AVL: Approved Vendor List 2.0

Is the approved vendor list a good idea? If you have ever been involved in electronic development for anything manufactured in volumes, you know how important second sourcing is. For as many parts of the system as possible, you want to have multiple independent suppliers. That just makes procurement so much easier when the thing is actually in production.

So how do you handle that in practice?

At the Bill of Materials (BOM) level, there are basically two methods:

• Method A: Each line on the BOM refers to an internal part number for which one or more parts are registered. This is often called an Approved Vendor List (AVL). So a 100nF, 0603, x7R capacitor may have an internal part number that refers to specific parts from three different manufacturers.
• Method B: Each line on the BOM refers to a number of different parts with a sufficiently similar function. Each part may have its own internal part number, so one BOM line may list several internal part numbers right away.

At first glance, the difference may not seem to matter much. Method A seems to be the most common, but it does have some interesting side effects.

What’s wrong with this?

Method A will in general work quite well, but does have a few significant problems:

• As you would want to avoid having the same part listed under too many different internal part numbers, there will be a pressure on the designer to approve all parts on the AVL when selecting a component. Sometimes the design may actually be tested with all parts on the AVL – but most times not. So the designer hopes someone else did the work to verify the parts were sufficiently alike. This is a problem because technology changes so quickly. The parameters that matter today may have changed. Read about how X7R is not a very good specification, as an example of what I mean.
• When you want to add one new manufacturer’s part to the AVL for an internal part number, you really should verify this with all the designs using this part number. This may be too much work, so the reflex reaction is to not add the extra manufacturer. This hampers flexibility.

One good thing about Method A is that it’s supported by all kinds of PDM/PLM systems etc. So it can easily be the default selection because of “the system” – not because it’s a good idea. When this happens – watch out.

Method B seems to be more work, as the designer will have to make a conscious choice to find and select each 2nd source part, but I imagine modern PDM/PLM systems could easily provide very good suggestions based on other BOM’s. So done right, this could actually be a much better way.

How does your system work?

Let me know in the comments below if you are using Method A or B? And why?

Disclaimer: I have always been interested in better and more efficient methods for engineering, but my interest in this subject was re-awakened lately when the Danish PDM/PLM system developer Highstage asked me to join their board. What advice should I give them?