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The Shaughnessy Report: The Hole Truth

For such a simple structure, the PCB via certainly stirs up more than its share of intrigue.

The via is another one of those topics that pop up in our reader surveys when we ask about your ongoing challenges. And it’s not just the blind and buried vias that draw readers’ attention. Something as basic as a hole drilled through a circuit board can generate a whole lot of controversy.

To get a handle on this issue, we sent readers a survey dedicated solely to vias. We asked readers to describe their greatest via challenges, and the comments told the tale. Here is a small sample of the replies: 

• Understanding the PCB manufacturing process
• Impedance matching
• Routing high I/O .65 mm pitch vias
• Tolerances or limitations of the PCB house
• The cost of blind and buried
• Via-in-pad
• Finding the smallest via that can be created with a high yield
• The correct size for HDI and IPC Class 3
• The cost of filling and plating over them
• Not enough pad for annular ring in the design
• Designers do not understand aspect ratio.
• Blind via plating technology
• Vias under components
• Tenting vias
• In-house politics: cost, fear of the unfamiliar
• Reliability concerns due to thermal cycling
• Vias with large board thicknesses
• Strength when temperature cycled
• Cost of standard vias vs. state of the art

Other bits of interesting info from our via survey: 

• About 85% of respondents said they use blind and/or buried vias
• 83% use thermal vias
• Only one respondent uses landless vias; many said their fabricator couldn’t manufacture them if they asked
• Dog bone and via-in-pad were the most popular methods to breakout vias for BGAs
• Many readers have never used or even heard of landless vias or back-drilling vias 

We asked what you wanted to know, and as usual, you were not shy. In a typical cry for help, one respondent asked for an “inexpensive method to increase packing density before resorting to microvias and/or blind and buried vias.” Another asked, “What is the difference between tented and capped vias?” Still another wondered, “How do we form vias that are conducive to plating?”

To read this entire article, which appeared in the November 2016 issue of The PCB Design Magazine, click here.