16 layer PCB with 90 & 100 OHM diff pairs. Xilinx Ultrascale FBGA & DDR4 memory DDR4 tracking DDR4 signals to Dimm Socket 100 Ohm 25 Ghz

4 layer PCB with 50 OHMs SARA-G450 2.5G GSM/GPRS cellular module

Case Study - Cloud based telecoms system Background We were approached by a company specialising in cloud-based telecoms to develop a revolutionary comms device for virtual call centres. The PCB would need to interface with other bespoke and off-the-shelf devices. All with their own functions and requirements. Our PCB would have to be the “brain” to control all of these devices.  Requirements All of these peripherals have their own high speed signal requirements: PCI-E connector, Ethernet connector, USB connector, QSFP+ connector, DDR4 SODIMM connectors, DDR4 RAM 8Gbit. If any one of the interactions between PCBs does not perform correctly, costly reworks would be required. Time would also be lost to identify the problem, this could also lead to our customer losing ground to competition. The PCB would also be the power supply for most of these interfacing PCBs. 60 A is required, flowing through various SMPS (switch mode power supply) to provide power to each connector. The high speed requirements for this PCB are extremely complicated, adding SMPS as well can cause problems with the high frequency electrical noise. For the high speed signals, we would need to route the signals at 50 ohms (DDR), 90 ohms (USB), 100 ohms (PCI-E, DDR diff pairs, Ethernet connector). The QSFP connector would need to use 100 ohm tracks at 25 Ghz. Most complex microprocessors have rules to follow. Chip manufacturers supply these rules as well as guidelines and reference designs to follow Using the numerous tools at our disposal, we were able to adjust the PCB stack up, the gap and track thickness to obtain the required impedance for each peripheral to operate correctly. Rules Nets are assigned to differential pairs, buses and classes to for complex rules to be assigned. These rules control the track thickness, track length and clearances to other nets and classes. Assigning the rules accurately allows the PCB to be routed without reworking and unnecessary mistakes. As the majority of these signals need to run at 50 ohms, we decided to organise the PCB stack for all of the signals to run at 50 ohms.  PCB Layout QSFP connector - TE Connectivity 2299940-5 16 diff pairs 100 ohm 25 GHZ, tracks with no 45 corners. The diff pairs are connected using 100 ohm diff pair coplaner signals. As the tracks are running at 25 GHz, there can be no 45 degree bends in the tracks. Track lengths…

26 layer PCB with 75, 90, 100 & 120 OHM diff pairs Zynq Ultrascale+ FBGA & DDR4 memory

What was it like to start working as a PCB design engineer? I Started working for DL Designs as an apprentice after I completed my A-Levels. I came to DL Designs with qualifications in physics, electronics and maths. University wasn't the best option for me and learning on the job whilst gaining working experience was the best for me. Therefore, I found the apprenticeship with DL Designs. I found it challenging at first. For instance, learning a new set of skill whilst working in a new environment. How did you find the job initially. What did you struggle with? It was surprising how complicated PCB software was. Different PCB layout software work and function differently. For instance, Cadence Allegro is the main tool at DL Designs. I started learning the basics with Allegro, particularly creating footprints and tidying references. DL Designs works to a high standard to a satisfy it's customers. However, my colleagues were helpful and encouraging to enhance my skills as a PCB designer. What was your role within the business at the beginning? Once I had learned the operation of DL Designs, my main role was to generate the footprints using an IPC generator. This creates the part as well as supplying the optimal pad size, solder mask and paste sizes may differ depending on the part. Above all, creating footprints is one of the most important parts of PCB design. After that, I moved into the routing the PCBs. I started with Allegro at first and then onto Altium and PADS. What do you enjoy most from designing PCBs? What give you the most satisfaction? I find routing PCB layouts the most satisfying part of my job. Cadence Allegro is the main tool at DL Designs. I started learning the basics with Allegro, creating footprints and tidying references. Most of our designs are very complex. For instance I have to adopt various routing strategies to complete my objectives. Thinking 2, 3 or even 10 steps ahead is key to routing complicated areas such as BGAs or Ethernet signals. I also enjoy knowing working products will be developed from my designs. Meeting my customer's needs around the world, even in Outer Space! What do you hope to learn in the future to better yourself as a PCB designer? I am currently learning how to work with PCB layouts using DDR technology. Allegro is the best tool for…

Information It's important to have everything necessary to make the perfect PCB Layout. A good engineer would foresee any complications that may crop up; problems with sourcing datasheets, lack of available space on the design to avoid manufacturing headaches. Three types of information are crucial for a successful PCB design. DXF or mechanical drawing, BOM (parts list) and a schematic. A layout guide provided by the design engineer and necessary reference designs is also useful for a successful PCB layout. Mechanics Today's PCB designs are very complicated with limited space. Some projects may involve multiple layouts fitted together in a box. The best way to ensure the PCBs fitted together correctly without complications is with a CAD package such as solid works. The PCB design import the CAD drawings. This saves a lot of time, we place the parts on the imported locations. This is the most accurate and cost-effective way of placing components in specified areas.   Design Rules This is a crucial stage and makes up the backbone of any PCB layout. Accurate placement is essential, there could be major flaws with the functionality of the circuit board. The rules basically control any clearance and track thickness on the design. For more complicated layouts; rules for impedance controlled signals, extra clearances for noisy tracks, implementation for relative propagation delays and constraint regions are necessary.   Component stage It is crucial to start and maintain a parts library during the PCB layout stage. Most of the PCB design errors come from incorrect footprints. Using a standard footprint name such as IPC can help design engineers and colleagues select the correct part without recreating the same footprint over again. Part generators are useful tools to create parts. Entering part sizes into the generator,  the software calculates the optimum size for pads, including the paste (reducing this by 30% to prevent excessive solder shorting pads together). Other useful information such as component and placement outlines, component heights and keepouts simplify and aid the PCB layout. All components must be double checked before added to the library and updating the PCB design. Time and money's saved when using a library with reliable components. Placement stage Each PCB layout is unique, there are many questions that are asked to make sure the design meets the customer or engineer's needs. Failing to resolve these queries, could end up with the placement reworked multiple times. Is there…

When using components such as switch mode power supplies (SMPS), the PCB layout is critical. Faults in the PCB layout cause a number of problems including switching jitter.  Poor output voltage regulation and possible failure with the PCB design. Issues like this can be avoided, saving money and time on scrapped circuit boards and PCB modifications.   Datasheets When putting together a PCB layout the best approach is to review datasheets for devices such as SMPS. A respectable manufacturer such as Texas Instruments will offer guidelines and reference designs to follow for your PCB layout. Usually a layout guide will show a PCB design with all of the parts, copper tracks and vias arranged for an optimum performance. It will show lots of space with no other components interfering. This does not happen in the real world, most of the time there is not enough room to keep parts and tracks away from critical areas. The best way is to follow the guide and bend the rules only when it's absolutely necessary to do so. Below is a part of the schematic that show the SMPS and the related components. The second diagram is the recommended PCB layout from the manufacturer.   Layout Guide The decoupling caps (input and output) must be close to the regulator. The most important aspect of SMPS is to reduce high current loops. The recommended layout shows a GND plane under the component, flooding over other components connecting to GND. There is also a skinny blue line representing a track on the bottom side of the board.  This is the feedback signal, the track is on the bottom side to reduce interference and must not be in the high current path. The PCB layout must follow this guide for it to function correctly. Here is the schematic and PCB layout to highlight the key areas, orange for input, purple for output and burgundy is feedback.   Comparison The PCB layout shows the input signal running from a plane (using vias) through the decoupling caps through the inductor and into the module (REG1 highlighted in yellow) via more caps. The output signal runs through decoupling caps and away through the inductor. The GND signals connect to the GND plane through vias at the module and at the decoupling caps. The burgundy feedback signal is routed from pin 4 of the module, through the resistor and capacitor…

  1. Smarter design Planning the PCB layout and assembly process is one of the most smart and cost effective ways of saving money. The strategical engineering of these boards can result in using fewer and more cost effective parts which will significantly lower the cost of each PCB. In the long run, this will enable your company to reduce costs and deliver high quality PCB layouts.   2. Use manufacturers reference designs Engineers designs can look good on paper but when it comes to design, costs could impact on overall cost and reduce profit. Costs can increase during the manufacturing stage. One of the cost effective ways is to refer to manufacturers notes. The information provided can save effort, time and money for the design to be produced. A decent chip manufacturer will provide a schematic, BOM, gerber and assembly drawings and reference designs. The reference designs are created by the manufacturer to show how the design is made to their specification.   3. Panelise Placing multiple PCBs on the same panel allows all of them to processed at the same time, instead of separately. Not only are boards manufactured like this, they are assembled and shipped on a single panel. The more PCBs on one panel, the more cost effective it becomes.   4. Get the Manufactures involved Providing the manufacturers with any information during the design process can pay dividends when it comes to releasing the production files. Board stack up, clearance issues, materials and special requirements - these could cause problems for the manufacturer and these could be costly if told in the last-minute. By communicating and agreeing with in advance this would give the manufacturer time to resolve any issues and even offer an alternative solution. You could have time to find an alternate manufacturer if your demands are not met.   5. Using the same assembly house for prototyping and mass production Once the boards have been designed and manufactured, the assembly process can begin. If there are no design changes between prototyping and productions it would be practical to use the same assembler for both and to start mass production as soon as possible. Material costs are fairly low, significantly lower when bought in bulk. The main costs are time spent assembling the PCB. It takes time to review the design and resolve any potential problems. It takes even more time to add…

  1. Lack of planning With PCB layouts, preparation is the most important part of the job.  The amount of time spent preparing will affect the success of the design.  Selecting the right PCB design software is the most important; each having advantages, disadvantages and limitations. Each PCB is unique it it's own way. Some areas of the design are more important than the rest, for example power supplies, impedance signals, DDR, address and data bus.  If these areas are not completed before the rest of design, precious time is lost and considerable effort is then spent reworking the layout. Setting up rules and constraints are there to guide from the placement stage till the gerbers are completed.  When a PCB is planned correctly, the rest of the design will become a much simpler process.   2. Constraint rules There isn't anything more powerful than the human mind, unfortunately it is not perfect! There are lots of things to think about with a PCB design, and it is easy to get lost with all of the information.  By using the tools available from PCB software, constraints can be implemented; spacing, keepouts, length matching, propagation delays. Once these rules have been implemented, the designer can focus on other areas of the layout.   3. Poor Communication As PCBs become more complex, the communication between engineer and PCB designer is essential.  By eliminating any placement or routing issues early on can save on costly reworks. It is very important for the engineer to review the circuit board as often as possible.  Using on-line meeting tools can allow the engineer to inspect the board in real time and discuss potential issues. By setting out clear objectives and agreeing on them from the start of the layout can give the designer a better understanding of what you want to achieve and can shorten time-to-market.   4. Using ineffective layout techniques PCB layouts are becoming more complex thanks to advancements in electronic technology.  Problems such as electrical noise, crosstalk, impedance mismatch, timing issues, ESD - all need careful consideration. Practical PCB design rules, board stackup, PWR & GND planes, decoupling capacitors, faraday shields - these are valuable when used correctly. Reference designs provides the optimum solution to meet requirements for complex layouts.  Some of their suggestion may be difficult to achieve, but they do give some insight on how the PCB should be designed correctly.   5. Forgetting to backup…

Despite increasing levels of semiconductor integration and readily available systems-on-chips for many applications. In addition to the increasing availability of highly-featured development boards, electronics often still require a custom PCB. Even for “one-off” developments, the humble PCB still performs an important role. It’s a physical platform for a design, and the most flexible for pulling an electronics system together. In this article, we outline ten best practices of PCB design, most of which have stayed consistent for 25 years. These rules are in no particular order and applied to any PCB design project. This should prove as a useful guide both to veteran design engineers as well as makers alike…   Use the right grid Find a grid spacing that suits as many of your components as possible and use it throughout. Although multiple grids may seem appealing. A little additional thought at the early stages of the layout can avoid spacing difficulties and maximize board use. Many devices are available in different package sizes, so use that to your advantage. Furthermore, as the polygon is an important shape when adding copper to your board. Boards with multiple grids will often produce polygon-fill discrepancies, not standardizing on one grid can make your life difficult.     Keep trace lengths as short and direct as possible This rule applies even if it means going back over parts of the layout again to optimize track lengths. This applies particularly in analogue and high-speed digital circuitry where impedance and parasitic effects will always play a part in limiting your system performance.   Whenever possible, use a power plane to manage the distribution of power lines and ground. Using pours on the power plane is a quick and easy option in most PCB design software. It applies plenty of copper to common connections and helps ensure power flows as effectively as possible with minimal impedance or voltage drop. That ground return paths are adequate. If possible, run multiple supply lines in the same area of the board and remember that if the ground plane runs 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.   Group related components and test points together Place the discrete components needed for an opamp close to that device so the bypass capacitors and resistors are co-located with it. This helps with the track…