Not a Fan of Bonded Touch Screens

After replacing the touchscreen module of a Pixel 3a phone, I’ve decided I’m not a fan of a modern evolution in their design. A touchscreen module has two major components: an output module to show information to the user (display) and input module to detect location of user’s fingers (digitizer). While they are both advanced glass technologies, they are made with very different manufacturing processes. Thus they are built on two separate pieces of glass, and assembled together into a touchscreen module. The straightforward way to do this is to place one on top of the other, like this Amazon Fire tablet I took apart. In that case, I found the display was intact and it was only the digitizer glass that had cracked.

There were some downsides to this approach. Aesthetically, it means it’s possible for dust and dirt to get between the layers, where it is very difficult to clean. These surfaces also mean there’s more chance for reflections, and two separate pieces of glass meant the user’s finger is a few millimeters away from the visual interface they are interacting with. Mechanically, as separate pieces they are each on their own resisting mechanical stresses.

To address these problems, many newer touchscreen devices use an optically clear adhesive (usually a resin formulated for the task) to bond the touch digitizer to the display. Once bonded, there’s no way for dust and dirt to get in between those layers. The resin eliminates reflections between the two layers and visually connect the two layers. This help build the illusion that the user is directly manipulating onscreen objects with their finger by putting the display closer to the fingertip. And finally, bonding them together makes the module mechanically stronger as both layers work together to resist mechanical stresses. This is especially useful for phones using OLED displays, which are thinner (and more fragile) than backlit LCD displays.

But stronger touchscreens still have a limit and once exceeded, we’re back to the problem of a cracked screen. In the case of the Pixel 3a I just worked on, only the digitizer layer is cracked. The display layer is still intact and functioning. Unfortunately, due to the fact they are bonded, there’s no practical way to replace just the digitizer portion. So, the entire module has to be replaced. Trying to pull the digitizer glass away from the display glass stretches the resin and once released, we see bubbles between the two layers ruining optical clarity.

As expensive and wasteful as it is, the perfectly functional OLED display can only be thrown away. In comparison, cracked digitizer on a device without a bonded screen could be replaced independent of the display unit. One such high-volume repair is replacing Apple iPad touch digitizers. Amazon vendors sell digitizers for $20-$50 USD, depending on iPad generation. In comparison, as of this writing replacement Pixel 3a modules start at double that cost. This difference is even more stark when considering the fact an iPad has a much larger screen.

The bonded touchscreen module of a Pixel 3a is so expensive that, as of this writing, it actually isn’t economically sensible to replace the screen even at the lowest bidder unknown vendor option of $85. Because if we browse eBay we can find secondhand Pixel 3a for sale for as low as $50. If this keeps up, there’s a business opportunity for a phone chop shop: buy these secondhand Pixel 3a, disassemble them, and sell the components piecemeal. I don’t see any used/salvaged Pixel 3a touchscreen modules for sale at the moment, but maybe it’s a matter of time before they start popping up. But still, I hated throwing away this OLED screen

I understand the reasons why bonded touchscreen modules exist, but since they make repairs difficult, wasteful, and less economical, I am not a fan of this feature.