heat exchanger 4 according to the first and second exemplary embodiment is illustrated in fig5 the top and bottom plates 30 31 have two through holes 36 for conducting the working medium in this regard a flow channel 20 is worked into plate 30 31 as first flow chamber 19 which connects the two through holes 36 together as a result the working medium can flow from the top inlet through hole 36 through flow channel 20 to the bottom outlet through hole 36 according to fig5 spacers 37 with through holes 25 are disposed between two plate pairs fig2 and 3 in each case at through holes 36 in this case different temperature changes can arise in plate pairs 29 during the operation of evaporator heat exchanger 4 for example a plate pair 29 can be heated much more greatly than a plate pair 29 lying below as a result plates 30 31 of the more greatly heated plate pair 29 expand much more greatly so that as a result shear stress must be absorbed on spacers 37 because plate pair 29 which is heated more greatly expands more greatly than plate pair 29 which is not heated or heated only slightly such shear stress can lead to damage of the solder joint between plates 30 31 and spacers 37 for this reason there are two expansion openings 22 each formed as expansion slit 26 between the two through holes 36 because of the two expansion slits 23 plates 30 31 can deform slightly with temperature changes so that as a result only low stress occurs in plates 30 31 between through holes 36 and thereby only low shear stress occurs at the solder joints also between plates 30 31 and spacers 37 in.