In search of Gate driver flex tab

[AmpWare]

Hello. Perhaps one of you fine professionals with a bit more experience can point me to a possible source for the part pictured below. It's the top left LCD gate driver from a LC470WUH (SB)(R1). New or used is fine if you are reasonably sure the part is good. The driver IC was pulling VGH down to 3.3v and running very hot. Removed the flex cable and the VGH voltage came up and the majority of the display functions now. Want to try my hand at ACF bonding so i figured was a good set to practice on. Easy fix if I get it right and no major loss if it goes horribly wrong

[ReeceyBurger123]

Re: In search of Gate driver flex tab

You can find them on smashed panels, good luck trying to replace it back onto the Lcd though :L

[AmpWare]

Re: In search of Gate driver flex tab

You can find them on smashed panels, good luck trying to replace it back onto the Lcd though :L

I enjoy a good challenge

[ReeceyBurger123]

Re: In search of Gate driver flex tab

Haha look for a smashed version of this panel, its very hard to do keep us updated though

[stj]

Re: In search of Gate driver flex tab

i wonder if you could use zebrastrip?

[AmpWare]

Re: In search of Gate driver flex tab

i wonder if you could use zebrastrip?

If the pitch for the conductive strips were fine enough I don't see why it wouldn't work technically but it would probably be quite a bit more fiddly than just heat bonding using ACF

[ReeceyBurger123]

Re: In search of Gate driver flex tab

Can you possibly do a yt video of you doing the fix ?

[AmpWare]

Re: In search of Gate driver flex tab

Can you possibly do a yt video of you doing the fix ?

Sure if I can locate a suitable replacement flex tab

[ReeceyBurger123]

Re: In search of Gate driver flex tab

Awesome thanks

[tom66]

Re: In search of Gate driver flex tab

I had a friend try this, it didn't work but they got bloody close as you could see picture data on the screen, just every other line was white instead. Although they were bonding it on the PCB side, it was still attached to the panel.

[AmpWare]

Re: In search of Gate driver flex tab

I had a friend try this, it didn't work but they got bloody close as you could see picture data on the screen, just every other line was white instead. Although they were bonding it on the PCB side, it was still attached to the panel.

I've done SMT soldering with pin pitches comparable to the fingers on the pcb side of those flex cables. pretty easy to line up even with the naked eye... he may have been shifted one to the right or left when he bonded it?

The contacts on the glass are far finer. hard to make out with the naked eye with any distance so I'll def need to make a jig with a threaded fine adjust and use a magnifying glass at the least.

[AmpWare]

Re: In search of Gate driver flex tab

As a quick update. I started thinking that although it might be pretty uncommon perhaps the ACF itself was causing a short somewhere. Not too familiar with the failure rates in regards to that but I imagine with the very fine space between the traces it was at least possible.

Since I had already used acetone to dissolve the old ACF I figured why not line up the flex tab I removed and see what happens when I press it into place.

I lined up the fiducial marks and secured it with a strip of kapton tape then used a bit of hard rubber cut to length to apply pressure along the edge and powered the tv on.

To be honest... it worked better than the display did originally. VGH still dropped but to "only" 11.6v this time vs 3.3 before I removed the tab.

All of the display worked minus a few random lines that went in and out as I adjusted pressure on the rubber piece but the drop in VGH from 26v to 11v and the fact the gate driver IC was still running extremely hot leads me to believe that it's still a faulty gate driver and the search for a replacement continues

[Moreno83]

Re: In search of Gate driver flex tab

Hmm those IC's always run hot? Every lcd that i fixed the driver ic gets "hot" after a while. Its the heat that causes the "glue" to come loose. Because one or 2 pads got loose , the lines appear.

[AmpWare]

Re: In search of Gate driver flex tab

Hmm those IC's always run hot? Every lcd that i fixed the driver ic gets "hot" after a while. Its the heat that causes the "glue" to come loose. Because one or 2 pads got loose , the lines appear.

The source drivers (the ones across the top of the LCD) run around 150F roughly. The gate drivers run much cooler. around 95F on this panel at least.

I'm not 100% sure but I believe it's because the source drivers are controlling more of an analog signal and generating some internal heat via a resistive ladder where the gate drivers are probably just fully swinging the voltage to rail full on or off for the current line and offering a very low on resistance and in turn low heat output on the die.

Of course I'm far from an expert on TFT panel design but that's what I've gathered from the small amount of LCD panel design material I've read.

[Moreno83]

Re: In search of Gate driver flex tab

I have a Vestel tv with a failing lcd panel. Im going to order uv glue which they use on samsung and apple cellphones to connect the glass to the lcd panel so no air/dust etc comes between the 2 parts.

My idea is to line up the pads from the driver flex tab and the lcd with uv glue between them and glue them together with uv light. Not sure if this works but i can give it a try. Worst case scenario is that i loose 6 euro's for the glue........

Also , i don't know how the glue will react to heat from the ic. Will try it.

[Moreno83]

Re: In search of Gate driver flex tab

Im not an expert either but i do know that those driver ic's on the driver flex tab get really hot. ( Cant touch them with my finger ).

[AmpWare]

Re: In search of Gate driver flex tab

I have a Vestel tv with a failing lcd panel. Im going to order uv glue which they use on samsung and apple cellphones to connect the glass to the lcd panel so no air/dust etc comes between the 2 parts.

My idea is to line up the pads from the driver flex tab and the lcd with uv glue between them and glue them together with uv light. Not sure if this works but i can give it a try. Worst case scenario is that i loose 6 euro's for the glue........

Also , i don't know how the glue will react to heat from the ic. Will try it.

The bonding tape the LCD assemblers use is Anisotropic Conductive Film (ACF) or also sometimes called Z-axis tape. It contains microscopic conductive particles that smash between the contacts when heat and pressure is applied to bond and cure the adhesive.

The glue they use to bond the glass/digitizer and LCD together on cell phones is Liquid optically clear adhesive (LOCA) and electrically insulative. it won't work for tab bonding unfortunately would be nice since it's so cheap


3M ACF datasheet

Since the gap between the conductors on at least the glass side of the flex ribbon is so tiny you have to use tape that has very very small particles to avoid shorting out the adjacent contacts so even the Z-axis tape avail on adafruit for a few dollars I don't think is any good. What I linked above is around $200 for a small roll of it and should be fine for LCD panels.

Of course a roll of tape contains enough ACF to do dozens of LCD panels but for a one off fix it's a steep buy in.

[Moreno83]

Re: In search of Gate driver flex tab

Thanks for the reply and information. I havent really dig in to these failing lcd's or how to fix them professionally. Ofcourse i fixed a lot of LCD's with failing flex tabs but always with hard carbon.

I found a ACF Conductive Strip for $89 , not sure how many lcd you can repair with it though.....
If you fix a lot of these tv's it would pay it back itself.....


Found it on aliexpress!

[AmpWare]

Re: In search of Gate driver flex tab

I found a ACF Conductive Strip for $89

aliexpress link

Is this what you found? Pretty decent find. Looks to have roughly the same specifications as the 3M tape and less than half the price.

Below is the datasheet for it.

ACF specs

Keep in mind this product is intended to be stored sealed in a freezer until it's ready to be used. Only have a shelf life of ~1month at room temperature.

[AmpWare]

Re: In search of Gate driver flex tab

First I apologize for the shameless bump

I haven't had any luck thus far locating a shattered panel or somebody with one willing to sell me a couple gate driver tabs. I figured since i was bumping I'd toss in a few of the shots I took with my microscope to show a bit more about how the ACF tape works to connect these flex cables and for scale.



The above image is of the edge of a iphone 5s lcd with the flex cable removed. you can see the area where the ACF was applied outside of the flex cable contact area and has hardened in a puddle. The small dark specs that look like dirt are conductive particles.



In this one if you look at the lighter strips that is where the bump contacts are compressed during heating of the ACF and you can see shiny dots where the conductive particles have been crushed between the conductive pads on the flex cable and LCD.



This last image is the contact edge of the gate driver I need to replace with a human hair for scale.

So basically yes they are very small but with a reasonably usable microscope you can easily line things back up

Here is a link to the USB microscope I used for these pictures.

Microscope