How do you judge that the chip doesn't work if the ambient temperature rises to 75 ℃?
What's the state of the chip, broken or recoverable?
Where did you buy these chips?
Thank you for the reply
1. The PCB works in High and low temperature test chamber. When temperature set to 25℃ ,it works well.
2. Chip is brand new.
3.Purchase through an agent
What specifically doesn't work?
As LinglingG said: Is the chip broken @ 75C?
If the problem is that the DAC, ADC or other subsystems go out of spec, there may be solutions that could be exercised.