1. A housing assembly, having an insertion opening adapted for insertion of an electronic unit, and comprising:a first housing;
a second housing, opposite to the first housing, wherein a space is formed between the first housing and the second housing, and the space is in communication with the insertion opening;
a thermal pad, disposed on one side of the first housing facing the second housing; and
a guide structure, disposed inside the space, wherein the guide structure is a boss, the electronic unit comprises a protrusion, the protrusion slidably abuts against the boss, and the boss is adapted to guide the protrusion to make the electronic unit move towards the first housing when the electronic unit is inserted into the space through the insertion opening and moves, so that the electronic unit comes into contact with the thermal pad.