My original iPhone 6 battery was running down so fast, I was often caught off-guard with no service. Now, my phone has gone down only 3% in 3 hours or more!
The repair was fine until all re-connected and the screen kept displaying intermittent white bars at the tope of the screen, just deep enough to cover the Service, Time and Battery details.
The following finally validated that this is 'static' and it will fade - and the bars did fade away!:
The URL below was based on the iPhone 5C but I think the same logic still applies. This link was mentioned in the above blog.
Do not waste hours looking for a problem... If you see white bars in your display after reconnecting all parts inside your phone, they will probably fade away! After 3 hours, I can barely see the bars and I can absolutely see what was originally covered - the Service, Time and Battery Life!