I use the PN532 to read data from a JCOP Card.
My problem is, that some of my Prototypes generate no rf field.
I tested many things, and finally I found out:
When I heat up the PN532 (60-100°C with hot air gun) I see on my scope that suddenly the rf field is there, and all is working well.
I can see this behavour at 4 of 7 curcuit boards, the other 3 are working well.
After cooling down the boards and repowering them, there is no field again.
When I repower them, when they are hot, all is working well.
I did the following things without success:
- Powered the Chip from an other power source
- Reseted and reinit the PN and the CPU during the power wasn't removed
- Reading Error Register (no Errors were detected)
- lower the SPI frequency from 4MHz tto 2,7MHz
Could it be, that the parts are damaged, because of hand soldering with hot air gun (380°C for 15s)?
Or do you think it's because of some part tolerance?
Please tell me your ideas, we want to start our first production series very soon.