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ImanCarrot
04-21-2010, 05:41 AM
I got a customer (god bless him) who wants me to opticaly coat a glass window- no problem with that, we do that every day, but he also wants a copper busbar mounted at each end of the window. Any ideas how to attach copper to glass?

The window is about 150mm long, 100mm wide, 2mm thick and the busbar has to be 2mm wide and 0.2mm thick and it goes along both of the shorter sides.

I'm stuck! *scratches head*

Oh, the coating is conductive, so when the copper is attached to the coating it will conduct from one busbar to the other.

epineh
04-21-2010, 08:07 AM
I have seen UV glue used on glass to glass type applications, the strength is incredible, and found this with a bit of googling :

http://www.glass-etching-kits.com/uv_glass_glue_orders.htm

It does say glass to metal for some of the glues, couldn't say if it is of any use to you, it is possible that the glue itself may act as an insulator between your coating and the copper, possibly the copper would go on first then the coating, if your process allows...

Other than that, its late, I tried :D

Good luck !

Russell.

ImanCarrot
04-21-2010, 08:19 AM
Cheers Russel, but UV adhesive (I've got loads here) is not electricaly conductive so that wouldn't work, but thanks for looking though!

Sod it, I'm gonna "no- bid" on the busbar bit. Where the hell do they get these deigners? primary school?

Geof
04-21-2010, 09:53 AM
Enameled copper is glass welded(?) to copper. Or at least it is fused glass tightly adhering to a clean acid etched copper surface; in one sense the glass is acting as its own glue.

I know enameling is done at a temperature high enough that the glass flows under the influence of surface tension but I don't know the minimum temperature. Perhaps the copper bars could be attached by clamping them against the glass and heating the whole lot in an oven with them resting on a flat polished stainless steel surface. Perhaps if the copper was 'tinned' with a layer of glass first by enameling at a high temperature then the glass-to-glass final bond could be done at a lower temperature.

But when everything together how are you going to stop thermal expansion in the copper cracking the glass; think windows in, or rather not in, Hancock Tower.

ImanCarrot
04-21-2010, 11:21 AM
Thanks Geof, but the glass will have a semi- conductive coating (Indium Tin Oxide) which is only a few nanometers thick, welding would destroy this layer where the copper contacts this coating. I looked at conductive adhesives and there are some out there, but truth be told, I'm gonna "no bid" it- it's just too much hassle and I can forsee the scrap rate being in excess of 50% Can you picture trying to glue a 100mm long X 2mm wide X 0.2mm thick strip of copper to the edge of a window lol... without getting any overspill... nahhhh...

I'll bid for the coating without attaching the bus bars. I got so much on at the moment I don't need another prototypye "finger in the air" job. Cheers though!

CalG
04-21-2010, 02:20 PM
Contacts are vacuum coated on glass substrates by the Physical vapor deposition process.

A mask protects the substrate area where the metal film is not wanted, The substrate is exposed to thermal heated metal "evaporant", until a sufficient thickness of material is deposited or "grown" on the surface. Copper is pretty easy, but you need the correct vacuum equipment.

wildwestpat
04-21-2010, 03:48 PM
Think about the car rear screen heaters. The terminals for these can be repaired using silver rich epoxy available from car repair specialists. It might be prudent to use a flexible spider so that the differential expansion can be accepted as the copper and glass have very different expanions coeficients.

In many electronic applications there are glass (LCD pannels) connections and these are made using flexible PCB material with either a conductive glue or conductive rubber.

The question is why the cross sectional area of the copper strip - what currents are involved - how is the glass plate mounted - is the plate to be stress free optically - etc. Sorry but there are a lot of questions so you might be right in passing on this one as it may not be part of a practical design.

Regards

Pat

ImanCarrot
04-22-2010, 06:10 AM
Nope, it has to be a physical bit of copper, it's got a tab on each side 5mm long sticking out away from the side of the window with a 2mm hole in it- presumably so they can attach something to it.

I'm very up on coating, we have about 6 high vacuum chambers for vacuum deposition- we can coat anything, I could go into details but it's pro'lly best to let the web site speak for itself (I do the "Diamond Turning" bit)-

www.siltint.com

The lads in the coating lab are about the best in the country, we can ITO coat it, Antireflection coat it and coat copper on it, but there's no way you can coat up to 0.2mm of copper- the thickness of vacuum deposited coating is in the order of Angstroms and Nanaometers.

*Thinks* you've given me a though though... might be able to attach the tabs with electrivley conductive adhesive directly to the ITO coating and do away with the busbars... hmmm lemme have a ciggy and a think....

*peers intently at the drawing*

Nope, that wouldn't work

Signmaker
04-22-2010, 07:03 AM
Have you thought about soldering ultrasonically?

If you google ultrasonic soldering irons you'll find an outfit in Kent who manufacture a whole heap of them.

As far as I know ultrasonic works on just about EVERYTHING... glass, steel, aluminium, copper and a ton of other stuff.

ImanCarrot
04-22-2010, 10:04 AM
Ultrasonic soldering? that's a new one on me... I'll check it out! cheers mate. Kent aint that far from Manchester either. Thank you.

CalG
04-22-2010, 10:32 AM
Sorry

I missed the buss bar dimension. Solid metal it is.

The real question then is "how to attach a buss bar to an conductive coating on a glass substrate" Such needs are common for heated glass "anti-fog", and for electro-chromic or Liquid crystal applications.

The conductive adhesives may be the best and PVD copper may be the correct interface coating.

You coating lab looks very refined.

CalG