These packages comprise a printed circuit with at least one chip, encapsulated by a protective resin, and are provided on their lower surface with connection balls. These are for example packages of the BGA (Ball Grid Array) or FBGA (Fine Ball Grid Array) type.
They are stacked to form an electronic module. FIG. 1a shows, in cross section, a known electronic module 100 comprising two packages 10a, 10b. It includes, for each package, a circuit 20 for interconnecting the package shown in FIG. 1b seen from above, the area of which is the same size as that of the package, and the tracks 21 of which connects pads 22 positioned facing the balls 12, at the edges of the circuit. A central band, with no connections or pads, corresponds to the central band of the lower surface of the package that protects the wires of the wiring connecting the balls to the printed circuit of the package. These circuits 20 are connected together via their edges, in this case by a metal bus 30 located on one side of the module. Connection balls 12 are placed beneath the lower interconnection circuit 10a for connecting the module 100 to an interconnection substrate 200. An insulating lacquer 14 is placed beneath the lower surface of body 11 of the package.
At the present time, electronic modules are subject to thickness and area constraints—a module with two packages must not exceed 2.7 mm in thickness and its area must not exceed that of a package. A package body 11 typically has a thickness of 0.8 mm, a printed interconnection circuit 20 has a thickness of 0.15 mm and a connection ball 12 has a thickness of 0.4 mm. The overall thickness is 3.1 mm, and therefore exceeds the required limit.