per principles of the present invention the extender frame 38 is cast from a metal such as aluminum that has a relatively high thermal conductivity alternatively the extender frame 38 can be stamped and it can be made of a metal other than aluminum owing to its low cost light weight and good thermal conductivity however aluminum is preferred fig2 shows that the extender frame 38 includes a flat plate 42 that defines a plane preferably a plurality of elongated fins 44 are formed on the plate 42 preferably two sets of three parallel fins 44 are formed on the base 42 as shown such fins can be placed on either or both sides of the plate without the extender frame 38 air ordinarily does not flow between the enclosure 18 and the circuit board 28 in accordance with the present invention however the extender frame 38 defines an air flow passageway 46 between the circuit board 28 and the enclosure 18 and the fins 44 are oriented parallel to the direction 48 of air flow from a system cooling fan 49 through the air flow passageway 46 the fins 44 increase the surface area to promote convective heat transfer as is common in the art in the preferred embodiment shown in fig2 the air flow passageway 46 is on both sides of the extender frame 38 consequently the extender frame 38 advantageously directs air over both a lower surface 50 of the enclosure 18 and an upper surface 52 of the circuit board 28 with the extender.