Malfunction Phenomenon
iPhone XS Max touch function was abnormal
Trouble Shooting
We disassembled the phone and checked, there wasn’t any obvious malfunction phenomenon. Then we separated the two layers, and we found some pads were lost. We checked the pads with bitmap, the pad in red color was on the rail of AP_TO_TOUCH_SCAN_CLK which was related to touch.
We made a pad with solder paste on the pad and checked with iSocket, touch function was back to normal. Then we soldered the two layers together and tested again, everything was back to normal.
Tips:
For the double-layer motherboard like iPhone X/XS/XS Max/11 Pro/11 Pro Max, between the two lays, the pads used low-temperature solder paste, compared with medium or high-temperature paste, it’s not stable.
What’s more, most of the pads related to the touch function are nearby the sim card reader area, there is a gap between the sim card reader and the upper layer. So pads in this area were easier to be damaged compared with other pads. (It’s similar to iPhone 7 audio issue and iPhone 6 baseband issue). For this kind of issue, we can fix it by jump wire and make pads.
iPhone X
iPhone XS
