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The Democratization of DFM
Continued from page 63 Simplify…Simplify
“Our life is frittered away by detail,” wrote Henry David Thoreau. “Simplify…simplify.” Engineers like to tinker with complex things. We even make them our hobbies. However, there are many more peo- ple who just want the solution. Some people don’t really care how the watch works. The watch is simply a tool to tell time. And, with virtually every company trying to do more
more and more features and options and flexibility in the product, the cost piles up. The old adage “less is more” rings true here.
Sometimes we need to step back and ask ourselves, “How can we make it so that more people can ben- efit from this tool?” Seldom is the answer to add more features or com- plexity. Almost always, the answer is to simplify.
The challenge is to provide the same kind of solution with less
the DFM solution needs to serve products regardless of where they fall on the complexity scale. How do we improve DFM for PCBs? How do we make DFM more accessible to more people? How do we streamline the DFM process so that optimized designs get released to manufacturing during the initial design process?
Two Steps to Improve DFM
First, make it easy to set up and maintain DFM rules. If the setup is simplified, they are easier to main- tain as the board technology and sup- plier’s process capabilities evolve. This way, DFM results will yield only true DFM issues that need attention, without the time-consuming filtering of false calls.
The DFM rule set needs to be intuitive to anyone familiar with PCBs. The GUI must facilitate simple set up of the factors, classifications, and constraints required. An intelli- gent DFM system will also know the hierarchical relationship between dif- ferent DFM categories and allow set- ting up the minimum, while receiving the maximum benefit.
Expertise embedded in the application enables a truly concurrent DFM flow.
with fewer resources today, no one can afford the luxury of tools that come with a heavy support burden. The managers of these companies want good designs that are optimized for manufacturing — and they want them to be right the first time. Many software engineers are not unlike hardware engineers in that they associate “better” with more powerful or more capable, each problem solved by adding more fea- tures to the product. Over time, with
expertise required of the person using the tool. In the past, when we wanted to simplify a solution, we merely removed functionality. The less a product can do, the simpler it is, right? But, that does not work when the problem itself is complex. Today’s PCBs are extremely complex, as a result of our requiring electronic products to do more in smaller form factors, at lower cost. Those factors drive various creative manufacturing applications. Ideally,
Second, put the logic of the DFM process into the software itself, mak- ing it an expert system. Let the DFM software application read the intelli- gence inherent in the PCB design data to automatically determine the PCB classification and which DFM rules to apply. The layer count, board thickness, via hole sizes, and con- struction method are all attributes or properties within the CAD data. Leverage that intelligence.
Multiple factors affect the DFM rules to be used. For example, a com- mon factor is the copper weight of the layer. The PCB fabricators will add
September, 2017
an etch compensation value to each layer, and the amount of compensa- tion will depend on whether it is 0.5, 1 or 2 oz (14.2, 28.4 or 56.7g) copper. When DFM analysis is performed for etch, a different spacing value and line width is used, based on the cop- per weight for that layer.
Another example is the construc- tion of the PCB. If it is conventionally laminated in a single step, the manu- facturing process tolerances will be different from PCBs constructed using sequential lamination or buildup tech- nology. Accordingly, the DFM rules will vary by construction type. As a final example, the aspect ratio of the PCB also affects the man- ufacturing process tolerances. PCB fabricators will stack multiple panels on their drill machines, if possible, to save money.
However, if the PCB aspect ratio is too high, they need to drill the panels separately, which will make the cost of the boards higher. Designers need to know the accept- able aspect ratios that their fabrica- tors can accommodate.
A smart system is one that incorporates the knowledge of a sub- ject matter expert into the applica- tion software. More people can profit from the expertise — the knowledge becomes scalable. Because we often equate expertise to efficiencies and quality, it behooves the electronics industry to employ expert systems whenever possible. DFM for PCBs needs an expert system approach so that every company, regardless of size, can benefit. Contact: Mentor, A Siemens Business, 8005 SW Boeckman Road, Wilsonville, OR 97070 503-685- 7000 E-mail:
tessent@mentor.com Web:
www.mentor.com
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