Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
2000-05-18
2001-04-03
Picard, Leo P. (Department: 2835)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S761000, C257S712000, C174S261000
Reexamination Certificate
active
06212072
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an electronics package comprising a plate made of aluminum or of an aluminum alloy that constitutes a heat radiator. That plate has an insulating oxide layer on a major surface, and carries a network or pattern of equipotential connection tracks designed to receive electronic microcomponents.
A particularly important, although non-exclusive, application of the invention lies in the field of the automotive industry where it is desirable to have structures that are as simple as possible and where it is also often necessary to evacuate large amounts of heat power under conditions of relatively high temperature.
Methods are already known for anodizing aluminum that make it possible to obtain a surface layer of oxide on which it is then possible to form conductor tracks by silk-screen printing. An advantageous method for achieving this result is described in French patent application 97 06107 or EP-A-0 880 310.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an electronics package of the above-defined kind that is particularly adapted to situations where at least some of the tracks and microcomponents or “chips” carry high currents.
Consequently, according to an aspect of the invention, there is provided an electronics package comprising:
a plate of aluminum or aluminum alloy having trenches formed on a major surface thereof,
an insulating oxide layer on at least the whole of said major surface of said plate,
a network of equipotential electrically conductive connection tracks on said major surfaces arranged to receive electronic microcomponents, some at least of said tracks being above said trenches, and
a plurality of electronic microcomponents having contacts electrically connected to some at least of said tracks.
When the equipotential connection tracks are conventionnally formed by a silk screen printing technique, those tracks which overlie the trenches present a certain amount of increased thickness and thus, for a given width, a greater cross-section since silk-screen inks are leveled off substantially uniformly prior to baking or curing. It suffices to make such trenches in register with those tracks which are to convey high current in order to ensure that the tracks are larger in cross-section. This makes it possible to reduce the width of tracks that carry high currents and thus the amount of space that such tracks occupy, thereby increasing circuit density.
The electronics package can include power circuits as well as control circuits. Because of the direct contact between the components and the aluminum plate constituting the substrate, heat transfer takes place via a path that presents low thermal resistance. The oxide layer can be very thin, providing the anodization techniques used avoid the appearance of cracks or pinholes. In practice, the thickness of the oxide layer will generally lie in the range 10 micrometers (&mgr;m) to 200 &mgr;m.
By placing components in cavities, the extent to which they project is reduced, thereby reducing the size of the package.
According to the invention there is also provided a method of fabricating an electronics package comprising the steps of:
making a plate of unalloyed or alloyed aluminum and forming trenches in a major surface thereof;
forming an oxide layer on the plate and trenches and forming a network of equipotential connecting tracks on the plate, with at least some of the tracks overlying trenches, if trenches are provided; and
mounting electronic microcomponents on said oxidized major surface and soldering contacts of the microcomponents to the tracks. In a preferred embodiments at least some of the microcomponents are located in cavities or recesses provided in the plate and coated by said oxide layer. Such microcomponents may be connected to the tracks formed on the major surface by soldered wires.
The method is particularly advantageous for packages in which only some of the tracks and only some of the microcomponents carry high currents.
The current-carrying cross-section of the tracks can then be adapted to the current that they will carry, with a width which is the same for all tracks.
If those microcomponents which support power are placed in recesses with their contact tabs outside of the recesses, then heat transfer between such microcomponents and the plate is improved because they contact the plate over their entire surface area that is free from any electrical connection tabs.
It is thus easy to adapt the cross-section of the tracks as a function of the power they are to convey and/or to place the power circuits in such a manner that the heat they generate is evacuated under good conditions and that the space they occupy is small.
In practice, an aluminum plate that is only a few millimeters thick will often be used. The plate can have projections from its surface remote from the surface carrying the microcomponents (or at least most of the microcomponents). The trenches and/or the recesses can be several tenths of a millimeter deep.
Depending on the thickness of the aluminum plate, it can be fabricated by various different methods. Often it can be fabricated by casting. If the trenches and the cavities are shallow, they can be made merely by stamping. When the plate is thick and the cavities or recesses are deep, it may be necessary to machine the recesses.
In still another aspect of the present invention, there is provided an electronics package of the above-defined kind including a connector fixed directly to the plate, constituting a one-piece assembly therewith, and suitable for being implemented by a method of manufacture that is simple.
For this purpose, the invention uses the surface oxidation of the aluminum to form an insulating layer covering through-holes formed in the plate for receiving electrical connection pins.
Consequently, there is then provided an electronics package comprising:
a plate of aluminum or aluminum alloy, constituting a radiator, formed with an array of through holes, at least one major surface and the holes being covered with an oxide layer carrying a network of equipotential connection tracks on said major surface;
electronic microcomponents having contacts fixed to some of the tracks by soldering; and
electrical connection pins passing through the plate, soldered to some at least of said tracks of the network and projecting from a major surface of said plate opposed to said one surface of the plate into a connector which is fixed to the plate and which is arranged to receive a mating connector.
The connector fixed to the plate can be sealed by an internal “potting” compound covering the pins. Since the connector is placed on the side remote from the major surface that receives the electronic microcomponents, it leaves said major surface completely free.
When the package comprises both power circuits and signal circuits, the pins of the connector will often be of different types. It is possible to incorporate them in a single connector or else in different connectors all of which are placed on the side remote from the face which carries the microcomponents.
There is still provided a method of fabricating an electronics package, comprising the steps of:
a plate is made of pure or alloyed aluminum, in which an array of through holes is formed;
the plate and the holes are covered in an oxide layer and a network of equipotential connection tracks is formed on the plate;
electronic microcomponents are mounted on said face and their outlets are fixed to the tracks by soldering; and
electrical connection pins are mounted through the plate in the holes, the pins projecting through the opposite face of the plate, and the pins are connected to tracks of the network by soldering during the same step as fixes the microcomponents.
Because the pins are soldered to the tracks during the same soldering step as the step used for fixing the electronic microcomponents, the manufacturing method is simplified. Furthermore, the oxide layer covering the walls of the holes provides insulation between the pins
Boutin Xavier
Dreyfus Alain
Hoche Jean
Prolonge Alain
Datskovsky Michael
Larson & Taylor PLC
Picard Leo P.
Sagem SA
LandOfFree
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