Deengineering PCB
Deengineering PCB
(OP)
Good day all,
I am presently trying to find a design flaw inside a PCB. It looks to be a trace problem but I need to get inside to see. Does anyone know what chemical will allow me to delaminate the board a layer at a time in order to find this problem without destroying the traces? Any suggestions will be very helpful. Thanks all Dino40
I am presently trying to find a design flaw inside a PCB. It looks to be a trace problem but I need to get inside to see. Does anyone know what chemical will allow me to delaminate the board a layer at a time in order to find this problem without destroying the traces? Any suggestions will be very helpful. Thanks all Dino40





RE: Deengineering PCB
The typical method of repairing internal traces to a board other than trace cutting-jumpering around the problem is to carefully grind away over the known fault to correct the problem but this is done only on very expensive boards where trained personnel and copies of the artwork are available.
RE: Deengineering PCB
RE: Deengineering PCB
Thanks again
RE: Deengineering PCB
RE: Deengineering PCB
RE: Deengineering PCB
As for your quest, a good machinist with a surface grinder can expose the inner layers. Ask him to stop a few thou short of where the copper is supposed to be. At that point, you may be able to image the copper through the remaining resin.
Mike Halloran
Pembroke Pines, FL, USA
RE: Deengineering PCB
Trivial things like bus tracks shorted with a whisker... and the real classic was an offcenter drilled via that shorted all 4 planes together.
Class.
So what's the theory behind bare board testing?
Make little impressions on the pads so the customer thinks that you've done something?
Or is that too cynical?
RE: Deengineering PCB
In general, my decision as to paying for bare baord test is based on the complexity of the board and what the value is fully loaded with parts. If both are low, then the first test any component sees, both board and electronics, is in-circuit or functional test.
-Bill
CE Designer Forum
www.cedesigner.com
RE: Deengineering PCB
TTFN
RE: Deengineering PCB
If it is just one, this is a manufacturing problem. If all the boards show the problem, if still can be a manufacturing problem. Has this design worked in the past? If not it can be a pcb design issue. Is it a short, an open, can you identify which electrical connections are faulty?
You could tell with the CAD tools, from the PCB designer side, or with the CAM tools (those used by the PC fab to generate the manufacturing masks) if there is any potential problem with a given trace or electrical node. You can evaluate all the clearances and impedances. No reason to stripe off the layers to find a bug. IF teh PC fab does not cooperate, go to another place next time.
RE: Deengineering PCB
But then this is just my experience, hopefully most board houses really do tests.
Ah who are we kidding
Keith Cress
Flamin Systems, Inc.- <http://www.flaminsystems.com>
RE: Deengineering PCB
And missing 4 planes shorted together is beyond belief in my opinion.
Unless there's something about bare board testing that I'm unaware of.
RE: Deengineering PCB
To tell the truth I did find two boards with a shorted trace. They happened to be shorts that have been detected by the test machine, but that have not been properly reworked... I saw the rework and under the varnish there were the shorts.
RE: Deengineering PCB
It was a short hair, of course.
Mike Halloran
Pembroke Pines, FL, USA
RE: Deengineering PCB
TTFN
RE: Deengineering PCB
Dan
Owner
http://www.Hi-TecDesigns.com
RE: Deengineering PCB
To answer your question, the hair was straight, probably from the fur of rattus rattus, a stable population of which lived in our pcb production facility.
The hair's image was actually present in the photomask, so it appeared in several hundred circuit boards. Because they were only two-sided boards, it was possible to rework them while replacements were being made. They were memory boards fully covered with big SRAMs, and of course the flaw was under a socket.
It was embarrassing that the boards had passed a board- level test, and a functional test after assembly, and were being used in production. We just couldn't get them to save and restore data in a prototype in the R&D lab, and we had a stubborn ex-Navy tech who knew how to use an ohmmeter.
Mike Halloran
Pembroke Pines, FL, USA
RE: Deengineering PCB
At one time I worked for a company that had one of the early low cost personal computers. The computers were produced at several locations in Europe. I setup test equipment for the North America customer service repair. One computer that came back never had the board etched at all. Just drilled, plated, masked, and silkscreened - and yet it got completely through assembly and test at a production facility, shipped to a customer, and returned!
RE: Deengineering PCB
I once got a linear power supply. Triple output with 20A on the 5V. Installed it into our product. Didn't work! I pulled it out opened it up, the controller IC a Usomething or ruther (Unitrode) wasn't even present. I called the supplier up and said, "I have one of your supplies here. It was DOA." The guy interrupts me and sez,"that cannot happen since we test each one before shipping". He had a bad day following that.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Deengineering PCB