I had a 70% success rate with with all phones, including iPhone 5 Series(80% with 5s), 4 series, and most other Samsung, Motorola, and LG's.
I use all the typical solutions including ultrasonic with IPA, as I did with the others; but for some reason the iPhone 6 is noticebly lower, maybe 10-20%. Most up them don't fire up at all, and if they do, get hot under the shield just up from the SIM card housing.
My board guy got out of the business, so I'm really at a loss here. Any suggestions will be greatly appreciated.