I am working on a magnetic sensors design and noticed that my measured magnetic field bias shifts over time. I have studied the bare PCB and measured that it can be magnetized with a strong magnet.
I tested two blank (unpopulated PCBS). The first PCB I tested had an ENIG plating and could be slightly magnetized. I degaussed the PCB and confirmed that the magnetism was removed, and repeated the experiment to confirm. After a while I realized that the nickel in the ENIG may be playing a part in that.
So I tested a PCB with an immersion silver plating, but it also exhibited the same behavior. Once again, I degaussed it, confirmed the magnetism was removed, and re-magnetized it to confirm that the behavior I was seeing was real.
I don't think it should matter, but the ENIG and immersion silver PCBs were on Isola P95 substrate.
I then tested two PCBs with HASL finish, and they could not be magnetized. These PCBs were on FR-4 substrate.
Any ideas?
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