Case study: old components sold as new
One of our customers was buying some ICs which they had XRF tested before committing to buy, in the country they had been sold in. The ICs were deemed tin/lead, and so suitable for our customer, due to the presence of lead in the alloy.
However when we looked at the report, we noticed that the lead content varied across the sample, and it did not come close to the Sn63/Pb37 our customer was sourcing.
On further investigation, it became clear they were not new. In fact they were originally lead free ICs placed on a PCB using tin/lead paste, so had acquired lead this way. The non presence of lead at the part of the termination closest to the IC body told us this.
This proved they were used when they were sold as new, and in fact they looked very good, there were no other indicators that they were used ICs.
So buyers need to look out for this, that the % of each metal present can tell a story about the IC history.