4 Documents Required to Quote a PCB Assembly
1. Bare Board Print
2. Assembly Print
3. Bill of Materials
4. Approved Vendor List
Bare-Board Print - Commonly referred to as a fabrication drawing or fab drawing, this print gives us the basic documents required to have your bare PCB fabricated. The bare-board print should include outer dimensions, board thickness, material, finish, number of holes along with the smallest hole size required, the number of layers required, solder-mask color one side or both, silkscreen color one side or both, and any other cost drivers. Lastly, your bare-board print should include both part number and revision. Typical file formats include gerber files, or better yet, ODB++ files.
TIP⇒ Always Check Your Data – After any and all revisions to your drawings, ensure that all necessary changes are made to your assembly print and bare-board print, and that revision numbers match on all the documents. Mismatched revision numbers are a leading cause of confusion during quoting and first-time builds.
Assembly Print - Essentially the manufacturer’s blueprint, it shows the location of the parts, as well as any information on special markings or packaging required for the PCB. Like the bare-board print, the assembly print should include the assembly part number and revision. Most commonly provided in a PDF document.
Bill of Materials - (BOM) is the controlling document for components. At a minimum the BOM should have an internal part number, description, quantity per, and a reference designator for each line item. Often BOMs include the approved vendor list (AVL), eliminating the need for a separate AVL. Best-practice BOMs will include the fab part number and revision. BOMs are most commonly provided in Excel format. Please note, we will need separate drawings for any custom parts (i.e. cable assemblies, sheet metal, machining) to obtain pricing for these items.
TIP⇒ Practice Consistency – Make a standard format for your BOM that is easy to navigate and remains constant through every revision. The best file format to use is Excel, and it’s best to have a single line for each part number (called a ‘flat file’).
Approved Vendor List - (AVL) provides the manufacturer and the manufacturer’s part number associated with your internal part number (IPN) or reference. There can be multiple approved manufacturers for each IPN. Commonly this information is included as part of the BOM.
TIP⇒ Keep Records of Previous Revisions - It’s important to keep documentation on all previous versions of your design.
Further Reading: Online PCB Assembly Price Calculator
This post originally appeared on the DigiSource Blog