As one of the representatives of modern technology, drones’ circuit boards are the core components for the normal operation of drones. For drone enthusiasts or practitioners, mastering circuit board making skills is crucial. In the process of making a drone circuit board, every detail may affect the final performance and stability.

1. Material selection and preparation
Material quality: Choose high-quality electronic components, wires, solder and other materials to ensure their stable performance and high reliability. Avoid using low-quality materials, which can cause the board to degrade or malfunction.
Material matching: Select suitable components and materials based on the functional requirements and circuit design of the drone. Pay attention to the components’ packaging form, pin spacing and other parameters to ensure that they match the circuit board design.

2. Things to note during the design stage
Layout rationality: When designing a circuit board, fully consider the layout and routing of components. Make sure the components are arranged neatly and compactly, and the wiring is clear and concise. Avoid excessively long traces or cross traces to reduce signal interference and electromagnetic radiation.
Thermal design: Heat dissipation is an important consideration for drone circuit boards. During the design process, heat sinks, fans and other heat dissipation equipment must be reasonably arranged to ensure that the circuit board can maintain good heat dissipation performance during operation.

3. Things to note during the production process

Environmental control: When making circuit boards, pay attention to controlling the temperature, humidity and cleanliness of the working environment. Avoid making circuit boards in a humid and dirty environment to avoid affecting the welding quality and circuit board performance.
Soldering skills: Soldering is one of the key aspects of circuit board production. During the welding process, the welding temperature, time and intensity must be mastered. Avoid excessive welding temperature or too long time, which may cause component damage or poor welding.
Testing and debugging: After completing the soldering, the circuit board needs to be fully tested and debugged. Use professional testing instruments to conduct functional and performance tests on the circuit board to ensure that the circuit board has no hidden faults and has stable performance. During the debugging process, it is necessary to carefully observe the operating status of the circuit board and find and solve problems in time.

4. Safety protection
Anti-static: During the production process, be sure to pay attention to anti-static measures. Use anti-static bracelets, anti-static mats and other tools to prevent static electricity from causing damage to electronic components.
Anti-corrosion: The metal parts of the circuit board are susceptible to corrosion, so pay attention to anti-corrosion measures. Avoid exposing the circuit board to a humid environment for a long time, and clean and maintain the circuit board regularly.

5. Recording and Summary
Production records: During the production process, it is recommended to keep detailed records, including materials used, production processes, problems encountered and solutions, etc. This helps to summarize experiences and lessons and improve production levels.
Problem summary: Problems and difficulties encountered during the production process should be summarized and analyzed in a timely manner. Find out the cause and solution of the problem to avoid repeating mistakes in subsequent production processes.
Drone circuit board production is a job that requires care and patience. Only by mastering the correct production methods and precautions and putting them into practice can we produce a drone circuit board with stable performance and reliable quality.

1. Right-angle routing (three aspects)

The impact of right-angle wiring on signals is mainly reflected in three aspects: first, the corners can be equivalent to capacitive loads on the transmission line, slowing down the rise time; second, impedance discontinuity will cause signal reflection; third, right-angle tips produce In the field of EMI and RF design above 10GHz, these small right angles may become the focus of high-speed problems.

2. Differential routing (“equal length, equal distance, reference plane”)

What is Differential Signal? In layman’s terms, the driving end sends two equal and opposite signals, and the receiving end determines the logic state “0” or “1” by comparing the difference between the two voltages. The pair of traces that carry differential signals are called differential traces. Compared with ordinary single-ended signal wiring, the most obvious advantages of differential signals are reflected in the following three aspects:

1. Strong anti-interference ability, because the coupling between the two differential traces is very good. When there is noise interference from the outside, it is coupled to the two lines almost at the same time, and the receiving end only cares about the difference between the two signals. Therefore, external common mode noise can be completely offset.

2. It can effectively suppress EMI. In the same way, since the polarity of the two signals is opposite, the electromagnetic fields radiated by them can cancel each other out. The closer the coupling, the less electromagnetic energy released to the outside world.

3. Accurate timing positioning. Since the switching change of the differential signal is located at the intersection of the two signals, unlike ordinary single-ended signals that rely on high and low threshold voltages to judge, it is less affected by process and temperature, and can reduce timing errors. , and it is also more suitable for circuits with low amplitude signals. The currently popular LVDS (low voltage differential signaling) refers to this small amplitude differential signaling technology.

3. Snake line (adjust delay)

The serpentine line is a type of wiring method often used in Layout. Its main purpose is to adjust the delay and meet the system timing design requirements. The two most critical parameters are parallel coupling length (Lp) and coupling distance (S). Obviously, when signals are transmitted on a serpentine line, coupling will occur between parallel line segments in the form of differential mode, S The smaller it is, the larger Lp is, and the greater the degree of coupling. It may lead to a reduction in transmission delay and a significant reduction in signal quality due to crosstalk. The mechanism can be referred to the analysis of common mode and differential mode crosstalk. Here are some suggestions for Layout engineers when dealing with serpentine lines:

1. Try to increase the distance (S) between parallel line segments, at least greater than 3H. H refers to the distance from the signal trace to the reference plane. In layman’s terms, it means routing the wire around a big bend. As long as S is large enough, mutual coupling effects can be almost completely avoided.

2. Reduce the coupling length Lp. When twice the Lp delay approaches or exceeds the signal rise time, the crosstalk generated will reach saturation.

3. The signal transmission delay caused by the serpentine line of Strip-Line or Embedded Micro-strip is smaller than that of Micro-strip. In theory, stripline will not affect the transmission rate due to differential mode crosstalk.

4. For high-speed signal lines and those with strict timing requirements, try not to use serpentine lines, especially in small areas.

5. Snake wiring at any angle can often be used, which can effectively reduce mutual coupling.

6. In high-speed PCB design, serpentine lines have no so-called filtering or anti-interference capabilities and can only reduce signal quality, so they are only used for timing matching and have no other purpose.

7. Sometimes spiral wiring can be considered for winding. Simulation shows that its effect is better than normal serpentine wiring.

Surgery is very important, and postoperative recovery is also essential! Now that we’ve talked about PCB wiring, is it enough to finish laying out the wiring? Obviously, no! Inspection after PCB wiring is also necessary, so how to inspect the wiring in PCB design to pave the way for subsequent design? See below!

General PCB design drawing inspection items

1) Has the circuit been analyzed? Is the circuit divided into basic units for smoothing the signal?

2) Does the circuit allow short or isolated critical leads?

3) Are the places that must be shielded effectively shielded?

4) Have you made full use of the basic grid graphics?

5) Is the size of the printed circuit board the optimal size?

6) Are the selected wire widths and spacing used where possible?

7) Are the preferred pad sizes and hole sizes used?

8) Are the photographic plates and sketches suitable?

9) Are the minimum number of jumpers used? Do jumper wires pass through components and accessories?

l0) Are the letters visible after assembly? Is it the correct size and model?

11) In order to prevent blistering, are windows opened on large areas of copper foil?

12) Are there tool positioning holes?

PCB electrical characteristics inspection items:

1) Have the effects of wire resistance, inductance, and capacitance been analyzed? Especially the impact on the critical voltage drop phase grounding?

2) Do the spacing and shape of wire accessories meet the insulation requirements?

3) Is the insulation resistance value controlled and specified at key points?

4) Is the polarity fully recognized?

5) From a geometric perspective, has the influence of wire spacing on leakage resistance and voltage been measured?

6) Has the medium used to change the surface coating been identified?

PCB physical characteristics inspection items:

1) Are all pads and their locations suitable for final assembly?

2) Can the assembled printed circuit board meet the impact and vibration power conditions?

3) What is the spacing between the specified standard components?

4) Are the components that are not firmly installed or heavy parts fixed?

5) Is the heat dissipation and cooling of the heating element correct? Or is it isolated from the printed circuit board and other heat sensitive components?

6) Are voltage dividers and other multi-lead components positioned correctly?

7) Is the component arrangement and orientation easy to inspect?

8) Have all possible interferences on the printed circuit board and the entire printed circuit board assembly been eliminated?

9) Is the size of the positioning hole correct?

10) Are the tolerances complete and reasonable?

11) Have the physical properties of all coating layers been controlled and signed?

12) Is the hole to lead diameter ratio within an acceptable range?

PCB mechanical design factors:

Although the printed circuit board mechanically supports components, it cannot be used as a structural member of the entire device. On the edge of the printing plate, provide a certain amount of support at least every 5 inches. Factors that must be considered when selecting and designing a printed circuit board are as follows;

1) Structure of printed circuit board – size and shape.

2) Types of mechanical accessories and plugs (seats) required.

3) The adaptability of the circuit to other circuits and environmental conditions.

4) Consider mounting the printed circuit board vertically or horizontally based on factors such as heat and dust.

5) Some environmental factors that require special attention, such as heat dissipation, ventilation, shock, vibration, and humidity. Dust, salt spray and radiation.

6) Degree of support.

7) Maintain and fix.

8) Easy to take off.

PCB printed circuit board installation requirements:

Support should be within 1 inch of at least three edges of the printed circuit board. According to practical experience, the spacing between support points of printed circuit boards with a thickness of 0.031–0.062 inches should be at least 4 inches; for printed circuit boards with a thickness greater than 0.093 inches, the spacing between support points should be at least 5 inches. Taking this measure improves the rigidity of the printed circuit board and destroys possible resonances in the printed circuit board.

The mounting technology used for a certain printed circuit board can usually be decided after considering the following factors.

1) Size and shape of printed circuit board.

2) Number of input and output terminals.

3) Available equipment space.

4) The desired convenience of loading and unloading.

5) Type of installation accessories.

6) Required heat dissipation.

7) Required shieldability.

8) The type of circuit and its relationship with other circuits.

Printed circuit board allocation requirements:

1) Printed circuit board area that does not require mounting components.

2) The influence of plugging and unplugging tools on the installation distance between two printed circuit boards.

3) Mounting holes and slots must be specially prepared in the printed circuit board design.

4) When the insertion and removal tool is to be used in the equipment, its size must be especially considered.

5) A plug-in device is required, usually with rivets to permanently fix it to the printed circuit board assembly.

6) In the mounting rack of printed circuit boards, special designs such as load bearing flanges are required.

7) The adaptability of the plugging and unplugging tools used to the size, shape and thickness of the printed circuit board.

8) The cost involved in using plug-in tools includes both the price of the tool and the increased expenditure.

9) In order to tighten and use plug and pull tools, it is required to have access to the inside of the equipment to a certain extent.

PCB mechanical considerations:

The substrate properties that have an important impact on printed circuit assemblies are: water absorption, thermal expansion coefficient, heat resistance, flexural strength, impact strength, tensile strength, shear strength and hardness.

All of these characteristics affect both the functionality and productivity of the printed circuit board structure.

For most applications, the dielectric backing of a printed circuit board is one of the following substrates:

1) Phenolic impregnated paper.

2) Acrylic-polyester impregnated randomly arranged glass mat.

3) Epoxy impregnated paper.

4) Epoxy impregnated glass cloth.

Each substrate can be flame retardant or combustible. The above 1, 2 and 3 can be punched. The most commonly used material for metallized hole printed circuit boards is epoxy-glass cloth, which has dimensional stability suitable for

It is used for high-density circuits and can minimize the occurrence of cracks in metalized holes.

One disadvantage of epoxy-glass cloth laminates is that they are difficult to punch within the common thickness ranges of printed circuit boards. For this reason, all holes are usually drilled and patterned.

Milling operation to form the shape of the printed circuit board.

PCB electrical considerations:

In DC or low-frequency AC situations, the most important electrical properties of insulating substrates are: insulation resistance, arc resistance, printed wire resistance and breakdown strength.

In high-frequency and microwave applications: dielectric constant, capacitance, and dissipation factors.

In all applications, the current carrying capacity of printed conductors is important.

Wire pattern:

PCB routing path and positioning

Under the constraints of prescribed wiring rules, printed wires should take the shortest route between components. Limit coupling between parallel conductors as much as possible. Good design requires a minimum number of wiring layers

, corresponding to the required packaging density, the widest wires and the largest pad size are also required. Because rounded and smooth inner corners may avoid some possible electrical and

Mechanical problems, so sharp corners and sharp corners in the wires should be avoided.

PCB width and thickness:

Ampacity of etched copper conductors on rigid printed circuit boards. For 1 oz and 2 oz wires, a reduction in nominal value is allowed to take into account etching methods and normal variations in copper foil thickness and temperature differences.

10% (based on load current); for printed circuit board assemblies coated with a protective layer (substrate thickness less than 0.032 inches, copper foil thickness more than 3 ounces), components are reduced by 15%; for

Dip-soldered printed circuit boards are allowed to be reduced by 30%.

PCB wire spacing:

Minimum spacing between conductors must be determined to eliminate voltage breakdown or arcing between adjacent conductors. Spacing is variable and depends primarily on the following factors:

1) Peak voltage between adjacent wires.

2) Atmospheric pressure (maximum working altitude).

3) Coating layer used.

4) Capacitive coupling parameters.

Critical impedance components or high-frequency components are generally placed very close to reduce critical stage delays. Transformers and inductive components should be isolated to prevent coupling; inductive signal leads should

Arrange orthogonally at right angles; components that produce any electrical noise due to magnetic field motion should be isolated or rigidly mounted to prevent excessive vibration.

PCB wire pattern inspection:

1) Are the wires short and straight without sacrificing functionality?

2) Are the wire width restrictions observed?

3) Is there any minimum wire spacing that must be ensured between wires, between wires and mounting holes, between wires and pads?

4) Have all wires (including component leads) been routed in close proximity to each other in parallel?

5) Are sharp angles (90°C or less) avoided in the conductor pattern?

PCB design project inspection item list:

1. Check the rationality and correctness of the schematic diagram;

2. Check the correctness of the component packaging of the schematic diagram;

3. The distance between strong and weak electricity and the distance between isolation areas;

4. Check the schematic diagram and PCB diagram accordingly to prevent the loss of the network table;

5. Whether the packaging of the components matches the actual product;

6. Whether the components are placed appropriately:

7. Whether the components are easy to install and disassemble;

8. Whether the temperature-sensitive component is too close to the heating component;

9. Whether the distance and direction of the components that can produce mutual inductance are appropriate;

10. Whether the placement of connectors is smooth;

11. Easy to plug in and out;

12. Input and output;

13. Strong electricity and weak electricity;

14. Whether digital simulation is interleaved;

15. Arrangement of components on the upwind and leeward sides;

16. Whether the directional components are incorrectly flipped instead of rotated;

17. Whether the mounting holes of the component pins are suitable and whether they can be easily inserted;

18. Check whether the empty pin of each component is normal and whether it is a leak;

19. Check whether there are via holes in the upper and lower wiring of the same network table. The pads are connected through the holes to prevent disconnection and ensure the integrity of the circuit;

20. Check whether the characters on the upper and lower layers are placed correctly and reasonably. Do not put components to cover the characters to facilitate the operation of welding or maintenance personnel;

21. The very important connection between the upper and lower layer lines should not only be connected by the pads of the directly plugged components, but also preferably by via holes;

22. The arrangement of power and signal lines in the socket must ensure signal integrity and anti-interference;

23. Pay attention to the appropriate proportion of soldering pads and soldering holes;

24. Each plug should be placed on the edge of the PCB board as much as possible and easy to operate;

25. Check whether the component numbers match the components, and the components should be placed in the same direction and neatly as possible;

26. Without violating design rules, power and ground wires should be as thick as possible;

27. Under normal circumstances, the upper layer adopts horizontal lines and the lower layer adopts vertical lines, and the chamfer is not less than 90 degrees;

28. Whether the size and distribution of the mounting holes on the PCB are appropriate to reduce the bending stress of the PCB as much as possible;

29. Pay attention to the height distribution of components on the PCB and the shape and size of the PCB to ensure easy assembly.

We know that when designing circuits, in order to improve the performance of the product, we must take into account the electromagnetic interference it receives. There are many ways to solve EMI problems. Modern EMI suppression methods include: using EMI suppression coatings, selecting appropriate EMI suppression components and EMI simulation design, etc. This article starts from the most basic PCB layout and discusses the role and design techniques of PCB layer stacking in controlling EMI radiation.

Power bus

Reasonably placing a capacitor of appropriate capacity near the IC’s power pin can make the IC’s output voltage jump faster. However, the problem does not end there. Due to the finite frequency response of the capacitor, the capacitor cannot generate the harmonic power required to cleanly drive the IC output over the full frequency band. In addition, the transient voltage formed on the power bus will form a voltage drop across the inductor of the decoupling path. These transient voltages are the main source of common-mode EMI interference. How should we solve these problems?

In the case of ICs on our circuit boards, the power plane around the IC can be thought of as a good high-frequency capacitor, which collects the energy leaked from the discrete capacitors that provide high-frequency energy for a clean output. In addition, the inductance of a good power supply layer should be small, so the transient signal synthesized by the inductor should also be small, thereby reducing common-mode EMI.

Of course, the connection from the power layer to the IC power pin must be as short as possible, because the rising edge of the digital signal is getting faster and faster. It is best to connect it directly to the pad where the IC power pin is located, which needs to be discussed separately.

To control common-mode EMI, the power plane must aid in decoupling and have sufficiently low inductance. This power plane must be paired with a reasonably well-designed power plane. Some may ask, how good is good? The answer to the question depends on the layering of the power supply, the materials between the layers, and the operating frequency (i.e., a function of the IC rise time). Typically, the spacing between power layers is 6mil, and the interlayer is made of FR4 material, so the equivalent capacitance of the power layer per square inch is about 75pF. Obviously, the smaller the layer spacing, the greater the capacitance.

There are not many devices with a rise time of 100 to 300ps, but according to the current IC development speed, devices with a rise time in the range of 100 to 300ps will account for a high proportion. For circuits with 100 to 300ps rise time, 3mil layer spacing will no longer be suitable for most applications. At that time, it will be necessary to use layering technology with layer spacing of less than 1 mil and replace the FR4 dielectric material with a material with a very high dielectric constant. Today, ceramics and ceramic-coated plastics can meet the design requirements of circuits with rise times from 100 to 300ps.

Although new materials and approaches may be adopted in the future, for today’s common 1 to 3ns rise time circuits, 3 to 6 mil layer spacing, and FR4 dielectric materials, it is usually sufficient to handle the high end harmonics and keep the transients low enough, that is , common mode EMI can be reduced very low. The PCB layer stackup design examples given in this article will assume a layer spacing of 3 to 6 mils.

Electromagnetic shielding

From the perspective of signal routing, a good layering strategy should be to place all signal routing on one or several layers, with these layers next to the power layer or ground layer. For power supply, a good layering strategy should be that the power layer is adjacent to the ground layer, and the distance between the power layer and the ground layer is as small as possible. This is what we call the “layering” strategy.

PCB stacking

What kind of stacking strategy helps shield and suppress EMI? The following layered stacking scheme assumes that the supply current flows on a single layer and that single or multiple voltages are distributed on different parts of the same layer. The case of multiple power planes is discussed later.

4 layers board

There are several potential problems with the 4-layer board design. First of all, for a traditional four-layer board with a thickness of 62 mil, even if the signal layer is on the outer layer and the power and ground layers are on the inner layer, the distance between the power layer and the ground layer is still too large.

If cost requirements are the first priority, you can consider the following two alternatives to traditional 4-layer boards. Both solutions can improve the performance of EMI suppression, but are only suitable when the component density on the board is low enough and there is sufficient area around the components to place the required power copper layer.

The first is the preferred solution. The outer layers of the PCB are both ground layers, and the two middle layers are signal/power layers. The power supply on the signal layer is routed with wide traces, which allows the supply current to have a low impedance path and the signal microstrip path to have a low impedance. From an EMI control perspective, this is the best 4-layer PCB structure available. In the second solution, the outer layer carries power and ground, and the middle two layers carry signals. Compared with the traditional 4-layer board, this solution has smaller improvements, and the interlayer impedance is as poor as the traditional 4-layer board.

If you want to control the trace impedance, the above stacking scheme must be very careful to arrange the traces under the power and ground copper islands. In addition, copper islands on power or ground planes should be interconnected as much as possible to ensure DC and low-frequency connectivity.

6-layer board

If the density of components on a 4-layer board is relatively high, it is best to use a 6-layer board. However, some stacking schemes in the 6-layer board design do not shield the electromagnetic field well enough, and have little effect on reducing the transient signal of the power bus. Two examples are discussed below.

In the first example, the power supply and ground are placed on the 2nd and 5th layers respectively. Since the copper impedance of the power supply is high, it is very unfavorable for controlling common mode EMI radiation. However, from the perspective of signal impedance control, this method is very correct.

As an electronic engineer, designing circuits is a necessary and hard skill, but no matter how perfect the principle design is, if the circuit board design is unreasonable, the performance will be greatly reduced, and in serious cases, it may not even work properly.

No matter what software is used, there is a general procedure for PCB design. Going in order will save time and effort, so I will introduce it according to the production process. (Because the Protel interface style is close to that of Windows, the operating habits are also similar, and it has powerful simulation functions, so many people use it, so this software will be used as an explanation.)

Schematic design is the preliminary preparation work. It is often seen that beginners directly draw the PCB board to save trouble. This will not be worth the gain. For simple boards, if you are familiar with the process, you may as well skip it. But for beginners, they must follow the process. On the one hand, they can develop good habits. On the other hand, this is the only way to avoid making mistakes with complex circuits.

When drawing schematic diagrams, when designing hierarchies, attention should be paid to the final connection of each file into a whole, which is also of great significance for future work. Due to differences in software, some software may appear to be connected but actually not connected (in terms of electrical performance). If you don’t use relevant testing tools to detect it, if something goes wrong, it will be too late until the board is ready. Therefore, I have repeatedly emphasized the importance of doing it in order, hoping to attract everyone’s attention.

The schematic diagram is based on the designed project. As long as the electrical connections are correct, there is nothing much to say. Below we focus on discussing the specific issues in the board making process.

1. Make physical borders

The closed physical border is a basic platform for future component layout and wiring, and also constrains automatic layout. Otherwise, the components coming from the schematic diagram will be at a loss. But you must pay attention to accuracy here, otherwise you will be in trouble if there are installation problems in the future. In addition, it is best to use arcs at corners. On the one hand, it can avoid sharp corners from scratching workers, and at the same time, it can reduce stress. In the past, one of my products always had the case PCB board broken during transportation. It was fine after using arc.

2. Introduction of components and networks

It should be very simple to introduce components and networks into the drawn borders, but problems often arise here. You must carefully follow the errors prompted to solve them one by one, otherwise you will have to spend more effort later. The problems here generally include the following:

The packaging form of the component cannot be found, there is a component network problem, there are unused components or pins, the comparison prompts that these problems can be solved quickly.

3． Component layout

The layout and wiring of components have a great impact on the product’s life, stability, and electromagnetic compatibility, and should be paid special attention to. Generally speaking, there should be the following principles:

(1) Placement order

First place the fixed-position components related to the structure, such as power sockets, indicator lights, switches, connectors, etc. After placing these components, use the LOCK function of the software to lock them so that they will not be moved accidentally in the future. Then place special components and large components on the circuit, such as heating components, transformers, ICs, etc. Place the widget last.

(2) Pay attention to heat dissipation

The component layout should also pay special attention to heat dissipation issues. For high-power circuits, heating components such as power tubes and transformers should be placed as far apart as possible to facilitate heat dissipation. Do not concentrate them in one place, and do not have high capacitances too close to avoid premature aging of the electrolyte.

4． wiring

Wiring principles

The knowledge of routing is very profound, and everyone will have their own experience, but there are still some general principles.

◆It is better for high-frequency digital circuit traces to be thinner and shorter.

◆Attention should be paid to the isolation between large current signals, high voltage signals and small signals (the isolation distance is related to the withstand voltage to be withstood. Normally at 2KV, the distance between the boards should be 2mm, and the distance above this should be increased proportionally. , for example, if it wants to withstand the 3KV withstand voltage test, the distance between high and low voltage lines should be more than 3.5mm. In many cases, in order to avoid creepage, slots are also made between high and low voltage on the printed circuit board.)

◆When wiring two panels, the wires on both sides should be routed perpendicularly, obliquely, or bent to avoid being parallel to each other to reduce parasitic coupling; printed wires used as input and output of the circuit should avoid adjacent parallel lines as much as possible. , to avoid feedback, it is best to add a ground wire between these wires.

◆Make the wiring corners larger than 90 degrees as much as possible, avoid corners below 90 degrees, and use 90-degree corners as little as possible

◆If they are both address lines or data lines, the length of the lines should not be too different, otherwise the short lines will need to be artificially bent to compensate.

◆Try to run the traces on the welding surface as much as possible, especially for PCBs with through-hole technology

◆Use as few vias and jumpers as possible

◆The soldering pads of single-sided panels must be large, and the wires connecting the pads must be thick. Use teardrops if you can. The quality of ordinary single-sided panel manufacturers will not be very good, otherwise there will be problems with welding and RE-WORK.

◆Large areas of copper should be covered in a grid pattern to prevent the board from generating bubbles and bending due to thermal stress during wave soldering. However, in special occasions, the flow direction and size of the GND must be considered, and it cannot simply be filled with copper foil. , but need to route

◆Components and wiring should not be placed too close to the edge. Common single panels are mostly made of paper boards, which are easy to break after being stressed. If you connect wires or place components at the edge, they will be affected.

◆The convenience of production, debugging and maintenance must be considered

It is very important to deal with ground issues for analog circuits. Noise generated on the ground is often unpredictable, but once it occurs, it will cause great trouble and should be avoided. For power amplifier circuits, extremely small ground noise will have a significant impact on the sound quality due to the amplification of the subsequent stages; in high-precision A/D conversion circuits, if there are high-frequency components on the ground line, there will be a certain temperature drift, which will affect the sound quality. Amplifier work. At this time, you can add decoupling capacitors to the 4 corners of the board, connect one leg to the ground on the board, and connect the other leg to the mounting hole (connected to the chassis through screws), so that this component can be eliminated, and the amplifier and AD can also It’s stable.

In addition, the issue of electromagnetic compatibility has become even more important now that people are paying more attention to environmentally friendly products. Generally speaking, there are three sources of electromagnetic signals: signal source, radiation, and transmission line. Crystal oscillator is a common high-frequency signal source. In the power spectrum, the energy value of each harmonic of the crystal oscillator will be significantly higher than the average value. A feasible approach is to control the amplitude of the signal, ground the crystal oscillator shell, shield the interference signal, and use special filter circuits and devices.

What needs special explanation is the snake-shaped wiring, because its functions are different depending on the application. It is used on some clock signals in the computer motherboard, such as PCIClk and AGP-Clk. It has two functions: 1. Impedance matching 2. Filter inductor.

For some important signals, such as the HUBLink in the INTELHUB architecture, there are 13 wires in total and the frequency can reach 233MHZ. They must be strictly equal in length to eliminate the hidden dangers caused by time lag. At this time, snake wiring is the only solution.

Generally speaking, the line spacing of snake-shaped traces is >= 2 times the line width; if it is used in an ordinary PCB board, in addition to having the function of a filter inductor, it can also be used as an inductor coil of a radio antenna, etc.

5. Adjustment and improvement

After completing the wiring, all that needs to be done is to make some adjustments to the text, individual components, and wiring and apply copper (this work should not be done too early, otherwise it will affect the speed and cause trouble to the wiring), also for the convenience of production, Debugging and maintenance.

Copper coating usually refers to filling the blank area left after wiring with a large area of copper foil. You can lay GND copper foil or VCC copper foil (but this will easily burn the device in the event of a short circuit. It is best to ground it unless you have to. To increase the conduction area of the power supply to withstand larger current, connect to VCC). Ground wrapping usually refers to wrapping a bunch of signal lines with special requirements with two ground wires (TRAC) to prevent them from being interfered by or interfering with others.

If you use copper instead of ground wire, you must pay attention to whether the entire ground is connected, the current size, flow direction, and whether there are any special requirements to ensure that unnecessary mistakes are reduced.

6. Check the network

Sometimes due to misoperation or negligence, the network relationship of the drawn board is different from the schematic diagram. In this case, it is necessary to check. Therefore, after finishing the painting, you must not rush to hand it over to the plate maker. You should check it first and then proceed with the follow-up work.

7. Use the simulation function

After completing these tasks, if time permits, software simulation can also be performed. Especially for high-frequency digital circuits, some problems can be discovered in advance and greatly reduce the workload of debugging in the future.

As an electronic engineer, designing circuits is a necessary and hard skill, but no matter how perfect the principle design is, if the circuit board design is unreasonable, the performance will be greatly reduced, and in serious cases, it may not even work properly. Based on my experience, I have summarized the following things that should be paid attention to in PCB design. I hope it can inspire you.

No matter what software is used, there is a general procedure for PCB design. Going in order will save time and effort, so I will introduce it according to the production process. (Because the Protel interface style is close to that of Windows, the operating habits are also similar, and it has powerful simulation functions, so many people use it, so this software will be used as an explanation.)

Schematic design is the preliminary preparation work. It is often seen that beginners directly draw the PCB board to save trouble. This will not be worth the gain. For simple boards, if you are familiar with the process, you may as well skip it. But for beginners, they must follow the process. On the one hand, they can develop good habits. On the other hand, this is the only way to avoid making mistakes with complex circuits.

When drawing schematic diagrams, when designing hierarchies, attention should be paid to the final connection of each file into a whole, which is also of great significance for future work. Due to differences in software, some software may appear to be connected but actually not connected (in terms of electrical performance). If you don’t use relevant testing tools to detect it, if something goes wrong, it will be too late until the board is ready. Therefore, I have repeatedly emphasized the importance of doing it in order, hoping to attract everyone’s attention.

The schematic diagram is based on the designed project. As long as the electrical connections are correct, there is nothing much to say. Below we focus on discussing the specific issues in the board making process.

1. Make physical borders

The closed physical border is a basic platform for future component layout and wiring, and also constrains automatic layout. Otherwise, the components coming from the schematic diagram will be at a loss. But you must pay attention to accuracy here, otherwise you will be in trouble if there are installation problems in the future. In addition, it is best to use arcs at corners. On the one hand, it can avoid sharp corners from scratching workers, and at the same time, it can reduce stress. In the past, one of my products always had the case PCB board broken during transportation. It was fine after using arc.

2. Introduction of components and networks

It should be very simple to introduce components and networks into the drawn borders, but problems often arise here. You must carefully follow the errors prompted to solve them one by one, otherwise you will have to spend more effort later. The problems here generally include the following:

The packaging form of the component cannot be found, there is a component network problem, there are unused components or pins, the comparison prompts that these problems can be solved quickly.

3． Component layout

The layout and wiring of components have a great impact on the product’s life, stability, and electromagnetic compatibility, and should be paid special attention to. Generally speaking, there should be the following principles:

(1) Placement order

First place the fixed-position components related to the structure, such as power sockets, indicator lights, switches, connectors, etc. After placing these components, use the LOCK function of the software to lock them so that they will not be moved accidentally in the future. Then place special components and large components on the circuit, such as heating components, transformers, ICs, etc. Place the widget last.

(2) Pay attention to heat dissipation

The component layout should also pay special attention to heat dissipation issues. For high-power circuits, heating components such as power tubes and transformers should be placed as far apart as possible to facilitate heat dissipation. Do not concentrate them in one place, and do not have high capacitances too close to avoid premature aging of the electrolyte.

4． wiring

Wiring principles

The knowledge of routing is very profound, and everyone will have their own experience, but there are still some general principles.

◆It is better for high-frequency digital circuit traces to be thinner and shorter.

◆Attention should be paid to the isolation between large current signals, high voltage signals and small signals (the isolation distance is related to the withstand voltage to be withstood. Normally at 2KV, the distance between the boards should be 2mm, and the distance above this should be increased proportionally. , for example, if it wants to withstand the 3KV withstand voltage test, the distance between high and low voltage lines should be more than 3.5mm. In many cases, in order to avoid creepage, slots are also made between high and low voltage on the printed circuit board.)

◆When wiring two panels, the wires on both sides should be routed perpendicularly, obliquely, or bent to avoid being parallel to each other to reduce parasitic coupling; printed wires used as input and output of the circuit should avoid adjacent parallel lines as much as possible. , to avoid feedback, it is best to add a ground wire between these wires.

◆Make the wiring corners larger than 90 degrees as much as possible, avoid corners below 90 degrees, and use 90-degree corners as little as possible

◆If they are both address lines or data lines, the length of the lines should not be too different, otherwise the short lines will need to be artificially bent to compensate.

◆Try to run the traces on the welding surface as much as possible, especially for PCBs with through-hole technology

◆Use as few vias and jumpers as possible

◆The soldering pads of single-sided panels must be large, and the wires connecting the pads must be thick. Use teardrops if you can. The quality of ordinary single-sided panel manufacturers will not be very good, otherwise there will be problems with welding and RE-WORK.

◆Large areas of copper should be covered in a grid pattern to prevent the board from generating bubbles and bending due to thermal stress during wave soldering. However, in special occasions, the flow direction and size of the GND must be considered, and it cannot simply be filled with copper foil. , but need to route

◆Components and wiring should not be placed too close to the edge. Common single panels are mostly made of paper boards, which are easy to break after being stressed. If you connect wires or place components at the edge, they will be affected.

◆The convenience of production, debugging and maintenance must be considered

It is very important to deal with ground issues for analog circuits. Noise generated on the ground is often unpredictable, but once it occurs, it will cause great trouble and should be avoided. For power amplifier circuits, extremely small ground noise will have a significant impact on the sound quality due to the amplification of the subsequent stages; in high-precision A/D conversion circuits, if there are high-frequency components on the ground line, there will be a certain temperature drift, which will affect the sound quality. Amplifier work. At this time, you can add decoupling capacitors to the 4 corners of the board, connect one leg to the ground on the board, and connect the other leg to the mounting hole (connected to the chassis through screws), so that this component can be eliminated, and the amplifier and AD can also It’s stable.

In addition, the issue of electromagnetic compatibility has become even more important now that people are paying more attention to environmentally friendly products. Generally speaking, there are three sources of electromagnetic signals: signal source, radiation, and transmission line. Crystal oscillator is a common high-frequency signal source. In the power spectrum, the energy value of each harmonic of the crystal oscillator will be significantly higher than the average value. A feasible approach is to control the amplitude of the signal, ground the crystal oscillator shell, shield the interference signal, and use special filter circuits and devices.

What needs special explanation is the snake-shaped wiring, because its functions are different depending on the application. It is used on some clock signals in the computer motherboard, such as PCIClk and AGP-Clk. It has two functions: 1. Impedance matching 2. Filter inductor.

For some important signals, such as the HUBLink in the INTELHUB architecture, there are 13 wires in total and the frequency can reach 233MHZ. They must be strictly equal in length to eliminate the hidden dangers caused by time lag. At this time, snake wiring is the only solution.

Generally speaking, the line spacing of snake-shaped traces is >= 2 times the line width; if it is used in an ordinary PCB board, in addition to having the function of a filter inductor, it can also be used as an inductor coil of a radio antenna, etc.

5. Adjustment and improvement

After completing the wiring, all that needs to be done is to make some adjustments to the text, individual components, and wiring and apply copper (this work should not be done too early, otherwise it will affect the speed and cause trouble to the wiring), also for the convenience of production, Debugging and maintenance.

Copper coating usually refers to filling the blank area left after wiring with a large area of copper foil. You can lay GND copper foil or VCC copper foil (but this will easily burn the device in the event of a short circuit. It is best to ground it unless you have to. To increase the conduction area of the power supply to withstand larger current, connect to VCC). Ground wrapping usually refers to wrapping a bunch of signal lines with special requirements with two ground wires (TRAC) to prevent them from being interfered by or interfering with others.

If you use copper instead of ground wire, you must pay attention to whether the entire ground is connected, the current size, flow direction, and whether there are any special requirements to ensure that unnecessary mistakes are reduced.

6. Check the network

Sometimes due to misoperation or negligence, the network relationship of the drawn board is different from the schematic diagram. In this case, it is necessary to check. Therefore, after finishing the painting, you must not rush to hand it over to the plate maker. You should check it first and then proceed with the follow-up work.

7. Use the simulation function

After completing these tasks, if time permits, software simulation can also be performed. Especially for high-frequency digital circuits, some problems can be discovered in advance and the future debugging workload can be greatly reduced.

In the world of electronics design, high-performance design has its own unique challenges.

1 The birth of high-speed design

In recent years, the increasing number of high-frequency signal designs has been closely linked to the steadily increasing performance of electronic systems.

As system performance improves, the challenges for PCB designers are increasing day by day: smaller chips, denser circuit board layout, and lower power consumption chip requirements.

With the rapid development of all technologies, we are at the core of high-speed design and need to consider its complexity and all factors.

2 review

PCB design has changed a lot over the past 30 years. In 1987, we thought 0.5 micron was the end of the technology, but today, 22nm has become the norm.

As shown in the figure below, the edge rate in 1985 promoted the increase in design complexity (typically 30 nanoseconds), and today the edge rate has become 1 nanosecond.

Changes in marginal rates over the past 30 years.

3 Technological progress is accompanied by various problems

The advancement of technology is always accompanied by a series of problems. As system performance increases and high-speed designs are adopted, some issues must be addressed in the design environment.

Below, we summarize the challenges faced:

Signal quality

IC manufacturers favor lower core voltages and higher operating frequencies, which results in sharply rising edge rates. Edge rates in unterminated designs will cause reflections and signal quality issues.

crosstalk

In high-speed signal designs, dense paths often lead to crosstalk—the phenomenon associated with electromagnetic coupling between traces on a PCB.

Crosstalk can be edge coupling of traces on the same layer or broadside coupling on adjacent layers.

The coupling is three-dimensional. Parallel paths and wide-side traces cause more crosstalk than side-by-side trace paths.

Broadside coupling (top) compared to edge coupling (bottom)

Fast edge rates in traditional designs can cause ringing on unterminated transmission lines, even when using the same frequency and trace length as before.

This essentially results in higher emissions, well in excess of the FCC/CISPR Class B limits for unterminated transmission lines.

Edge rate radiation at 10 nanoseconds (left) and 1 nanosecond (right).

4 Design Solutions

Signal and power integrity issues occur intermittently and are difficult to diagnose. Therefore, the best way is to find the root cause of the problem during the design process and eliminate it, rather than trying to solve it in the later stages and delaying production.

The stackup planning tool makes it easier to implement solutions to signal integrity issues in your design.

5 Circuit board stackup planning

The number one priority in high-speed design must be circuit board stackup. The substrate is the most important component of the assembly, and its specifications must be carefully planned to avoid discontinuous impedance, signal coupling, and excessive electromagnetic radiation.

When looking at the circuit board stackup for your next design, keep these tips and suggestions in mind:
All signal layers need to be adjacent and tightly coupled to an uninterrupted reference plane that creates a clear loop and eliminates broadside crosstalk.

The substrate of each signal layer is adjacent to the reference plane.

There are good planar capacitors to reduce AC impedance in high frequencies. The tightly coupled inner electrical layer plane reduces the AC impedance of the top layer and greatly reduces electromagnetic radiation.

Reducing the dielectric height significantly reduces crosstalk without impacting the available space on the board.

The substrate should be able to accommodate a range of different technologies. For example: 50/100 ohm digital, 40/80 ohm DDR4, 90 ohm USB.

6 Cabling and Workflow

With your stackup carefully planned, the next step is to focus on board routing. Based on design rules and careful configuration of your work area, you can route your board most efficiently and successfully.

These tips can help make your wiring easier and avoid unnecessary crosstalk, radiation, and signal quality problems:

Simplify the view to clearly see the split planes and current loops.

To do this, first determine which copper foil plane (ground or power) serves as the reference plane for each signal layer, and then open the signal layer and internal electrical layer planes to view them at the same time. This helps you more easily see the traces that split the plane.

Multiple signal layers (left), top and adjacent plane views (right)

If a digital signal must cross a power reference plane, you can place one or two decoupling capacitors (100nF) close to the signal. This provides a current loop between the two power supplies.

Avoid parallel routing and broadside routing, which can cause more crosstalk than side-by-side routing.

Unless you are using a synchronous bus, keep the parallel intervals as short as possible to reduce crosstalk. Leave room for signal groups so that their address and data spacing is three times the trace width.

Be careful when using combined microstrip layers on the top and bottom layers of the board. This can lead to crosstalk between traces on adjacent board layers, compromising signal integrity.

Routing the clock (or strobe) signal with the longest delay by signal group ensures that the data has been established before the clock is read.

Routing embedded signals between planes helps minimize radiation and provides ESD protection.

7 Signal clarity

In the future, the complexity of electronic design will undoubtedly continue to increase, which will bring a series of challenges to PCB designers that need to be solved. Ensuring the correct configuration of circuit board stackup, impedance, and current loops is the basis for design stability.