Late to the party, but for anyone woundering. The way this is done in industry is to use a low temp solder paste on witch ever surface you want bonded and then put the whole thing in a reflow oven (basically a fancy high precision oven). The getto way of doing it would be to put it in your kitchen oven at the apropriate temp with the oven fan running. It is critical not to overheat the pipes due to it containing water ( in most standard pc cases), witch you would likely do with a solder iron or blow torch approach.
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