Transfer molding process for encapsulating semiconductor devices

In a transfer molding method of encapsulating devices which utilizes apparatus which comprises a mold, said mold having a top portion and a bottom portion, either of said portions including at least one pot and a plunger in each said pot, package cavities, and runners connecting said package cavities with said pot, each of said pots, plungers, package cavities, and runners having surfaces, wherein a device is inserted in each of said package cavities, a preform tablet of encapsulating composition is inserted in each said pot, and wherein said encapsulating composition becomes soft and said plunger is used to force the soft encapsulating composition along said runners and into said package cavities;

• the improvement comprising using a preform tablet of encapsulating composition having a density Of at least 90% and a water content of 0.1% or less, providing a liner film over the surfaces of said package cavity, runners, and pot prior to inserting said preform tablet in said pot and said device in said package cavity, wherein said liner film is provided for each of said top and bottom portions so as to line all surfaces which come into contact with said soft encapsulating composition, and wherein vacuum is applied to form the liner film to all resin transfer surfaces of the top and bottom portions.