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tech.com
July, 2011 Prototyping with Multi-Layer Boards Continued from previous page
ahead of schedule and under budget, leaving them valuable breathing room with which to optimize down to a production-ready two-layer board. The benefits to the design team:
l l l
Better DFM tolerances, reduced risk of shorts or design mistakes.
Shorter design time, less labor cost.
Fewer prototype spins, saved budget dollars on boards and, more importantly, components and assembly labor.
Well Established Technique Large PCB design firms have
been using this prototyping tech- nique for a number of years. It works well for designs in which there isn’t a lot of high-speed design, and where strict compliance is not a require- ment. Obviously not all designs fit into this sweet spot, but when they do, you can use the technique to great advantage. So how does this all pencil out? Let’s look at an example using some hypothetical numbers. As always, your specifics will be differ- ent than the ones in this example. Work the numbers with your specific data to estimate the savings you’ll see in your environment. For the meantime, though, let’s assume: l
l l
The design in this example takes 10 days of schematic work.
One layout designer costs you $100/day. Whether employee or contractor, this number is proba- bly conservatively low, once you factor in the costs of health care, and facilities costs.
The design in this example takes 12 work days to lay out as a two- layer, or four days to lay out as a
Engineers are shortening key phases of the PCB prototyping
process by making use of multi- layer boards.
tion, reduces layout design time from twelve days to four, and saves the design team one spin overall. The overall effect to the design
team is that the layout portion of the process takes much less time. The saved design team labor cost is the big savings here. The multi-layer board may cost a few extra dollars ($150) in this case, but the reduction in layout design time saves $800 per engineer in days saved alone, netting $650 per spin just in payroll. When we factor in the removal of one complete design spin — rework, revalidation, reorder, remanufacture, retest — the savings from the reduced spin just compounds on top of the per-spin savings. In this example the project cost
numbers roll up like this, resulting in a multi-layer prototype that’s actual-
l l l
A typical prototype process requires three spins. Let’s also assume that the
$1,500 in parts and assembly costs to populate your board.
multi-layer technique results in a $600 per order cost for PCB fabrica-
Two-layer PCB bare boards cost $450 to fabricate.
multi-layer.
ly 61 percent of the cost of the 2-layer approach, and requires 54 percent of the overall design cycle. Now, for this technique to work
well there are a few prerequisites. If only some of these conditions apply, your payoff may not be as noticeable. If none apply, you’re proba- bly not a good candidate for this approach.
l Your board will fit with-
even begin. l
in the restrictions of a two- layer format once opti- mized. The first step is to assure yourself that you’ll be able to get your circuit to fit on your target pro- duction format before you
more limited value. l
for staff labor as a part of the project cost. If you’re a hobbyist or an individual working on your own (no- cost) time, then this tech- nique still works but is of
Your company accounts
mized before production. If your pro- totype is likely to be used unchanged for production, your product will carry an ongoing incre- mental cost increase as a result of the multi-layer board. If your plan all along is to optimize down to a two-layer configuration, then the 33 days you saved ought to give you plenty of time to get the optimiza- tion “just right.” Given the economic environ-
Your prototype board will be opti-
ment we’ve all be working under in recent months, and the inexorable march toward smaller, faster, cheaper, the trend is no longer just to be found in the features and
dimensions of our product designs. It also can be found in the business practices of our design teams. By making full use of multi-layer, along with strategic use of assembly serv- ices, design teams can dramatically shorten key parts of the PCB proto-
The increased use of SMT
components is shifting the PCB prototyping process.
typing design process, thereby vali- dating their designs faster and easi- er. And, without a negative impact on the process of optimizing for pro- duction. In fact, the extra man weeks saved in prototyping are like- ly to deliver the extra time design- ers wish they’d had to get their pro- duction designs beyond merely good and into the realm of great. Contact: Sunstone Circuits,
13626 S. Freeman Road, Mulino, OR 97042 % 800-228-8198 fax: 503-829-6657 E-mail:
mohara@sunstone.com Web:
www.sunstone.com r
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