When I install those guides, I found out that one of the heatsink does not have those two drops of glue on its side, thus it can be easily tilt or shake by hands. I removed it, cleaned thermal grease, it turns out all of the chip's corner are broken. Without those 2 drops of glue, I can imagine it get knocked by each vibration during transportation
This is a weakness of the cooling system. Like Spondoolies-Tech pointed out, The RockerBox ASICs with the FCBGA package aren't suitable for mechanical stress, since its die directly exposed, and it is small: only 10x11.5mm in size.
The problem is, the heat sink is just too big for the small contact surface of the die, and it has only 2 point of tension. To make things worse, its tension is flexible because of the spring in each screw, this means it will just tilt to any direction and break the corner of the die with the least amount of incaution during install/transportation. So that's why they end up using some glue to permanently fix the heatsink on the board
And, to my surprise, the copper plate is just attached together with the aluminum heatsink with thermal compound without any screw.
They can slide against each other. This means most of the heat will be transferred to the heatsink by this layer of thermal compound, which has magnitudes lower thermal conductivity than either aluminum or copper. When installed, the pressure between them is decided by the spring of those 2 screws, and it is very weak (otherwise it will break the die)