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I got my start out of college grinding and polishing PCB microsections. My thumbs are a bit arthritic today because of the experience (microsection grinders know what I mean). Back then, via structures were rather large, and getting to the center in six steps of grinding and polishing was easy compared to what my team has been doing recently at the lab.
HDI, ultra HDI, substrates, embedded components, and the plethora of (tiny) via structures (micro, stacked, buried, staggered, etc.) that connect everything in today’s “boards” make arriving at a via structure’s center using a microsection a true nightmare—and a miracle for the lab technician if attained.
Our historical faith in the microsection stems from the belief that:
- Evaluating the visible attributes of the via structure will demonstrate the quality and reliability that the PCB represents
- Looking at the two sidewalls at the center of a 360-degree via structure will demonstrate the quality and reliability of the entire structure
- Looking at a few via structures from the many thousands on a panel will demonstrate the quality and reliability of all the structures on a panel
You can likely discern that more “faith and belief” are involved in interpreting the results from the microsectioning process than in statistical significance.
In addition to looking at the visual attributes (“prettiness”) of sections from a few via structures, some are also floated on a solder pot before microsectioning. We are meant to believe those few floated via structures will demonstrate the PCB’s ability to survive the component attachment process. While a single wave solder process may have been the norm many years ago, we now primarily attach components with convection reflow. Today’s component attachment process may also include replacement of components, attachment of connectors, and hand soldering of various parts and wires, which ultimately exposes the PCB to several soldering temperature cycles before truly beginning its life in the field. This is something that is not being captured in today’s solder float and microsection process.
To continue reading this article, which originally appeared in the June 2025 issue of PCB007 Magazine, click here.
