.

After this step, apply Auto router. It will give output as well routed copper traces PCB layout. But sometimes Auto router cannot route completely, in such cases, we have to edit traces manually. There is more manual routing in multi-layer designing.

Step 3: Generating Gerber files.

After finishing routing, apply CAM process to generate Gerber files. In CAM process we can get Gerber files, NC drill files, Assembly drawings, etc. These files will help the manufacturer in preparing PCB.