PCB007 Magazine

PCB-Apr2014

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38 The PCB Magazine • April 2014 I meticulously explained all of the electrical and physical details of the board (e.g., multiple im- pedance needs, test coupons, milling challeng- es). I asked him to please get back to me at first convenience with a) a preferred layer stackup, and b) trace widths and spacings for the impedance trace groups for all involved signal layers. He ended this brain-dump of mine with both a compliment to my thor - oughness and a question as to how I became so prepared in identifying all of these design needs. When I told him of my history in PCB fabrication, he again thanked me for being pre- pared to talk with him, and offered his time to answer any future fabri- cation technology question I had going forward. Two days later, Tom called me back with all of the fabrication information I needed for routing and documenting the design. During the next six weeks, I finished everything on the design, and after the final design review, I called Tom to tell him that we were about to send the fab - rication build package to the shop. When Tom asked me if there were any deviations to what we discussed in the first phone call, I answered no; everything was exactly as per our first discussion. When Tom's first prototypes arrived back to our team, they were tested unpopulated (conti- nuity tested for potential shorts between power potentials), and then sent on to our in-building assembly shop. Less than a week later, the first fully populated board was received, and all of the verification probes and instruments were at- tached. Now came the very moment to power up the board. "Wow! The circuit works!"I said, feeling a huge rush of relief. I called Tom imme- diately and thanked him for supplying a great product. The time finally came when our high pin- count BGAs could no longer be successfully rout- ed with just through-hole vias. My co-worker "Little Dave" attended an HDI workshop taught by Happy Holden (who I eventually partnered with on many HDI education collaborations), who brimmed with new design ideas to help us catch up to and stay ahead of the ever-changing interconnection technology challenges. When I found out I was to start working on my first HDI design the following week, I called Tom to ask him if he had ever fabricated HDI designs. When he said yes, he also said "We need to talk about this in detail." For the next 30 min - utes, Tom did a brain-dump on me of designer "dos and don'ts" and the current costs associated with the complexity of fabricating HDI boards if we were going to continue to be successful. When I called him the follow - ing week regarding the first HDI design (an IPC HDI Type I) I was sending to his shop, I found myself using the very vo- cabulary that Tom had instilled in me the week before. After my usual litany of design details, he said, "Yes, I can fab- ricate that design for you. I look forward to see- ing your design in our shop." That design, like all of the others I had sent him before, came back perfect. As the design complexity grew into IPC-II and IPC-III HDI types, as well as other fabrica- tion challenges, that first phone call to Tom about prototype designs always gave me the re- assurance that with Tom as my number one and only fabricator, I truly had a fabrication partner. One day, when I called Tom about anoth- er prototype that I was about to send him, he chuckled while asking me a question, "Should we just assume we'll use our three phone call method in this design, too?" Tom truly caught me off-guard, and I asked him to explain his whimsical humor. He said, "You and I have developed a process where it only takes three phone calls to prepare me for fabricating your prototypes. Call one: You tell me what you need. Call two: I call you back and tell you what materials and stackups are required. Call three: The design is on the way. When I get your third phone call, I get your pro - totype immediately into our production sched- ule because there are no surprises between us." We both laughed that we had created a "virtual fabrication design process," but both realized it was based on fabrication process knowledge and complete respect for each other's expertise. In my second score of my years in electronics, FROM SINGLE-SIDED TO HDI continues You and I have developed a process where it only takes three phone calls to prepare me for fabricating your prototypes. " "

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