Housing for Fitting in Motor Vehicles to Hold Electronic Components

The invention relates to a housing for fitting in motor vehicles to hold electronic components, with the electronic components being disposed on an electronic carrier, in particular a PCB, a film or a hybrid carrier.

Electronic control and regulating systems are being used increasingly in motor vehicles, the components of which are accommodated in housings to protect them from the stresses and interference occurring in operation. These housings are constructed either partially or completely of metal in order to suppress electromagnetic interference (EMV interference). A housing of this type at the same time serves to dissipate the heat from the electrical power loss, with cooling fins, for example, being used in addition to achieve this at an ambient temperature of between -40.degree. C. and 125.degree. C.

This requirement with relation to the constancy of temperature, in particular for thermal shock load, together with the requirement for the housing to be tight, including against high-pressure steam jet cleaning equipment, makes the whole housing suitable for the engine compartment. Watertight housings of this type, that can also withstand mechanical shocks, are usually made of diecast aluminum with pressure compensating pellet using PCB technology, or as hermetically sealed hybrids. The costs for enclosing the electronic systems in this way amount in many cases to some 30% of the overall costs.

The object of the invention is therefore to provide a tight housing of the type mentioned at the outset that is of simple design, permits simple production at low cost, and ensures dependable protection of the electronic systems.

The above object generally is attained according to the present invention by a housing containing electronic components for use in motor vehicles wherein: the electronic components are disposed on an electronic carrier, in particular a PCB, a film or a hybrid carrier; a metal plate is provided to accommodate the electronic carrier, with the area of the metal plate having a larger area than the electronic carrier in order to form an edge all around said electronic carrier; the surface of the electronic carrier provided with the electronic components is provided with a protective lacquer; as a protection against moisture, a flexible and watertight film is spanned over the array formed by the metal plate and the electronic carrier provided with the electronic components such that the film is connected to the all-round edge in an airtight and watertight fashion and is largely matched to the surface contours of the electronic components; and a housing cover is provided as a mechanical protection and forms the housing in conjunction with the metal plate.

The invention substantially consists of the electronic components mounted on the electronic carrier and provided with a protective lacquer being closed off by an airtight and flexible film, the latter being a thermoformed part largely matching the contours of the components. The flexibility of the film ensures that it matches the volume changes undergone by the sealed-in air volume over the temperature range at constant air pressure, so that the sealing points formed by the edge of the metal plate running all round the electronic carrier and connected in airtight and watertight fashion to the film are not subjected to strains sufficient to cause leaks.

Since this film, preferably of plastic, is not used for mechanical protection, but can only protect against moisture, a housing cover is provided that together with the metal plate forms the housing.

In accordance with an advantageous embodiment of the invention, an aluminum foil coated with plastic on both sides can be used as the film, affording additional advantages as regards screening against electromagnetic fields.

Furthermore, in another preferred embodiment of the invention the film can also be provided with impressions as found in barometric cells, to achieve better adjustment of the film to the volume of the air enclosed by the film as this volume changes in response to temperature changes.

The protective lacquer applied to the surfaces of the electronic components and of the electronic carrier prevent electrical interference due to condensation from the small volume of air enclosed by the film above these surfaces. In accordance with a further embodiment of the invention, a UV-hardening lacquer or a polyurethane lacquer can be provided as the protective coating.

Finally, the housing cover can be designed such that it clips onto the metal plate, thereby enabling a particularly simple assembly sequence. The housing cover can be preferably manufactured as a plastic injection molded part.

The invention is described and explained in the following on the basis of an embodiment in conjunction with the drawing

FIG. 1 is a cross-sectional view of an embodiment of the invention.

FIG. 2 is a partial enlarged view of the embodiment of FIG. 1.

The housing 1 according to FIGS. 1 and 2 comprises a metal plate 4, for example of aluminum, to which an electronic carrier or substrate in this case a PCB--carrying the electronic components 2 is affixed. This PCB 3 is therefore provided with these electronic components, which are of various heights and sizes. Furthermore, the area of this PCB 3 is smaller than that of the metal plate 4, so that an edge 5 is formed by this metal plate 4 all around the PCB 3. Before a film 6 is spanned over the array formed by the PCB 3 and the metal plate 4, said PCB 3 together with the electronic components 2 is provided with a protective lacquer 9, by means of which electrical interference due to condensation from the small volume of air enclosed the film 6 above these surfaces is prevented. The film 6, which is largely matched to the contour of the electronic components 2, is glued onto the all-round edge 5 of the metal plate 4 in an airtight and watertight fashion. This film 6, for example a plastic film of 50-150 .mu.m thickness, is applied by a thermoforming process, with care being taken that the volume of air enclosed is kept as low as possible. Since the air volume enclosed by this film can undergo a volume change of up to 30% over the temperature range when the pressure is constant, the flexibility of this film 6 ensures that these volume changes can be matched by the film, as otherwise the increased air pressure could lead to leakage. Impressions 8 in the form of a barometric cell in this film 6 facilitate its volume change with low forces.

As an alternative to a plastic film 6, an aluminum foil coated with plastic on both sides can be used, affording additional advantages as regards screening against electromagnetic fields.

This film 6 represents an airtight but soft cover and provides protection against moisture. Mechanical protection of the array is assured by a hood-like cover 7 that is slipped over the PCB 3 and clipped onto the metal plate 4. This ensures a defined and technically acceptable external contour of the housing 1. This housing cover 7 can be produced inexpensively as a plastic injection molded part that can have screw fastening positions if necessary.

The design of this housing in accordance with the invention permits its assembly in a simple process on an automatic production line at low cost and ensures dependable protection of the electronics even in high temperature applications. High temperature applications of this type occur particularly when electronic assemblies have to be arranged directly on the engine block of a motor vehicle.