What Separates Us From The Rest
There are 2 major kinds of glues used to hold the iPhone digitizer (touch screen) with the frame. They are Hot Melt Glue (HMG) and Cold Press Glue (CPG).
Hot melt glue is widely used to assembly screens, that’s because it’s cheaper and most importantly, it’s easier and takes less time and effort. It doesn’t need strict working environment and it only takes less than 30 seconds for solidification.
For iPhone 4/4s/5/5s/5c, the hot melt glue is working fine, it doesn’t have any quality problems. That’s because the connecting area on the frame is wider, and the surface is flat. So the HMG can hold it firmly.
But for iPhone 6 and above models, hot melt glue cannot meet the requirement. There are 2 reasons, first, the frame of iPhone 6 is thinner than 4 and 5 series, that means there’s less connecting area for the frame and the digitizer. Secondly, the edge of iPhone 6 is curved, not flat as iPhone 4/5. So the hot melt glue cannot perform well.
Only the cold press glue works perfectly for iPhone 6 and above. It’s not much more expensive, but not many companies want to use it. Because the cold press glue requires dust-free workshop, and after the glue applied to the frame and digitizer, it needs 3 hours to completely solidified.
So most of the companies use hot melt glue for iPhone 6 and above to save time and money. They didn’t care much about quality, it’s easier to make money in this way.