PCB Assembly - The Basic Design Rules You Must Know

Article Introduction:

All electronics in use today incorporate printed circuit boards of varying types and sizes. A Printed Circuit Board endures a process of manufacturing that is initiated by the creation of a PCB design. Understanding your PCB requirements are integral for a well-designed PCB.

In order to create a PCB layout or PCB design, you must have a basic understanding of PCB design software and CAD systems, and your final design proposal must be something that can be executed.  

While your PCB needs a well-experienced manufacturer to give satisfactory results, your PCB design is the core element that must be perfected foremost. This is why PCBs are generally designed using some basic guidelines/rules. We shall discuss the most basic ones you should be aware of.

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What is PCB Assembly?

PCB Assembly, Full name is printed circuit boards assembly. The circuit board before assembling electronic components is called PCB. Once the electronic components are soldered, the circuit board is called printed circuit board (PCA) or printed circuit board assembly (PCBA) or PCB assembly. Different manual and automatic PCB assembly tools are used in this process.

PCB Design Rules

1: PCB Board Design 

The base of a PCB includes its size, shape, area, and layers and these are the primary parts you must first decide on. 

• Choose the reference points on your PCB. These are holes/points which can be used by pick-and-place machines and for securing the PCB in a fixed place. They must not be obscured by components or tracks. Since the edges of the PCB are more prone to scratching make sure you don’t place any tracks near them, or they may cause scratches and cracking. 
• Make sure your PCB is designed using adequate area. Study the device you will fit the PCB inside and the components you will be adding to the surface and figure out if your PCB board area can accommodate them and the copper tracks. 
• Determine the number of layers you will need, additional layers equate to increased cost but also make room for additional tracks. More complex PCBs demand more layers so tracks can be easily accommodated. 

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2: Component Placement

Sketch out an overview plan which will indicate the placement of the components in specified areas and the tracks that will connect them. Try to establish the most efficient design for your PCB. 

The component placement itself must be strategic. The way your board layout is set up will determine exactly how easy it might be to manufacture your PCB while keeping your requirements at hand. 

• The orientation determines how easy and effective your routing will be. This will also mark the efficiency of your soldering process. 
• Ensure that you place your components with adequate space for copper traces. Group the components by function and keep them away from heat-dissipating areas as this will reduce the chances of failure/faults in the PCB. 
• Organization in terms of component placement also matters. Organize your surface-mount components on the same side of your PCB and similarly place all through-hole on the top side of the PCB. 

Image Courtesy: NextPCB

3: Rules Regarding Ground, Tracing, and Power

Once your components are placed the next step usually involves the routing of signal traces, power, and ground. 

• Your power and ground planes should be placed inside the board, usually, a complete layer is dedicated for this purpose. This will help prevent your board from bending and prove advantageous in terms of noise and current capability. 
• Do not leave gaps between your ground or power planes, or use partial planes as this can lead to stresses and functional failure due to fracturing. 
• Place the traces that will connect your components as shortly and directly as possible. Also, keep in mind that if one side of your PCB has horizontal tracing then the opposite side will have vertical tracing (for two-layer PCBs). 
• The more layers you add to your PCB, the more complex routing will get and you may have to alternate between horizontal and vertical tracing. 
• Make sure your tracks aren’t too narrow or too close as this may lead to shorts. Similarly don’t leave too much space between your tracks or you may be compelled to use extra planes.
• Consider the track size for the current-carrying traces. Your net width must be according to the current that will pass through. Extremely thin traces can only carry a limited current. 

4: Interference and RF 

Your PCB may run into issues with signal integrity, RF, and interference. You want to minimize the interference caused by power surges or nearby components. 

• Make sure your power ground and control ground are separated. 
• In case you have your ground place as the middle layer, try to place an impedance path that will reduce the risk of interference. 
• Try not to run tracks parallel to one another for a certain length as there is always a chance of crosstalk with signals on one track to another which can lead to problems in the performance of your PCB. 
• In case two signal lines need to cross, cross at right angles as this will reduce the level of capacitance and mutual inductance. 

Image Courtesy: NextPCB

5: Overheating Issues

• Heat issues are not unheard of. The prime cause? Improper heat dissipation.
• You should first identify the components which will dissipate larger quantities of heat, then do some research on the best method to divert the heat produced.
• Keep your heat-sensitive components away from components that will dissipate heat.
• If your PCB has multiple heat-dissipating components then try to place them further apart rather than clustered together.

To conclude we can say that the PCB design process demands attention to detail. Any negligence on the part of the designer, or manufacturer can lead to faults in your PCB. In order to ensure you avoid any errors, follow the basic guidelines above, always double-check and triple-check your design, and consult your manufacturer before you proceed. 

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