Tool/software:
Since the AM5728 chip has been failing before, we have added impedance testing of the main functional network in the production stage to ensure the conformity of the product before delivery. In the most recent production, an AM5728 was found to fail the impedance test, and the results are shown in Figure 1.
After removing the AM5728 from the circuit board, the corresponding 3.3V network pin was measured, and it was found that the overall 11 3.3V network pin impedances were low. 3.3V network pin schematic, as shown in Figure 2. The test impedance difference is shown in Figure 3
It should be noted that the AM5728 chips used in this production are all from the same production batch.Chip impedance test failed, but functional test is normal. Compared to other motherboards that have passed the test, this chip will quickly hot during the test and prompt a CPU overheating warning. So I want to understand the reason for the difference in chip pin impedance