Abstract: A heat exchanger is provided, including a first case, a second case, a substrate, an engaging structure, an evaporator, a condenser, a first tube, and a second tube. The first case includes a first plate structure and a first protruding structure. The first plate structure has a first inner surface. The first protruding structure protrudes from the first inner surface. The second case includes a second plate structure and a second protruding structure. The second plate structure has a second inner surface. The second protruding structure protrudes from the second inner surface. The substrate is engaged with the first inner surface, the first protruding structure, the second inner surface, and the second protruding structure via the engaging structure. The substrate is in contact with at least three different lateral surfaces of the engaging structure so that the substrate and the first case combine are bonded.