The heat from the AMC’s seem to be flowing very quickly to the temp sensor (inside the MCU) which is directly on the other side of the driver.
We dont know why it flows so quickly, but the best theory is a combination these 2 things:
1. The AMC chips are not touching the battery tube or body so they get hotter than normal.
2. Maybe there are vias too close to the legs of the MCU (the MCU absorbs heat through it’s 8 legs). The vias might be transferring heat directly from the AMC to the MCU, which is not good.
This new copper piece adds mass to the AMC’s making their temp go up much slower. This prevents the MCU from heating up so fast.
Here is the thread where the problem was discussed.