March 14, 2017
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?
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
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.
IPC 7721, 4.2.4 Conductor Repair Surface Wire Method for a
methodology. But, this method may not be acceptable for some types of
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.
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
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.
procedure, 4.2.2 is replacing the damaged section with a film adhesive backed
should work for your application and I think you'll find you'll have better
longevity and reliability in the repair.
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
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.
if you are needing to salvage the PCB, is conductive ink/adhesives.
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
In the end, this PCB
should be scrapped.
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.