More Thoughts on Via Near Pad

The other day, I wrote about vias near pads. The post got a couple of interesting comments.

In one of the comments, Mitch said, “When I was learning PCB design in the 1980s, I was taught by a mentor that understood assembly very well.” I think that highlights a big component of the problem. I suspect that a lot of folks doing layout today were not taught by anyone but themselves.

CAD packages may have instruction manuals and tutorials, but learning how to use a software package is a lot different than learning how to do the actual process well. It’s possible to be very proficient at using a word processor, but still not know how to write well.

It’s not an uncommon scenario these days, especially after the economic suckiness of last year, to come in to work expecting to hand off a schematic to the layout engineer only to find that “tag you’re it.”

Howard, in another comment, suggested that in his experience, filling and plating over vias in pads typically only adds about 8% to the PCB cost. In smaller prototype quantities, it may be a little more then that, but what’s the cost of a failed assembly? If you have the room to move the vias off the pads, the only cost may be in layout time. If space is critical or if there are signal/noise/thermal issues that force the vias to be in the pads, then you’ll just have to spend the extra to fill and plate.

If you do find yourself suddenly tasked with layout and you’ve never done one before, find a mentor (or maybe a Minotaur), read up online, call up a manufacturing person, study the Screaming Circuits blog. What ever you do, figure out all these little traps like vias in pad, components library foot print issues, spacing issues, thermal issues, etc. Then dive into the layout and learn from each one. Drink some tea too. It can relax you. Just try to stay away from Oreos and ice cream late at night.

Duane Benson
What’s the deal with 1729?

2 thoughts on “More Thoughts on Via Near Pad

  1. I have felt .. for some time now…
    Today’s tools are good enough, the engineer responsible for a product should be able to take more responsibilities for a given design.
    The engineer should know:
    a) the electronics (including physics )
    b) the manufacturing issues (including the related economic issues)
    c) the schematic and pcb layout tools.

    in other words.. the engineer should know everything the pcb designer knows plus more… so why not have the engineer design the pcb?

    To be able to produce a reasonable product, in the most efficient manner for a given product… this is the best solution.

    In simpler terms… unless the product is very complex…
    the engineer should be vertically integrated into the product line.

    alas… most engineers are too specialized (overwhelmed?) to cover all of the issues.
    The assumption: it is cheaper to have one engineer provide enough work for multiple support staff.
    My experience indicates this is not a valid assumption.

    If that is the case,
    the pcb designer better know the issues not being covered by the engineer in question (manufacturing issues of pcb , pcb assembly, environmental shock , vibration, temperature, moisture, mold, explosive gas exposure, mechanical clearances, ESD, EMI, etc….. )
    He needs allot more experience than just routing net lists.

    and if he is really on top of things…
    He should know component availability and if there are alternate components already available in the company’s inventory.
    He should be outputting data for the SMT line directly.
    He should be outputting assembly instructions/drawings.
    He should be directly exporting BOM information into manufacturing’s data base.
    Meaning: he should know everything about the manufacturing processes.

    The tools are there.. it really shouldn’t involve more people…
    it only requires a re-think of the organization and the skill sets of it’s personnel.

    just a thought….

  2. If only I had access to something like the internet when I was learning PCB design. Today designers have the IPC materials, assorted PCB design internet sites ( being the premier one), and then just about anything else you’d like to learn about online. If you can’t get an answer to just about any design question now-a-daz, in 2-4 hours, you’ve really got a complicated design issue. When I wanted to know how to do .4mm pitch designs, I studied what I could find online; then talked to my fabricator. Solved. What I like to explain to young designers, and fellow engineers alike is – search and you will find you’re learning new things! The designers I tend to help THE LEAST, are designers that want to be spoon-fed. The only thing I ask in return is an intelligent conversation.
    Now go learn. 🙂

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