Interesting question. I think this is a question for the PCB manufacturer.
I just sent a board with the above no-inner-annulars to a bunch of bargain-basement chinese PCB houses; I'll see if they come back okay.
They will all probably come back and say everything is fine and they can build the boards, I'm sure they will want their money before they ship the boards...only after you receive them, and they don't work, will you find out their process doesn't work.
But usual design rules require a larger drill to copper than copper to copper spacing. 0.25 mm drill to copper may be too small.
I think you need to find yourself a more reputable board manufacturer.
They will all probably come back and say everything is fine and they can build the boards, I'm sure they will want their money before they ship the boards...only after you receive them, and they don't work, will you find out their process doesn't work.
I think you need to find yourself a more reputable board manufacturer.
Generally, it's preferred to remove unconnected via pads on inner layers. But usual design rules require a larger drill to copper than copper to copper spacing.
0.25 mm drill to copper may be too small.
I remember someone telling me they always send a new job to a new board house with some known problem that should be flagged as a manufacturing DRC problem, if the board house doesn't say anything they look for another board house.
First of all, I read your thread just fine.Barry, please re-read the thread. I can't afford to be locked in to a specific board manufacturer, so asking any specific board manufacturer -- no matter how "reputable" -- if their specific fab can do this will not answer my question.
The question is if this structure is acceptable on the "least common denominator" PCB process, and if it is not, then what is the reason why it is not acceptable?
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First of all, I read your thread just fine.
If you want to be able to be "not locked in", then design for worst-case
You should take your own advice to barry and reread my post.quantized said:If your engineers rely on the board house to catch their mistakes they ought to be fired.
Specifically to check how honest and observant the board house is.
I've seen this stuff happen with crap board houses promising supper cheap prices to sucker clueless manaagers into switching.
Really? Every board house I've seen calls for at most 0.10mm annular rings around vias and 0.15mm trace spacing. So if the drill registration can be off by 0.25mm or more it will cause outrageous problems for all sorts of other things too. Copper-to-drill of 0.25mm has to be mechanically adequate or else the rest of their design rules are wrong (which is always a possibility, but if that's the case there are much bigger problems).
I was mostly wondering if there is some chemical reason related to the plating process (which I don't understand as well as things like layer registration) that would require annular rings on the inner vias. If they aren't required for chemical plating reasons then I'm safe.
You should take your own advice to barry and reread my post.
They ADD a mistake they know should be a problem for the board house to manufacture. Specifically to check how honest and observant the board house is.
I've seen bad board houses promising supper cheap prices to sucker clueless manaagers into switching. Then the competent and very good engineers get stuck trying to fix RF boards that have horrid impedance control problems.
Wow, where did all this hostility come from? I'm quite upset with the attacks you are making on what I was just suggesting you watch out for by using the cheapest board house you can find.Yes, I know what you're talking about. And it's stupid.
If the PCB house is paying some highly-trained human to manually look at my boards, they're Doing It Wrong. There is no way they will be cost-competitive for my weekly 10-board prototype runs (which I do MONTHS of before placing the big production run). Any board house with this kind of cost structure is not going to be able to afford my business.
I tell you people, the PCB industry is stuck in the dark ages. The VLSI world long ago gave up on human design inspection. There's a machine-readable DRC deck that specifies, unambiguously, exactly what the fab can manufacture. If your GDS passes DRC, they're claiming they can make it. It's not up to a human.
And they deserve what they get if they don't do a test run first.
Take your manufacturing snobbery somewhere else, it's getting increasingly dated.
The other problem is that voids in the substrate and prepreg layers can be filled with process chemicals or being metallized and create a short to nearby traces during throughplating. That's the reason why drill to copper and drill to drill spacing is usually larger than copper to copper.
I was just suggesting you watch out for by using the cheapest board house you can find.
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