But I believe they discuss via-in-pad dimples causing voiding within IPC-7094 and/or 7095, but I don't think there is any actual acceptance criteria.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Monday, November 17, 2014 2:49 PM
To: [log in to unmask]
Subject: Re: [TN] Dimple depth for Laser Drilled Plated-over Blind Microviasþþ
From a lot of bad experience, I can tell you that it is not only the size of the dimple, but also what type of solder paste is being used, and whether the other root causes of voids are controlled as well.
When using Kester R562 solder paste, I occasionally had small voids on those pads with thevia included, but plated over, with a small dimple no deeper than about 5 thousands by 10 thousands diameter.
However, when using a different brand of paste which I can't mention here, the voids in the solder balls for those same size dimples actually exploded under the BGA, with hundreds of solder balls blown all over the place. I would be happy to provide you the brand offline.
But I do know that even a very small dimple of that size can create a void using the Kester R562 which otherwise does not normally have ANY voiding, or very little, assuming all other voiding factors are not there (no moisture absorption in the water soluble paste, board is clean and dry, design uses only non-soldermask-defined pads, etc,...). Soldermask-defined pads are one of the biggest void factors, if the print is not 100% directly on the pad, the venting from under the soldermask on the soldermask-defined pads with small dimples can create some humongous voids, the kind where a crack propagates all the way through.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Gerry Gagnon
Sent: Monday, November 17, 2014 2:33 PM
To: [log in to unmask]
Subject: [TN] Dimple depth for Laser Drilled Plated-over Blind Microviasþþ
Hello Technet,
Is there a recognized (i.e. IPC or industry) specification for the maximum depth of the "dimple" typically formed in the surface of laser drilled blind plated-over microvias?
If not, is there a consensus amongst the group of the maximum depth of a dimple that does not create an assembly issue or a reliability issue with the potential for additional voiding beyond that which is normal for a solder joint?
Thanks in advance,
Gerry
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