Author Topic: blind via repair  (Read 2526 times)

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Offline tonyh88

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blind via repair
« on: May 30, 2015, 03:23:29 pm »
Hi Guys,

Long time lurker but it is my first post here. I'm trying to repair a complex multilayer board at work. It is part of a preamplifier system for an NMR chemistry system ( 400Mhz).

In this circuit there is a 50 ohm reference that gets compared to the NMR probe to match the impedance of the resonance frequency of the nucleus under test.

The problem with this unit is that the 50 ohm reference resistor lifted off of the pad. Usually simple enough fix but it also took the pad right off. Usually I would just hardwire it to the next component inline but the problem is that the pad was connected to a very small blind via that also lifted off under the force.

I have another of these units that is working available for testing and for the life of me I'm not able to trace where this blind via goes. I spent a couple of hours searching with my multimeter in continuity test mode and couldn't find anything.

Is there a way to repair these kind of blind via by scraping down to the next layer ? I'm not entirely sure I get how a blind vias are manufactured. Or is there a way for me to find where this via may go?

Any help would be appreciated as this replacement board is in the 7000$ range for a new unit. It would be sad to pay that much only for a lifted pad....

Thanks for you help !
 

Offline KJDS

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Re: blind via repair
« Reply #1 on: May 30, 2015, 03:29:07 pm »
You can dig down to the next layer, I've done it before with a scalpel and a lot of patience. I believe that there are drills available that will stop when they get to copper but I have no details of them.


Offline miguelvp

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Re: blind via repair
« Reply #2 on: May 30, 2015, 05:02:10 pm »
This old videos might help:

https://www.youtube.com/playlist?list=PL958FF32927823D12

As well as this goofy series:

https://www.youtube.com/playlist?list=PLZ4bp4FXracL-vD26gqx3HqpK7pLcoZZ3


I couldn't find blind vias on the first playlist but the goofy one does approach multilayer repair.
« Last Edit: May 30, 2015, 05:13:15 pm by miguelvp »
 

Offline John_ITIC

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Re: blind via repair
« Reply #3 on: May 30, 2015, 06:20:17 pm »

Perhaps best to send to someone that specializes in this kind of repair?
http://www.circuitrework.com/services/services.shtml
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Offline tonyh88

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Re: blind via repair
« Reply #4 on: May 31, 2015, 03:06:35 am »
Thanks for the info. That 3 part serie video was quite good actually and I had a good laugh at the same time.

I might try the repair very slowly digging until I can get some solder to stick on the via. We might decide to send it to a specialised rework facility too but I need to check if the investment is worth it in the end.

Thanks for the help
 

Offline miguelvp

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Re: blind via repair
« Reply #5 on: May 31, 2015, 03:42:16 am »
Thanks for the info. That 3 part serie video was quite good actually and I had a good laugh at the same time.

I might try the repair very slowly digging until I can get some solder to stick on the via. We might decide to send it to a specialised rework facility too but I need to check if the investment is worth it in the end.

Thanks for the help

they still sell repair kits

http://www.paceworldwide.com/products/circuit-level-repair
 

Offline Skimask

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Re: blind via repair
« Reply #6 on: May 31, 2015, 05:45:47 am »
As well as this goofy series:

https://www.youtube.com/playlist?list=PLZ4bp4FXracL-vD26gqx3HqpK7pLcoZZ3

I couldn't find blind vias on the first playlist but the goofy one does approach multilayer repair.
WOW!  The 2M/CCR (PCB repair) class I took back in '04-ish showed those videos as part of the cirriculum.  Had no idea they were on youtube.
Goofy...Yes.  Effective...Yes.
I didn't take it apart.
I turned it on.

The only stupid question is, well, most of them...

Save a fuse...Blow an electrician.
 

Offline miguelvp

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Re: blind via repair
« Reply #7 on: May 31, 2015, 08:26:39 am »

Perhaps best to send to someone that specializes in this kind of repair?
http://www.circuitrework.com/services/services.shtml

I agree, at least contact them for a quote.
 


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