How much isolation between pins for stenciling?

[alank2]

How much isolation between pins for stenciling?  I've got 8 mil and 12mil that is giving me trouble with bridges though I have done 17mil successfully before.  If you stencil, do you have a minimum isolation between pads that you use?

Part of the problem might be that I am not very good at stenciling!  When I pull up the stencil, some of the paste seems to smush down a bit and touched each other where there isn't a distinct separation...

[Simon]

If there is not too much solder paste when you hot air it or oven it the paste will be drawn to the copper pads. For example it is common to drag paste across the pads for a soic or sop part and the solder just pull into the pad.

[alank2]

So it is more of a problem of too much paste than the separation then.  I ordered a 0.15mm thick stencil from, perhaps I should have tried the 0.1mm or 0.12mm instead.

[peter.mitchell]

Spacing between stencil apertures doesn't matter so much, just make sure your stencil has the right aperture reduction so you have appropriate pad coverage (70-85%), and has the appropriate thickness for your pin density (ie, soic can be like 0.15mm thick stencil but 0.6mm bga needs 0.1mm thick stencil). If your stencil manufacturer does electropolishing, i recommend it, it makes the solder release much easier fro mthe stencil.

[alank2]

I've been doing the default with is 100% coverage...

[peter.mitchell]

I've been doing the default with is 100% coverage...

well theres your problem.

[alank2]

well theres your problem.

I hope so.  I changed my eagle settings to drc -> masks -> cream, min=0, 15%, max=10mil which reduced the cream layer pad size and ordered a new stencil from oshstencils.  We'll see how this one does.

[alank2]

Looking at the two different ipc standards, they both say:  The information provided for the openings in the stencil is usually indicated as being the same size as the lands on the board for all components.

Does this mean that 100% coverage should be used, but perhaps it is better to alter the size of the pads themselves for fine pitch parts to adjust their coverage?

[chicken]

Fresh solder paste sometimes works wonders.