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Prototyping

Prerequisites:

  • Physical design (PCB Layout)
  • Design review approval
  • Reconciled bill of materials (BOM)
  • Manufacturing & assembly specifications

Tools:

  • Design tool (Gerber Export)
  • ERP system (Inventory & Supplier Contacts)
  • Spreadsheet software

Next Step:

Once your BOM is reconciled, your design has been reviewed, and your PCB has been laid out you are ready to order some prototypes.

You will now need to start building an archive that you will send out to all of the different manufacturers and service providers involved in building your prototypes. Think of the archive as their guidebook to building your design. They will do their best to build exactly what you tell them to. If you tell them to do something wrong, or give them the wrong files, or are confusing in your documentation - chances are you will get the wrong thing back from them, and still have to pay for your mistake. This is why the design review stage is so important. Do your best to measure twice and cut once.

The archive should probably be a .zip file and it should be structured like this:

TODO: insert an example archive including a template .zip file [[ your company ]]_[[ board name ]]_[[ version ]].zip

  • readme.txt
  • assembly_info
    • assembly_spec.txt
    • bom.csv
    • centroids.txt
  • design_files
    • design_[[ version ]].json
    • link_to_online_design_viewer.url
  • manufacturing_info
    • manufacturing_spec.txt
    • drill_files
      • [[ long list of excellon drill files ]]
    • gerber_files
      • [[ long list of gerber files ]]
  • misc
    • [[ anything else you think they will need ]]

There are templates for all of these files in the reference section below. But here is a quick walkthrough of each of the files and why it’s needed.

readme.txt

Use this file to remind your suppliers who you are, your contact details, when the design was created, who owns the copyright, etc. You want this to be the first place they look when they have questions.

assembly_spec.txt

Use this file to remind your assemblers of the quality level you expect, any IPC specs you need met, what type of solder to use, any processes they should or should not use, what kind of pre or post-assembly inspection is required, etc. This should be the guidebook for your assemblers. Don’t shy away from calling out the obvious details.

bom.csv

Your assemblers may need your Bill of Materials to determine which parts belong in which locations. Depending on the size of your design and the quantity ordered they may even be doing the assembly by hand, and not in an automated way. This should simply be the BOM that was produced in the reconcile process.

centroids.txt

This is a machine consumable file that relates each part in the BOM to each part’s centroid in the layout. It should just be a matter of exporting this file from your design tools and including it.

design_[[ version ]].json

This / these files are optional. You gain the benefits of reduced cycle time (assuming your suppliers can open the files), in exchange for needing to trust your suppliers to keep your IP private. We recommend sending them to your suppliers, except for those in China and Southeast Asia.

manufacturing_spec.txt

Use this file to remind your Printed Circuit Board Manufacturers of the quality level you expect, any IPC specs you need met, your stackup, what type of preprag to use, any processes they should or should not use, what kind of post-manufacturing inspection is required, etc. This should be the guidebook for your manufacturers. Don’t shy away from calling out the obvious details.

drill_files

These are machine consumable files that includes the sizes and locations of all drill holes that need to be made in the board. Because of the manufacturing process there will probably be multiple files, or at least an order to the drilling and the files will include things that are not obviously holes like vias and fiducials. It should just be a matter of exporting these files from your design tools and including them.

gerber_files

These are machine consumable files that include include the layer by layer copper exposures (what the remaining copper should look like after a layer - a piece of fiberglass covered in copper foil - is etched). Each file describes a single layer. And each file contains a huge list of vectors, some added to the plot, and others subtracted from it, that sum to describe the layer. Silkscreens and the board outline are often also included as gerber files. It should just be a matter of exporting these files from your design tools and including them.

Once you have collected all the files you need and assembled in your archive you need to start contacting suppliers. Some of the hobbyist and more forward-thinking suppliers allow you to do it all through a web form, while most of the professional grade suppliers will still require a phone call and an upload to an FTP server. Whatever it takes get your BOM parts ordered, your PCB boards ordered, your logistics figured out (so that the boards and parts will both arrive at your assembler), and your assembly ordered. In the end you should expect to receive your final assemblies (sometimes called PCAs) in between 5 and 45 days.

After your order has been placed comes the worst part of the whole process... waiting. Getting that sick feeling that you messed up somewhere and going back through and checking your design a few dozen more times. This will also probably be the first time in the whole design flow where you weren’t the critical path - so try to take a few days off and recharge.

Once your prototypes have been manufactured, assembled and finally show up at your door you’re ready to move on to inspection & turn-on checking.

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