I want to attempt to fix corroded traces with conductive glue

[erwin1978]

I acquired a broken 46" LCD television that would blink every second and there was a multi-colored band running vertically. Upon inspection I concluded the previous owner spilled soda on it as the leftover residue was sticky and pink. The residue has been sitting there for at least two months. It corroded several gold traces and a few capacitors on the strip of PCB running across the bottom of the panel. The PCB is connected to the panel via eight polyamide ribbon cables.

I've seen a video of Tape Automated Bonding. My question is how do they bond the polyamide cable to the PCB and panel? Do they use conductive adhesive? I don't believe it is soldered on. I also want to attempt to fix the corroded traces where the PCB and the polyamide cable mate. Would conductive ink or glue be sufficient or do they present too much resistance? I don't think I should attempt to solder since the traces are less than a millimeter wide and apart. I also don't want to melt the ribbon cable.

 

[alzan]

Disclaimer: not an electronics technician

It could work as long as you thoroughly clean the PCB to get the residue off. There are several guides/how-to's on the web, I Googled "cleaning dried soda from PCB" to find them.

I've never used the glue myself (I'm barely proficient with a soldering gun) but Google searches turned up several different brands.

Good luck!

 

[Micrornd]

Resistance of the glue could add to the circuit and be a problem, I don't know for sure, but it seems logical.
Is there no chance of soldering a jumper wire (24-32awg) from an available solder point to solder point on either side of the bad trace.

BTW - I'm still trying to wrap my head around how one spills soda on the circuit board of a 46" TV.
Must've been a wild party

 

[erwin1978]

Here's a couple of images comparing the good and the corroded traces. My main concern is the current traveling through them and whether a conductive ink or glue will impose too high a resistance. I only need to bridge 4mm at most so the ad hoc connection isn't too long. I may even lay down a tiny copper wire for each missing trace and then cover it with the conductive glue to minimize the resistance. I just don't think it's solderable which brings me back to my question: how was the cable affixed to the PCB?

Corroded Connection

https://drive.google.com/file/d/0B1Lh39bavLYVd1U2V19falk3d3M/edit?usp=sharing


Good Connection

https://drive.google.com/file/d/0B1Lh39bavLYVNlpjcktaZ2IycGs/edit?usp=sharing

 

[magomago]

Zero experience with conductive glue, but two main ideas come to mind...

(1) Is the trace moving power around, or is it simply propagating a signal? If the former, conductive glue might be a bad idea.

(2) What is the frequency of the signal? Conductive Glue probably is for use with DC or low frequency AC; I wouldn't be surprised if high frequency doesn't work out well.

(3) Is the conductive glue capable of dealing with the long term operating temperature of a LCD? It would be sad if they eventually short two traces to eachother.


Honestly as long as its just a signal, I'd give it a shot and see if it works

 

[Micrornd]

Based on your photos, it looks like the corrosion itself is shorting several traces together.
Perhaps simply cleaning well with distilled water (and maybe running an Xacto or other knife blade between the fingers to be sure of complete removal) might be enough.
If so then follow up with a conformal coating to prevent the return of the corrosion.

 

[gbeirn]

These are very hard to repair. What I would try to do is clean the contacts with a soft toothbrush and some electronic contact cleaner.

The damages capacitors are more likely the cause of the problems.

The ribbon is held on to the contacts via some type of adhesive. As seen here:

I would try to clean the contacts first, then test and replace any bad caps. As a last resort if that still doesn't work, you can try pulling up the ribbon and clean the contacts underneath, but it will likely be very hard to reattach. You may be able to warm up the adhesive and press the ribbon back on, but alignment is going to be very hard.

 

[erwin1978]

Do you think they used conductive glue on the traces themselves or around them? Like in your picture, you can see a faint layer of what looks like glue on all the gold traces even the ones that aren't connected.

 

[gbeirn]

It looks like it is across the whole row of contacts. That is a broken laptop screen I took apart because I was curious about what they used.

 

[erwin1978]

They call the cable attached to the board LVDS(low voltage differential signaling). So I guess not a ton of power is flowing through them.

I initially tried to apply conductive adhesive but the paste was so thick that I couldn't properly create thin lines for the traces. It also only had 30 minutes of pot life. In retrospect I should have placed a stencil and then brush on the adhesive. I ended up soldering bridge wires on the corroded traces. Long tedious process. After that the TV still malfunctioning as if I had not done a thing. I will try to find a replacement Timing Control Board next and if that doesn't work I will call it quits.

 

[PottedMeat]

i'd just try desoldering the capacitors in your first pic, then hosing it down with electronic contact cleaner.

did you try pressing on the contact strip when it was on in various pressures/locations? if that fixes it you found your problem

 

[erwin1978]

It doesn't appear to be a loose cable connection. I tapped on all the drivers around the panel with no difference. I also disconnected each half of the panel and the same result. I reflowed the solder on the caps as well.

If the replacement board doesn't make any improvement I will unglue the ribbon cable and clean it up just in case there's still residue underneath. I spent $70 on a broken TV so I'm looking to spend another $50 for parts. Gotta have profits for resell.

 

[inachu]

Resistance of the glue could add to the circuit and be a problem, I don't know for sure, but it seems logical.
Is there no chance of soldering a jumper wire (24-32awg) from an available solder point to solder point on either side of the bad trace.

BTW - I'm still trying to wrap my head around how one spills soda on the circuit board of a 46" TV.
Must've been a wild party

Correct!

If not too many leads are bad then just use wire. Cheaper in the long run.

 

[inachu]

That tape adhesive is also the type that many times is used as a arbitrary heat sink.

I hate those because then those tapes soak up more heat.