solder
釬 centers on joining metal pieces together by melting a filler metal: soldering. It is a specialized metalworking term.
釬 combines 金 (metal) with 干, which likely contributes the sound カン. The character is used for soldering, a metal-joining process.
The left side 金 is metal, and the right side 干 looks like a dry joint or a rod. Picture a metal rod being joined to another piece with molten solder.
For カン, imagine a can of solder being heated to join metal pieces: can -> カン, and the metal flows to make the joint.