Just came across this subject at my job, as this "Tin Whiskering" is the reason we Conformal Coat some off-the-shelf items used for Aerospace Flight Hardware. I had never heard of this before today , but I found a few NASA sponsored sites displaying their findings in this subject. Im sure this info could be useful to a few people here.

https://nepp.nasa.gov/whisker/

This is very interesting. So the way I look at it, its makes sense to conformal coat the boards prior to soldering any wires or components to avoid tin whiskers.

bring back the LEAD in solder!

this is mainly an issue for operating in the vacuum of space. We're lucky to have oxygen and air pressure down here on the ground.

Source: my career has been electronics packaging for space applications

^yep. Unless you're flying to space, no need to worry. I'm a EE and have several designs floating around in space right now.

Reading those papers throughout that site shows Zinc and Leadless Tin performing whiskering in Server farms and Data Centers, not just in weightless LEO. The reason NASA has a big paper on it was due to a few satellites failures and a Data Server Room that was 20 years old getting refurbished and all the whiskers from the galvanized floor panels getting knocked off into the cooling air stream and getting distributed through out the sever racks. This caused multiple power losses and data corruption. I will agree that you wont run into this much on a drone you make by hand, but I did read that Lead free solder does experience this. Though it is at a 1mm per year rate, I can imagine some of the PCBs that you buy could have been in storage long enough for this to happen.

Ultimately, I feel it doesn't hurt to take a Magnifying glass and check your equipment over time. Other than that, I just found this fascinating. There is even an article about a lawsuit involving a company that made infant monitoring machines for hospitals. The Baby Monitor Compnay ended up getting sued over a spring loaded push button that was Tin Plated and causing error faults. The company tried to research this problem for 10 years before someone figured it out by holding the spring into the sunlight and seeing rainbow like glitter on the spring which was Whiskers.

Sorry for the novel, but Im a nerd about mechanical systems and electronics, close to 46 years old and have never heard of this effect. any who..Godspeed.

look up what cadmium does in space, if you're in research mode.