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With the supply chain problem showing no signs of letting up, the idea of designing PCBs with fewer materials has begun to take hold. So, as we mapped out this issue on conserving materials, we knew it was important to hear from Happy Holden about this topic. Here’s why:
Happy has been a proponent of cost-aware PCB design for decades. At HP, Happy helped develop the relative cost index (RCI), which allows PCB designers to compare the costs of PCB structures and their alternatives. With this in mind, we spoke with Happy about the potential benefits of designing for material conservation, and why many of the old design concepts may be ripe for updating, such as the 0.062" board.
Barry Matties: Happy, in the past you mentioned that 75% to 80% of the cost of the board is controlled by design and just 20% by the fabricator. To help designers control cost, you developed a relative cost index. Tell us about that.
Happy Holden: We came up with the relative cost index because it was almost impossible to get fabricators to provide cost predictors. First, they didn't want to have people hold their feet to the fire in case you left something out. Second, they were unsure if the information would get out to their competitors. So, we came up with the relative cost index. It allows you to compare architecture design alternatives as a percent savings or percent increase in cost from that fabricator. It doesn't give you the absolute value, although the RCIs are calculated based on the costs of a conventional eight-layer FR-4 through-hole multilayer PCB.
Matties: So, you have a benchmark board, and then you're either adding or subtracting based off that benchmark.
Holden: In terms of percentages, not in terms of dollars. It’s only good for that fabricator because some other fabricator, depending on their eight-layer through-holes and what they charge, will have different RCIs. But at least RCIs give you some help in design when you're comparing alternatives.
Matties: Are the designers driven to reduce cost or conserve material, or are they just driven by schedule?
Holden: They're singularly driven by schedule.
Matties: Now with supply chain issues hitting, though, I would think that they have to now start thinking about reducing the number of materials they use in each PCB.
Holden: Ah, yes, and that's the big bugaboo. This came out of nothing, that now people who can't get to components, you've got to change this component, which changes its footprint, etc. The whole supply chain and virus lockdown has changed many rules, but nothing is available. Nobody was prepared for this. I've had that RCI chart out for 30 years now. Manufacturers actually like how bad designers are because that gives them a much greater profit. If designers were designing optimally, much of their extra profits would go away, so what's their incentive to educate the designer to do it better?
Matties: That's the question that's percolating in my mind. What's the incentive for the designer to conserve material?
Holden: Right now, his biggest incentive is getting his boards out, and figuring out what he’s going to do when fabricators come back with a huge increase in pricing on materials because of the scarcity.
Matties: Inflation is the driver, of course. We have to lower the cost by whatever means we have, because of supply chain issues. So, you have double incentive to create a shift in the paradigm.
Holden: Yes, but nobody teaches this. So, how does a designer learn this?
Dan Feinberg: Happy, I don't think that the design team's management rewards them for this sort of behavior.
Holden: Yes. It certainly will punish them if they don't meet the schedule, but it won’t necessarily reward them. You're right.
Matties: So, you fall back on tried-and-true methods. You just need to make sure that this is functional, rather than spending a lot of time saving the company money when there's little in it for you individually.
Holden: If you sandbag and over-design a board, it still works, and only its cost goes up. But if you're trying to minimize the cost, then you've taken on risk, in terms of meeting the schedule and everything else. You know how much everybody likes to avoid risk. The solution to risk aversion is just to make things more complicated and expensive. At least it won't come back to you.
To read this entire conversation, which appeared in the August issue of Design007 Magazine, click here.