Metal matrix Composite (MMC) materials are finding increasing use within the electronics packaging industry due to their excellent CTE, stiffness and thermal management properties. One in particular, a spray formed aluminium/silicon composite, can be compositionally modulated to achieve thermal matching to the electronic materials currently in use. One problem with using these materials lies in their specialised machining requirements - the use of very sharp carbide tools which blunt quickly. An alternative approach has been developed that makes use of thin shell (≤ 1.0 mm) electroforms that can be used as electrical discharge machining electrodes to machine the packages. The technology of TSE is described together with measurements of packages produced by this novel technique.