Printed Circuit Design & Fab - June 2008 - (Page 16)

The Art of Questioning Life is a learning excursion, and the more questions you ask, the richer your journey. ONe OF THe THINGs I have learned after twenty years of design work is that questioning is an art. Whatever situation you find yourself in, you will eventually be given instructions that seem contrary to what you have learned. Should you follow the instructions without question? Knowing when you don’t know enough and then knowing the jAcK right questions to ask that will allow you to olSon perform the task at hand is germane to the art of questioning. I remember starting a new job designing cell phone amplifiers, and the pre-amp was a 1.67 GHz circuit on a Teflon board. The circuit was entirely on Layer 1, and Layer 2 was a back side ground plane. When I showed the engineer my preliminary layout, he instructed me to move the components so close to the main signal line that the component pads were sitting directly on top of the wide trace. Well, this just didn’t seem right to me. So, I proceeded to tell him how we frown on this practice, because the pads would have no thermal relief, and without solder mask on this design we wouldn’t even have the advantage of having solder mask defined pads. I was quite proud of myself for pointing this out, having just recently learned about these things from a seminar. With great patience he explained how he was very aware of good soldering practices, but had technical concerns that far outweighed the well-meaning guidelines I was quoting. I was slightly embarrassed, but learned an important lesson. In certain cases engineers will consciously break rules and bend guidelines to get the results they need. We’ve all heard the term, “Rules of Thumb.” A rule of thumb isn’t really a rule, it’s more like a guideline that is easy to remember. But what happens if people learn the rule and repeat it to others who in turn pass it on to others? Eventually, no one has an idea of where it came from or the real purpose that was intended. If we are making decisions without understanding the foundation the rule was built upon then we don’t know what the decision means, or under what circumstances it should be changed. The value of a rule of thumb is that it makes it easier to remember something, but to be a good designer you have to know what is behind the rule so that you know when it needs modification. The best designers will know when the rule of thumb should be abandoned or modified to get better results. When you hear something that conflicts with your own understanding of good design practices, first try to determine if the difference is important enough to question. If so, try to determine if the person providing the conflicting rule is merely repeating something without understanding the basis for it, or if it is someone who truly has a deeper understanding and is making a conscious decision to veer away from the guideline. Not that it matters who is "right," but if it helps you to initiate a discussion it 16 may result in a better product and in gaining valuable knowledge for future designs. It’s important to make a distinction between guidelines and rules. Guidelines provide a place to start in the absence of any other factors – a foundation to build on. Rules are often legal requirements and should not be ignored. For example, UL may require a certain distance between high-voltage conductors. This rule is probably not negotiable. If someone is asking you to bend a rule that will affect safety or could cause legal trouble, you are obligated to question it. Sometimes it is helpful to be able to ask questions outside of your organization. I have three suggestions for appropriate public venues for questions. First, find out if the software you are using supports a User Group. If so, you can present your situation to a focused group of people who will be more familiar to your situation because they are using a similar tool. Secondly, the IPC supports a number of free email-based forums (sometimes called “listservers”) for many different areas of our industry. To find out more about them you can go to www.ipc.org and look under the “Knowledge” tab. Finally, attend conferences like PCB East, PCB West and others sponsored by IEEE, IPC and other industry organizations. In any of these you will find knowledgeable people willing to help. When you are using a public forum like a web-based user group or an IPC listserver, here’s some advice. Try to find out what has already been written about it before you ask your question, and be specific in how you ask the question. If you ask a general question, people may wonder if you’re just writing a term paper or trying to get others to do your work for you. On the other hand, something like, “I searched the archives for this subject, and found a post I don’t understand," or “I’m being told this from one source, and another source seems to contradict it," you will probably get a better response. Ask questions! We all have a natural desire to appear competent, and admitting that you don’t understand something may seem contrary to building other’s confidence in you, but people respect someone who has the courage to say “I’m not sure about that subject, but I’m willing to research it and get back to you as soon as possible.” None of us was born knowing everything. In the world of design, the technology is advancing so quickly that even if you knew everything it would still be hard to keep up. Remember, we are all somewhere along a lifelong learning curve and none of us should be afraid to ask questions along the way. The more questions you ask, the more opportunities you will have to learn new things and get a better understanding of another person’s point of view. Ask on! pcd&f Jack olSon is a guest columnist this month on Tip Jar. Olson is a circuit board designer for Caterpillar, Inc. and can be reached at olson_jack@cat.com. JUNE 2008 printEd circuit dESign & fAB http://www.ipc.org

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Printed Circuit Design & Fab - June 2008 Contents Our Line Market Watch Around the World Happenings ROI Tip Jar Interconnect Strategies Final Finish Forum DFA/DFT Signal Integrity From the Field DFA Fab Basics Drill Off the Shelf Marketplace Ad Index BGA Bulletin

Printed Circuit Design & Fab - June 2008

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