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Microvia laser hole size vs trace width

avion , 11-09-2017, 08:00 AM
My pcb manufacturer offers size 20um for microvias but my single ended traces are minimum 100um. The guy from manufacturer says the trace width is not related to laser hole diameter. Is there a relationship and what is the calculation for this?
robertferanec , 11-10-2017, 05:06 PM
Diameter of uVIA depends on depth of drilling. Usually it is 1:1, so if you need to drill 100um deep, you need 100um hole - so the hole which you need depends on your stackup (how far the layers are from eachother).
avion , 11-15-2017, 05:25 AM
What about trace width to uVia hole? if I have a 100um trace width can I use 20um uVia hole size as long as it penetrates from L1 to L2. The stackup suggested to me here seems like it requires at least 79um uVia hole.

robertferanec , 11-15-2017, 09:02 AM
@avion, if they use 1:1 via aspect ratio for uVIA hole, they need to drill 9um (copper plate thickness) + 70um (prepreg thickness) deep = 79um uVIA hole. The minimum uVIA hole size depends on how deep they need to drill.

Or by other words, if you use 20um hole in your uVIA, you only can drill up to 20um deep. That would not be enough for your stackup.
avion , 11-16-2017, 03:01 PM
I asked the manufacturer about this and they said:
aspect ratio of 1:1 for blind vias is related to the production diameter means we are adding as usual for each plated hole 100µm extra in order to meet your final diameter (CAD-hole diameter) after galvanic copper process. The adding of 100µm is usual in the PCB business.

CAD-hole diameter= 20µm
Production diameter= 120µm

Does this mean they add 100um to all the vias I specified? what is the difference between cad-hole and production diameter???
robertferanec , 11-17-2017, 05:26 PM
PCB manufacturer always makes the through holes bigger (tool size is bigger), but I am not sure how much bigger. When they do the plating (growing copper inside the hole), the hole will become smaller (finished hole - that is what you usually specify in design files).

However, I am not 100% sure how it is with uVIAs (blind VIAs). These are drilled by laser, and their edges are under an angle (so they can plate it). Have a look at this video - we speak there a little bit about laser drilled holes and plating, it may help you: https://www.fedevel.com/welldoneblog...u-should-know/
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