the Art of PCB Design Basics

2024-03-17

PCB design is the entire process of creating a Printed Circuit Board (PCB) through collaboration and integration between multiple disciplines and multiple domains which includes electrical, mechanical, software, system, test, and manufacturing. It’s a team effort that requires constant bi-directional communication.

1. PCB design in brief

Printed circuit board begins with the creation of a conceptual block diagram,This block diagram is converted into a schematic design using CAD software. A schematic is the representation of component symbols and net connections between them, Nets are the traces on the board.

Pre-layout is the next phase in the design process where the BOM (bill of materials) from the schematic is verifying for long lead time components and obsolete components. validation involves verifying manufacturer part numbers (MPNs) and vendor par numbers (VPNs). Additionally, this stage includes the stack-up design

Next comes the PCB layout stage. it involves setting up the board parameters, determining its outline, routing the components, and generating the production documents by adhering to a suitable design checklist.

2. PCB design basics 

While designing a new PCB,it is necessary to adhere to circuit design basics. If neglected, it will result in a poor board design that will be very difficult manufacture. Therefore, it is necessary to pay attention to the following concepts:

3. Choose appropriate components and package sizes 

As a board designer,you should thoroughly study the BOM and examine the parts that go into the design. When there is sufficient space on the board, you may opt for larger components for resistors and capacitors, t is beneficial to use a 0603 or 0805 size capacitor resistor instead of a0402/0201. select the smaller package version of the component if you have spacing issues. Moreover, choose your appropriate component and package based on the required current, voltage, and frequency.

Smaller components are manufactured by vendors vendors, it allows designers to choose alternate parts without modifying the schematic or layout providing a timely solution for components that are not in stock. Furthermore,it is crucial to decide the appropriate size of the package during the PCB design phase. It is recommended to choose smaller packages only when necessary; otherwise, choose larger packages. Using too many small component packages can create issues during circuit board assembly.which leads to difficulties during cleaning and reworking.

As soon as you determine the ideal package size, you can choose components in the same density category.

4. Avoid long lead-time components

The unavailability of components can cause considerable delays. So, it is better to check the availability while confirming component spacing. If your component has a long lead-time, order it immediately. It can be beneficial to have alternate components with the same footprint, Assembly vendors can also procure the widely available parts so that every component will be readily available when it is time to assemble the boards

5. Schematic checks 

A schematic is a well-structured circuit diagram that represents the electrical connections between various electronic components.

Schematic design basics often get ignored. Make sure you verify the following.

50. Verification of pin numbering and labels in component symbols
50. A polarity check for all the polarized components
50. Overlapping labels and Pins
50. Ensuring the base, collector, and emitter pins according to the schematic symbols, datasheet, and footprint package
50. Validation of the component value, location, and reference designators
50. Descriptions of the schematic symbols
50. Off-page connectors
50. Checking the inter-sheet reference
50. Decoupling capacitor check for all ICs, ground pin separation according to the signal type (analog, digital,signal, ground)
50. Netlist check for design correctness and wrong connections

6. Add test points to allimportant signals  

Design for testing is required to check the electrical conductivity ofthe board.It is necessary to add test points for all important signals to faclitate electrical tests (E-test) and in-circuit tests (lCT). Keep an eye on the following:

50. Board side: If possible, all test points should be located on the same side of the board to facilitate testing
50. Minimum test point distance: The minimum distance between test points is 0100 inches, it maximizes test effectiveness
50. Test point distribution: Distributing test points evenly on a circuit board makes testing easier with multiple probes.
50. Area for taller components: Designating the area for taller components can streamline the testing.
50. Manufacturing tolerances: Make sure to consider manufacturing tolerances while designing a layout to accommodate a space for test points

7. Make sure your BOM is up to date while designing 

A BOM is a detailed list of all the components required to produce a product, Keep your BOM up to date while designing, and if you make any changes to your design.ensure you have also implemented those changes in your bill of materials, For example, if you change the part number in the schematic, update the BOM as well.

Before you validate your BOM file, ensure that all the active parts are included in it. The parts should be validated with respect to the following fields:

50. Serial number
50. Part description
50. Designators matching the schematic
50. Quantity of the parts
50. MPN
50. VPN
50. DNl (do not install) components

8. Stack-up preparation in PCB design  

Stack-up is an important attribute in the basics of PCB design. It defines the structure of a multi layer circuit board in a sequential manner, Stack-up provides information about the material thickness and copper weights that are vital for circuit board manufacturing. When boards are precisely stacked, electromagnetic emissions and crosstalk are reduced, and the signal integrity is improved.

Know your board's mechanical constraints, which include board thickness and component height, It is important to know the controlled impedance requirements.including the number of differential pairs, as it will impact the number of layers in your board. The routing density of the circuit board will also impact the number of layers, Choose a PCB material based on the fastest rise time.

Verify the manufacture ability of your stack-up using our free Stack-up Planner. The following parameters are necessary for the planner:

50. The PCB material (FR4, I-Speed, Rogers, etc.) depends on the frequency requirements and environment.
50. Layers including signal and power layers.
50. Impedance requirements such as 50Ω single-ended, 90Ω differential, or 100Ω differential
50. Copper thickness (1/2 or 1 or 2 ounces)

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