Stephen,

I found a rule somewhere relating the smallest aperture size that should be used based on a multiple of the largest solder sphere size. (I don't remember the details, maybe someone else knows this rule.)
I ran into this issue with Type 3 paste, and the limit was around 8 or 9 mils, so you might be close with Type 4 and a 6 mil aperture. 

Ben

-----Original Message-----
From: TechNet <[log in to unmask]> On Behalf Of Vargas, Stephen M (US)
Sent: Wednesday, March 6, 2019 4:56 PM
To: [log in to unmask]
Subject: EXTERNAL: [TN] Solder Paste Size

Good afternoon:

    We've got an assembly down here where I need to screen-print down to an aperture size of 6mils round (uBGA). I am using a type 4 solder paste and I'm specifying a 4 mil thick (fine grain stainless steel) stencil with a Nano coat. Boards have ENIG finish. Just wondering what success (or lack of) others are having with this type of application. Might I need to consider a move to type 5 solder paste? Anything else I should be considering? Thanks in advance.

Regards,
Steve Vargas