July 7, 2020

How to Catalog Parts

This part of the design process is as much record-keeping as it is anything else.  What information do you need to keep?


Manufacturer Part Numbers

Every manufacturer has their own unique part numbering scheme.  In addition to the part type, the numbering scheme helps to differentiate between alternate footprints.

Assembly houses might not be able to solder a part with a particular footprint to the wrong land pattern.  Designers have to be especially careful with parts that have multiple footprints; it is very easy to select a footprint that doesn’t match a land pattern.

These mistakes happen every day in an assembly house.  Here are a few examples.

These parts are the wrong size for the provided land pattern.  The parts may not solder correctly.

This is the wrong part of for the provided land pattern.  The parts will not solder correctly.

It can happen due to inattention to detail, it can happen because the purchasing department thought they could save a few dollars by selecting a different part number.  But either way, it will stop your project dead in its tracks.

Distributor Part Numbers

Distributors often have millions of unique parts on hand.  And they have the added difficulty of having those parts in different packaging.  Some parts might be on cut-tape, others on reels, and others still in a tray.  They are the same part with the same footprint — but different packaging.  This is another opportunity for error.  

Before you ever order a board — you should obtain a Design For Assembly check of your design.  Advanced Assembly offers free DFA checks whether you order a part from them or not.

Spreadsheet Setup

Once you find the part you will need to record some information that will eventually be used to create a Part Library.  For now, we will create a spreadsheet/database with at least the following data for our reference when creating our parts libraries. 

This can be a spreadsheet on your computer, the part library in Altium Designer, the BOM builder on the Digikey website, or something else.  The key is accuracy and consistency.  (We’ll work together to populate a sample database in the next activity Bill of Materials.)

The “Add to BOM” link is directly below the “Add to Cart”

If you do create your own spreadsheet, keep in mind that this is different than the BOM that you will submit to your assembly house.  We will use this initial spreadsheet to create a parts library for our design. 

Your spreadsheet needs to at least have these columns to save you time later.

The assembly house will want the data in a slightly different arrangement.  We’ll worry about that format in the very last stages of design before the DFA check but I’ll present it here to offer contrast.

While assembly houses will take a BOM in almost any format, the preferred document will likely be .xlsx or .csv.  Advanced Assembly requests the following columns in txt, csv, or xlsx formats.  It’s easy enough to merge the Descriptions Value Package columns before submission or leave it for the part sourcing department to do.

Get organized now!  Electrical Engineering is too complicated a subject to “wing-it” or work from post-it notes or other poorly organized note-taking schemes.  Almost every PCB layout mistake I’ve ever made can be traced back to an interruption of some sort and a disrupted thought-process.

Mark Hughes, Advanced Assembly
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