Hi Paresa,

Although I haven't extensively tried this method, a UV-curable adhesive would work between  SU-8 and glass. We can spincoat a UV-curable adhesive on the substrate while protecting the channel with a tape and bond with glass substrate by exposing it through a UV lamp. 

Even if a spincoated PDMS layer also works nice, if the fluids you use don't have tendency to react with PDMS. 

I would have thought that a standard superglue (cyanoacrylate) would be fine here - the viscosity is really low and this could be a problem.  Plus it bonds instantly.  In the LCD industry we may be thinking of a 2-part epoxy (allows the pieces to be moved) containing spacers (polystyrene spheres) of say 25 um to prevent the channels being blocked.

Hi Paresa, 

I would recommend using Norland 61 or 65 for bonding, I have been using this for making my devices. once its cured you can give a sealing layer by araldite (its not necessary but Its a good practice to do so to avoid minor leaks in your device.

As mentioned by avanesh. Its an UV-curable adhesive which work quite well for SU-8 and glass slide bonding. 

You can find link to these products here 

https://www.norlandprod.com/adhesives/noa%2061.html

You can easily find araldite on most of the online shopping websites 

https://www.amazon.ca/Araldite-2-Tubes-Crystal-Epoxy-15/dp/B01L4Q1B74/ref=sr_1_4?ie=UTF8&qid=1478638699&sr=8-4&keywords=araldite

Hope this helps. 

PS. If you are looking for glue which doesn't create a stress on your device once its dried I would recommend using Norland Alone. Avoid Using Araldite in this case. 

Thanks everyone for your answers. 

Akhshay: Wouldn't an adhesive cause clogging of the channel or cover the pattern on the top slide? The only reason that I avoided using an adhesive was that I was not sure how to control the spread of the adhesive. Do you have any experience in regards to my concern or is there a special technique for applying the glue?

Hello Paresa See above: "In the LCD industry we may be thinking of a 2-part epoxy (allows the pieces to be moved) containing spacers (polystyrene spheres) of say 25 um to prevent the channels being blocked".  I too have use the Norland adhesives back in the 1980's.  Good to see that they're still going strong!

Hi Alan, thank you so much for your reply. I was wondering if you could please help me to understand how polystyrene spheres of 25 um can prevent channel clogging? Don't the spacers add to the channel height?

Also, on the top slide, I have patterned electrodes which I don't want to be covered with the adhesive. Is this possible? 

The spacers prevent the glue being squeezed out (and across your channels) by keeping the plates a fixed distance apart.  You can get spacers down to 20 nanometers in size - 25 um was only a suggestion as I'm not sure exactly what your structure looks like and a drawing or picture would help.  The spacers stop your channels being clogged with (spreading) glue.  Cyanoacrylate ('SuperGlue') is a pain for bonding immediately and not being able to move or rework the pieces. If you were doing this in high volume then screen printing of the adhesive would be the route, but I'm sure you're doing this as a one-off or with limited numbers of pieces.

Hi Paresa, 

Alan already gave detailed  answer to your problem. In my case I always use spacers. polyethylene terephthalate sheets (23 micron). 

If you are still not sure about this please share diagram of you device. we might be able to help you. 

Thanks 

Akhshay

Thanks Alan. Thanks Akhshay. 

I have attached a sketch of my device. As you see in the sketch, I don't want to get any glue in the channel and over the pattern on the top. 

Where do I get the 2-part epoxy with small spacers (around 1 micron) from? Do Norman products provide glues with spacers?

Thanks again!

I am still confused by your diagram. What is glass and what is channel?  Norland (not Norman) is the name of the adhesive supplier - they make UV curable adhesives if I recall correctly. You can get polystyrene spheres of different sizes from ThermoFisher Scientific (the old Duke Scientific standard materials) and will have to make them up yourself. See: 

https://www.thermofisher.com/us/en/home/clinical/clinical-translational-research/particle-technology/size-standard-particles.html

You can buy a 2 part epoxy from any hardware store e.g. Home Depot, Lowes.  It's even available in many supermarkets.