Touchscreen control components on iPhone 6 logic boards have insufficient support, including a lack of underfill—which strengthens and stabilizes integrated circuits, and a lack of rigid metal shielding on the logic board unlike previous iPhone models; the touchscreen controller is instead shielded by a flexible "sticker".
Normal use of the device can cause the logic board to flex internally, which strains the touchscreen IC connectors and leads to a degradation or outright loss of touchscreen functionality.
A symptom that has been associated with this type of failure is a flickering grey bar near the top of the display.
iFixit reported that this issue, nicknamed "touch disease", was a byproduct of the previous "Bendgate" design flaw because of the device's demonstrated lack of rigidity.
As such, the larger iPhone 6 Plus is more susceptible to the flaw, but it has also been reported on a small percentage of iPhone 6 models.
The devices' successor, the iPhone 6S, is not afflicted by this flaw due to changes to their internal design, which included the strengthening of "key points" in the rear casing, and the re-location of the touchscreen controllers to the display assembly from the logic board.

Initially, Apple did not officially acknowledge this issue.
The issue was widely discussed on Apple's support forum—where posts discussing the issue have been subject to censorship.
The touchscreen can be repaired via microsoldering: Apple Stores are not equipped with the tools needed to perform the logic board repair, which had led to affected users sending their devices to unofficial, third-party repair services.
An Apple Store employee interviewed by Apple Insider reported that six months after they first started noticing the problem, Apple had issued guidance instructing them to tell affected users that this was a hardware issue that could not be repaired and that their iPhone had to be replaced.
However, some in-stock units have also been afflicted with this issue out of the box, leading to an employee stating that they were "tired of pulling service stock out of the box, and seeing the exact same problem that the customer has on the replacement".
The issue received mainstream attention in August 2016 when reported by iFixit.
On August 26, 2016, Apple Insider reported that based on data from four "high-traffic" Apple Store locations, there was a spike in the number of iPhone 6 devices brought into them for repairs following mainstream reports of the "touch disease" problem.

On August 30, 2016, a group of three iPhone 6 owners sued Apple Inc. in the United States District Court for the Northern District of California and filed for a proposed class action lawsuit, alleging that Apple was engaging in unfair business practices by having "long been aware" of the defective design, yet refusing to acknowledge or repair it.

On November 17, 2016, Apple officially acknowledged the issue and announced a paid repair program for affected iPhone 6 Plus models, stating that "some iPhone 6 Plus devices may exhibit display flickering or Multi-Touch issues after being dropped multiple times on a hard surface and then incurring further stress on the device".
Touchscreen control components on iPhone 6 logic boards have insufficient support, including a lack of underfill—which strengthens and stabilizes integrated circuits, and a lack of rigid metal shielding on the logic board unlike previous iPhone models; the touchscreen controller is instead shielded by a flexible "sticker". Normal use of the device can cause the logic board to flex internally, which strains the touchscreen IC connectors and leads to a degradation or outright loss of touchscreen functionality. A symptom that has been associated with this type of failure is a flickering grey bar near the top of the display. iFixit reported that this issue, nicknamed "touch disease", was a byproduct of the previous "Bendgate" design flaw because of the device's demonstrated lack of rigidity. As such, the larger iPhone 6 Plus is more susceptible to the flaw, but it has also been reported on a small percentage of iPhone 6 models. The devices' successor, the iPhone 6S, is not afflicted by this flaw due to changes to their internal design, which included the strengthening of "key points" in the rear casing, and the re-location of the touchscreen controllers to the display assembly from the logic board.
Initially, Apple did not officially acknowledge this issue. The issue was widely discussed on Apple's support forum—where posts discussing the issue have been subject to censorship. The touchscreen can be repaired via microsoldering: Apple Stores are not equipped with the tools needed to perform the logic board repair, which had led to affected users sending their devices to unofficial, third-party repair services. An Apple Store employee interviewed by Apple Insider reported that six months after they first started noticing the problem, Apple had issued guidance instructing them to tell affected users that this was a hardware issue that could not be repaired and that their iPhone had to be replaced. However, some in-stock units have also been afflicted with this issue out of the box, leading to an employee stating that they were "tired of pulling service stock out of the box, and seeing the exact same problem that the customer has on the replacement". The issue received mainstream attention in August 2016 when reported by iFixit. On August 26, 2016, Apple Insider reported that based on data from four "high-traffic" Apple Store locations, there was a spike in the number of iPhone 6 devices brought into them for repairs following mainstream reports of the "touch disease" problem.
On August 30, 2016, a group of three iPhone 6 owners sued Apple Inc. in the United States District Court for the Northern District of California and filed for a proposed class action lawsuit, alleging that Apple was engaging in unfair business practices by having "long been aware" of the defective design, yet refusing to acknowledge or repair it.
On November 17, 2016, Apple officially acknowledged the issue and announced a paid repair program for affected iPhone 6 Plus models, stating that "some iPhone 6 Plus devices may exhibit display flickering or Multi-Touch issues after being dropped multiple times on a hard surface and then incurring further stress on the device".
IPhone 6