Track Repairs

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Hi Folks, trying to track down if there is a std for the ... - Nov 27, 2003 by johnwnz

John, I typically specify no more than three repairs per ... - Nov 28, 2003 by

IPC-6012A finds "circuit repairs" as acceptable in Class 1, ... - Nov 30, 2003 by davef

johnwnz

#26457

Track Repairs | 27 November, 2003

Hi Folks,

trying to track down if there is a std for the max number of track repairs that you can don on a PCB. IPC 610 gives me an indication of what is acceptable in term's of the amount of damage I can have on a track before it's a fail however nothing on the max number I can rework. I got some boards from my vendor that have a number of damaged track's n the surface from what I can only guess is a cleanliness issue with thier pressing or lay up process.

cheers

John

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Tom B

#26461

Track Repairs | 28 November, 2003

John,

I typically specify no more than three repairs per PWB or assembly. Using the IPC 700/7711/7721 and Circuit Tech's Guidlines for reference. If PWB cost is only couple of $$ then repair may not be worth it (you do not want to make repair, then maybe have quality reject from customer cause it didn't hold up). Base the rework on how much of your labor is vs pwb cost. If Bare PWB, I would discard it, if you already have open problems, then there maybe other issues with that pwb (trace width reduction, annualr ring breakout, etc)

I would ask if the customer allows repair/rework pwb's. This can open a can of worms as far as quality is concerned. Your customer most likely would insist on some answers to why you have recieved these (are these pwb's tested), and if there is potential of others in the recieved lot that may be latent.

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davef

#26462

Track Repairs | 30 November, 2003

IPC-6012A finds "circuit repairs" as acceptable in Class 1, 2, and 3 only "As agreed by user and supplier." So, it is your call, basically.

Generally these repairs, if done properly, are reliable. See IPC-7721, 5.2.3, for conductor repair by welding. Most use a Hughes welder to bond a gold ribbon "Kovar" over the open. The ribbon is welded to the remaining trace at each end of the break.

Above, the operative word is "if done properly". However, we have advised against doing such repairs by welding. The skill and science required are, in our opinion, too high for comfort. In the past, we have waived this on inner layers, but never on outer layers. We believe that the lamination process is too brutal.

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