Tie bars are not usually the limiting factor.  Because of the short length they heat sink to the surrounding copper reducing their temperature.  In 2 oz. copper a 10 mil 150 mil long tie bar is good for 3.15 amps, so you would need 4 tie bars for 10 amps.  This about 3 times what a long trace could handle.  This is based on the tie bar rising about 10 degrees C over the adjacent area.

Robert Hill

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Jack Olson
Sent: Wednesday, March 16, 2016 11:33 AM
To: [log in to unmask]
Subject: EXTERNAL: [TN] Hole Fill and Thermal Relief

Maybe I should know better than to ask two questions in the same email, but they're related...
I got into a discussion about the hole fill requirement for some large through-hole power devices and connectors. The supplier is worried about using a "percentage" hole fill measurement, because he says that even if the hole is 75% full (or whatever percentage we want to use) the hole wall will not be WETTED 75%. He maintains that the cold solder can extend up farther than the actual portion that makes a good joint. So he is looking at the TOP PAD WETTING for verification of a good solder joint, even though we don't require it.

Q1) It seems like an inspection procedure looking for WETTING instead of HOLE FILL is not what is intended in IPC, but does he have a point? The hole fill problem is with Selective Soldering, not Reflow

Q2) Wanting to provide bare board designs using good DFM practices, I would be willing to reduce my thermal spoke widths so the solder will flow better, but I can't find a calculation that would tell me what I need for something like 10A. There is nothing about this in the IPC-2152 Current Carrying standard. Is there a rough guideline I can use for current through planes using thermal relief??

thanks
Jack


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