Best Practices for Preparing Documentation

IMG_4002Preparing the Documentation Package
Documentation is typically provided to us in a .zip file that contains documentation related to details of the PCB, assembly work required, materials required, design schematics, test procedures, special instructions, and more. Ideally, the documentation files should be separated into discrete folders. We prefer either:

  • A distinct .zip file for each type of data (e.g. schematics, bill of materials, assembly, test); or,
  • One .zip with an embedded directory structure that keeps these types of data discrete.

Common Errors to Avoid
The following are common errors related to manufacturing documents. Avoiding these errors will improve delivery time and quality.

CAD Data
While almost everyone—including OCM—uses CAD systems, not everyone uses them to the same degree, or to the same level of accuracy. Accurate CAD data improves information flow and can cut manufacturing time and reduce design errors. For example, we are able to query CAD data for accurate dimensions and other details of the product. But it’s critical that your CAD files always be up-to-date.

You may be using a third-party to create your CAD layout, or you may be doing it in-house. If you are using a third party, you will need to request the CAD layout data from that company. This short paper explains the required format and why it’s needed.

If you are producing the CAD layouts in-house, follow these guidelines:

  1. ASCII CAD is the typical data format. ODB++ and GENCAD are common equivalent formats. We provide instructions specific to each customer’s CAD tools. Please also refer to this short paper about Intelligent CAD Data.
  2. Ensure that you send us the correct version of the data. Double-check the version you send us, or rely on a rigorous documentation control program to ensure the correct versions are employed.
  3. Send Gerber data only one format, rather than multiple formats. RS-274x is the preferred format for Gerber data.
  4. Verify that the aperture data you send is correct – we often see aperture dimensions of “0”, requiring us to halt our process and request clarification.
  5. Avoid sending redundant data, such as sending both Gerber files and aperture data containing aperture data separately. RS-274x Gerber files already contain the aperture data.
  6. In the Gerber data or a separate PCB document, include specifications for layer stack-up, solder mask colour, copper weight, surface finish, laminate, and the revision of the board. This information ensures accurate quotations from the board shop.
  7. Include details about testing, masking, conformal coating – anything to ensure that someone new looking at the product understands every detail.

Schematics & Drawings
Adhere to these best practices when preparing your schematics and drawings for a contract manufacturer:

  1. Include PCB schematics – these tell the contract manufacturer how parts on a board are to be connected. We refer to these drawings to ensure interconnect is accurate and to solve problems if they arise. EDIF format is preferred because an EDIF file carries intelligence that we can cross-reference with CAD data and assembly drawings to speed debugging. PDF format is also acceptable, but does not contain intelligence. If your contract manufacturer will be doing testing, providing a schematic is essential for debugging.
  2. Include assembly drawings in your documentation package. An assembly drawing provides higher-quality information about board assembly than Gerber data. Ensure that you reference a workmanship standard to which we must adhere. If special assembly steps or requirements exist, indicate these on the drawing. Note that part-reference designators are best labeled on top of the box or component, rather than on the outside edge of the part, with can create confusion about which part they reference. PDF format is acceptable for assembly drawings.

Bill of Materials
Follow these guidelines when preparing your BOMs for the contract manufacturer:

  1. Send a BOM in only one file format. A spreadsheet is preferred to a text or PDF file.
  2. Always include alternate parts in your BOM – this ensures you will get the benefit of lower pricing or reduced lead times on parts.
  3. Always include complete manufacturer part numbers in your BOM; not doing so can cause delays.
  4. Assign a unique internal part number to each part, assembly, and sub-assembly in order to reference and identify parts quickly. The part numbers you assign should be referenceable across all of your designs – that is, if you use the same part for many products, that part should always be identified with the same part number. Avoid creating duplicates, and reuse part numbers consistently across all of your designs

Functional Specification
A functional specification of how the product is meant to function is very helpful if testing is being undertaken. This information cannot be conveyed by a schematic or CAD data. A functional specification should describe how the product is designed to work and what its acceptable limits are. This, in combination with the other documentation, allows technicians to understand the product quickly and move on to efficient testing and debug.

At OCM Manufacturing, we can work with designers to ensure that their plans and prototypes are manufacturable and therefore marketable. Contact one of our Program Managers for details about how we can help.

See attached PDF.