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50 DESIGN007 MAGAZINE I JUNE 2020 Dack: I like to say that a PCB layout designer needs the creativity to see six different ways to approach a design challenge. An app note usu- ally provides only one way. And without ex- perience, reliance on an app note is the only way for some designers to move forward. An app note serves as a starting point for the de- sign. As a designer, I recognize that I am not always enough of a subject-matter expert to challenge the validity of an app note for a com- plex IC as it relates to a given set of manufac- turer-controlled circumstances. In cases where I find myself in over my head, it is important for me to stay well connected with the experts. I attend trade shows where I can touch, listen, and discuss design considerations for compo- nents. If I do not understand the information in a datasheet or app note, I will first make an effort to contact the supplier to discuss the de- sign criteria with an applications engineer. For alternative and more in-depth perspectives, I read magazines like Design007 Magazine. I tell a story in my CID design certification classes regarding some design app notes for LEDs. I designed a lot of LED boards in my ca- reer as a designer for a gaming company. At the time, I worked with engineers who were constantly upgrading our light boards with the latest LEDs to provide stunning backlighting for our machines. The form factors for most of these PCBs had already been determined months or years prior. Many were narrow PCB strips only 1.5 inches wide with driver chips, discrete parts, and circuitry filling up the secondary side. The primary side was reserved for banks of bright LEDs. Over several years, LED technology ex- ploded, and I recall a time in which some of these bright LEDs began get- ting really hot. They came with special app notes describing how to lay out patterns in the copper topology to serve as a heat sink to help cool the parts. Now, I didn't doubt these app notes— especially after I'd already burned my fingers touching a few operating sam- ples of these parts. I knew they need- ed heat sinking to prevent PCB surface damage or their own soldered power contacts from reflowing. But you know what? Though I never distrusted these app notes, I never had a chance to follow them either. The app notes for these LEDs provided a single, lab-proven solution to keep these little buggers from burning up. The notes recommended that all the designer had to do was to surround the LED with three square inches of copper at- tached to the center contact of the LED, sol- der it on, and everything would be okay. They even provided a lab photo of what the etched copper should look like. With its exposed ENIG finish, it was so large I could almost see my own full-face reflection on its surface, saying, "OMG! How would I fit this much copper onto the limited surface area of my design?" I called a meeting with our industrial engi- neers who had selected these parts. I includ- ed our mechanical engineering team that had already been incorporating these parts into their mechanical layouts before our electronics engineering group had even heard they were coming. To make a long story short, I'll just say that I wouldn't have formally proposed that these engineering teams widen the 1.5- inch PCB strips to 3.5 inches to allow for heat sinking unless I fully trusted those app notes. But frankly, I was told the mechanical designs were frozen and would have to find anoth- er way. Ironically, it was mechanical design- ers who had disregarded these app notes and specified them to be incorporated onto these skinny PCBs. Now what?

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