At the beginning of the new design, most of the time was spent on circuit design and component selection, and the PCB layout and wiring stage was often not considered comprehensively due to lack of experience. Failure to devote sufficient time and effort to the PCB layout and routing phase of the design can result in problems at the manufacturing stage or functional defects when the design is transitioned from the digital domain to the physical reality. So what is the key to designing a circuit board that is authentic both on paper and in physical form? Let’s explore the top five PCB design guidelines to know when designing a manufacturable, functional PCB.
1 – Fine tune your component layout
The component placement phase of the PCB layout process is both a science and an art, requiring strategic consideration of the primary components available on the board. While this process can be challenging, the way you place the electronics will determine how easy it is to manufacture your board and how well it meets your original design requirements.
While there is a general general order for component placement, such as sequential placement of connectors, PCB mounting components, power circuits, precision circuits, critical circuits, etc., there are also some specific guidelines to keep in mind, including:
Orientation – Ensuring that similar components are positioned in the same direction will help achieve an efficient and error-free welding process.
Placement – Avoid placing smaller components behind larger components where they may be affected by soldering of larger components.
Organization – It is recommended that all surface mount (SMT) components be placed on the same side of the board and all through-hole (TH) components be placed on top of the board to minimize assembly steps.
One final PCB design guideline – when using mixed technology components (through-hole and surface-mount components), the manufacturer may require additional processes to assemble the board, which will add to your overall cost.
Good chip component orientation (left) and bad chip component orientation (right)
Good component placement (left) and bad component placement (right)
No. 2 – Proper placement of power, grounding and signal wiring
After placing the components, you can then place the power supply, grounding, and signal wiring to ensure that your signal has a clean, trouble-free path. At this stage of the layout process, keep the following guidelines in mind:
Locate the power supply and grounding plane layers
It is always recommended that the power supply and ground plane layers be placed inside the board while being symmetrical and centered. This helps prevent your circuit board from bending, which also matters if your components are positioned correctly. For powering the IC, it is recommended to use a common channel for each power supply, ensure a firm and stable wiring width, and avoid device-to-device Daisy chain power connections.
Signal cables are connected through cables
Next, connect the signal line according to the design in the schematic diagram. It is recommended to always take the shortest possible path and direct path between components. If your components need to be positioned horizontally without bias, it is recommended that you basically wire the components of the board horizontally where they come out of the wire and then vertically wire them after they come out of the wire. This will hold the component in horizontal position as the solder migrates during welding. As shown in the upper half of the figure below. The signal wiring shown in the lower part of the figure may cause component deflection as the solder flows during welding.
Recommended wiring (arrows indicate solder flow direction)
Unrecommended wiring (arrows indicate solder flow direction)
Define network width
Your design may require different networks that will carry various currents, which will determine the required network width. Considering this basic requirement, it is recommended to provide 0.010 “(10mil) widths for low current analog and digital signals. When your line current exceeds 0.3 amperes, it should be widened. Here’s a free line width calculator to make the conversion process easy.
Number three. – Effective quarantine
You’ve probably experienced how large voltage and current spikes in power supply circuits can interfere with your low-voltage current control circuits. To minimize such interference problems, follow the following guidelines:
Isolation – Ensure that each power source is kept separate from the power source and control source. If you must connect them together in the PCB, make sure it is as close to the end of the power path as possible.
Layout – If you have placed a ground plane in the middle layer, be sure to place a small impedance path to reduce the risk of any power circuit interference and help protect your control signal. The same guidelines can be followed to keep your digital and analog separate.
Coupling – To reduce capacitive coupling due to placing large ground planes and wiring above and below them, try to cross simulate ground only through analog signal lines.
Component isolation Examples (digital and analog)
No.4 – Solve the heat problem
Have you ever had circuit performance degradation or even circuit board damage due to heat problems? Because there is no consideration of heat dissipation, there have been many problems plaguing many designers. Here are some guidelines to keep in mind to help solve heat dissipation problems:
Identify troublesome components
The first step is to start thinking about which components will dissipate the most heat from the board. This can be done by first finding the “thermal resistance” level in the component’s data sheet and then following the suggested guidelines to transfer the heat generated. Of course, you can add radiators and cooling fans to keep components cool, and remember to keep critical components away from any high heat sources.
Add hot air pads
The addition of hot air pads is very useful for fabricable circuit boards, they are essential for high copper content components and wave soldering applications on multilayer circuit boards. Because of the difficulty of maintaining process temperature, it is always recommended to use hot air pads on through-hole components to make the welding process as simple as possible by slowing the rate of heat dissipation at the pins of the components.
As a general rule, always connect any through-hole or through-hole connected to the ground or power plane using a hot air pad. In addition to hot air pads, you can also add tear drops at the location of the pad connection line to provide additional copper foil/metal support. This will help reduce mechanical and thermal stress.
Typical hot air pad connection
Hot air pad science:
Many engineers in charge of Process or SMT in a factory often encounter spontaneous electrical energy, such as electrical board defects such as spontaneous empty, de-wetting, or cold wetting. No matter how to change the process conditions or reflow welding furnace temperature how to adjust, there is a certain proportion of tin can not be welded. What the hell is going on here?
Quite apart from the components and circuit boards oxidation problem, investigate its returning after a very big part of the existing welding bad actually comes from the circuit board wiring (layout) design is missing, and one of the most common is on the components of a certain welding feet connected to the copper sheet of large area, these components after reflow soldering welding welding feet, Some hand-welded components may also cause false welding or cladding problems due to similar situations, and some even fail to weld the components because of too long heating.
General PCB in the circuit design often need to lay a large area of copper foil as power supply (Vcc, Vdd or Vss) and Ground (GND, Ground). These large areas of copper foil are usually directly connected to some control circuits (ICS) and pins of electronic components.
Unfortunately, if we want to heat these large areas of copper foil to the temperature of melting tin, it usually takes more time than individual pads (heating is slower), and the heat dissipation is faster. When one end of such a large copper foil wiring is connected to small components such as small resistance and small capacitance, and the other end is not, it is easy to welding problems because of the inconsistency of melting tin and solidification time; If the temperature curve of reflow welding is not adjusted well, and the preheating time is insufficient, the solder feet of these components connected in large copper foil are easy to cause the problem of virtual welding because they cannot reach the melting tin temperature.
During Hand Soldering, the solder joints of components connected to large copper foils will dissipate too quickly to complete within the required time. The most common defects are soldering and virtual soldering, where solder is only welded to the pin of the component and not connected to the pad of the circuit board. From the appearance, the entire solder joint will form a ball; What is more, the operator in order to weld the welding feet on the circuit board and constantly increase the temperature of the soldering iron, or heating for too long, so that the components exceed the heat resistance temperature and damage without knowing it. As shown in the figure below.
Since we know the problem point, we can solve the problem. Generally, we require the so-called Thermal Relief pad design to solve the welding problem caused by the welding feet of large copper foil connecting elements. As shown in the figure below, the wiring on the left does not use hot air pad, while the wiring on the right has adopted hot air pad connection. It can be seen that there are only a few small lines in the contact area between the pad and large copper foil, which can greatly limit the loss of temperature on the pad and achieve better welding effect.
No. 5 – Check your work
It’s easy to feel overwhelmed at the end of a design project when you’re huffing and puffing all the pieces together. Therefore, double and triple checking your design effort at this stage can mean the difference between manufacturing success and failure.
To help complete the quality control process, we always recommend that you start with an electrical Rule check (ERC) and design Rule check (DRC) to verify that your design fully meets all rules and constraints. With both systems, you can easily check clearance widths, line widths, common manufacturing Settings, high speed requirements and short circuits.
When your ERC and DRC produce error-free results, it is recommended that you check the wiring of each signal, from schematic to PCB, one signal line at a time to make sure that you are not missing any information. Also, use your design tool’s probing and masking capabilities to ensure that your PCB layout material matches your schematic.