Controlled Impedance: A Real-World Look at the PCB Side

DAN BEAULIEU: When I was a very young man, way back in the taped artwork days of the 1970s, I was a program coordinator (a fancy name for expeditor) at Rockwell’s Maine Electronics in Lisbon, Maine. One of my programs was the Burroughs Scientific Processor (BSP) created by Burroughs Corporation, based in Paoli, Pennsylvania. We were building very high-tech 14- and 16-layer boards for this program. We were told that these BSP computers were so powerful that the first one was already “running” the airport in Narita, Japan.

Now, this was 1975, mind you. The only computer I had ever seen was being installed in a glass room at the company. I was walking around tracking my PCBs with a pen and clipboard and I had no idea what “running an airport with a computer” even meant. By the way, I did get a chance to see a BSP system being built. It was quite an impressive sight, especially since they had slimmed it down to three refrigerator/freezer-sized units. I remember being amazed that something that small could run an entire airport!

And this was the first time I had ever heard of impedance. All I knew about it was that these two guys, Bob McQuiston from Burroughs and Andy Yenco from Maine Electronics, spent weeks building literally hundreds of boards, inventing ways to measure this impedance thing and then throwing out most of them. It would break my heart to carry all of these great looking boards to the scrap heap day after day.

Finally, one day I heard Andy let out a whoop and slap Bob on the back (there was no man-hugging back then). They had done it! They had finally built and measured some boards with the right controlled impedance. That was 40 years ago, so I’m thinking that maybe I saw the first controlled impedance boards being built and measured. Now, can somebody please tell me what controlled impedance is? Bob Tarzwell, can you help me out here?

BOB TARZWELL: Sure, Dan. And to make this really useful (I’m never sure if you really understand my answers to your eternal questions anyway), I’ll direct my answer to those guys who really care: the PCB designers.

As a designer, your project may require a specific impedance of, say, 52 ohms, plus or minus 7%. The big question is: Does the fabricator give you what you ask for? Well, maybe, and maybe not. Here is why.

The standardized coupon the PCB manufacturer inserts into the panel is designed to reproduce the same impedance effects your circuit should see, but because it is not inside the circuit it’s only a close approximation test. When PCB manufacturers set up the panel, of course they use as much of the panel as possible, which means the impedance coupon will be on the outside of the production 18x24” panel. The question would be, is there any difference between the center of the circuit board and the very outside where the impedance coupon is located? Unfortunately many times the answer is yes. 

To read this entire column, click here.

Back

2015

Controlled Impedance: A Real-World Look at the PCB Side

03-18-2015

Bob Tarzwell writes, "As a designer, your project may require a specific impedance of, say, 52 ohms, plus or minus 7%. The big question is: Does the fabricator give you what you ask for? Well, maybe, and maybe not. Here is why."

View Story
Back

2014

The Key to Increasing Quality - Bribe Your Employees

12-10-2014

Back in the 1990s when Bob owned a board shop in Canada, the company was going through a bad stretch, as board shops sometimes will. Yields were way down and they were losing a lot of boards for stupid reasons, many having to do with carelessness and apathy. Bob tried yelling and screaming, but, not being a naturally gifted yeller and screamer, Bob proved ineffective at this method. So he knew he had to try something new.

View Story

Bob and Me: The Key to Increasing Quality - Bribe Your Employees

12-10-2014

Back in the 1990s when Bob owned a board shop in Canada, the company was going through a bad stretch, as board shops sometimes will. Yields were way down and they were losing a lot of boards for stupid reasons, many having to do with carelessness and apathy. Bob tried yelling and screaming, but, not being a naturally gifted yeller and screamer, Bob proved ineffective at this method. So he knew he had to try something new.

View Story

Tarzwell's First--and Last--Lean Meeting

11-12-2014

In their latest column, Bob Tarzwell and Dan Beaulieu discuss the joys of Lean manufacturing, which lead Bob to murderous thoughts, and the four-year process that lead to the creation of a "super board."

View Story

Bob and Me: Tarzwell's First--and Last--Lean Meeting

11-12-2014

In their latest column, Bob Tarzwell and Dan Beaulieu discuss the joys of Lean manufacturing, which lead Bob to murderous thoughts, and the four-year process that lead to the creation of a "super board."

View Story

A PCB Potpourri

10-01-2014

In their latest column, industry veterans Bob Tarzwell and Dan Beaulieu discuss polyimide laminates, a board that could never be built, getting fired from consulting jobs because you're smarter than everyone else, and guaranteeing to save a company at least $250,000 after a short plant tour.

View Story

Bob and Me: A PCB Potpourri

10-01-2014

In their latest column, industry veterans Bob Tarzwell and Dan Beaulieu discuss polyimide laminates, a board that could never be built, getting fired from consulting jobs because you're smarter than everyone else, and guaranteeing to save a company at least $250,000 after a short plant tour.

View Story

Spacing is Irrelevant Below 270 Volts

09-03-2014

Dan Beaulieu writes, "[Bob] claimed (and this was 1997, mind you) that he was building boards with 18 ounces of copper on a routine basis. He also told me that he was producing lines down to 2 mils without any special equipment. My first reaction was that this guy was full of it; there was no way he was doing what he claimed he was doing. So I had to go see for myself."

View Story

Bob and Me: Spacing is Irrelevant Below 270 Volts

09-03-2014

Dan Beaulieu writes, "[Bob] claimed (and this was 1997, mind you) that he was building boards with 18 ounces of copper on a routine basis. He also told me that he was producing lines down to 2 mils without any special equipment. My first reaction was that this guy was full of it; there was no way he was doing what he claimed he was doing. So I had to go see for myself."

View Story
Back

2010

PCB 101: Coefficient of Thermal Expansion

09-22-2010

Coeffecient of thermal expansion (CTE) is one of the phrases we use daily in the printed circuit business. But how many of us really know what CTE is and how it affects the way a circuit board is designed and fabricated? If you're working with large BGA packages, CTE is already a big part of your life.

View Story

The Bleeding Edge: Serious as a Heart Attack

09-08-2010

This Bleeding Edge is a bit different, though the word "bleeding" is quite appropriate. My ticker is on the mend and I'm feeling better. But I have to wonder: Did my 40 years of working with medical equipment companies save my life? I certainly believe so.

View Story

PCB101: Fabricating High-Voltage Boards

08-19-2010

If a customer asks you to build a PCB that can withstand 20,000 volts, would you know how to build such a board? First things first: You cannot just say, "Well, I think FR-4 will work." It won't, and the board will fail. Boom! Here's how to avoid arc-overs, coronas and, most importantly, any booms.

View Story

New Column: PCB 101

07-28-2010

We all know the buzz words: impedance, 50 ohms, 10%, balanced lines, CTE, dielectric constant and loss and countless more. In this new series, PCB 101, I will break down some of these buzz words in layman's terms in the hopes that more people will understand what's happening inside the circuit.

View Story
Back

2009

The Bleeding Edge: Carbon Nanotubes 101

10-21-2009

We can't use nanotubes in PCB applications--yet. But the carbon tubes' natural benefits, such as creating only 1% of the heat generated by current flow in copper, are enough to keep teams of researchers working to implement them at board-level.

View Story

Printed Electronics: A Glimpse Into the Future

09-10-2009

And I mean the not-too-distant future! Printed electonics will eventually work their way into household items like toothbrushes and newspapers. But besides being useful to consumers, printed electronics are also a marketing executive's dream.

View Story

The Bleeding Edge: A Green, Profitable PCB Process

07-07-2009

As a conservationist, I'm often caught between my desire to be green and my need to pay the bills. But over the years, I've found that going green often means going profitable too.

View Story
Back

2008

The Bleeding Edge: Engineering Low CTE Boards

12-10-2008

The first requirement for engineering low coefficient of thermal expansion (CTE) printed circuit boards is to understand the physics behind the properties of CTE. One must know what creates problems and how to engineer methods to minimize the CTE effect on printed circuits.

View Story

The Bleeding Edge: The Very Latest in R&D

08-08-2008

Sierra has been producing lines as small as 380 nanometers in the lab for some time and will soon move the technology forward for limited alpha testing in the 0.5-mil (10 micron) line area.

View Story

The Bleeding Edge: Why Do So Many Board Shops Fail?

06-25-2008

We've visited so many company auctions and read about so many closures that we wonder when the trend will end, and why the industry cannot stop such losses.

View Story

The Bleeding Edge: High Resistance Circuits

05-27-2008

Selecting the correct laminate is not really that difficult, but one must remember to account for all requirements and then try and balance cost and electrical and mechanical properties--all must agree with each other.

View Story
Back

2007

The Bleeding Edge: Inventing the 'VSHDIHTLCTEHF' Microcircuit

10-11-2007

Sierra Micro Electronics has just completed six months of R&D on an exciting new technology: a Very Small, HDI, High-Thermal, Low CTE, High-Frequency microcircuit.

View Story

A New Third Dimension Now Possible for PCBs with 3-D Copper Structures

09-06-2007

Three dimensional copper structures can be made to contact or align optics, position chip dies for testing, create locating pins for sockets or align bumps for components.

View Story

Future Evolution of the PCB: Are you Ready?

08-24-2007

With nano technology just starting to make its strength felt, we will see new laminates with significant changes in their properties.

View Story

Bleeding Edge: Improved Reliability of PCBs for the Automotive Industry

03-20-2007

The mechanicals of a printed circuit board that cause via failures after a series of thermal cycles are related to the coefficient of expansion differences between the laminate and the copper in the holes.

View Story
Back

2006

Bleeding Edge: Extreme Printed Circuit Boards -- "Down the Hole"

09-25-2006

For years, the "Down the Hole" industry used polyimide laminate. However, polyimide can suffer from early delamination caused by poor wetting and prepreg flow.

View Story

Burning Issues of Burn-in Boards Resolved Through New Technology

06-26-2006

A new technology for burn-in boards is the thermal plane, where the inner layers are made with 4 to 8 ounces of copper to handle the higher current and to provide a highly conductive thermal heat-sinking plane

View Story
Copyright © 2017 I-Connect007. All rights reserved.