Understanding Printed Circuit Boards

The printed circuit board ( PCB ) board serves as the foundation for electronic products. Also known as a Printed Circuit Board (PCB) or Printed Wire Board (PWB), it provides electrical connections for electronic components. It functions by using electronic printing to etch a pattern on the surface of an insulated, copper-clad laminate, forming a network of tiny circuits that allow various electronic components to establish predetermined connections and facilitate relay transmission between them. Most electronic devices and products require a PWB board.

Printed circuit boards, often termed PWB, are also commonly referred to as PCB substrates. The terminology can be somewhat confusing as the printed circuit board is not a typical end product. For instance, a personal computer’s motherboard is called a mainboard and not simply a circuit board. While motherboards contain circuit boards, they are distinct entities. Similarly, since circuit boards have integrated circuit components, media may refer to them as IC boards, but this is not entirely accurate. Typically, when we mention a printed circuit board, we are referring to a bare board, meaning a circuit board without any mounted components.

Based on the number of layers, electronic boards can be categorized into single-sided, double-layer, four-layer, six-layer, and other multilayer boards. The development of these boards is continually advancing towards higher precision, greater density, and enhanced reliability. The ongoing trends in reducing size, cutting costs, and improving performance have enabled printed circuit boards to remain crucial in the evolution of future electronic products. The future of PWB manufacturing technology is geared towards higher density, greater precision, smaller apertures, finer wires, narrower pitches, higher reliability, multiple layers, high-speed transmission, lightweight designs, and thinner profiles.

Based on the distribution of printed circuit boards:

Single-sided PCB Substrate

A single-sided PCB has a single layer of insulating substrate, with a thickness ranging from 0.2 to 5mm, covered with copper foil on one side. The printed circuit is created on the substrate by printing and etching. This type of board is straightforward to manufacture and assemble, making it suitable for simpler circuit needs like those in radios and televisions. However, it is not ideal for applications requiring high assembly density or complex circuitry.

Double-sided PCB Substrate

Double-sided boards feature printed circuits on both sides of an insulating substrate, also with a thickness of 0.2 to 5mm. These are used in electronic products with standard requirements, such as computers, electronic instruments, and meters. Double-sided PCBs have a higher wiring density than single-sided ones, which helps reduce the overall size of the device.

Multilayer PCB Plate

Multilayer PCBs consist of more than three layers of printed circuits on an insulating substrate, combining several thin single or double-sided boards. The typical thickness ranges from 1.2 to 2.5mm. To connect circuits embedded between the layers, the component mounting holes on multilayer boards must be metalized, coating the inner surfaces with a metal layer to establish connections with the circuits sandwiched between the insulating substrates.

Classified by the Nature of the Substrate

Rigid PCB Substrate

A rigid PCB provides certain mechanical strength and maintains a flat state when assembled with other parts. These are commonly used in general electronic products.

Flex PCB Substrate

A flexible PCB is made from soft layered plastic or other flexible insulating materials. It can be bent and stretched, adapting to various installation requirements. Flexible printed boards are often utilized in special applications, such as the rotating display screens of digital multimeters or the screens and buttons of mobile phones.

Rigid-Flex PCB Substrate

The combination of flexible and rigid PCB technologies led to the development of rigid-flex boards. These integrate flexible circuit board (FPC) and rigid circuit board (PWB) characteristics through pressing and other processes, resulting in a hybrid electronic board that features the benefits of both FPC and PWB.

Classified by the scope of application

PWB can be divided into low-frequency PCB and high-frequency PCB. High frequency of electronic equipment is the development trend, especially in today's wireless network and satellite communication, information products are moving towards high speed and high frequency, and communication products are moving towards the standardization of voice, video, and data of wireless transmission with large capacity and high speed. Therefore, the new generation of products needs a high-frequency printed circuit board, and the foil substrate can be made up of materials with small dielectric loss and dielectric constant, such as polyurethane, polyethylene, polystyrene, polytetrafluoroethylene glass cloth.

Classified by the special printed boards

At present, there are some specially printed boards, such as metal core printed board, surface mounted printed circuit board, and carbon film printed board.

Metal core PCB plate

The metal core circuit board is to replace the epoxy glass cloth board with a metal plate of the same thickness. After special treatment, the conductor circuits on both sides of the metal board are connected with each other and highly insulated from the metal part. The advantage of metal core PCB is good heat dissipation and dimensional stability. This is because magnetic materials such as aluminum and iron have a shielding effect and can prevent mutual interference.

Surface mount PCB
Surface mount printed circuit board (SMB) is a kind of PWB developed to meet the needs of light, thin, short and small electronic products, and with the installation process of surface mount devices with pin density and low cost. The printed circuit board has the characteristics of a small aperture, small line width and spacing, high precision, and high substrate requirements.

Carbon film printed substrate
Carbon film printed board is a kind of printed board that is printed with a layer of carbon film after the conductor pattern is made on the copper foil to form contact or jumper wire (the resistance value meets the specified requirements). It is characterized by a simple production process, low cost, short cycle, good wear resistance, and electrical conductivity.It can realize the high density of single panels and miniaturization and light weight of products. It is suitable for TV, telephone, video recorder, and electronic organ.

How to design PCB substrate?

When designing a circuit board, many complicated steps are often required. Whether it is the basics of micro-processing copper and solder or trying to ensure that the PWB is finally printed, or encountering more specific design problems, such as through-hole technology or design signals with through-holes, pads, and any number of layouts For integrity issues, you need to ensure that you have the correct design software. So now iPCB tells you how to design a PCB panel.

1. Create a schematic diagram of the PCB substrate

Whether you are generating a design from a template or creating a PCB panel from scratch, it is best to start with a PWB schematic. The schematic is similar to the blueprint of the new device, and it is important to understand what is shown in the schematic. Compared with designing directly on the PCB panel, not only is the circuit interconnection easier to define and edit, but it is also much easier to convert the PWB schematic diagram into the PWB board layout. For components, PCB circuit board design software has an extensive part library database.

2. Create a blank PCB plate layout

After creating the PWB schematic, you need to use the schematic capture tool in the PCB design software to start creating the PCB layout. Before that, you need to create a blank PCB document. To create a PCB panel, a PCB Doc file needs to be generated. This can be done easily from the main menu of the design software

If the PCB shape, size, and layer stack of the PWB panel have been determined, you can set it up immediately. If you don't want to perform these tasks now, don't worry, you can change the shape of the PCB plate later. By compiling SchDoc, the schematic information can be used in PCB. The compilation process includes verifying the design and generating several project documents so that you can check and correct the design before transferring to PCB. It is strongly recommended that you check and update the item options used to create the PCB information at this time.

When designing a PWB panel, it sometimes seems that it will be a long and arduous journey to reach the final design. Whether it is the basics of micro-processing copper and solder trying to ensure that the PWB is finally printed, or encountering more specific design problems, such as through-hole technology or design signals with through-holes, pads, and any number of layouts For integrity issues, you need to ensure that you have the correct PWB design software.

3. Capture the schematic diagram of the PCB prototype board and link it to the PCB

All the tools in the PCB prototype substrate design software can be used in a unified design environment. In this design environment, the schematic, PCB, and BOM are related to each other and can be accessed at the same time. Other programs will force you to manually compile the schematic data.

4. Design the PCB stack up

When you transfer the schematic information to PCB Doc, in addition to the specified PCB plate outline, the package of the component will also be displayed. Before placing components, you should use the "Layer Stack Manager" as shown below to define the PCB layout (ie shape, layer stack).

If you are not familiar with PWB plate design, although any number of layers can be defined in the PWB panel design software, most modern designs will start with a 4-layer board on FR4. You can also take advantage of the material stacking library; this way, you can choose from a variety of different laminates and unique panels.

If you want to design a high-speed/high-frequency circuit board, you can use the built-in impedance analyzer to ensure impedance control in the PCB prototype board. The impedance curve tool uses Simberian's integrated electromagnetic field solver to customize the geometry of the trace to achieve the target impedance value.

For more detailed PWB stack-up reference instructions, click Download

5. Define Design Rules and DFM Requirements

There are various categories of PWB design rules, and not all are necessary for every design. You can customize which rules to apply by right-clicking the specific rule in the list within the PWB rule and constraint editor below.

The rules you choose, particularly those for manufacturing, should match the specifications and tolerances of the PCB manufacturer's equipment. Advanced designs, like impedance control designs and many high-speed/high-frequency designs, might require adherence to very specific design rules to ensure proper functionality. Always consult your component datasheet to understand these design rules.

6. Place Components on the PWB Prototype Substrate

Current mainstream PWB design software offers significant flexibility, allowing quick placement of components on the circuit board. You can arrange the components automatically or manually, or use a combination of both to benefit from the speed of automatic placement while ensuring adherence to good component placement guidelines.

7. PWB Board Insertion Hole

Before laying out the PWB, it's advisable to place drill holes (mounting and vias). For complex designs, you may need to adjust some via locations during the routing process, which can be easily done through the "Properties" dialog box.

Your preferences should align with the circuit board manufacturer's DFM specifications. If you have defined DFM requirements as design rules (see step 5), the PWB design software will automatically check these rules when placing vias, drill holes, pads, and traces in the layout.

8. PWB Plate Layout Tracking

After positioning the components and any other mechanical elements, you can prepare the layout. Ensure you use proper wiring guidelines and leverage PWB design software tools to simplify the process, such as net highlighting and color coding through wiring.

9. Add Labels and Identifiers to the PWB

Once the PWB layout is verified, add labels, identifiers, marks, logos, or any other images on the PCB. Using reference identifiers for components is helpful for PWB assembly. Additionally, include polarity indicators, pin 1 indicators, and any other labels to identify components and their orientation. For logos and images, consult your PWB manufacturer to ensure the fonts are readable.

10. Generate the Gerber File for the PCB Layout Design

Before the PCB manufacturer can proceed, it is crucial to verify the PCB layout by running a design rule check (DRC).

After the PWB board passes the final DRC, generate design files for the PCB manufacturer. These files should include all necessary information and data to build the board, along with any notes or special requirements to ensure clarity. Most PCB manufacturers accept Gerber files, though some may prefer other CAD file formats. Now, do you understand what a PCB is?

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