A low-CTE packaging material for assembling a semiconductor die into a package and a method for assembling a semiconductor die into a package, in which the packaging material comprises a negative-CTE material. Preferred means for preventing unauthorized access through the zipper include a rigid barrier attached internally to a first side of the luggage, positioned alongside and extending to the length of the zipper track, and extending past the plane of the zipper towards the second side of the luggage. A preparation of the treatment agent is made by a precipitation method, wherein a copper salts solution serves as a precipitation mother solution, and a mixture solution of either alkali hydroxide or alkali carbonate and alkali silicate serves as a precipitating agent. In some embodiments, the vessel employs refractory liner units of different thermal conductivity to maximize heat penetration into the molten metal from heaters in the gap, but to minimize heat loss at the inlet and outlet of the vessel where the end units contact the housing.