A modular construction, power circuit arrangement being highly compact and efficient in terms of heat dissipation

Abstract: A modular construction, power circuit arrangement is disclosed which comprises a thin metal plate (1) performing holder and heat sink functions, a multiplicity of electronic devices in the form of semiconductor material chips (23,25) having metalized pads as their terminals, a printed circuit board (9) attached to the thin metal plate (1), electric conductors between the metalized pads and the printed circuit on the board (9), terminating rheophores (5) which form a part of the printed circuit board (9) for connecting the circuit arrangement to external circuits, and a plastics material body (3) which conglomerates a portion of the thin metal plate (1), the semiconductor material chips (23,25), and the printed circuit board (9). At least one of the semiconductor material chips (23,25) is attached directly to the thin metal plate (1) and extends therefrom through an opening (17) in the printed circuit board (9).

Description: This invention relates to electronic circuits, and particularly to a modular construction, power circuit arrangement which is by itself capable of performing a specific electronic function with no assistance from external components. Known are circuit arrangements which comprise a printed circuit board, that is a laminate of insulative material and metal whereon metallic paths are formed, as by photolithographic and/or metalization techniques, to create electric interconnection lines, and a plurality of electronic devices and components having respective terminals soldered to the ends of the electric interconnection lines. The printed circuit board has terminals which can be coupled to an electric power supply and to external components and devices in order to have the circuit arrangement serve its designed electronic function. Modular structures of this kind are used in several applications to both perform signal processing and control functions for electric or electromechanical devices. The latter applications require that such structures be designed to provide effective dissipation of the heat generated in operation by their active and passive electronic components. The trend toward increased miniaturization of electronic systems dictates modular arrangements of ever more compact design. However, a limitation to compactness of design comes from the sizes of the devices and the components that go into the modular structure and of the heat sinks which must be coupled thereto to dissipate the heat generated by their operation. To circumvent this limitation, besides providing smaller size components, so-called multi-chip structures have been proposed wherein the active electronic components -- i.e., basically integrated circuits and power transistors formed on different chips of a semiconductor material -- are assembled within a single package including a thin metal plate which combines the functions of a holder and a heat sink and can be connected to an external heat sink of a larger size, and a metallic conductor arrangement for connecting the chips together and to the outside which is formed from thin sheet metal as by blanking. A structure of this kind is described, for instance in US-A-4.924.296 assigned to this same Applicant. Such a structure can only be used to advantage where the electric chip interconnections are not too crowded, because of such links being usually formed of thin wires soldered to special metalized pads on the chips which, of course, should not be allowed to contact one another. Thus, it does not lend itself for use with circuits involving a large number of interconnected devices and components, unless considerable complication becomes acceptable in the manufacturing process. The article in Navy Technical Disclosure Bulletin, XII, (1986), June, No. 4, describes a power chip mounted on a PCB opening and in contact with an underlying metal plate. It is an object of this invention to provide a power circuit arrangement of modular construction which is extremely compact, can provide a high rate of heat dissipation, and can include both active and passive devices and circuit components in large numbers. This object is achieved, according to claim 1 of the invention, by a power circuit arrangement as defined and chacterized in the claims appended hereto. The invention will be better understood from the following detailed description of an exemplary and in no way limitative embodiment thereof, to be read in conjunction with the accompanying drawings, in which: Figure 1 is a full-size perspective view of a power circuit arrangement according to the invention; Figure 2 shows a cross-section taken along the line II-II in Figure 1, with major parts in exploded view; Figure 3 is a top plan view of the arrangement shown in Figure 1; Figure 4 is a top plan view or a printed circuit board incorporated to the arrangement in Figure 1; and Figure 5 is a sectional view taken through a modified embodiment of the circuit arrangement according to the invention. With reference to the drawings, there are shown at 1 a thin plate of a metal such as copper, which performs holding and heat dissipation functions: at 3 a body made of a plastics material such as a thermosetting epoxy resin, which is anchored on the plate 1; and at 5 terminating conductors for electrically connecting the circuit arrangement to a power supply and electrical or electromechanical devices. The plate 1 has two clearance holes 7 for attaching the arrangement to a large-size heat sink. The plastic body 1 conglomerates a printed circuit board 9, for example consisting, in a manner known per se, of a GRP insulating layer and metallic paths and areas 11 and 13, respectively, across each of its faces. The paths 11 and areas 13 are interconnected electrically at selected locations through clearance holes 15 formed with metalized wall surfaces. If required, the board 9 may conventionally comprise two or more overlaid insulating layers, each provided with metallic paths and areas across its faces. The terminating conductors 5 comprise fully metalized parts of the board 9. In the example shown, these are shaped and sized such that they can be fitted with standard slide connectors of a commonly used type in several industrial applications. The printed circuit board 9 has two openings 17 and is joined to the thin metal plate 1 with the interposition of a thin layer 19 of an electrically insulative material formed with openings 21 in registry with those through the board 9. Attached to the plate 1 as by soldering, for example, are two chips of a semiconductor material 23, which may be two integrated power circuits and are positioned to register with the openings 17 and 21, thereby they extend from the plate 1 to bring their top surfaces to the same level as the top surface of the printed circuit board 9. Another semiconductor material chip 25, such as a signal processing IC, is soldered to a metallic area 13 on the board 9. Thin electric connection wires 27, e.g. made of gold or aluminum, are soldered with their ends between metalized pads of the integrated circuits 23 and 25 and adjacent metallic areas 13 on the board 9. Additional components, such as resistors and capacitors, not shown in the drawings for clarity, are soldered with their terminals across specially provided metallic areas 13 on the board 9. The method of assembling the parts that form the aforesaid modular structure generally comprises the steps of soldering the integrated power circuits 23 to the thin plate 1, cementing the insulating layer 19 onto the plate 1 and the printed circuit board 9, (to this aim, said insulating layer may be applied preliminarly an adhesive material over both of its faces), soldering the integrated circuit 25 onto its corresponding metallic area 13 of the board 9, soldering the terminals and additional components to their corresponding metallic areas 13, soldering the interconnection leads 27, and forming the plastics body 3 by a conventional technique of injecting an epoxy resin in the liquid state into a suitable mold, followed by curing. In a modified embodiment of the invention, as shown in Figure 5, the insulation between the printed circuit board and the thin metal support can be provided by securing on the thin plate, indicated at 1' in the drawings, posts (two in the drawings) 29 which are shaped such that the board 9' -- being formed with clearance holes at the locations of such posts -- will come to bear on rest surfaces provided by radially enlarged portions of the posts, and upsetting the post heads to secure the board 9' in place. During the molding process, the liquid state epoxy flows into the gap between the board 9' and the plate 1' to form an insulating layer therein which will impart stability and rigidity to the structure. It may be appreciated that the circuit arrangement of this invention can be made extremely compact on account of it having no production, and hence bulky, active devices mounted on its interior, highly efficient in terms of heat dissipation because of the power chips being in direct contact with the thin metal plate acting as a heat sink, and possibly as a heat conductor where arranged to contact a larger heat sink, and can be used without problems with internal devices and components in large numbers as the electric interconnections are provided by the printed circuit on the board. It should be noted that, owing to the internal connections being quite short in length, the losses from Joule's Effect due to the high currents involved -- which are considerable in conventional structures on account of the significant lengths of their connection lines -- are here much attenuated, which reflects in a very favorable energy balance over the prior art. The circuit arrangement could also include, for example, active and passive devices and components connected to metallic areas and paths on the inward, rather than outward, face of the PC board; in that case, they could be set in the board itself or fitted in specially provided openings and joined electrically to the areas or the paths using means other than those described. Alternatively, as further variations, the semiconductor material chips could be cemented, not soldered, and the insulating layer 21, as a separate structural element, could be omitted and the PC board 9 be provided with an insulating layer as its finish ply. Lastly, in a further variation, the PC board 9 may have, as its finish ply, a metal layer, and accordingly, be soldered to the thin plate 1, instead of being cemented thereon.

Claims: A modular construction of a power circuit arrangement comprising a thin metal plate (1) with holder and heat sink functions, a plurality of electronic devices in the form of semiconductor material chips (23, 25) having metallized pads as terminals thereof, means of electrical interconnection comprising conductors (27) which are connected to said metallized pads a printed circuit board (9) joined to the thin metal plate (1), the printed circuit on said board comprising metallic paths connected to some of said interconnection means, at least one (23) of the semiconductor material chips (23,25) being attached directly to the thin metal plate (1) through an opening (17) in the printed circuit board (9), characterized in that the printed circuit on said board includes terminating connectors (5) for connecting the circuit arrangement to external electric circuits and in that it further comprises a plastic material body (3) conglomerating the thin metal plate (1), the semiconductor material chips (23,25), the printed circuit board and the electric interconnection means, the terminating connectors (5) and a surface portion of one of the thin metal plate faces being not covered by said plastic material body. A circuit arrangement according to Claim 1, characterized in that at least one in said plurality of electronic devices comprises a semiconductor material chip secured on the printed circuit board (25). A circuit arrangement according to either Claim 1 or Claim 2, characterized in that the printed circuit board (9) is joined to the thin metal plate (1) by a double-sided adhesive layer (19). A circuit arrangement according to either Claim 1 or Claim 2, characterized in that the printed circuit board (9) is joined to the thin metal plate (1) by rivets (29) being fast with the thin plate (1) and shaped to provide spacers between the board (9') and the plate (1'), and that the plastics body (3) extends in the gap defined between the board (9') and the plate (1') by the spacers.

Inventors: CASATI PAOLO, LIBRETTI GIUSEPPE, CASATI, PAOLO, LIBRETTI, GIUSEPPE
Applicants: SGS THOMSON MICROELECTRONICS, SGS-THOMSON MICROELECTRONICS S.R.L.
Application year: 1992
Main classification: H01L25
IPC codes: H01L25, H01L23