Many people can't differentiate between the chip itself and the heatsink, it must be a language-related issue rather than a technical one, most gears I have seen have bad heatsinks, it's very unlikely that the chip will heat and burn because if the heatsink falls or is loose, the hash board will shut down right away, long before it heats up to the extend that will make it burn.
The problem with troubleshooting heatsinks is that in many cases you can't see the bad once with your naked eye, the heatsink will seem like it's perfectly glued when it's slightly loose and that alone is enough to shut-down the board, which is why companies like Zeusbtc manage to sell fixture devices for a premium.
Anyway, your problem is very common, it has been discussed numerous times in this
thread, things from placing a heavyweight on the hash boards all the way to freezing them in the freezer have been tested and talked about, you should have a look.