At last, a question testing Touch Guy’s expertise. Touch International is an expert in all of the ways to assemble and laminate p-cap touch sensors including OCA or optically clear adhesive using pressure and heat, DFA or dry film adhesive using vacuum and heat, OCR or optically clear resin, using heat and UV radiation, and two-part epoxy, using chemical cross-linking.
Optical bonding, however, is a process which attaches the touch panel (or other filter or overlay) directly to the LCD, filling the small air gap between the front of the display and the back of the touch panel. The reason one chooses an optical bond is to make it easier to read the display through the overlay, especially in sunlight, and most importantly to make the touch screen/LCD assembly more rugged, sometimes called the Army boot-kick test. Touch guy only does liquid optical bonding, so he had to seek expertise of others to discuss the advantages and disadvantages of dry optical bonding.
There are three common ways to do optical bonding which include a two-part Epoxy using a long heat cure, OCR using UV radiation, and dry optical bonding using heat and pressure. The names for the optical bonding methods are not the same processes for same names used for the optical laminations described above; dry bonding is the same method as OCA lamination, and OCR optical bonding is unlike the OCR lamination process.
Now that you have read all of that as background, the answer is that, if you get a properly manufactured optically bonded assembly, there is almost no difference between the three methods. Almost all of the differences have to do with the manufacturer which does the optical bonding for you. The differences are in cost of equipment, manufacturing time, space requirements in the factory, skill levels (none of the methods are easy to do), cost of materials, damage to LCD, design of overlay, and the ability to rework parts with blemishes.
Here is a chart which shows the steps for liquid optical bonding (OCR) and dry optical bonding (OCA):
In addition to the optical bonding line in the US, TI has recently opened its new China-based clean room line for optical bonding consumer products.
Throw some more questions at me! I’ll be happy to answer any more, until then…