PCB Layout Examples
High Speed Layout
Poorly done high speed boards can cost your company tremendous amounts of time and money due to regulatory failures, low manufacturing yields or warranty returns. High speed signals behave like RF signals so incorrect routing techniques can result in a multitude of tribulations. Awareness of the return current path is essential; clocks must have clean edges and skew must be accounted for as well as signal termination and appropriate buss topology.
Comprehension of high speed issues and relevance of common design decisions and trade-off's results in the best planning and greatest possible success for a high speed project. This is how we do it:
Rely on our printed circuit board layout proficiency and be more confident in your design.
Did you know that the bulk of re-designs on digital boards are as a result of high speed issues? These issues can begin as digital noise contaminating the analog signals and flow on down in a domino effect to product or regulatory failure.
Signal Integrity Analysis - Characteristic Impedance - Cross-Talk
EMI Analysis - Thermal Analysis - Board Material Stack Up Simulations
RF & Wireless Layout
Radio Frequency or RF designs are often infamous as "black magic". This belief exists because the fundamental mechanisms of how RF energy is developed within a printed circuit board is not well understood by many. Many aspects of RF design are theoretical mathematical calculations. An understanding of how this relates to the physical layout world is imperative to a functioning design. During layout, proper design techniques must be used.
Good design practices and knowledge can help to keep the bad aspects of that ole "Black Magic" from cropping up.
Pb-free is having some effect on printed circuit board layouts. For Pb-free assemblies, one of the most important layout issues is the component's physical footprint. It is important to determine whether or not components can resist the higher reflow temperatures needed in the lead-free process. These temperatures can be in excess of 250º or 260ºC. If your existing components can withstand these temperatures then there is no need to select new ones, but if the component can only withstand temperatures around 235ºC, then it is important to replace the component with one that is appropriate for reflow at higher temperatures. If no change to the component, then obviously there is no change in the footprint or layout.
An assembly concern that needs to be considered is whether or not there are SMT components mounted on both sides of the board. The components on the bottom may be glued and must be able to withstand solder temperature of over 250ºC. If they can not, a wave soldering fixture will be needed to shield them.
Additionally, layer stackup and impedance control calculations change if the pcb laminate material is changed to be lead-free complaint. Microstrip, dual stripline or single-ended, these impedances ensure signals get to their destination with minimal crosstalk and as clean as possible so it is important to re-run the calculations on the new chosen material. This can effect a layout globally and require different trace and space for the routing, so don't underestimate the impact of this on densely routed boards. Materials such as FR406 or FR408 can withstand upwards of 270ºC or higher, but commonly, especially for high-speed boards other materials are required and the calculations using those materials may greatly affect a printed circuit board's routing.
|Advantage Electronic Product Development Inc.
34 Garden Center, Broomfield, Colorado 80020