PCB Design Tips to Reduce Electromagnetic Interference Part2

PCB design becomes more difficult since electronic equipment have been more sensible and required excellent capability to reduce noise and electromagnetic interference. Thus, how to improve the design becomes one of the key issues that many engineers are concerned about. This article describes some tips for reducing noise and electromagnetic interference when designing PCB boards.

11.Single-sided board and double-sided board access to power and grounding by single point, thus power lines and ground lines should be as thick as possible.

12.Keep clock, bus wire and chip select signals far away from I/O lines and connectors.

13.Keep analog voltage input line and VREF away from the digital signal lines, especially the clock.

14.For A/D components, the digital part and the analog part should be unified rather than cross.

15.Both component’s pins and decoupling capacitor’s pins are as short as possible.

16.The key lines should be as thick as possible with protection on both sides, while high-speed lines should be short and straight.

17.Don't keep noise-sensitive lines parallel with high-current, high-speed switch lines.

18.Do not route below quartz crystals and noise sensitive components.

19.No current loop around weak signal circuit or low frequency circuit.

20.Do not form a signal loop, if inevitable, keep the loop area as small as possible.

21.One decoupling capacitor per integrated circuit. Add a small high-frequency bypass capacitor to the edge of each electrolytic capacitor.

22.Use high-capacity tantalum capacitors or poly condenser capacitors instead of electrolytic capacitors for charging and discharging storage capacitor. When using tubular capacitors, the housing should be grounded.

PCB Design Tips to Reduce Electromagnetic Interference

PCB design becomes more difficult since electronic equipment have been more sensible and required excellent capability to reduce noise and electromagnetic interference. Thus, how to improve the design becomes one of the key issues that many engineers are concerned about. This article describes some tips for reducing noise and electromagnetic interference when designing PCB boards.

1.High-speed chips are used in the key areas.

2.To reduce the upper and lower edge of the control circuit toggle rate, you can string a resistor.

3.Use the lowest frequency clock that meets system requirements.

4.The clock generator is as close as possible to the device using the clock. Quartz crystal oscillator housing shall be grounded.

5.Use the ground wire to enclose the clock area; the clock line should be short as far as possible.

6.I/O driver circuit should be as close to the board edge as possible. Signals should be filtered when entering the printed circuit board, so as signals from the high noise area. At the same time, it is necessary to use string termination resistor approach to reduce the signal reflection.

7.MCD unused end shall be connected to ground or defined as the output end.

8.Don’t keep the input end of gate circuit unconnected; positive input of unused op amp shall be grounded, while negative input should  be connected to the output end.

9.Printed circuit board should use the 45-degree fold line instead of the 90 one in order to reduce the launch and coupling of high-frequency signals.

10.Areas on printed circuit boards should be divided by the frequency and current characteristics of the switch; keep enough distance between noisy components and non-noisy components.

Useful PCB Layout Software

With the introduction of high-density circuit boards, printed circuit board design becomes more and more challenging as more functionality are required in a smaller space. Electronics and PCB boards are integrated into almost all devices in our daily life, such as smart phones, tablets, home appliances, home automation, even children's toys, etc.

Designing smaller boards with tighter routing and a larger number of components can make circuit board layout more complex. Thus, PCB layout software is almost a mandatory tool for designing effective layout that can be successfully converted to a working product whether for prototypes or production-ready boards.

PCB layout software can contribute to design and production efficiency in a number of ways:

PCB Board Quality

Layout software can analyze complex designs which may cause conflicts between components or circuit paths where problems may be produced from track widths, physical components, board size, or even electromagnetic interference from other circuit board components.

Design for Manufacturing or DFM

PCB layout software designed for this purpose can prevent the creation of PCB layouts that look good on paper or screen, but can not be made in the current world of manufacturing. Many software tools will warn you to avoid such situation.

Design Rule Check or DRC

Verification features like DRC can detect problems before they are designed into the PCB. Based on component types, these features ensure that the spacing is within tolerance, there are no size limit issues, and other layout rules related to object type, layer, etc.

Documentation

Software tools save layout designs in a standard format for future reference and reuse. Illustrations and layout documents can also be printed for working with manufacturers or for submitting designs for quotes by potential suppliers.

Ease of Placement

Drag and drop simple board layout can improve layout design efficiency.

Process Flow

Layout software enforces best practices for PCB design. By using tools in the software, designers can make schematics and layouts in accordance with standard methods and techniques.

Save Templates for Reuse

When you create a template with similar capabilities in the past, you do not need to recreate the new template. Starting with a working template, make sure the process starts with a time-proven design and add or remove components from that point. And this will shorten the development cycle and improve the quality.

Best Practices of PCB Design

Though the demand for highly-featured boards is increasing, custom PCBs still performs an important role in electronic industry. In this article, we outline several best practices of PCB design, which are very useful and can generally be applied to any PCB design project.

Decoupling capacitors are not optional. Do not try and optimize your design by avoiding decoupling power lines. Capacitors are inexpensive and robust, you should take the time to fit them in wherever possible.

Design rule check as often as possible. The design rule check function on PCB software takes a little time, but it can save hours on more complex designs. Though every layout decision is important, the design rule check is absolutely the most important one.

Double check your PCB manufacturing data before fabricating PCBs as per your data. You may catch an error unintentionally before it's set forever in fiberglass, resin, and copper, etc.

Get a right grid. Find a grid spacing that suits as many of your components as possible and use it throughout. A little additional thought at the early stages of the layout can avoid spacing difficulties and will maximize board use. 

Keep trace length as short and direct as possible. This applies particularly in analog and high-speed digital circuitry where impedance and parasitic effects will always play a part in limiting your system performance.

Use silkscreen wisely. The silkscreen can show the board builder, device operator, etc. Full use of silk screening on both sides of the board streamlines can reduce re-work.

Manage the distribution of power lines and ground. Using a power plane is a quick and easy option in most PCB design software. It helps ensure power flows as effectively as possible with minimal impedance or voltage drop. If possible, run multiple supply lines in the same area of the board and remember that if the ground plane is run over a large section of one layer, it can have a positive impact on cross-talk between lines running above it on an adjacent layer. 

Hope the above 7 basic rules can help you in printed circuit board design. 

Benefits and Drawbacks of HDI

High density interconnect (HDI) is a technology that is rapidly becoming popular in PCB design and various electronic product integrations. It offers a more denser construction on the board by placing smaller components in a closer position, which also leads to shorter paths between components. However, every coin has two sides, so in this article, let’s discuss its benefits and drawbacks.

Benefits of HDI

HDI board has micro vias of incredibly diameter, buried or blind vias or a combination to facilitate the incorporation of more technology into less space with fewer layers. Multilayer HDI boards are commonly used, many of which are accommodated by various building methods that use blind, buried, stacked, and staggered vias.

With smaller components, blind via and via in pad technology, components can be placed closer together, and this can increase signal transmission rates, and reduce crossing delays and signal loss. These are all key considerations for improving HDI PCB performance.
HDI board is the top choice for applications where space, performance, reliability and weight are concerns. This makes them suitable for almost every applications related to electronics, consumer products, computers and aerospace.
Multilayer HDI boards provide a powerful interconnection with stacked vias, so they are of high-level reliability even in more extreme environments.

HDI Drawbacks
While the benefits of HDI are considerable, HDI has its drawbacks as well.
Machine used to manufacture HDI boards are expensive. Such equipment includes laser drilling machine, laser direct imaging processes, and other specialized manufacturing equipment and materials. 
Attention to detail is crucial in the design and manufacture of HDI printed circuit boards, and this requires professional knowledge and experience. Thus, the high cost of HDI board also includes operator training expense.

11 Rules for PCB Components Placement

PCB components placement is a major part during the board design. In this article, we concluded 11 rules for your reference, but please note that we will not take any responsibility for anything that results from this article.

1.Start by placing big/ major /critical components (such as MCU, DSP, FPGA, DDR, clocking devices), and then placing support components like resistors, capacitors, etc., around them.  

2.Use 50 or 100mil as a component grid to place these large components (like QFP, BGA, SOP, SOIC or through-hole connectors). Use 25mil as component gird for these SMT resistors/ capacitors or other small passive components.

3.Isolate analog, digital and power sections.

4.The clock driver/ synchronizer should be placed as close as possible to the clock oscillator.

5.Arrange components in rows and columns with the same orientation for easy installation, inspection and rework. If possible, all polarization components like tantrum capacitors and diodes are placed in the same direction. The polarity of these components should be marked on the silkscreen.

6.Keep at least 40mil space between components, and 100mil space from component to board edge is at least. Locate connectors on one edge or one corner of the board.

7.Try to place all components on the top side only. If not possible, small size and low thermal dissipation components (such as SMD passive components) can be on the bottom side.

8.Placing the decoupling capacitor as close as possible to the VCC pin on the active component.

9.Maintain a gap of at least 200 mils from transformer to electrolytic capacitor.

10.Placement for indication LEDs, test points, switcher, jumpers and adjustable components should be easy access.

11.Carefully check signals about analog, high frequency, RF, high voltage, high profile, high heat signals or heavy components before starting to trace routing.   

Snap Grid

A major rule of PCB design which always missed by beginners is to lay out your board on a fixed grid. This is called snap grid, as your components and tracks will snap into fixed grid positions. 100 thou is a standard placement grid for very basic through-hole work, while 50 thou is a standard for general tracking work. For even finer work, you may use a 25-thou snap grid or even lower. 

Why is a coarse snap grid so important? That’s because it will keep your components neat and symmetrical. Besides, it makes future editing, dragging, movement and alignment of your tracks, components and blocks of components easier as your layout grows in size and complexity.

Enough PCB layout practice is very crucial for your future. You’re required to start out with a coarse grid like 50 thou and use a progressively finer snap grid if your design becomes tight on space. Drop to 25 thou and 10 thou for finer routing and placement when needed. This will do for 99% of boards. Make sure the finer grid you choose is a nice, this means 50, 25, 20, 10, or 5 thou is a good choice.

More info., pls visit www.epcb.com

PCB Design Rules

When you design a printed circuit board, you need to follow the PCB design rules of your manufacturer. These rules are the limits of the machine that makes the circuit boards.

The rules we need to pay attention to are these:

Minimum trace width: The minimum trace width is the minimum width of your traces. So you have to make sure you draw your circuit board “wires” with a width of more than 0.1524 mm.

Minimum trace/ vias/ pads space: Outside each trace, via or pad needs some space. In this case it has to be at least 0.1524 mm. 

Minimum silkscreen width: The silkscreen is what we use to draw or write text on a circuit board. The width of the silkscreen has to be at least 0.1524 mm.

Drilling hole and finish hole: The drilling hole has to be between 0.3 mm and 6.35 mm. And the finish hole between 0.8 mm and 6.35 mm.

SMT minimum solder mask width: This is the minimum width of the solder mask. Solder mask is something that the solder doesn’t like to stick to. So it is around all pads to keep the solder on the pad. And in this case it has to be at least 0.1 mm.

Min solder mask clearance: The solder mask clearance is the space that is needed around the solder mask. 0.13 mm is better.
Learn more about PCB design tips, pls visit www.epcb.com

PCB Design Guidelines

Here are some simple PCB design guidelines that can help you create better board layouts.

Board size: There are always limits to how big your board can be, how thin your traces can be and the smallest drill size you can use. You can visit your PCB manufacturers’ website to check their capabilities. You should keep those data in your mind when you design a new board

Trace width: It must be at least the size of the smallest allowed trace width, but should generally be thicker because thin traces are more vulnerable to damage when soldering. The more current that is going to flow through the trace, the thicker it should be. 

Placement of components: Place your components in a similar way is easy for you to troubleshoot your circuit. When place your components, pay great attention to your large components and connectors.

More PCB design guidelines, please visit www.epcb.com

Single, Double-Sided and Multi-Layer PCBs

During the printed circuit board design process, you have to know the differences between different PCB types, such as single PCB, double-sided PCBs, because it really impact the working efficiency on your finished PCBs. EPCB is here to give you some suggestions about how to choose a suitable PCB type for your application, so you can start in a right direction. Single sided boards are made from rigid laminate with copper on one side of varying thickness. Double-sided boards differ in that they have copper on both sides of the laminate. A multi-layer PCB has copper foil on the top and bottom and inner layer cores. Each type of PCB has its own unique advantages, so you’d better work with an EPCB expert to choose a suitable one.