What adhesives do you recommend for bonding the touch screen to the LCD? – Scott

Dear Scott:

Touch Guy could simply say to use any VHB adhesive (VHB stands for very high bond), most commonly 3M 4956 mm, but it is not his style to be anything less than verbose. Touch Guy is usually not negative either, but he needs to be this time. There are two big no-no’s… neoprene and common RTV Silicone. This is because both of them are acid producing (sulfuric acid from neoprene and glacial acetic acid [vinegar] from the RTV). Those acid molecules will jump out and eat away at your electronics and your touch screen thin films. You can use a water based RTV silicone, but the cure time is much longer. And, while you are at it, resist the temptation to make a watertight seal between your plastic enclosure and your resistive touch top screen. This is because plastic (usually PMMA) excursion under temperature is usually more than the touch surface, which may leave you with a puffy topsheet.

Where was I… oh, back to that VHB that you asked about. You should use 1.6 mil (mm) thick adhesive, because even the most noise resistant touch technology (resistive) benefits from being away from those busy-beaver transistors in the display and it will reduce “puddling” (as is the case with “puffy”, a very technical term) from heavy touchers. Most companies provide strips of VHB, but many of Touch International’s touch screens come with a continuous die-cut gasket which gives you an elegant dust and water resistant seal.

The VHB has a shelf-life and will begin to activate (grow stronger) over time and pressure, so don’t use old stuff. Once aligned to the LCD, you will have a few seconds to easily pull off the touch panel and reposition it if you make a mistake. Most important of all, you really need to do this in a clean-room because the smallest dust particle in the gap will be grounds for your customer to send product back.

Don’t forget, Touch Guy can optically bond your touch panel for better optics and more rugged performance.

So, Scott, stick away!!!

Until next time,
Touch Guy