I am looking for a guidebook that covers lead tarnish and acceptability/failure criteria for class I, II,II standards. For some reason it is not easily found and there are some varying opinions on what is and is not rejectable. Please advise.
Any relevant pass/fail criteria would presumably be spelled out by the same defining authority that set forth the standards that are being referenced. It’s not entirely clear which standards those are, so clarification on the point may be helpful.
I don’t think DigiKey has an official policy/position on lead tarnish.
After receiving parts on your end if a solderability test fails you can bring that to Applications Engineering Department’s attention, we can facilitate a discussion between our supplier if there is a quality concern.
I have found conflicting feedback on tarnish that if it is heavily tarnished and solders it passes – then others say no tarnish is acceptable at all since it is like rust and should not be there for reliability concerns.
I was hoping Digi-Key had a reference they used as a guideline that I could use as well.
We had a similar customer question regarding tarnish but turned out their leads only had exposed copper. For reference, that post is found here.
The TI support download form found on this search (TI E2E support forums J-STD-002D solderability tests for component) may be what you are looking for or perhaps some kind of Jedec standard such as J-STD-002D may be something to look into, otherwise the manufacturer of each specific part should have information on their website regarding reliability and soldering such as this post, as some manufacturers purposely use a roughed lead frame with a NIPDAU | SN lead finish. This finish is less shiny but is better for solderability than smooth shiny leads.
Hello and thank you for the feedback. I am sure that depending on Class I,II,III applications the answer will vary depending on the product and end user specifications. Tarnish on terminals reflects questionability of surface finish and in my experience – especially with military applications – there is little to no room for that. Though tarnished leads may wet most incoming inspections would segregate the parts and fail them from my experience. (They could always decide to send the parts out for retinning if that is an option to ensure wettability). I have a lot of experience reworking pc boards with black pads / contaminated pads and honestly dark tarnish looks a lot like that and of course black pads will not wet .
We will continue to take the 0 tolerance approach here unless the customer approves any deviation from target conditions.