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I've found the following suggestions around the web, but I found no source which I could trust completely:

  • Tinned Steel
  • Kovar
  • A copper alloy

As suggested, I'll edit a little bit of background info here, which I have also posted in the comment section. Im currently learning about soldering, in the context of research. Its a lateral entry for me, and since I have a background in materials I wanted to know exactly what alloys can be involved. It is background research. I realise that normally, an electronics engineer doesn't care that much about it since there are standardized techniques for soldering in the industry.

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  • \$\begingroup\$ Why do you care? That is not sayingthat you shouldn't, but that understanding the larger question may help with an answer. Note fyi that many IC's can be picked up with a magnet. \$\endgroup\$
    – Russell McMahon
    Jan 19, 2015 at 9:48
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    \$\begingroup\$ @RussellMcMahon - It can certainly be very, very relevant if you're doing something interesting, like building things to go into a MRI. \$\endgroup\$ Jan 19, 2015 at 10:06
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    \$\begingroup\$ .... increase the corrosion rate. Tin and tin+... was once used - and leads to tin whiskers which I assume you've met. Take SOME old components and you can see and feel a "stubble" on the surface, and whiskers in some cases. Very very very long whiskers sometimes. Very ... zap ... bzzt .. wow ... die whiskers sometimes. At least comms satellite is believed to have died of tin whiskering. | Electronics engineers who have been around a while CARE heaps about it even if they do not KNOW heaps about fine detail. They care enough to know that they use people who do NOT care & know to make their ... \$\endgroup\$
    – Russell McMahon
    Jan 23, 2015 at 23:05
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    \$\begingroup\$ ... boards at their peril. Standardised techniques are fine enough BUT if the keepers of the arcane knowledge do not really KNOW what does what AND if their material suppliers do not KNOW their stuff or if there is not traceability in the supply chain then one day things start dying and nobody knows why. PCBs have solderability lifetimes and components have too. (Components also have moisture ingress lifetimes to stop then becoming popcorn but that is only a related issue). I have seen decades old components eg 1N400x or 1N4148 diodes that still solder adequately using 60-40 SnPb , and .... \$\endgroup\$
    – Russell McMahon
    Jan 23, 2015 at 23:09
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    \$\begingroup\$ .... others of similar age that must be mechanically abraded to solder even 1/2 OK and are often better discarded. || Above I was starting on tin nickel cadmium zinc .... -> Cadmium was good and you may meet it in old stuff but ROHS has cast it into outer darkness. I imagine you are well versed in this arcanery, or becoming so. Anon ... \$\endgroup\$
    – Russell McMahon
    Jan 23, 2015 at 23:11

2 Answers 2

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Wikipedia suggests it may be FeNi42:

The lead frame (and therefore the pins, if any, formed from that lead frame) are occasionally made from FeNi42, a kind of Invar.

I remember reading somewhere that the leads of most components — resistors, capacitors, IC pins and the like — are made of steel. Turns out to be the cheapest material suitable for the task.

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  • \$\begingroup\$ Thank you! - But, what kind of steel? - There are so many alloys! \$\endgroup\$
    – JHK
    Jan 19, 2015 at 9:27
  • \$\begingroup\$ I don't remember reading details about the specific alloy. The article about Invar is more bold about FeNi42 usage: "FeNi42 ... is widely used as lead frame material for electronic components, integrated circuits, etc." \$\endgroup\$
    – anrieff
    Jan 19, 2015 at 9:31
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the pins of ICs are made of Copper plated with nickel or nickel alloy because of its good electrical conductivity, if you live in a humid place like close from the sea you may notice that the pins and lead of all components in the old circuit board turned green (copper oxidation) or you can try it out by scratching them ;)
wikipedia Leadframe

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