We nearly found 1.0%~2.0% defective boards in each batch on this IOT models.I often ask help from customer's side. Please see the recently emails. Sometimes we communicate those defective issues by wechat.What we found most are MCU(U7) and (BLE)U1 in those defective boards. I asked them to check the sordering under X-Y ray, they were no problem. The board can work good after they changed a new IC.The second problem is in BIST test. Sometime the tester told it's IOT responce timeout?