Any PM's in LCD screens?

I am sponsoring a mini-recycling event at a local grade school. The principal gave me almost 40 of these. I tore down a few to see what was inside. Very simple. Two circuit boards, one shows lots of gold contact points the other none. Then there is the LCD screen. No gold showing, but is there anything worth recycling on these?

My recycling buyer offered my 10¢ each, I am paying 50¢ each. So that is a no go. They are sporadically selling on feeBay for around $5 to $925 each. (yes, $925 with a claim of 28 sold)

I will list some but they take up a lot of space and if they do not sell all the boards will get pulled and listed.

I don't know that exact one. But have torn apart a lot like it. If it has a small board right behind the screen a lot of times it would have 1-3 spots that were dobbed with black resin. Those almost always had gold bonding wires under them.

LCD

In principle the display is made up of a back lighter, a polarizer (plastic film) and two sheets of glass with liquid crystals in between. To control the light passing through the display the conductors have to be transparent. A mixture of indium and tin oxides are used and sits on the inside of the glass sheets.
The amount of indium used in a screen is tiny, about 0.01% of the weight of the glass. (0.1g / kg)
The liquid crystal is a mixture of 10 to 25 different compounds and are highly toxic to the environment. It can be dissolved in a solution of 17% (vol%) isopropyl alcohol assisted by ultrasonic.

http://goldrefiningwiki.com/mediawiki/index.php/Flat_panel_displays

Göran

acpeacemaker said:

I don't know that exact one. But have torn apart a lot like it. If it has a small board right behind the screen a lot of times it would have 1-3 spots that were dobbed with black resin. Those almost always had gold bonding wires under them.

Click to expand...

Yes, you know this machine. the small board behind the screen probably has close to 200 gold spots. these make contact with the LCD back, which in turn spells out letters.

The other board only has a plug (not USB but simular) on it and that has a couple of gold spots and nothing else. Could there be PMs in this board?

There could be other pms on this board. However, its hard to give a direct evaluation without seeing it. (Pics of course would be helpful.) Its also been a couple years since I've done anything with a lot of scrap. I've found simalar styles in a certain model phone as well. The larger board consisted of mainly nothing except a few gold plated contact points and a couple phone jacks. So instead of soaking the whole board in Ap. I just got out the shears and cut the pieces off. Other styles I believe had some gold LEDS and some monolithic's. Does yours have mylars or direct contact to the board?

Best wishes
Andrew

acpeacemaker said:

(Pics of course would be helpful.)

Click to expand...

I uploaded a pic yesterday, then deleted it from my computer. Good thing even when deleting it is still there. I will try again.

These look similar to a display board from a fire alarm system I tore apart. I didn't know what I had and threw away some larger parts with values. Check the rubberish material between the gold spots and LCD screen. There is SOMETHING in there for bonding wires, but I don't know its composition. Anybody else know what I mean and what it is?

Could be silver or graphite loaded rubber. Incinerate and test.

No bond wires inside, bond wires are for bonding die to a conductor on a substrate.

Göran

I found some references online that state that the chemicals used in the actual liquid crystal are dioxins and furans among other things. The plastic is PET, the gate electrode contains Tantalum, Molybdenum, Tungsten, or chromium. The gate insulator contains compounds of tantalum as well as silicon compounds. The ITO is around 0.1g/kg of glass. Unless you have over half a metric ton, there's no profit from recovering the indium
http://www.ijestr.org/IJESTR_Vol. 1, No. 7, July 2013/Liquid Crystal Display.pdf

These boards look vaguely similar to others I've seen. Anywhere you see Gold showing, scrape away some of the green around it. Oftentimes, the entire board is gold plated (underneath the solder mask).