ohminator,
In the document you posted I did see them speaking of a lead free solder, but what it looked to me like was the indium foil was not the solder but possibly what was being soldered to.
I could be wrong but from looking quickly at the document it looks like the processor does have indium foil probably part of processor composition not the solder, as well as gold, nickel, possibly other metals and other materials, and it also looks like they show where these metals mix when soldered with lead free (solders figure 17), it looks like they are discussing the cracking of the very thin indium foil (250-300Um) when soldered, my guess possibly from oxidation after being solder with lead free solder possibly a problem they had with one of the lead free solders they used at one time, I do not see here were they say they are using pure indium as a heat spreader solder but could be soldering to gold and a thin indium foil.
Although the solder whatever they used could have dissolve some of the other metals into it like gold.
I still am unsure if they are not using one of the common lead free solders to attach the heat sinks.
I will study this document more closely when I have time, to see if I can get more from it.
It seems somewhat vague, and looks like you would have to understand the background information of what they are discussing in the document to figure it out for sure.
As far as I can tell at this point there is at least a little indium in this processor, I am still unsure how much would be in the heat sink solder.
Thank you for posting it, it is informative, I am just a little unsure how to interpret it yet.
Göran
I added some documents in the post above.