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October 15, 2018

Acceptable Conductor Repair

Acceptable Conductor Repair
An operator attempted to repair 3 damaged conductors using buss wire over-coated with epoxy. Do you consider this repair acceptable? If we start the repair process over, is their an IPC spec we should follow?


Experts Comments

IPC 7711/7721, Rework, Repair and Modification of Electronic Assemblies, is an incredible resource for recommended rework and repair practices.

The picture makes it difficult to give a good visual assessment (most pictures aren't), and I'm not sure what product class we're talking about, but if the wires and the traces are prepped properly and there's good wetting, fundamentally what your technician did is a sound procedure.
Garry McGuire
Sr. Engineer
NASA/Marshall Space Flight Center
Garry McGuire is a manufacturing process engineer and Chair of the IPC J-STD-001 and IPC/WHMA A-620 Space Addendum committees.
See IPC 7721, 4.2.4  Conductor Repair Surface Wire Method for a methodology.  But, this method may not be acceptable for some types of hardware.
Mike Green
Design Engineering
Lockheed Martin Space Systems
Mike Green is co-chairman of the IPC Terms and Definitions Committee. He has been working with board design and manufacturing for 33 years.
Some people repair, some don't. It all depends on what your QC dept allows and the reliability requirements of the board. Certainly you should do some long-term reliability tests either on the board in question or on others to make sure that the proposed repair will withstand the environment that it's intended for. Also potential liability should be weighed. There is no easy answer for the question of repair or scrap. Each case should be weighed on its own merits and potential liabilities.
Lee Levine
President, Consultant
Process Solutions Consulting Inc.
Lee Levine has been a Process Engineer and Metallurgist in the semiconductor industry for 30 years. He now operates his own company Process Solutions Consulting Inc where he consults on process issues and provides SEM/EDS and metallography services.
From the looks of the repair is seems as though the operator attempted to simply bridge solder across the damages areas. I wouldn't typically take this approach, but it depends on the class (1, 2, or 3) of product. If this is a class 1, the repair may hold for the intended life of the product. If this is a class 2 or 3 product, I probably wouldn't allow this repair into the field.  

As to the proper method, I'm glad you asked!  

IPC-7721B has a couple different repairs you can try. I've attached two methods to this reply.  

The first one, procedure 4.2.1 is replacing the damaged section with a "foil jumper", essentially a strip of copper, and then covering the new section with the appropriate epoxy and mask.  

The second procedure, 4.2.2 is replacing the damaged section with a film adhesive backed replacement conductor.  

Either method should work for your application and I think you'll find you'll have better longevity and reliability in the repair.  

I'd recommend looking into a training course for your operators on the IPC-7721B. You can find training courses from any one of the authorized training centers at the following link. http://www.ipc.org/ContentPage.aspx?pageid=IPC-7711-IPC-7721#atc 
Kris Roberson
Manager of Assembly Technology
Kris Roberson has experience as a machine operator, machine and engineering technician and process engineer for companies including Motorola, and US Robotics. Kris is certified as an Master Instructor in IPC-7711 / 7721, IPC A-610 and IPC J-STD 001.
I would not accept this repair on a production, sold as new component.

The IPC specification for rework is specific on repair, and to be properly repaired the conductors should have insulated buss wire, soldered from pad to pad on the affected components and then staked at the prescribed intervals, of at least one / inch.

Soldermask is not epoxy to be used for dielectric, and solder of this amount directly soldered to the copper traces and the heat has probably degraded and caused the copper to delaminate from the PCB.  This was apparently done by an unskilled operator, as the heat transferred to the FR4 appears extreme.  I've seen Engineers and Asian competitors do this... but not my production teams.

Another alternative, if you are needing to salvage the PCB, is conductive ink/adhesives. 

Repair or Not-to-Repair?  This PCB failed, due to high amperage failure and extreme heat. I would check the active pad heat sink on this PCB for separation as well. 

In the end, this PCB should be scrapped.
Rodney Miller
Capital Equipment Operations Manager
Specialty Coating Systems
Rodney is currently Operations manager at SCS coatings, Global Leader in Parylene and Liquid Coating equipment. Rodney applies his BS in Computer Integrated Manufacturing from Purdue University, along with 20+ years of Electronic manufacturing and Equipment Assembly, to direct the Equipment business at SCS Coatings. "We provide unique, value added coating equipment solutions for our customers". Including conformal, spin and Parylene coating expertise.
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