Bill, Thanks for the detailed message. I answered your questions inline. I wish I had tried cool spray before I fixed it. The problem appears gone now that I scraped away some of the soldermask over the trace near the hole and tinned it with solder. I suspect there was a micro-fracture in the trace itself where it comes into the pad. It's just amazing, though, b/c this is a 40 mil trace, all on an outer layer, and the hole's pad diameter is sufficient. Regards, CJ From: Brooks, Bill [mailto:[log in to unmask]] Sent: Friday, September 18, 2009 12:23 PM To: (Designers Council Forum); Charles Gervasi Subject: RE: [DC] Open trace Hi Charles, If you are measuring continuity between the pads... from the outer surface of the board... and you have an open when there is no readily visible break in the trace... and the trace is on the outer surface of the board .... Then I would look for a micro fracture at the point where the pad intersects the trace or a crack along it that is very tiny... pad to pad on the same surface should connect... but if however you are measuring the open through the plated through hole, let's say to a trace on an internal layer... I would then ask if the board had been exposed to a thermal excursion in excess of the Tg of the material... (which of course would be a common failure point in PTH boards...) you may have a cracked or broken PTH barrel... or a fracture at the point where the PTH meets the trace on the internal layer... So this prompts a few questions, How thick is the copper? I believe it's 1.5oz after plating. Is the trace on the outer layers or inner layers? It's a single outer-layer trace with no vias. What happens if you heat or cool the trace? If it disconnects with cool... the copper shrinks and might be the cause of the open... I should have hit it with component cooler before I did my fix. What sort of environment has the board been exposed to? It's just been operated in the lab. I don't think we've done any thermal testing with this board. Is there a lead soldered into the hole? How does the solder joint look? Another common failure point is cracking in the solder joint around the lead due to work hardening of the solder from temp cycling... or vibration.... There are through-hole leads mounted in both holes at the ends of the trace in question. Cold solder joint was my first thought. The joint looked good, and the first thing I did was reflow both sides and add a bit of solder to be sure. It had no effect. Maybe those thoughts will prompt another avenue of investigation... You may have to section the board's plated through holes to determine the internal condition of the barrels... etc. Hope you figure it out. :) Bill ________________________________ From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Charles Gervasi Sent: Friday, September 18, 2009 9:41 AM To: [log in to unmask] Subject: [DC] Open trace I have a board with a power trace that's 2.75 in [70mm] long and 40 mils [1mm] wide. The trace goes between two plated through-holes. It carries 0.5A at room temperature. I've never seen any problems with the board design. On a particular board, however, this trace is intermittently open. I looks fine under the microscope, yet it is clearly open. I scraped away some of the soldermask and worked out which half of the trace had the problem. I know the problem must be where the trace comes into the PTH's pad, but I can see nothing. So I scraped away the soldermask over the trace where it comes into the PTH's pad and tinned it with solder. The open went away. I've worked with boards with PTHs for 11 years, and I've never seen such a thing. Has anyone seen a large trace fail open with no outward sign? ------------------------------------------------------------------------------- DesignerCouncil Mail List provided as a service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF DesignerCouncil To temporarily stop/(start) delivery of DesignerCouncil for vacation breaks send: SET DesignerCouncil NOMAIL/(MAIL) Search previous postings at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext. 2815 ------------------------------------------------------------------------------- --------------------------------------------------------------------------------- DesignerCouncil Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF DesignerCouncil. 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