Copper/titanium/aluminum joint, insulating circuit substrate, insulating circuit substrate with heat sink, power module, LED module, and thermoelectric module

A copper/titanium/aluminum bonded body in which a copper member made of copper or a copper alloy and an aluminum member made of aluminum having a purity of 99 mass % or more are bonded via a titanium layer,

• wherein an intermetallic compound containing Cu and Ti and an intermetallic compound unformed part which is a part free of formation of the intermetallic compound are formed at a bonded interface of the copper member and the titanium layer,
• a maximum value of a length Li of the intermetallic compound unformed part along the bonded interface is 4 μm or more and 20 μm or less in the bonded interface of the copper member and the titanium layer,
• a ratio ΣLi/L0 is 0.16 or less, ΣLi being a total length of the intermetallic compound unformed part along the bonded interface and of L0 being a total length of the bonded interface along the bonded interface,
• the length Li is a region between intermetallic compound phases at the bonded interface, and
• the intermetallic compound phases are regions, where the Cu concentration is 5 at % or more and 84 at % or less and the Ti concentration is 16 at % or more and 70 at % or less, in a concentration distribution of Cu and Ti of a region including the bonded interface of the copper member and the titanium layer using an electron probe micro-analyzer (EPMA).