PCB123 Design Flow

PCB123, backed by Sunstone Circuits manufacturing, provides a powerful and comprehensive design flow from initial research all the way to assembly and production.

Unless you fabricate your own PCBs, you need a manufacturing source (link to a “how boards are made” video) that will collaborate with you during the entire design flow. PCB123’s entire business model is based on consulting and collaborating with you from idea to finished product, and beyond.

Here’s how the design flow works, and where we fit in that process:

Parts Research

There is a back-and-forth process between parts research and capturing the schematic. Unless you’re designing your circuit at the “gate” level, using nothing but generic AND, NAND, OR, NOR, XOR type constructs, at some point you’ll be specifying components for your logical design. This becomes a back-and-forth process of researching parts available, selecting them based on specifications, and making sure the part chosen is defined in your parts library. Sometimes the part will already be there; other times, you’ll be adding a part from scratch.

It’s not unusual to find a designer with a schematic tool open on one screen and a web browser full of parts suppliers websites open on another. Parts research often boils down to scouring the parts distributors online to find a part that will work for your circuit.

PCB123 accesses information on the Digi-Key website for our library of 750,000 parts. For example, you can search by parameter in the PCB123 library directly. Just use the search function inside the library taxonomy pane. If a part looks like a candidate, you can click on the link to the part’s datasheet on the Digi-Key website, and complete your detailed review. Like it? Drop it into your design – the BOM updates automatically. Don’t like it? It’s easy to move on to the next candidate.

If you find your part by searching a parts distributor site directly, just copy and paste the manufacturer’s part number into the PCB123 taxonomy window to search for that exact part. If it’s there, you’re ready to verify and go; otherwise you know right away that you’ll need to define that part from scratch.

 

Schematic Capture

Specifying the functionality of the design in symbolic logic. Yep, that’s schematic capture.

PCB123 provides a full-featured standard schematic capture tool as an integral part of PCB123. This is a good place to start. As you drop component symbols on the schematic, the corresponding layout footprint is pre-placed on the layout page. Network connections on the schematic create pending traces on the layout page (represented by traditional “rats nest” lines between component pins)

If you prefer a different schematic capture tool, or if you receive finished schematic designs from someone else, then you can always use the netlist import features to load in the pre-existing schematic design.

 

Layout

  • Board Outline – doesn’t seem all that critical until you get started. Does your board need to fit inside a particular enclosure? Those constraints will need to be included in the board outline. While you probably don’t need to know the exact board outline and dimensions while you’re capturing the schematic, you’ll need to have the outline roughed in by the time you start layout.
  • Component Placement – With the board outline, the next step is to place your components. Connectors first in the required locations to connect to the rest of your system. Second, block out sections for functional ‘chunks’ of your design. Third, place the major components – complex functional components like IC’s, A/D Converters, etc., Finally, work the circuit conditioning parts (resistors, capacitors, etc.) in where they both fit and simplify trace routing. With some practice, you’ll start to ‘read’ the rats’ nests to understand whether your component placement is good. A lot of “crossing nets” from one component to another would imply that the placement of those two components needs to be changed.
  • Trace Routing – If you started with a schematic, you’ll now realize that your layout-in-progress is full of prompts for correctly connecting the components on your board. Without a schematic to drive the ‘rats’ nest’, trace routing becomes more time intensive and error-prone. For some new designers, this is the point in their first complex design where they realize that short-cutting the schematic is costing them time and effort during layout. In our resources section, and in the PCB123 manual, you will find extensive discussions of techniques for fast, efficient, accurate trace routing. If you’re just learning, we recommend you take whatever knowledge you can from these documents.
  • Prototyping – “first light” from a new design! Prototype boards can cover a spectrum from intentionally quick-and-dirty boards to highly-polished sub-assemblies – all depending upon the specific purposes of the project. PCB123 can assist you in delivering on either of these prototype methodologies and, with some forethought, can deliver your design into any of Sunstone’s board build service levels.
  • Layout Optimization – if you’re intending to turn your prototype into a fully fledged product, then chances are good that you’ll iterate your protos until you finalize the circuitry – so you’re not done yet. Next steps are to carefully optimize your final prototype. Can you simplify the components? Can you substitute for more robust or more affordable parts? Can you reduce board area? simplify routes? Drop from four layers to two? All in the interests of creating more robust, higher yield and cost-effective production boards.

 

Bare Board Fabrication

With a completed and checked design file, you’re ready to have a PCB manufacturer fabricate your boards.

  • Prototype
  • Production – The key difference between a prototype and a production board is this: is your board design finalized? If you’re still revving through the design phase, you’re prototyping. Chances are, your next order will have design changes and a roll of the rev identifier. But if you’ve set the design and you’re looking to re-order in the future, you’ve just moved into production.

 

Assembly

Without a substrate to which to attach your circuit components, all you have is a pile of chips. Conversely, PCBs are just fiberglas and metal film until you attach the components. Depending upon your needs, you might assemble your boards yourself (links to how to hand solder), or choose to have a professional service assemble your boards.

PCB123, in partnership with Screaming Circuits, makes professional machine pick-and-place assembly available to you. During your order process, you can request quote information for assembly of your project by Screaming Circuits. You can either send a kit of your necessary components to Screaming Circuits, or you can also place an order with Digi-Key from inside PCB123’s LiveBOM tab. Within 24 hours of the Sunstone-fabricated boards and parts from Digi-Key, converging at Screaming Circuits, your boards can be assembled and shipped completed to your desk.

 


 

PCB123 delivers a stable, well-maintained suite of tools, highly connected to the manufacturing chain.

Here are some more resources to help you learn about design flows:

The Engineer’s Guide To High-Quality PCB Design“, Electronic Design magazine, published July 17, 2013