Abstract: A heat exchanger includes a housing and a plate having four corner areas secured together, and four outer peripheral sides spaced from each other, and a flowing channel formed between corrugated structures of the housing and the plate, the housing and the plate each include a recess for forming a higher side platform and a lower side surface, and a casing and a board are disposed below the plate and have four corner areas secured together and four outer peripheral sides spaced from each other, and having a passageway formed between corrugated structures of the casing and the board, the casing and the board each include a depression for forming a higher platform and a lower side surface and located below the lower side surfaces and the higher side platforms of the housing and the plate respectively.