Last Sunday, I woke up at 4 AM with a song in my head that I had never heard before—at least not that I could remember! The lyrics had me so perplexed that I had to jump out of bed and check it out. Two things came up on my word search when I looked up “the want of a nail:” the first was the song I had just heard in my head, and the second was something about “the butterfly effect” from a number of chaos theory texts.
First, I re-played the song titled “The Want of a Nail” by Todd Rundgren and listened to the lyrics I had heard in my head just 20 minutes before in my sleep.
“For the want of a nail, the shoe was lost,
For the want of a shoe, the horse was lost,
For the want of a horse, the rider was lost,
For the want of a rider, the message was lost,
For the want of a message, the battle was lost,
For the want of a battle, the war was lost,
For the want of a war, the kingdom was lost,
For the want of a nail, the world was lost.”
Then I read the blogs on the butterfly effect. In the example I found, a butterfly flapping its wings can lead to a tornado weeks later, meaning that small events can lead to larger consequences. I believe this wholly. I see that small changes to the initial design or information gleaned at the start of a project lead to much larger issues all the time.
After I digested as much as I could about the butterfly effect, I chanced upon a TV show about bridge failures that focused on a device used to check for voids in the concrete-to-steel wire construction. It was very much like a time domain reflectometer (TDR). Whereas a TDR is mainly used to determine the characteristics of a given electrical line by observing reflected waveforms, they can also be used to locate discontinuities in a connector. In the case being shown regarding a large braid of steel cable encased in concrete, some of the back-filling of the concrete did not fully encapsulate the wire bundle, leading to areas of moisture entrapment and, therefore, oxidation of the wire strand, causing a failure of the bridge.
So, why the Sunday morning revelation? I began to think about how small changes in design characteristics at the PCB fabrication level can have larger consequences for the final product. Some of these include changes in trace geometry, dielectric, material type, copper weights, etc. Let’s go through a basic list of them and discuss each one.
To read this entire column, which appeared in the December 2019 issue of Design007 Magazine, click here.