We are mounting an microphone device (SMT package) onto a PCB - how? Surface mount line or hand soldering?
Contamination can only come from the solder paste, solder wire, flux, or burning the component/PCB assembly during hand soldering. Unless the component was contaminated prior to assembly.
Would look at the datasheet of the part, and check the reflow/soldering temperature against what temperature was used.
Only rosin type fluxes would contain carbon or carbon-derived products.
Any pictures added, would help everyone to understand your situation better.
Regards, Tom
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