Multichip module connected to flexible, film-like substrate

Multichip module connected to flexible, film-like substrate The present invention relates to a multichip module comprising a substrate with components connected to it, said module being provided with connection pieces for its connection to a circuit board.

At present, multichip modules are implemented using a rigid substrate (Common Circuit Base). Components are only connected to one side of the substrate. The other side of the substrate is a connection surface with pins for connecting the module to a printed wiring board. The components used in multichip modules may consist of conventional IC circuits, which are connected to the substrate using e. g. bond wires, as well as so-called flip-chip components, which are connected to the substrate using e. g. bonded joints. Flip-chip components have the advantage of having a small size and a small space requirement.

A drawback with present multichip modules is that the modules have a relatively large area and therefore take up much room on the circuit board as the components are only connected to one side of the substrate.

The object of the present invention is to eliminate the disadvantages of prior-art solutions and to achieve a new type of three-dimensional (3D) multichip module that will not take up much room on a circuit board and allow a compact package to be achieved. In the module of the invention, a flexible, thin substrate film is used to which the components are connected on either side. The multichip module of the invention is characterized in that the substrate is substantially film-like and flexible, that the components are connected to either side of the substrate, and that the module comprises filler layers fitted on either side of the substrate to stiffen the structure.

Using the multichip module of the invention, a very compact package is achieved and a small surface area is needed on the circuit board because components can be packed in two or more layers on either side of the substrate. In addition, very short electric connections are achieved, thus reducing electric interference. Moreover, thanks to the thin substrate and compact package, effective cooling of the module is achieved.

A preferred embodiment of the invention is characterized in that the substrate extends outside the filler layers and is bent against the outer surface of at least one filler layer to form the electric connection pieces of the module. Therefore, no separate connecting leads are needed, but the connecting surfaces can be formed directly in the area of the edge of the substrate.

Another embodiment of the invention is characterized in that the components in the upper layer are so disposed that their upper surfaces lie at the same plane, and that placed on top of them there is a cooling component comprising a platelike part, so that a simple and effective cooling arrangement is achieved.

A further embodiment of the invention is characterized in that the substrate is bent so as to form a substantially closed structure, producing within the closed structure an electrically and magnetically protected space suitable for e. g. EMC components.

In the following, the invention will be described in detail by the aid of an example with reference to the attached drawings, wherein Fig. 1 presents a cross-sectional view of a multichip module according to the invention, Fig. 2 presents the module in Fig. 1 provided with soldering studs, Fig. 3 presents a perspective view of a multichip module according to the invention, and Fig. 4 presents the substrate of another multichip module according to the invention in perspective view.

The multichip module presented in Fig. 1 has in its middle a flexible, thin substrate film 1 (Common Circuit Base), which may be made of e. g. polyimide. The film 1 may consist of e. g. four film layers provided with conductive metal films forming the conductor surfaces of the substrate. Connected to the film 1 on either side of it are IC components 2a-2f. The components 2a-2c in the upper layer are so-called flip-chip components, which are connected to the substrate 1 using e. g. a glue bonded joint 3a-3c. The components 2d-2f in the lower layer may be conventional IC circuits, which can be connected to the substrate 1 e. g. by soldered joints 3d-3f.

To encapsulate the module and to stiffen the structure, filler layers 4,5 of e. g. cast resin, which is a dielectric material, are cast so as to surround the components 2a-2f. In this way, a rectangular box-like package is formed.

The upper filler layer 4 fills the spaces between components 2a-2c, and so the upper surface of the module consists of the upper surfaces of layer 4 and the upper-layer components 2a-2c. The upper surfaces of the flip-chip components 2a-2c and of the upper filler layer 4 can be fitted to the same plane e. g. by grinding, so that a cooling plate 6 can be mounted upon them using e. g. thermopositive glue for cooling components 2a-2c and the entire module. The lower filler layer 5 covers the lower-layer components 2d-2f completely, thus forming a continuous lower surface consisting of dielectric material.

The edges 7a, 7b of the substrate film 1 extend outside the filler layers 4,5 and are bent under the module so that they form connecting surfaces for connecting the module to a circuit board. The connection may be implemented using e. g. soldering studs 8a, 8b as shown in Fig. 2.

Fig. 3 presents a perspective view of a multichip module according to the invention. As shown, the surface of the substrate 1 may consist of conductive and non-conductive stripes, metalized areas 9 and non-conductive, e. g. polymerbased areas 10, the connecting surfaces of the module thus consisting of stripes 9.

Fig. 4 presents an embodiment in which the side edges 12a, 12b of the substrate 11 have been bent so that they cover the entire lower surface of the module, with only a small gap left between them. In addition, the end edges 13a, 13b of the substrate 11 have been bent to the sides of the module. Thus, inside the substrate 11 a closed structure is formed, the continuous conductive surface of the substrate 11 forming inside the structure a space protected from electric and magnetic fields, so the components placed in this protected space may be EMC components.

It is obvious to the person skilled in the art that different embodiments of the invention are not limited to the examples described above, but that they may be varied within the scope of the claims presented below. For instance, in addition to the one-layer film described above, the substrate may be bent into folds, allowing components to be placed in several layers.