Both firms specialise in making kit for many of the big players in the computing industry. Flextronics will operate Solectron as one of its business units.
Both Solectron and Flextronics, along with other players like Foxconn, are members of the "supply chain" - companies which make all sorts of stuff for people with brand names who don't want to manufacture. µ
See Also
Solectron CEO warns against over reliance on
China
Flextronics buys Iwill
Foxconn pounds third party manufacturers