The Bill of Materials (BoM)
Nobody likes getting the bill. But why? Perhaps it’s because it’s a sobering reality check at the end of a long night full of excitement (and possibly questionable decisions). Or maybe it reminds us of the costs of our journey and all the stops along the way, the good, the bad, and the ugly. The bill tells us a story.
That story is a funny kind of similar in the electronics engineering world. When we drop the Bill of Materials (or BoM for short) we are reminded not only of what makes up our electronics design, but also of the material costs and the lessons we learned along the way.
But What is a BoM and Why Should I Care?
A BoM is a list of all the materials required to manufacture and produce a particular electronics design or product. This includes all electronic components, any Printed Circuit Boards (PCBs), mechanical parts, cases and enclosures, connectors–everything. We also include required quantities, prices, part numbers, manufacturer and supplier information, in addition to parametric details such as component values and electronic package sizes. All this detail permits the electronics engineer to make substitutions in case of supply chain or part obsolescence issues.
In “short”, the BoM tells us what we need, and what it’s going to cost us. In the case of the ENA Short-circuit Finding Brush, our BoM indicates that we need to purchase varying quantities of about 50 different components–resistors, capacitors, ICs, diodes, transistors, etc.–for a total cost of about $112 for a single unit. This includes the cost of ordering 3D-printed parts for the enclosure. That’s the price for low-volume or prototype production of the product.
Yeah But I Want to Make Lots and Lots of Them!
OK, that sounds great! If we were to ramp up to high-volume production our engineers could take advantage of price breaks (cheaper prices when you buy large quantities) and economies of scale (decreasing fixed costs per unit when you make lots of units) and ultimately offer a better value to our customers.
In terms of the BoM, we typically start with a low-volume prototype BoM, and then graduate to a high-volume optimized production version.
Conclusions
So maybe now you know a little bit more about how engineers keep track of all the bits and pieces of their designs–and stay sane along the way!
Stay tuned for Part 6 where we’ll review and conclude this series on the Short-circuit Finding Brush and finally release the design files for all to cherish!