Well, why don't we go to our resident expert on the matter--Mr. Article.
Munger also reported the problems with the connector pins, which Oak Ridge Today's John Huotari noted was due to too much gold mixed in with the solder. Gold is used for connectors because it does not oxidize quickly, and because of its high electrical conductivity; however, when mixed with solder that contains tin, the gold and tin can combine, making the combination brittle under certain conditions. Cray is reportedly replacing the connectors to alleviate the problem.
Seriously, if you want more information badly enough to go into the comments and create a post asking for answers, is it really too much effort for you to click on the link in the summary?