You must know the steps and principles of PCB design

pcb design is the foundation of pcb manufacturing assembly, a complete pcb contains a variety of circuits and components. pcb design involves locating and aligning the various electronic components on the board, ensuring that everything works in harmony to bring the electronic device to life. During PCB design, careful planning is required to optimize performance, minimize signal interference and efficiently utilize available space.

In this article we will focus on giving you an overview of pcb design ideas and processes, so that you can grasp all aspects of the key points of pcb design, avoid mistakes in the design process and design the perfect pcb.

 

Requirements for pcb design

Before pcb designing, we first need to plan the following to ensure that we can complete the pcb design task accurately and on time.

Project Definition
In the initial phase of PCB design, requirements and specifications become critical because the project objectives, performance measures, and regulations are all spelled. To do so, one has to define key performance indicators, comply with industry standards, and take into consideration the demands of components, time, and money.

A comprehensive risk assessment, cooperative strategies, and scalability further provide a solid grounding for the entire design process. This approach guarantees that the latter phases are in line with project goals hence facilitating effective and successful implementation of PCB designs.

Perform Criteria
Determining performance criteria, or establishing and identifying the critical metrics that govern the effectiveness and functioning, is an essential phase in the PCB design process. Such criteria include processing speed, power consumption, and environmental impact among other issues that relate to reliability. These predetermined criteria must be surpassed by or at least met by PCBs through careful examination thus providing a clear roadmap for maximizing overall system performances of electronic systems. Performance requirements therefore need to be specified at the early stages of design to guarantee that a PCB is delivered in conformity to its intended application and user expectations.

Regulatory Compliance
An important part of PCB design is regulatory compliance. A product must meet industry and legal guidelines in terms of use or the making of electronic devices. As such, it is necessary to go through all applicable regulations, safety precautions, and EMC (electromagnetic compatibility) standards. These parameters ensure the safety of users, the reliability of products, and the ease of interacting with the regulatory framework.

It is up to the designer to guarantee that the PCB adheres to these rules. All necessary modifications are made to ensure that the design satisfies the specifications. Thorough documentation and testing are essential for verifying adherence. Proactive approaches towards regulations within PCB designs not only satisfy legal requirements but also set a basis for reliable and economically successful electronic products.

Budget and Timeline
Along with determining realistic financial limits and establishing a deadline, managing money and timeframe effectively is one of the crucial elements in PCB design. Regarding the cost of purchasing, fabrication, and testing of components, designers have to be economical in their use of resources. Meanwhile, there will be a clear timetable with critical milestones that will enable tracking progress as well as meeting project completion dates.

To reconcile the requirement to produce a high-quality PCB with financial constraints, the budget and schedule must be regularly reviewed and modified during the design cycle.

Component Requirements
A designer should ensure that the electronic components that make up the circuit are properly for meeting component requirements in PCB design. Designers have to indicate the required types and qualities of components, taking into account such factors as cost, compatibility, and usefulness.

A critical analysis of part availability and viable substitutes results in a firm design that aligns with the technical requirements and financial constraints.

Scalability and Future Considerations
Further considerations in the future require that designers examine how robust their work will be when it comes to upgrades or modifications. This includes looking at market trends, technological advances, and possible changes in project parameters going forward. With its scalability-conscious design, the PCB can resist future expansions or updates without needing to be completely redesigned.

Using a flexible design approach and accounting for emerging technology extends the life and usefulness of the electronic system. This establishes the foundation for further creativity and adaptability as the project grows. This perspective ensures that the PCB will remain viable and functional for an extended time.

Collaboration and Documentation
Collaboration and documentation ensure communication and thorough records throughout the entire design journey. Within the design team having roles and responsibilities promotes teamwork. This documentation proves invaluable when it comes to design iterations, troubleshooting, and sharing knowledge among team members. Efficient collaboration and meticulous documentation not only strengthen team cohesion but also preserve institutional knowledge and facilitate smooth transitions between different phases of PCB design.

Risk Assessment
Conducting a risk assessment is a step in the PCB design process. This involves identifying and evaluating obstacles or uncertainties that could impact the project. Designers proactively consider factors such as component accessibility, production complexities, and external market influences. The goal is to anticipate risks by developing alternative strategies to address challenges.

By systematically addressing uncertainties early in the design phase, the risk assessment lowers the likelihood of issues during manufacturing and testing. By assuming measured risk, the PCB design process remains adaptable and responsive to unforeseen challenges, thus increasing the project’s overall success.

To sum up, a comprehensive risk assessment makes it easier to recognize and address potential roadblocks, which in turn creates a resilient design that can effectively handle uncertainty during the manufacturing and testing stages.

You must know the steps and principles of PCB design

PCB Design Process and Principles

PCB design 7 steps

1, network table input
The network table generated from the schematic diagram is input into the computer software to ensure the consistency of the schematic diagram and the PCB diagram to minimize the possibility of error.

2. Rule Setting
If the PCB design rules have been set up in the schematic design stage, there is no need to set up these rules, because when entering the netlist, the design rules have been entered with the netlist.

3. Component Layout
After inputting the netlist, all the components will be placed at the zero point of the workspace, overlapping together, the next step is to separate these components and arrange them neatly according to some rules, i.e. component layout.

Manual Layout
①Tool the structure of the printed circuit board dimensions to draw the board edge (Board Outline).
② Disperse Components, the components will be arranged around the board edge.
③ Move and rotate the components one by one, put them inside the board edge, and arrange them neatly according to certain rules.

4. Wiring
There are two ways of wiring, manual wiring and automatic wiring. The manual wiring we provide is very powerful, including automatic extrusion, online design rule check (DRC), automatic wiring by Specctra’s wiring engine, usually these two methods are used in conjunction with the common steps are manual-automatic-manual.

5. Inspection
The items to be checked are spacing, connectivity, high speed rules and power layer, which can be done by selecting Tools->Verify Design. If high speed rule is set, it must be checked, otherwise you can skip this item. If an error is detected, the layout and wiring must be modified.

6. Review
Review according to the “PCB checklist”, including design rules, layer definition, line width, spacing, pads, hole settings; but also focus on reviewing the reasonableness of the device layout, power supply, ground network alignment, high-speed clock network alignment and shielding, decoupling capacitor placement and connection.

7. Design output
PCB design can be output to a printer or output light drawing files. Printers can print the PCB layered, easy to check the designer and reviewers; light drawing files to the board manufacturer, the production of printed circuit boards.

 

PCB layout principles:

Good wiring depends on a good layout. The location of the components of the arrangement, mainly from the anti-interference, heat dissipation, alignment topology type, cross-interference, power decoupling, ground connection and other considerations. The most primitive and ultimately the most effective approach is manual layout. This is more laborious, and often has to be constantly adjusted to make the layout more reasonable.

Layout of the first principle is to ensure that the wiring of the cloth through the rate, move the device to pay attention to the connection of the flying wires, the use of flying wires and schematic diagrams to connect the relationship between the tight device together, the components of the functional blocks are separated, and to determine the initial position of the device inside the functional blocks. Then adjust the relative position between each functional block.

1. Determine the component information First of all, you need to have a complete understanding of the selected component device and various socket specifications, size, area, etc.. For example: mounted on the printed circuit board of the larger components, we must add metal attachments fixed to improve vibration resistance, impact resistance, the attachment will also take up a certain amount of board area. Information such as this must be considered carefully.

2. Determine the form and size of the printed circuit board The size of the printed circuit board is limited by the size of the chassis shell, in order to be able to just put into the shell as appropriate. Consider the printed circuit board and external components (mainly potentiometers, jacks or another printed circuit board) connection. Printed circuit boards and external components are generally connected through plastic wires or metal isolation wires. However, sometimes they are also designed in the form of sockets. That is: the installation of a plug-in printed circuit board in the device to leave the contact position as a socket.

3. digital device area and analog device area and power device area, etc. to be separated, and their respective ground last single-point connection.

4. Decoupling capacitors as close as possible to the device VCC.

5. Place the device to consider the future welding, not too dense.

6. Try to put the devices that generate a lot of heat on the edge of the PCB.

7. Printed circuits are not allowed to have cross-circuit, for possible cross-lines, you can use “drill”, “winding” two ways to solve. That is, so that a lead from other resistors, capacitors, transistors, feet under the gap in the “drill” over, or from the possible cross of one of the leads of the end of the “winding” over, in special circumstances how the circuit is very complex, in order to simplify the design also allows for the use of wires across the solution to the problem of cross-circuit. Circuit problems.

8. Resistors, diodes, tubular capacitors and other components have “vertical”, “horizontal” two types of installation. Vertical refers to the component body perpendicular to the circuit board mounting, welding, the advantage is to save space, horizontal refers to the component body parallel and close to the circuit board mounting, welding, the advantage is that the component is mounted on the mechanical strength of the better. These two different mounting components, printed circuit boards on the component hole spacing is not the same.

9. The grounding point of the same level of circuit should be as close as possible, and the power supply filter capacitor of this level of circuit should also be connected to the grounding point of the level. In particular, the transistor base, the emitter of this level of grounding can not be too far away, or because the two grounding points between the copper foil is too long will cause interference and self-excitation, using this “one-point grounding method” of the circuit, the work is more stable, not easy to self-excitation.

10. Ground must be strictly according to high-frequency – mid-frequency – low-frequency level by level of weak power to the principle of sequential arrangement of strong power, can not be casually flipped back and forth to connect the level and the level of the level of the intersection can be wired longer, but also to comply with the provisions of this regulation. In particular, the inverter head, regeneration head, FM head of the grounding line arrangement requirements are more stringent, such as improperly will produce self-excited so that can not work. FM head and other high-frequency circuits often use a large area surrounded by ground to ensure a good shielding effect.

11. Strong current leads (common ground, amplifier power leads, etc.) should be as wide as possible to reduce the wiring resistance and its voltage drop, can reduce parasitic coupling and self-excitation.

12. high impedance of the alignment as short as possible, low impedance of the alignment can be longer, because the high impedance of the alignment is easy to send flute and absorb the signal, causing circuit instability. Power line, ground, no feedback components of the base line, the emitter leads are low impedance line, the base line of the emitter follower, the recorder two channels of the ground must be separated, each into a way, until the end of the efficacy and then together, such as the two ground lines are connected to connect, it is very easy to produce crosstalk, so that the separation of the degree of decline.

13. Potentiometer, IC seat placement principles

①Potentiometer: used to adjust the output voltage in the voltage regulator, so the design of the potentiometer should be full of clockwise adjustment when the output voltage rises, counterclockwise adjustment of the output voltage decreases; in the adjustable constant-current charger potentiometer is used to regulate the size of the charging current folding, the design of the potentiometer should be full of clockwise adjustment when the current increases. Potentiometer should be placed in the whole machine structure installation and panel layout requirements, so it should be placed as far as possible on the edge of the board, rotating handle facing out.

② IC holder: When designing printed boards, in the case of using IC holders, special attention must be paid to the correct orientation of the positioning slots on the IC holder, and to the correct position of each IC pin, for example, pin 1 can only be located in the lower right corner of the IC holder or the upper left corner, and immediately adjacent to the positioning slots (as viewed from the soldering surface).

14. Arrangement of inlet and outlet terminals

Do not place the two associated terminals too far apart.

The inlet and outlet terminals should be concentrated on one or two sides as much as possible and not be too discrete.

15. The spacing between the two pads of the capacitor should be as close as possible to the spacing of the capacitor’s lead wires;

16. The wiring rules can be pre-set, including the number of bends in the alignment, the number of through-holes, the number of steps, etc. Generally, exploratory warping is performed first. Generally the first exploratory cloth warp, quickly connect the short line, and then automatic wiring to see whether the wiring density is uniform, according to the wiring density to adjust the component arrangement.

17. When wiring manually, turn on the DRC option to check which lines do not comply with the rules.

 

The principle of pcb wiring

1, in accordance with the “first after the small, difficult after the easy” principle of layout, the first layout of important unit circuits and core devices, such as MCU minimum system, high-frequency and high-speed module circuits.

2, with reference to the schematic block diagram, the first schematic layout of each unit circuit first, and then the whole for the patchwork, in the patchwork, we must consider the circuit signals of the main mention of the direction.

3, try to meet the following requirements: the total line as short as possible, the shortest key signal line; high voltage, high current signals and small current, low voltage weak signals are completely separated; analog signals and digital signals are separated; high-frequency signals and low-frequency signals are separated; high-frequency components should be spaced out adequately.

4, decoupling capacitor layout should be as close as possible to the IC power pins, and to ensure that the power supply and ground between the formation of the shortest circuit, in order to achieve the best effect of decoupling, the power supply and the ground need to go through the decoupling capacitors at both ends, and then connected to the IC power supply and ground at both ends.

5, for some of the products that need to be tested over static electricity, the device placed as far as possible from the edge of the board distance greater than 3.5mm; if the board space is limited, you can be more than 0.45mm from the edge of the board out of the perforated holes to ground.

6, in the completion of the board performance based on the layout of the need to consider the beautiful, for the same structure of the circuit part, as far as possible, using the “symmetrical” layout, the overall layout can be in accordance with the “uniform distribution, the center of gravity balance, layout and beautiful” standard.

7, for heat-generating devices, such as MOS tubes, you can take the form of adding a heat sink to give heat.

8, the PCB of digital circuits can be used to form a circuit with a wide ground lead.

9, in advance of the more stringent requirements of the line (such as high-frequency line) for wiring, the input and output sides should be avoided adjacent to the parallel, so as to avoid reflective interference.

10, the oscillator shell grounding, clock line should be as short as possible, and can not lead everywhere. Clock oscillation circuit below, special high-speed logic circuit part to increase the area of the ground, and should not go other signal lines to make the surrounding electric field tends to zero.

11, as far as possible to use 45º folding line wiring, not to use 90º folding line to reduce the radiation of high-frequency signals.

12, any signal line should not form a loop, if unavoidable, the loop should be as small as possible; signal line over the hole to minimize.

13, the critical line as short and thick as possible, and add a protective ground on both sides.

14, through the flat cable transmission of sensitive signals and noise field band signals, to use the “ground – signal – ground” way out.

 

PCB pad design principles

 

1. Pad size and spacing: pads on one side of the minimum of not less than 0.25mm, the maximum diameter of the entire pad is not greater than 3 times the aperture of the component. Try to ensure that the spacing between the two pad edges is greater than 0.4mm. in the case of dense wiring, the recommended use of oval and oblong connection plate.

 

2. Pad shape: for aperture diameter of more than 1.2mm or pad diameter of more than 3.0mm pad, should be designed as a diamond or plum-shaped pad.

 

3. Pad location: for plug-in components, in order to avoid the phenomenon of copper foil breakage when welding, single-sided connection plate should be completely covered with copper foil; and double-sided plate minimum requirements should be supplemented with a tear drop. All organic plug-in parts need to be designed along the direction of the curved foot for the drip pad to ensure that the curved foot at the solder joints full. Large area of copper skin on the pad should be used to daisy-like pads, not to false soldering.

 

4. Filling and solder resist film: the bottom filling device and square device spacing 200um or more. Appropriately reduce the pad area, widen the pad spacing, increase the filler gap. PCB bottom filler devices and the surrounding SMT patch components should be greater than the minimum spacing of the outer diameter of the dispensing needle (0.7mm). All half-through holes need to be filled and covered with soldermask on their surfaces to prevent open half-through holes that may create a void phenomenon. Soldermask shall cover all metal substrates outside the pads. Reduce substrate flexing and ensure flatness of the substrate. Eliminate trench-like openings in the soldermask where possible to ensure consistent flow, keep the soldermask intact and flat, and ensure that there are no small gaps to accommodate air or flux residue.

 

5. Reflow: If the PCB pad design is correct, the placement of a small amount of skew can again be corrected by reflow (known as self-positioning or self-correcting effect), on the contrary, if the PCB pad design is incorrect, even if the placement of the position is very accurate, after reflow instead of the component position will be shifted, bridging and other soldering defects.

 

LSTPCB is an EMS (electronic manufacturing service) PCBA supplier that provides PCB design and assembly. You can have PCB, PCBA, and final product designed, manufactured, and assembled by LSTPCB.

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