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PCB Prototyping

PCB Prototyping- Best Practices for Fast and Accurate Results

When designing a printed circuit board the prototyping process is one of the most important steps. It’s essential to get it right the first time so that the end product meets all of your specifications. To ensure fast and accurate results in this case, you must follow certain best practices. From choosing the right design software to properly testing the boards, we’ll cover everything you need to know to get the most out of your PCB prototyping projects.

Use the Correct Board Material

When it comes to PCB prototyping, selecting the right board material is crucial. The type of material you choose can impact the board’s durability, and performance. Some materials are more prone to overheating or warping, while others may be more conductive or have better insulating properties.

One popular option for PCB prototyping is fiberglass. It is a relatively low-cost material and can provide good insulation properties. It is also ideal for single-sided boards. However, it may not be the best option for more complex designs.

For multi-layered boards, you may want to consider a material like FR4. This type of material is more expensive but provides better durability and stability, which is critical for high-performance circuit boards.

Before selecting your board material, you must consider the specifications of your design, including the application, environment, and electrical properties you require. Don’t be afraid to consult with PC Board experts to help determine which material is the best fit for your project.

Using the right board material is just one of the many best practices to consider when it comes to PCB prototyping. By following these tips, you can achieve faster, more accurate outcomes and set yourself up for success in your PCB design projects.

Invest in Quality Components

When it comes to circuit board prototyping, investing in high-quality components is crucial to achieving fast and accurate results. While it may be tempting to cut costs by using cheaper parts, this can lead to several issues down the line, from malfunctioning circuits to reduced durability.

Using quality components ensures that your circuit board will function properly and last longer, saving you time and money in the long run. You must find the components that have been tested and verified to meet industry standards and specifications.

Another benefit of using high-quality components is that they are less likely to fail during testing, reducing the need for repairs or replacements. This not only saves you time but also minimizes the risk of damaging other components or causing additional issues with the circuit board.

Make Sure Your Board Design is Complete and Accurate

Before starting your PCB prototyping project, you must ensure that your board design is complete and accurate. This step may seem obvious, but it is often overlooked, resulting in errors and the waste of time and money.

Start by double-checking your PCB design for errors, missing connections, or any other issues. Use reliable design software and go over your schematic and layout files thoroughly. Get a second pair of eyes to review your design before moving forward with prototyping.

Another best practice is to perform a Design Rule Check (DRC). This automated check ensures that your board meets the minimum manufacturing requirements. A DRC can identify potential errors, such as overlapping pads, inconsistent track widths, or drill holes that are too small or too close to each other.

If your board design has multiple layers, it is crucial to verify that your stack-up is correct and that the signal integrity is maintained. You can use a simulation tool to predict and optimize the electrical performance of your board.

Follow the Data Sheet

Following the datasheet is essential to achieving accurate and reliable results while PCB prototyping. The data sheet contains crucial information about the board’s electrical characteristics, material properties, and manufacturing specifications.

The data sheet typically contains the following information:

  • PCB layer stack-up and dimensions
  • Minimum and maximum board thickness
  • Trace and via size, spacing, and clearance
  • Impedance requirements
  • Material composition and properties
  • Surface finish options
  • Solder mask and silkscreen specifications
  • Thermal management guidelines

Such a practice can ensure that your PCB prototype meets the manufacturer’s specifications, as well as any relevant industry standards. Failure to follow the datasheet can result in design flaws, manufacturing errors, and functionality issues.

Moreover, you should communicate with your PCB manufacturer if you have any questions or concerns about the datasheet. A reputable manufacturer has a team of experts who can guide you throughout the prototyping process. So, following the datasheet is the best practice for fast and accurate PCB prototyping.

Make Test Points Accessible

Make sure that the test points are easily accessible. This helps have easy testing and debugging of the PCB during the prototype stage.

Test points are small metal points on the board where you can attach the testing equipment to measure the voltage. You can find them near components to be tested. By making them easily accessible, you can avoid having to take the board apart or maneuver equipment to access them. You should consider this factor during the design phase. Ideally, you should choose unobstructed areas. You should also consider adding extra test points to ensure thorough testing of the entire board.

Moreover, you should consider the size and type of test points to use. Small test points can be difficult to use, while larger test points can take up more space on the board. You should also consider the technology, such as surface mount or through-hole.

By making test points accessible during the prototyping phase, you can save time and ensure accurate results. It can also help to identify any issues with the board early on in the development process, helping in easier debugging and revisions.

Consider Your Assembly Options
After the PCB prototype process, comes the assembly. There are several assembly options available, and you should consider which one is best for your particular project.

One option is hand assembly, which involves soldering components to the board by hand. This method is cost-effective and works well for small-scale production runs, but it is time-consuming and may result in inconsistencies.

Another option is automated PCB assembly, which involves using machines to place components onto the board. This method is efficient and accurate, but it may be more expensive and more suitable for larger production runs.

You should also consider whether you want your board to be surface-mount or through-hole. Surface-mount components are smaller and lighter, making them ideal for compact designs. However, through-hole components can provide a stronger mechanical bond and are ideal for larger components or those that require high voltage.

Make sure to consider the assembly options before finalizing your PCB design and prototyping process. This will help ensure that the end product meets your expectations and requirements.

Don’t Forget the Silkscreen

When it comes to printed circuit board prototyping, people often overlook the importance of the silkscreen. The silkscreen is the layer of ink on top of the PCB that indicates component placement, orientation, and other important information. It may seem like a minor detail, but an accurate silkscreen can save a lot of time and confusion during the assembly process.

First and foremost, make sure your silkscreen is complete. This means double-checking that all component labels are correct and aligned properly with their respective pads. Make sure there are no overlapping labels or missing information.

Next, consider the size and color of the silkscreen. A too-small or too-light font may be difficult to read, especially for those with vision impairments. Conversely, a font that is too large or too dark can clutter the board.

Finally, be mindful of the placement of the silkscreen. It should not cover up any important traces or pads. Besides, it should not interfere with any assembly processes or inspection.

Final Thoughts

Prototyping printed circuit boards is a complex and time-consuming process, but with the right techniques, it doesn’t have to be. If you want to ensure fast and accurate results, you must follow best practices, in this case. Investing in quality components is an essential step in achieving fast and accurate PCB prototyping outcomes. Don’t compromise on quality to save a few bucks as it will end up costing you more in the long run. Also, make sure that your board design is complete and accurate, as it will save you time and money.

Before starting your PCB prototype, you should thoroughly review and understand the data sheet provided by the manufacturer. It ensures that your design meets the manufacturer’s specifications and industry standards, preventing errors and functionality issues. Also, don’t hesitate to consult with your prototype pcb manufacturer if you have any concerns about the datasheet.

Also, remember the importance of the silkscreen when prototyping your PCB. A well-designed silkscreen can improve the overall functionality and aesthetics of the PCB. Make sure to choose the right font and color, and be mindful of placement. A little attention to detail can go a long way in the success of your PCB prototyping project.

Would like to know more about PCB prototyping or printed circuit board assembly? Email us at sales@pnconline.com

AOI in Printed Circuit board Fabrication

Engineers have to make sure of the quality of PCB through different tests, including AOI (Automatic Optical Inspection) AOI. It involves sophisticated imaging technology to identify potential defects on printed circuit boards in real-time and enhances effective production and better quality assurance. This state-of-the-art technology can detect even the smallest flaws, making it the ideal choice for manufacturers looking to maintain high levels of quality control without sacrificing production speed. Stay with us to learn more about how AOI in PCB manufacturing is revolutionizing the industry.

What is Automatic Optical Inspection?

Automatic Optical Inspection or AOI is an automated technique that engineers use in printed circuit board manufacturing for quality control. AOI uses computer-controlled cameras to capture images of the PC Board and then compare the images to an effective model. The AOI system will then analyze the images and detect any defects or abnormalities in the board, such as open connections, shorts, missing components, incorrect components, misalignments, and many others.

The AOI system can quickly identify any defects and make necessary corrections, ensuring that only perfect PCBs make it to the next stage of the manufacturing process. AOI is an important part of modern PCB production and is used to improve its efficiency and reduce costs. PCB manufacturers are turning to AOI systems to get more accuracy and reliability when it comes to inspection and quality control. With AOI technology, a PCB manufacturer can inspect the boards quickly and accurately without manual inspection processes. This not only increases productivity but also reduces the cost and waste associated with manual inspection processes.

Moreover, AOI systems can detect even the smallest defects on the PCBs which would otherwise have gone undetected by a manual inspection. By implementing the AOI into the PCB manufacturing processes, manufacturers are able to produce reliable PCBs that meet their exact specifications while also cutting down on time, labor, and cost that goes into manual inspection.

Automated optical inspection is ideal for SMT even though inspection through X-ray is trending in the PCB industry. Manufacturers consider the AOI cheaper and more reliable than several other methods. The assemblers use different cameras to take pictures of an assembled board and then compare all images to see any defects.

How Does AOI Work?

Automatic optical inspection works by using a camera or other imaging technology to capture the visual images of the PCB and its components. The inspectors then compare the images to a predetermined set of tolerances to determine if any defects are present. This comparison occurs through specialized software which determines whether a part or component on the Printed Circuit Board is acceptable or not.

The AOI process begins by mounting the PCB on a stage that is connected to the camera. The camera takes multiple images from different angles of the PCB and gets the data from these images to identify any defects. After the analysis, the results appear on a monitor for further review and evaluation.

AOI allows for faster, more reliable, and more accurate inspection compared to manual inspection processes. It also reduces the risk of human error in the inspection process as it eliminates the manual handling of different parts and components. AOI also provides significant cost savings when compared to manual inspection since it requires fewer personnel and resources.

Moreover, AOI can detect small defects and abnormalities that may be difficult to detect by the naked eye, making it much more reliable than traditional or manual inspection methods. By using this technology, PCB manufacturers can ensure quality assurance at every step of their production process in terms of reliability and accuracy. With the continued advancements in AOI technology, PCB manufacturers can now inspect their products with confidence and provide better quality control solutions.

Furthermore, automated testing enables pc board manufacturers to reduce their production costs significantly due to increased efficiency. As such, implementing AOI into their production line has become increasingly popular among PCB manufacturers. With all these advantages, it is easy to see why automatic optical inspection has become so important in PCB manufacturing and why its use will increase even further in the future.

When To Apply The AOI

You can apply this testing method to an assembled or a bare PCB, depending on your needs. AOI should be able to test any component, find barcode details, check measurements, check package size, and lead condition to produce the yield rate. It should also test the number of defects and their types. You can find a lot of info from this type of inspection, such as:

  • Components Position
  • Body Measurements
  • Missing Parts
  • Polarity Issue
  • Tombstone Issue
  • Bridging &Marking Issue
  • Solder Fillet Level
  • No Lead Issue
  • Billboard And Pad Shifting Defects
    Understanding AOI Fundamentals

Generally, AOI involves an image-taking system, such as CCD, and image processing techniques, as well as workbench and AC servo management. All these elements are the core of this inspection. Various elements work together in this case, such as drivers and axis, sensors and optical systems, as well as software systems and they all should be compatible and synchronized in terms of speed.

As digital computing is advancing, image processing and camera vision are becoming necessary for automating inspection through high-resolution devices, illumination methods, and lighting devices, as well as effective processing.

The processor should work fast to reduce the processing time for a camera to generate the information. Especially, high-volume PCB production requires high-speed AOI. Besides, you need specific software for specific testing techniques to have better results.

For example, a machine to inspect solder paste would be different from the one that inspects component issues. This difference is in terms of light and software, height to be measured, etc. You can measure the height of PCB components with AOI, but you need SPI to measure the solder paste height. The projection provided by AOI is either four-way or eight-way, whereas it is two or four-way in SPI.

Benefits of AOI

Using automatic optical inspection in PCB manufacturing provides many benefits. One of the main advantages of using the AOI is its ability to quickly detect even small defects in the printed circuit boards. With the help of a powerful computer-controlled system, AOI can quickly scan the board for any irregularities and can help to identify them with great accuracy.

Another major benefit of AOI is its cost efficiency. The use of this technology helps to reduce the labor required for manual inspections, which ultimately lowers production costs.

You can use the AOI multiple times throughout the production process, ensuring that the quality of the product is consistently high.

Furthermore, AOI can improve the overall accuracy of PCB inspections since it is highly sensitive to even the smallest details. This means that there are a few chances of releasing a faulty board and you can detect any issues with the board and correct them before they reach the customer.

AOI also allows for higher throughput rates in PCB manufacturing, as it can inspect several boards at once. This means that more PCBs can be produced in less time without compromising on quality.

Drawbacks of AOI

While AOI is an invaluable tool in PCB manufacturing, there are some drawbacks to consider when deciding to use this technology. One of the biggest drawbacks is that it is a relatively expensive technology and requires ongoing maintenance.

Besides, the accuracy of automation is limited by the resolution of the imaging system and the underlying PCB design. While AOI can detect large defects in a board, it may not be able to detect very small errors.

Since AOI relies on the availability of complete documentation of the PCB design, any changes to the design after the initial testing phase can introduce undetectable errors in the PCBs. Moreover, if engineers can’t manage the process parameters of such inspection in PCB manufacturing for a particular set of boards, false rejections can occur.

Final Thoughts

The use of Automatic Optical Inspection in PCB Manufacturing is quickly becoming the go-to method of quality control. AOI is an automated process that uses visual inspection and computer vision technologies to inspect printed circuit boards for defects. By using AOI, PCB manufacturers can increase accuracy and reduce inspection times, resulting in higher-quality products. The above discussion helps readers find the advantages of using the AOI in PCB manufacturing and how it is becoming the future of quality control.

Automated optical inspection is ideal for SMT even though inspection through X-ray is trending in the PCB industry. Manufacturers consider the AOI cheaper and more reliable than several other methods.

So, automatic optical inspection has proved itself to be an invaluable tool for PCB manufacturers by providing numerous benefits. From its ability to detect even small defects to its cost-efficiency and high throughput rate, AOI is essential for ensuring the quality of the finished product.

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smt-assembly

SMT Assembly and Thru-Hole/Chip Functionality

Printed circuit boards are parts of various electronic devices, home appliances, and vehicles. The function of these green chips depends on their material and assembly technology. Each step of PCB assembly is important and needs careful processing considering essential features.
Two methods are popular in PCBA, including, MT and THT. Let’s study them in detail.

Through-Hole Technology (THT)

Traditional PCB has through whole technology, involving both automatic and manual processes. THT is PCB packaging technology that involves pins or leads, besides, you have to insert the chips in the PCB through holes, soldering from below. The technique gives it the name through-hole.
Through-hole technology was more in practice till 1980 and every PCB device had this technology. Then SMT emerged where chips are installed on the surface. However, some PCBs still need through-hole chips, like capacitors and resistors.
THT needs more drilling, however, the device with this technology has a durable bonding with the circuit board.
Let’s look at the important steps of THT.

Installation Of Components

Engineers place PCB components with their hands, however, it needs precision depending on the design.
PCB Inspection
PCB inspection is crucial because most devices need flawless PCBs to work well. Most of the through-hole process is manual, so you have to make sure that the assembly is without any mistakes.
Printed Circuit Board Soldering
Soldering of components is also important as you have to fix the components manually. This is the last part of assembly, and the manual work makes it more reliable than SMT.

Why Is THT Still In Use?

Though THT is an old PCBA technology, you still need it for certain reasons, such as:

  • Even a hobbyist can assemble a circuit board with THT by using a soldering iron. It involves less hassle because the holes are away from surface pads compared to SMT.
  • If you observe a hobbyist application of the THT circuit board, you will see the ICs with the 8 or 14-pin having centers up to 0.100”xp.300”. Sometimes even the DIP processors have such spacing between the holes that helps in manual soldering, making the PC Board assembly easier.
  • After assembly, the troubleshooting or revision reduces in THT because it does not involve bridges between the pins, be it single or multiple components.
  • THT has better professional assembly, especially when a project is at a prototype stage. You can apply the through holes in a prototype layout to assemble the board faster.
  • After evaluating the board function, you can swap in the SMT having the same value, revising the circuit board’s layout. The new layout has small footprints to be inspected before final production. Such techniques reduce the front cost of a project which can benefit a subcontractor.

Remember that small products demand more pricing from outside vendors as they prefer high-volume production for continuous machine work.

Benefits Of Through-Hole Technology

  • When it comes to PCB design revision, a through-hole technology doesn’t need to create an additional solder stencil. So, manufacturers can save a huge amount of money on a PCB design having 2 to 3 revisions before it is ready to use. Besides, you don’t have to arrange the equipment for the pick and place function.
  • The manual inspection of a small lot of printed circuit boards reduces the fixture expenses or any other cost regarding linked setups.
  • Soldering is also cheap in THT, such as the tin-lead solder. Besides the issue of HASL or hot air solder leveling does not occur in through-hole technology, unlike SMT where the HASL makes it hard to place the components having a precise pitch.
  • You can easily assess the mechanical faults, including twists, and warps, and can deal with them while redesigning without affecting the assembly as what happens in SMT. Issues like twist and warp are not as problematic in manual assembly as in SMT.
  • The hand assembly of a PCB helps fit hard components by changing the wrist angle. Whereas the automated assembly needs an extremely flat circuit board for proper functioning.
  • THT can help pinpoint mechanical faults before it gets hard to resolve them. Otherwise, the inspection becomes costly when it has to go into the hands of three persons, including you, the contract assembler, and the PCB Manufacturer.
  • The components for THT are easily accessible that keep the job going without interruption. Moreover, you don’t need a third-party assembly in the case of small production.
  • With THT, the project timeline is predictable and easy to manage with minimum issues without causing any production delays.
  • Even if you don’t want to prefer a through-hole assembly, you must consider it as a temporary solution at early stages like validation and development. So, it can benefit anyone, including a hobbyist, any established company, or a beginner in this industry.

Surface Mount Technology-Surface Mount Chip

Surface mount assembly and SMT is other popular PCB assembly technology. It is an advanced method involving automation. Besides, it is ideal for smart PCBs that today’s smart devices need.
As the name shows, PCB components are directly installed on its top surface, whereas the device having a surface mount technology is called SMD. You can say that traditional through-hole technology is being replaced by surface mount assembly.
However, through-hole technology is still in practice for big transformers or power semiconductors as their components are not compatible with SMT. Likewise, many other heavy electronic devices with heat sinks need through-hole PCBs.
Surface mount technology has more positive aspects than negative pros, so let’s discuss them in detail.

Positive Aspects Of Surface-Mount Technology

SMT Involves Minimal Surface: The component area, volume, and size in an SMT are 70% less than the component area in through-hole technology. Even the component area can become 90% less than its volume in a traditional PCB having a through-hole technology. Likewise, the overall weight of the PCB reduces, as the components’ weight reduces by 70 to 90%.
It Enhances The Signal Speed: a PCB assembled with SMT has a fast signal transmission due to a short circuit. The assembly density in such technology can go up to 5.5~20 solder joints in one square centimeter, like when there is paste on both sides of the PCB. Similarly, a PCB with SMT has a high impact and vibration resistance that helps create high-speed electronic devices.
Excellent Frequency: In SMT, the board has either no lead or it is very small which reduces its parameters, decreasing the interference in terms of RF. It means that the PCB gets high-frequency signals, and the device having it works faster.
Minimum Packaging Cost: when it comes to an SMT packaging price, you will see it much lower than THT. Since surface-mount technology involves effective production tools, the usage of packaging material reduces thus cutting down its cost. However, the decrease in the cost does not affect the quality of an SMT circuit board.
You don’t have to bend or cut the component leads in the SMT boards which reduce the assembly time, making production faster than THT. So, the production cost also reduces by 50% as the manufacturing process of SMT is quite simple.

Additional Info

In SMT, the solder paste is applied with a stencil printer that helps finish a raw board better and faster than a traditional method. In other words, you get fineness in an automated assembly.
The installation of the components becomes easier, as solder paste makes everything clear due to printing. Each SMT process is well-inspected that helps have accuracy.
In SMT, the process of reflow soldering also makes a circuit board highly durable. In reflow soldering, the technician places the circuit board under high temperature to melt and reshape the paste, making it permanent. You can use both reflow soldering and automation or can switch from one to another, depending on your needs.
The important thing is to design and assemble a PC Board considering all the dos and don’ts and have a flawless end product.

Some Negative Aspects Of SMT Assembly

Surface-mount technology is not full of benefits, instead, it has some drawbacks, such as:

  • It has less power
  • It is vulnerable to damage
  • SMT requires high-quality soldering because poor soldering can lead to leakage, tombstoning, bridging, and several other risks.
  • It involves delicate installation, resulting in dropped components.
  • Its inspection is hard, especially, the visual test as it has multiple types of solder joints.
  • The equipment cost is high.
  • It involves well-trained technicians that increase the learning expenses.
  • It needs consistent updates of assembly equipment due to fast development.

Final Thoughts

Printed circuit boards involve different assembly techniques, including a through-hole technology, and a surface-mount technology. The component area, volume, and size in an SMT are 70% less than the component area in through-hole technology.
When it comes to PCB design revision, a through-hole technology doesn’t need to create an additional solder stencil. So, manufacturers can save a huge amount of money on a PCB design having 2 to 3 revisions before it is ready to use.
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PC Board Electrical Schematic and Its Functionality?

Whatever we create, including a PC Board,is a picture or an idea that we convert to paper in the form of a diagram. You can’t proceed with manufacturing without a proper PCB layout or schematic.

An electrical schematic is a conceptual plan or drawing that helps understand the physical aspect of a PCB in terms of assembly.
The basic purpose of electrical schematicsis to have design communication.It should help manufacturers clearly understand it.Besides, the schematic directs you to makea PCB layout.

Schematics involve specific elements which are essential to understand, such as:

  • REFDES or reference designates
  • Symbols representing the components
  • Outputs
  • Nets

To know schematics in detail, you have to understand the above elements.

REFDES or Reference Designators-Identifying Labels

Identifying labels or reference designators help understand components because they describeso much about them. If REFDS is precise, it helps a reader to identify the types of the components and symbols,depicting every component.
So, each electrical component or part has a standard symbol.However, onlyspecific schematics follow such standards.
In some cases, reference designators can fully describe the component type, like when there is a generic box with pins itrepresents a passive component.

At the same time, reference designators also connect to theBOM, and bill of materials. Every Printed Circuit Board component needs a part number that BOM shows. Besides, it also helps find the area or location where components should be installed.
The format of the reference designators consists of a code in the form of a letter that describes the component, and its type having a specific number.

Symbols Representing Components

The electrical schematic has specific symbols of the physical components of PCB assembly in terms of soldering. They also describe the circuit boards’ structures, such as test points and vias.

The symbols are specific shapes or they are diagrams to indicate the type of PCB components. There are symbols for all electrical components like capacitors, diodes, resistors, and transistors.

The symbol of each component consists of pins that help in creating the electrical connections. The pins of all schematic symbols have specific numbers,depicting the physical components.

Designers can assign either a single symbol or multiple symbols to represent a single component of a PCB. Whereas the components having several pins are assigned many symbols to create a readable electrical schematic.

When a component is having multiple symbols, each symbol representing the same component has a similar designator.

Electrical Components-Resistors

PCB has many electrical components, including resistors. The U.S designers use a zigzag line to describe a resistor. Whereas its symbol is a rectangle according tointernational standards.On the other hand, the letter R in schematics isa representation of the resistor.

CapacitorSymbols and Letter

Capacitors have two types, includingpolarized capacitors and non-polarized, and both have different symbols. The curved line is a symbol of a negative terminal of a polarized capacitor. Whereas the plus sign denotes a positive terminal of a polarized capacitor.Whereas the letter C defines a capacitor in schematics with REFDES.

Inductor Symbol and REFDES Reference

Inductors are also important passive components of a PCB, and their construction involves a series of curves.Manufacturers use a coil of wire to make inductors. Whereas the letter L defines a capacitor in schematics with REFDES.

Diode Symbol and REFDES Reference

Some other PCB electrical components within the PCB design include diodes that permit the current to travel in just one direction. The diode has different types, including

  • Zener diodes
  • LEDs or light-emitting diodes
  • Schottky diodes

Zener diodesprevent the reverse flow of a current. However, the reverse flow can happen at a certain electrical power level.
There are also LEDs or light-emitting diodes which emit light when having a forward flow of a current.
The Schottky diode has simple features,but it switches quickly and the voltage drops in a lower forward direction.
Other than LED, the letter D or L defines a capacitor in schematics with REFDES.

Transistors Symbol and REFDES Reference

Transistors involve the flow of current at the primary terminal and they function like switches. The basic types of transistors include:
Bipolar Junction Transistors-BJTs: It is a current managing device that helps a current flow either into one base pin or out of it, changing to high currents passing through emitters and collectors.

Field-Effect Transistors-FETs: The FE transistor is another current-managing device that helps voltage turn on the current on the pin, via source pins and adrain. Various drawings indicate transistors and the letter Q and M define a resistor in schematics with REFDES and also represent the MOSFET. However, some designers use the letter T in the wrong way.
Variable Resistors’ Symbol andREFDES Reference

Variable resistors have two categories:

  • Potentiometers-three terminals
  • rheostats-two terminals

The function of the variable resistors is to customize resistance according to users. An arrow across the resistor represents the rheostats, whereas an arrow on the side of the resistor shows potentiometers.

There are also varistors or voltage-dependent resistors which resemble the variable resistors, but they are denoted by a line across them.The symbols of the resistors include R, VR, and RV, depending on the type of the resistor.

IntegratedCircuits, Symbol, and REFDES Reference

A single-package circuit developed with a semiconductor is an integrated circuit. You can also consider such circuits asamplifiers, processors, power regulators, and memory of a device. The shape of the integrated circuit is like a rectangle or a square that you can install on a PCB. It is a box with power inputs and outputs or pins and sometimes a board has many boxes.

The symbolof the integrated circuit in a schematic is the IC or the U.

Resonator, Crystals, and Oscillators, Symbol and REFDES Reference

PCB also has resonators, crystals, and oscillators, which give a consistent frequency output. These elements are different in terms of circuitry and characteristics but they have a commonfunction.

Some Other Symbols

There are also several other symbols to show interconnections on a schematic having labels to find their electrical nets.
Mostly there is no reference designator for non-component symbols, however, some have symbols like TP or test points, and X, and MH on REFDES.

Understanding Nets in Schematics

The wired connections on the printed circuit boards are what designers call nets. They are lines that connect symbol pins to the nets. You have to properly label the nets while making schematics to help manufacturers identify them. Specific symbols depict thenets to the same or different pages when you don’t draw them as connections, such as interpage and intrapage symbols.

Try not to overlap the nets to have good readability, however, you can’t ensure it every time. A dot or a circle on a schematic diagram shows two nets’ connection. If there is no DOT in a schematic, it means there is no connection between the nets. Whereas advanced drawings have wire hops to show that the nets don’t connect.

Outputs of Schematics-Netlists & BOM

The schematic diagram has two important outputs, including BOM, and netlists. The netlist is a file that designers use to understand routing and parts’ placement on a PCB. The format of thenetlists can vary in symbols. The name of the nets is presented in the netlist, showing thelocation of connectionsbetween the PCB parts. Netlist also has an output tool to give names to the nets which were without names.
Generally, there are several tables in a netlist, listing the PCB components and their names, net names, and some other essentials. Sometimes the netlists include additional information to help you understand the SPICE.

Bill of Materials-BOM

Bill of materials shows data in the form of a spreadsheet,matching the REFDES in schematicshaving a number and a physical component. Designers use different formats for BOM outputs, depending on the nature of schematics and your requirements in terms of output.
There can be many reference designators with independent partnumbers to help with manufacturing. Some detailed BOMs consist of specific part numbers of a company, quantities of components at different locations on a PCB, and the part numbers for different vendors. In other words, BOM has essential information to understand schematics and develop it through different steps, including SMT assembly.

Final Thoughts

You must know that the electrical schematic is a drawing that helps understand the physical aspect of a PCB in terms of assembly. The main aim of electrical schematics is to have design communication and help manufacturers construct the PCB. It should help you clearly understand parts and assembly. All electrical components have standard symbols. But, only specific schematics follow such standards. Different software help make electrical schematics that you can explore online.
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Six Basic PCB Design Principles

Six Basic PCB Design Principles

Printed circuit boards are vital parts of smart devices and several equipments as they provide current or electrical signals to run them. You need different elements to construct a PCB, such as:

  • Schematic design
  • Database login
  • Electronic component configuration
  • Design preparation
  • Wiring
  • Block division
  • Testing

If any issue happens during a process, you have to go back to the previous process to correct it. The layout of PCB components is a complex thin as it determines a board\s appearance and neatness. Moreover, it also affects the function of the end product or device. We will discuss below the six basic PCB design principles in terms of its components and other factors.

1-Components Layout and Clearance

You have to place the components evenly on the board, leaving some space on the edges. The components around the edge should be 3mm away from PCB edges. In general, designers leave 5 to 10 mm space around the edges.

The components should be only on a board’s one side. There should be a separate pad for each lead pin.

Don’t cross up and down the components’ layout and keep a certain distance between the nearby components on the board. However, this distance should not be too small as it can hinder PCB maintenance.

Components should be installed at a low height and its lead should not be more than 5mm away from the PCB, as it can affect its quality to bear vibration.

Printed Circuit Board components that reside on a pad’s both ends must be a bit larger than their axial dimensions. The pads should be located where the coordinate grid intersects. The central distance of the pad has to be more than the board thickness to have a neat layout.

According to IEC or International Electrotechnical Commission, the standard spacing of the coordinate grid should be 2.54mm, whereas the axillary spacing should be 1.27mm.

However, these standards practically impact a few processes, including automatic drilling, computer automated design, components welding, and automatic assembly. But, such a grid spacing is not restricted in the case of manual drilling.

2-Defined Solder Mask

Solder mask expansion should be well-defined as it can cause issues if you over-define or under-define it. Tombstoning may happen if you don’t define the solder mask properly. Like, one side cools down faster than another side, affecting the board. So, by following the right parameters, you won’t have to revise your design.

The solder mask opening should be larger than the pad. In general, it expands 4 mils or 0.1mm. However, both can also have the same size, depending on the Printed Circuit board Fabrication.

3- Via Type& Routing Width

You must use the right via for routing as it won’t work if its diameter or ratio is not precise. The current won’t pass correctly due to fused vias. So, via styles should be considered while routing the entire PCB.

The routs should have enough width to carry the current that your device requires. You must have an impedance-controlled routing that needs various impedance profiles. You have to apply these profiles to routing widths to ensure a functional layout. Don’t have routing at an acute angle even if the signals have a low speed as acute angle hinders manufacturing. Like, an acute angle can increase the corrosion, leading to an open circuit.

Whereas it is vital to avoid the acute angle in the case of high-frequency circuits because it fully changes the track width at the corners and results in poor signals and discontinued impedance.

Six Basic PCB Design Principles
Six Basic PCB Design Principles

4-Components Installation

Different PC Board components are installed either vertically or horizontally. The horizontal components are parallel to the surface of the circuit board. Whereas in vertical installation, components are perpendicular to the PCB surface.

Vertical components allow you to have more quantity on a board’s surface. It is ideal for hearing aids, semiconductor radios, portable instruments, or devices that need a dense placement of components. For vertical installation, components have to be lightweight. Don’t install heavy components in a vertical direction as it can affect a PCB’s mechanical strength. Moreover, it causes vibration, and components can collapse, making a circuit less reliable.

On the other hand, the horizontal installation provides mechanical stability, and the circuit board also looks neat. It also helps lay down the printed wires because it enhances the elements’ span.

You can use any installation method, depending on your needs but make sure to arrange components evenly and the circuit should be anti-vibration.

5-Considering The PCB Layout Type

PCB layout has either a regular arrangement of components or is irregular. In an irregular format, the axis of the components are not aligned with each other, so it seems messy. However, it helps lay down the printed wires easily as there is no restriction of direction. Such a layout is ideal for high-frequency circuits and involves a vertical installation.

Whereas in a regular format, the component axis is aligned and either parallel or perpendicular to the sides of a PCB. It provides a neat board and makes certain processes easier, like PCB assembly, debugging, welding, maintenance, and production.

Moreover, a regular format is ideal for low-frequency circuits where the board has a few component types and its surface is loose. However, the number of components is high and such an arrangement also suits electronic instruments. But, due to the direction restrictions, such a PCB has a complex layout of wires, increasing the overall length of the wires.

6-Factors That Affect the PCB Layout

You also have to consider the factors that affect a PCB layout, like the direction of the signals, device position electromagnetic interference, thermal interference, mechanical strength, etc.

  • Generally, the direction of the signal flow is from left to right of which left is the input and right is the output. It is also from top to bottom of which the top is the input and the bottom is the output. Connectors which are in direct connection to the input and output should be close to the input and output connectors. Integrated circuits or transistors should be the core components. Whereas other components should be located according to their electrodes’ location. You should also consider the size, a number of pins, shape, and polarity of components.
  • You should adopt certain ways to prevent electromagnetic interference that occurs due to different external factors, like spatial electromagnetic ways, poor wiring, poor installation of components, etc. You can avoid these issues during the layout design. But, interference will happen if the PCB design is not right
  • You should shield the components that interfere with each other. High-frequency components should have small wiring. Similarly, the components of weak and strong currents should be separated. Wires with high potential should be at a great distance to avoid 50Hz interference. Likewise, the metal components should not be adjacent or they should be well-insulated to avoid a short circuit.
  • While designing a PCB, you must know which components are temperature sensitive and which are heat components. The heating components like resistors should be located near the shell or near vent holes to dissipate heat. Don’t place many heating components near each other. Also, use fans or radiators to prevent the rise in temperature beyond its limit.
  • Whereas the temperature-sensitive components should be away from the heat source. In general, integrated circuits, transistors, electrolytic capacitors, and thermal components are temperature sensitive. These components get affected due to the rise in temperature, especially in a circuit’s long-term operation.
  • The board should also be mechanically strong and its center of gravity should be stable. Don’t install heavy or heating components directly on the board, instead, they should be under the chassis to have a stable board. If the board size is above 200mm it will cause mechanical stress, so it should be strengthened with a mechanical frame.

Finally, many PCB design software uses the power layer to have a fast design process. You can connect more wires to ensure the current has a minimum impedance or voltage drop down, thus giving enough ground return paths.

FAQs

1.How To Layout A Printed Circuit Board?
You have to follow certain steps to create a PCB layout. Such as making the schematic drawings, developing a blank PCB layout, creating a PCB stack-up, schematic capture, defining design principles, defining DFM, linking to PCB, placement of components, inserting drill holes, and the route traces.

2.Is It Hard To Design A PCB?
It is not hard to design your PCB if the electrical schematic is right. Besides, following the design parameters also makes the design process easy.

3.Why Is My PCB Green?
The color of the solder mask determines the PCB color. So, if the solder mask is green, you say that PCB is green. The solder mask shields a copper circuit to avoid shorts circuit or soldering issues.

4.What Is The Purpose Of Following PCB Design Rules?
PCB design rules or principles help you to develop a system to automate the testing of design requirements. You get an interface between the physical and logical sides to create a circuit board. So, you can automate the DFM tests by following the rules to ensure that you can build a PCB.
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