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Meet Our New Columnist: Mark Thompson
April 29, 2009 |Estimated reading time: 3 minutes
Hello everyone. My name is Mark Thompson, and I'd like to introduce myself and tell you what I plan to cover in my new audio column, The Bare (Board) Truth, which debuts next week.
I have been in the industry for 29 years. I started out in Stockton, California in 1980 - the year I graduated high school as a driller and photo tech. I moved to Santa Clara soon thereafter, and worked for Multiplex (which became ACI West). In 1993 I moved to the Pacific Northwest, where I worked at Pacific Circuits, (which became TTM) and Praegitzer Industries. I started working with Prototron in 1996, and have been with the company ever since.
I provide engineering support, and I've witnessed plenty of changes in technology and processes in the last 13 years.
In 1996, we rarely did 8-layer boards, let alone "broadside coupled impedance structures." Circuit boards have come a long way from standard multilayers with microstrip and stripline impedance requirements. It has become standard to see boards with 20-30 layers, with several different types of materials, all with different effective Dks and loss tangents, with different press values, while utilizing blind vias, buried vias, and alternative surface finishes. Almost every board necessitates a unique impedance modeling process.
Dr. Eric Bogatin calls himself the "signal integrity evangelist" and I can relate to that. Sometimes I feel like I'm preaching. Over the years, whenever new PCB designers and layout people come along, I've had the same conversations about the effective Dk of prepregs, and the correlation between percentage of resin content and glass content.
Sure, we have better tools than ever now - I'm a huge fan of Polar Instruments software - but tools can't do it all. We still need to understand the science.
For instance, as many of you may know, some of IPC's original calculations for differential pairs were flawed. Additionally, most online calculators do not take into account things like the actual Z-axis trace geometry - they show each trace as a rectangle. These are not reflective of reality; etchant can't make perfect 90-degree walls.
Also, nearly all free impedance calculators do not take into account the effective Dk of the polymer coating (i.e., soldermask). In the olden days, soldermask was purely as described - merely a mask designed to cover all features you did not want coated with a surface finish. In today's world, the thickness and effective Dk of the soldermask also plays a part in the signal integrity of the circuit board. Uncoated deep gold is a prominent example of a surface finish that impacts skin effect.
We provide customers with impedance calculations, stackups and advice on potential EMI issues. This engineering input from the fabrication perspective is very important for the ultimate success of the customer's project. This is the area that truly interests me.
In my column, I plan to cover design, layout and engineering practices as they relate to PCB fabrication. Not only signal integrity issues, but also topics like eliminating unintentional co-planar coupling due to board real estate issues and defining the features on netlists to minimize mismatches.
As vice president of the Pacific Northwest Chapter of the IPC Designer's Council, I can poll our members to see where their engineers are pushing them. Not only will this provide me with content for my column, but it will also help keep me prepared when it comes time to fabricate these cutting-edge boards!
I am also a pilot. I have been privileged to fly many biplanes from the 1930s and 1940s, including Fleets, Stearmans and N3Ns. I am a painter and photographer, and a huge fan of Formula One racing. I have a lovely wife, Shanan, and two kids, Neil (11) and Afton (4).
Despite the economy, this is a great time to be working in high tech. But the challenges are many. I believe my column will address some of the problems that you may be facing.
Drop me a line if you have any topic suggestions.
Mark Thompson provides engineering support at Prototron Circuits. He can be reached at markt@prototron.com.