Today, the world is full of marvelous electronic devices that can do incredible things that once were only a dream. Accomplishing these levels of technical performance, however, has required an incredible amount of growth in the way high-speed electronic circuits are designed. Where this kind of advanced printed circuit board design once was reserved for only a few unique applications, it has now become the standard mode of design. High-speed electronics are now in everything from consumer cell phones to the industrial and medical technology that we daily depend on in our lives.
For the optimum performance of today’s PCB designs, great care must be taken in the placement and routing of high-speed circuitry. Without this care, the integrity of the signal paths can be affected by a number of factors that could ultimately degrade the overall performance of the circuit board. To guard against these problems, PCB designers should be aware of good signal integrity practices while laying out their designs. They should also be in the habit of conducting regular signal integrity testing to make sure that their manufactured circuit boards will work the way that they intended them to. Here are some of the signal integrity concerns that they should be looking for.
The Importance of Signal Integrity Testing
To ensure the peak operating performance of your printed circuit board design, you need to know if there are any signal integrity issues that must be corrected before you go into manufacturing. Your contract manufacturer should conduct an array of testing on the board after it is completed, but signal integrity problems found at that point may not be able to be corrected.
The best thing is to design for the most optimum signal performance possible on your board from the beginning. This means working with your contract manufacturer to plan for the materials your board will use as well as the configuration of the board layers. You also will want to ensure that you are simulating and analyzing your design as you go, and that you follow good high-speed design layout principles.
Even if your board isn’t running at speeds that would normally qualify it as a high-speed design, there are a couple of important points that you need to keep in mind:
- As your board changes throughout its lifecycle, it is possible that some parts may be replaced with newer parts that run at higher speeds. If you haven’t created a clean design in the first place because the current signal speeds didn’t warrant it, you may find out it ends up being necessary at some point down the road.
- Second, your design may introduce signal integrity issues into other system-level boards through cables or other system interconnects. Not only should you consider the design needs of your board, but you need to consider its interaction with the other boards in the entire system.
With these points in mind, there are certain problems you should watch for that could hinder your PCB’s manufacturability.
Signal Integrity Problems That Can Affect PCB Manufacturability
Here are some of the signal integrity issues you should keep in mind, as they could cause problems with the performance of your completed circuit board:
- Speed: High-speed circuits need careful consideration of board materials, board layer stack-up configurations, component placement, and routing. The wrong choices here can cause your board not to function as designed.
- Grounding methodology: Impedance controlled traces need stripline or microstrip routing configurations for optimum performance. This requires ground planes to be directly adjacent to the layers that those signals are routed on, and care must be taken to plan your board materials and layer stack-up configurations.
- Split ground planes: High-speed signals need a continuous return path on an adjacent ground plane layer. A common signal integrity error is when the return plane gets split for power and or ground redistribution. Although this solves the power network problems, the lack of a return path will create a lot of noise for those high-speed circuits. Additional signal noise can create false signals triggering the circuitry to fail.
- Signal technology: Different types of signal technologies, such as analog, digital, ECL, or others, will require different approaches to routing. This will include trace widths, spacing, and which board layers to route on. The wrong approach to routing these circuits could introduce problems in the board.
- Analog/digital noise sensitivity: Areas of different design technologies also need to be isolated from each other. Sensitive high-speed transmission signals that are routed through noisy analog circuitry could cause performance problems in those signals.
- RF noise sensitivity: Areas of RF circuitry are especially sensitive to other circuitry and, in return, can affect other circuitry as well. RF circuits must be isolated with ground planes, stitching vias, and, in some cases, physical shielding.
- Sensitive components: Other components, such as high-gain amplifiers, may have special sensitivity needs as well. These devices may require voids in power and ground planes to isolate them from other circuitry.
All of these potential signal integrity problems, along with other characteristics, can impact the performance of the board. This can introduce additional costs if fabrication material changes are required, or if the board is not manufacturable as-is and requires a complete redesign.
How an Experienced CM Can Help You With Signal Integrity Concerns
Your contract manufacturer can provide a lot of help to you when you are designing your high-speed printed circuit board. The thing to remember is that when you work with an experienced CM, they have years and years of experience building high-speed circuit boards and are very qualified in the process.
By reviewing your design, they will be able to get a good understanding of your overall performance goals, interface requirements, and be in the best position to help you. With their experience, they can recommend board layer materials and layer stack-up configurations that will best fit the needs of your PCB. They will also devise the correct testing processes to verify the functionality of your high-speed circuitry, and they can even help guide you if you need help with signal integrity simulation and analysis.
At VSE, we start working on your project by conducting a thorough design review. This gives us a complete picture of what we will need to do to successfully manufacture and test your board. We can advise you on high-speed design techniques as well as make recommendations for board materials and layer configurations to give you the high-speed signal performance you’re looking for.
We can handle any PCB layout or circuit changes needed to enhance the overall signal integrity quality and performance, or we can help you to find external signal integrity analysis services if that is your preference. By leveraging our technical base and experience, you can minimize your PCB manufacturing time and iterations, and make certain that your signal integrity simulations and intentions are realized in your final product.
If you are looking for a CM that has the experience and technical prowess to ensure each high-speed PCB assembly is built to the highest standards, look no further than VSE. Contact us today to learn more about partnering with us for your next project.
