Hi Jack! It depends.... (who am I supposed to pay at TechNet for using that?) Generally, I agree with the article you found. But if you are dealing with very thin or low-flow prepregs, then the non-functional pads help make sure I don't get any voids in the vicinity of the through hole, which will reduce yield loss due to internal plating shorts. Wayne Thayer -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Jack Olson Sent: Monday, July 12, 2010 11:53 AM To: [log in to unmask] Subject: [TN] non-functional pad removal I know this topic has been discussed here before, but an article I just read by Paul Reid put a different twist on it http://www.pcb007.com/pages/zone.cgi?a=69569&_pf_=1 I wanted to ask about a paragraph where he says: "We know from many years of reliability testing that a board with non-functional pads removed tends to be more robust than the same board with non-functions at every layer. Occasionally, designers will have non-functional pads at every internal layer. In most applications this produces a reduction in reliability with an increase in barrel cracks in the central zone of the PTH. It appears that this produces a number of anchor points along the PTH and failure occurs in the barrel. Customers who remove non-functional pads for increased PTH reliability reduce the "anchor" point and stress is transferred to the knee of the hole." This is a very important point for me, because I have always heard it explained a different way. My (unfounded unscientific) understanding was that fabricators wanted to remove them to save drill bit wear (especially for high-volume boards in benign environments), but designers often want to keep them in because the extra ribs provide more support (especially for harsh environments). This article suggests that keeping inner layer pads is LESS reliable. The reason it is important to me is that our boards are expected to survive 20 years in an automotive environment, we have been allowing unused pads to be removed, but some have suggested we retain them for lead-free processing temperatures. We haven't cared about inner-layer pad removal until now, but soon we will be required to design for RoHS compatibility, and we were about to start specifying that they be retained. Am I misunderstanding these results? Jack ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. 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