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What does PCB Mean: PCB Functions and Designing 2020

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Tues, Nov 24, 2020

In very simple words PCB is a short form of "Printed Circuit Board". It comes with a couple of names. Most often, we call it PCB, or PCB board too.

What Does PCB Stand for?

The printed circuit board  or circuit board is a plate or panel consisting of one or two conductive patterns located on the surface of the dielectric base.

carbon ink pcb

It is a system of conductive patterns located in the volume and on the surface of the dielectric base, interconnected in accordance with the circuit diagram.

Circuit boards are used for electrical connection and mechanical fastening of electronic devices, quantum electronics, and electrical products - passive and active electronic components installed on them.

PCB Functions

The role of the PCB is to support the electronic components and to ensure the electrical connections necessary for the operation of the system.

PCB cannot perform these functions alone, soldering is necessary to make the mechanical and electrical connections between the components and the tracks of the circuit.

From calculators and microwave ovens to cell phones and aircraft control systems, all electronic equipment used today involves the use of PCBs. These devices are printed circuit boards. Its purpose is, in a simplified way, to connect electrical components in an organized manner, since the logic that your circuit must exercise is already defined.

Planning is the keyword that defines the production of a PCB since its entire creation process is methodical. There is basically an exchange of debugging troubleshooting of your circuit for the previous logical organization of its components. That is, it is necessary to think very carefully about the connections and functions of each of the elements of your circuit before making it, with this, it is possible to not have problems of bad contact in the wiring.

The Connection between PCB, Electric Circuit Diagram, and Electronic Components

The wiring diagram and the netlist
Note
The electrical design of a PCB starts from the circuit diagram (SEF, Functional Electrical Diagram).

Whether it is made with Cadence OrCAD or with Mentor DxD, the electrical designer proceeds to study the electrical functionality to be created. 

Once all the necessary components have been identified, the list of components (BOM, Bill Of Material) is drawn up for the purchase of the same. 

The drafting of the electrical circuit diagram takes place at the same time as the BOM; first place the electrical symbols and then connect through the so-called "net". 

Once the wiring diagram is frozen, the "netlist" is exported, a table representing the electrical connections present and the components used.

The placement of components

Once the netlist is exported, it is imported into the routing software which translates each line of code into connections and with all the indications of the components present. 

Positioning is one of the most critical phases of the Master PCB because the choice and positioning criteria adopted for the components will influence the routing of the tracks.

A good positioning at this stage will avoid many problems of interference, crosstalk, and coupling of critical signals. 

The positioning of the components will always be carried out taking into account the electrical functions of the components, avoiding the no-go areas for placement and for the routing of the tracks.

Track routing is the interconnection of all the connections present in the wiring diagram between the components. 

The tracks that will be created will connect the pin pads of the components and will use multiple interconnection layers to concentrate all the connections inside the PCB. 

Each layer is interconnected by metalized holes, also called vias. 

The size of the tracks will be suitably calibrated according to the electrical constraints of the signals that will cross the board. 

All electrical insulation (track-track, track-pitch, pitch-pitch, track-floor, floor-via, track-away, pitch-away, etc.) must be carefully chosen.

Impedance control, crosstalk, and signal Integrity

Special attention should be given to the impedance control and relative adaptation so that the condition of maximum power transfer between generator and user is always reached. 

During routing it is essential to pay attention to critical signals and treat them properly right away, avoiding crosstalk or crosstalk problems because it is the electromagnetic field that is generated in a track when current flows, generates an exchange of energy from one track to another. 

This creates an undesirable disturbance due to the induced spurious current which affects the quality of the signals which results in a reduction in communication speed. 

A good digital signal has fast transitions and logic levels that are clean and free of transient phenomena.

The circuit diagram is a diagram showing circuit connections within a code of a circuit element. 

Schematics are a type of schematic layout of components and their relationships drawn with physically and electrically standardized symbols for research and technical planning. 

Schematics can convey the working principles of components, analyze their performance, and provide a planning system for installing electronic and electrical products.

In the circuit design, the technician can settle on paper or a computer after confirming that the actual installation is complete. 

Improve, fix, and succeed through debugging. 

Using circuit simulation software for circuit-assisted design and virtual circuit experiments can improve the work efficiency of engineers, save learning time, and make real pictures more intuitive.

Parts in the circuit do not necessarily resemble or completely different in shape from the actual parts. 

However, it generally represents the characteristics of the element, and the number of pins matches the actual element.

Like many wires in radio schematics, they are not necessarily straight in the printed circuit board diagram, but they can also be copper films of a particular shape. 

A node represents a connection between multiple pins or wires. 

All pins and conductors of the components connected to the node are conductive, no matter how many. 

Annotations are very important in schematics and all text in the schematic can be categorized as annotations. 

If you look closely at the figure above, you can see that there are annotations in various parts of the schematic. Annotations are used to indicate the type, name, etc. of a component.

PCB Drawing Software

Since the official birth of commercial CAD systems (EDA), various design software has been developed since 1981. Printed circuit boards are the backbone of any hardware product. Prior to the development of EDA software, engineers typically designed electronic circuits and integrated circuits by hand or in some other non-automated way.

Autodesk Eagle

autodesk eagle

Eagle is perhaps one of the most famous programs for designing circuits and printed circuit boards. Formerly known as Cadsoft Eagle, this software suite is now called Autodesk Eagle following its purchase by Autodesk. Autodesk EAGLE contains a schematic editor for schematic diagram design and a PCB layout editor for designing printed circuit boards. It provides component placement, PCB routing, extensive library content, a thriving community, and more. You can also find a free version of Autodesk EAGLE. It is available for Windows, Linux, and Mac.


Expresspcb Plus

ExpreePCB Plus

ExpressPCB Plus is a CAD software for electronic circuit creation and design. It includes ExpressSCH Classic for schematic drawing and Express PCB Plus for PCB design. ExpressPCB Plus provides the ability to see the current development prices for your board, and even order a board to manufacture from within the program itself. ExpressPCB is available for use on Windows, Linux, and Mac.

Features of PCB Design for STM32WB

Microwave tracing of printed circuit boards must be carefully worked out. Let's consider the main aspects of PCB design for STM32WB. Let's start with impedance matching. It is known that to reduce signal reflection it is necessary to match the impedance of the source, receiver, and transmission line. 

The impedance of a transmission line depends on its geometry and the location of the supporting surface. By the reference surface, I mean a conductive layer with zero potential, the geometrical dimensions of which significantly exceed the dimensions of the conductive line. Let's list the main factors influencing the wave impedance of the transmission line:

  • Line type: microstrip, strip, coplanar
  • Line width
  • Distance to the support layer H (dielectric thickness).
  • Dielectric material parameters (dielectric constant)
  • The thickness of the conductive layer, which is more influenced by the thickness of the conductor T1, to a lesser extent by the thickness of the copper of the reference layer T2;
  • Solder mask thickness

The impedance of a transmission line depends on its geometry and the selected PCB layer stack. Depending on whether the priority is stack or geometry, there are two approaches to design. The first approach is that the developer of the board sets the geometric dimensions of the conductors convenient for him, and then selects the layer stack and production technology for them. However, it is far from always possible to find the required stack within the technological limitations of the PCB manufacturer. 

A situation may arise in which even if the manufacturer is able to produce a board on a given stack, its cost will be much higher than the typical one, especially when it comes to a small series or a prototype. Another approach is to select a generic stack from the manufacturer.

Each PCB manufacturer has recommended solutions, the use of which ensures the minimum production cost. But in this case, you will have to select the geometry of the transmission lines for the available parameters, and this does not always suit the developer. Both approaches require the developer to work closely with the manufacturer.