The current code in the repo would silently convert all vias to standard through-hole vias, my code makes it behave properly for blind/buried vias. With some additional modifications it could support microvias too but I haven't implemented that.
Are you saying you don't think this patch should be accepted until it also supports microvias? On Tue, 2014-07-22 at 20:06 +0200, jp charras wrote: > Le 22/07/2014 18:47, Andrew Zonenberg a écrit : > > With the attached patch, the router fully supports both routing > > over/under blind/buried vias and shoving them, but cannot yet add > > new blind vias. > > > > The current code cannot distinguish between blind vias and > > microvias. It uses a simple heuristic: if a via goes from the top > > to the bottom it must be a through-board via, otherwise > > blind/buried. This means that when a microvia is shoved, it's > > silently converted to a regular blind via. > > "it's silently converted to a regular blind via." > This is not a good idea. Why to convert them? > I do not understand the reason. > > > > > This may be the time for a discussion of why microvias are > > considered "special" compared to normal blind vias. I'm working on > > a board now that uses layer 1-2 and 1-3 microvias. These are > > implemented at the fab by drilling from layer 2-3 anywhere that a > > layer 1-3 via is needed, then laminating layer 1 and drilling from > > 1-2 anywhere that either 1-2 or 1-3 vias are used. > > > > In other words, real microvias (when using a stacked process) can > > go to layers other than 2 and N-1. If this is the only distinction > > between microvias and blind vias in KiCAD, I propose eliminating > > the microvia entity entirely. There could perhaps be a DRC mode to > > only allow blind vias between specific layer pairs if you're > > targeting a process with a limited number of microvia layers. > > Eliminating the micro vias is perhaps not a good idea. > > I agree the fact a micro via is a blind/buried via, just with > constraints on layers count. > > Micro vias are laser drilled and the hole has a limited depth. > (this is not the case for blind/buried vias which are not laser drilled) > > Most of time they are used to connect a footprint like a bga therefore > an external copper layer to the next internal layer. > > Having a special type for this kind of via is an easy way to handle > layers count constraints and make placing very small vias more easy. > > It also allows to easy place 3 different vias: through, blind and very > small (said microvias, with constraints) vias. > > If you are thinking eliminating the micro vias is a good idea, I > suggest you first to write an user documentation about usage of vias, > blind vias with no constraints and vias with constraints. > > In Kicad, micro vias (only allowed from an external layer to the first > internal layer) is just a convenient way to place very small vias, > which are expected laser drilled, i.e. which have a limited depth. > > However you easily can add a DRC test on vias which have a limited > depth, depending on the drill hole, and use only blind/buried vias. > -- Andrew Zonenberg PhD student, security group Computer Science Department Rensselaer Polytechnic Institute http://colossus.cs.rpi.edu/~azonenberg/
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