Method of encapsulating large substrate devices using reservoir cavities for balanced mold filling

A method for packaging an electronic device substrate in a plastic encapsulant, said substrate having a top surface and a bottom surface, said surfaces separated by a plurality of edges including first and second edges disposed on opposite sides of said substrate, the method comprising the steps of:

• placing the substrate to be encapsulated into a mold cavity of a mold, leaving an upper void space between the top surface of the substrate and a top surface of the mold cavity, a lower void space between the bottom surface of the substrate and a bottom surface of the mold cavity, and spaces along the edges of the substrate which connect the upper void space and the lower void space,
• introducing plastic molding material into the mold cavity at a first region in the mold cavity adjacent to the first edge of the substrate,
• flowing said molding material into the upper void space and into the lower void space so that the molding material flows with a first flow front through the upper void space and simultaneously with a second flow front through the lower void space with both of said flow fronts flowing toward a second region of the mold cavity located opposite to the first region and adjacent to the second edge of the substrate, with one of said flow fronts leading the other, thereby creating a leading flow front and a lagging flow front,
• flowing said molding material in the leading flow front through an opening in said second region into an overflow reservoir outside the mold cavity, thereby causing the molding material to flow into the overflow reservoir prior to complete filling of the mold cavity with the molding material and preventing said leading flow front from entering the void space occupied by the lagging flow front, and
• evacuating all air in the mold cavity through the opening into the overflow reservoir.