Digital PCB technology has come a long way in the field of Electronics, as innovations and developments fulfil the demands for faster, smaller and cheaper electronics devices and gadgets. Digital PCBs consist of several microprocessors and other electronic circuitry which have the capability to manage thousands of operations each second. When compared to analog circuit boards, digital PCBs come with a number of improvements, the major ones being better impedance matching and improved insertion loss control of transmission lines.
Source - ak.picdn.net
It is very important for digital PCBs to be carefully designed and engineered in order to eliminate problems like impedance discontinuities in transmission lines, improper plating of the through-hole interconnections, and other signal-integrity-related issues. Digital PCBs have a number of features that give them an upper hand during the functioning of an electronic circuit. Some of these features are:
There are various similarities and differences when it comes to analog and digital routing in PCBs in terms of bypass capacitors, power supply, ground design, voltage errors, electromagnetic interference (EMI), etc caused by PCB board routing.
Fig 1:-Analog and Digital signals
Source- Proto-Electronics
Analog circuits consist of a combination of Op-Amps, resistors, capacitors, and other electronic components used on a PCB. These combinations of various components forming an analog circuit can vary in different manners. The main two applications of analog circuits are:
On the other hand, digital circuits consist of a combination of logical and sequential components by making use of logic gates that work on digital signals. When compared to analog circuits, digital signals operate on the logic of 0’s and 1’s to represent data in a digital form on a single IC.
There are certain factors that should be taken into consideration while selecting materials for digital PCBs. Some of them include
The foundation or the base of a PCB antenna consists of a substrate and a laminate, which also determines the performance of the PCB. Qualities such as function, longevity, and cost efficiency should be kept as a priority while designing a PCB, hence selecting the proper type of PCB material is critical. The material that one considers while designing a PCB can have a short-term or long-term effect on the performance. The pricing of a PCB material is directly proportional to the performance of the PCB. When the high performance of a PCB is not essential, a material named lightweight polyester can be considered as it comes with a low cost and good versatility
While selecting the materials, the temperature is a parameter that must be considered. The heat resistance should be higher than the heat produced as due to surplus heat a circuit may fail. Tg (glass transition temperature) is when PCB loses its rigidity and ability to perform well. Tg should match the assembly process being used, as a Tg with a minimum of 170° C is recommended for lead-free assembly. For a high-performance PCB, Tg should be higher than 170°C whereas a standard PCB has a Tg of 130°C. The advantage of having a high Tg is that there is a great ability to resist chemicals and moisture.
Materials generally used in PCB substrates range from FR-1 and G-10 to PTFE. Laminates are formulated from CTE, PTFE, CEM, and various other compounds.
Most PCB design systems have the capability to transfer rules between the schematic and the layout. It permits the schematic to drive design rules instead of waiting to input all the constraints on the layout side, this is a huge advantage for designers. This level of organization offers designers the capability to form rules for specific net and component placing which are essential for circuit designing. Net or net class allows to group like nets together and assign a rule set to them. As the net rules are already present in the design database, so the designer need not rely on written instructions. For ensuring that the circuit board is designed precisely, here are some rules that need to be followed:-
Fig 2:- Installing classes
Source- Circuitstudio
For example, the unique trace widths and the spacing requirements can be configured for a particular value of nets, a designer can create a set of rules for one power class and add those to nets.
Fig 3:- Trace designing
Source - Pcbdesignworld
Fig 4:- PCB spacing
Source- Optimumdesign
Also, during the design process, components and circuit schematics must be properly represented in any CAD software which allows designers to view accurate simulations before mass production.
While designing digital PCBs, utmost care must be taken throughout the designing process to ensure the circuit, as well as the PCB, so that the system performs at its maximum potential. There are various factors to consider when it comes to selecting the right material for the digital PCB. The materials must have dimensional stability, high thermal management control, moisture and chemical resistance, etc for the signal to pass through the PCB smoothly and without any disruptions. FR4 is one of the best-suited materials when it comes to designing digital PCBs due to its high dielectric strength and superior signal integrity.
Before going into mass production, it is important for designers to simulate the electronic components and their functioning on the PCB to get the appropriate outputs. For high-speed digital circuits, designing trace lengths is essential as it improves signal stability for better transmission of signals. Spacing of components must be done in the right manner by keeping the right proximity to avoid signal interference. A via aspect ratio of 6:1 can be done for efficient fabrication and drilling on the board which helps in flexibility during the wiring and soldering process. The best possible practice to avoid electrostatic discharge and its effect on PCBs is to make use of various protectors like metal-oxide varistors, transient-voltage-suppression diodes, polymer-based suppressors, etc.
22.06.2022