Control PCB Fabrication Costs by Thinking About Panel Sizes
Getting the most for your money in custom printed circuit board manufacturing requires a little up-front knowledge of how they are made. Unfortunately, your manufacturing partner may not talk completely straight about their processes and pricing model (kudos to those that have live pricing on the websites). If you're new to the industry, or just looking for hints on how to lower your PCB costs, keep reading and perhaps you'll learn something new. Nothing in this article is rocket-science, it's really a matter of some common-sense math.
While designed-in features are the predominant driver of PCB manufacturing costs, the more subtle factor of panelization efficiency can also have a dramatic impact. One of the key things to understand about your PCB order is that the manufacturer (some would say "fabricator") probably doesn't build individual boards. For the sake of automation and repeatability, their machinery and processes are setup to handle uniformly-sized "panels" of material. Unless your board is large, or requires special processing, it's likely it will flow through the manufacturing process on panels with other designs.
The second key thing to understand is that the cost of manufacturing panels is basically fixed for a given set of technology. This obviously doesn't include non-reoccurring charges (i.e. the "one time" setup required for a new design) but it is the case for the actual fabrication processes. Other than the price of materials and labor, not much varies from panel to panel.
Working from a fixed panel cost, you can quickly see that more boards packed into a set of panels means more efficient (less costly) manufacturing. And, generally speaking, the more boards that fit on a panel the lower the per-board price. This works out well for both customers and fabricators. However, it's one of those things that seems to be missed during PCB layout. Costs can skyrocket when your design differs from "what everyone else is doing" because your boards will need to be on panels all by themselves. Boards that are done using "common" technology are easily aggregated; meaning the cost of manufacturing the panel can be spread among multiple customers. This can be a huge cost saver. But if you're boards are going to be on panels by themselves, you have to take a close look at panelization efficiency.
To make the best use of the available space on a panel (and thus lower your cost), carefully choose the size of your board. Ask you manufacturer for the details of the panel sizes they prefer, and if possible pick board dimensions that are an integer divisors of the length and/or width of the panel size. Don't forget to account for the margin around the edge of the panel and spacing between the boards. Your manufacturer should be able to provide specific instructions for sizing your board for maximal efficiency -- if they can't (or won't), you may want to consider a more cooperative manufacturer.
The math behind finding the best board size isn't complex, but it's tedious. So to save you a little time in a spreadsheet, we've added a little calculator at the bottom of this page. Before we get to that, however, I want to volunteer a couple examples of PCB panelization scenarios:
The point of the above examples is that size really does matter when it comes to effectively using the space on panels. Assuming panels have fixed cost (and they should, when they are identically built), then size choices can also impact your price. The difference between getting 2 boards per panel and 4 boards per panel may be a tiny fraction of an inch. The designer of the board in the third example above could cut their per-board price by as much as 50% by shaving a tiny bit off each dimension. Here are another couple examples, this time with the exact same size board and panel, but with the board rotated 90 degrees:
What a difference! Getting 60% more boards per panel seems like a win-win-win situation to me. Is your fabricator quoting your order based on only one rotation? You'll never know if you don't ask.
And, finally, keep the spacing between boards in mind. You might be temped to think that smaller boards would always lead to better panelization, but that isn't the case. As the board size gets closer to the inter-board spacing, efficiency drops like a rock. Consider these three cases:
