Electronic module having circuit boards and a plastic sealing ring that can be molded on by injection molding, in particular for a motor vehicle transmission control unit, and method for producing said electronic module

Abstract

An electronic module has a first circuit board element, a second circuit board element, and a spacer. Together, the first circuit board element, the second circuit board element, and the spacer enclose a central cavity, in which components attached to the first circuit board element are accommodated. Respective annular circumferential microstructures are provided on a surface of the first circuit board element directed outward and on a surface of the second circuit board element directed outward, adjacent to an outer periphery of the first circuit board element. In this region, a sealing ring is formed, which has a form-closed connection to both the first and the second circuit board element by means of the microstructures of the first and the second circuit board element. The sealing ring can be made of a resistant plastic, which is molded on by injection molding in the liquid state in the region of the outer periphery of the first circuit board element and flows into recesses of the microstructures and, after the curing, forms the form-closed and sealing connection between the two circuit board elements and the sealing ring thereby formed.

Claims

1. A method for producing an electronic module, comprising: providing a first circuit board element, a second circuit board element beneath the first circuit board element, and a spacer, the first circuit board element, the second circuit board element, and the spacer configured such that together they fully enclose a central cavity in which at least one electronic component of the first circuit board element is received; forming a first microstructuring in a shape of a first ring on an upwardly directed surface of the first circuit board element without microstructuring entire upwardly directed surface of the first circuit board element, forming a second microstructuring in a shape of a second ring on an outer circumference of the first circuit board element, and forming a third microstructuring in a shape of a third ring located outside of the cavity next to the spacer on an upwardly directed surface of the second circuit board element without microstructuring entire upwardly directed surface of the second circuit board element outside of the cavity; arranging the at least one electronic component on a surface of the first circuit board element facing toward the central cavity; and forming a sealing ring along the outer circumference of the first circuit board element such that the sealing ring is connected with a form fit to the first microstructuring and the second microstructuring formed on the first circuit board element and is connected with a form fit to the third microstructuring formed on the second circuit board element.

2. The method as claimed in claim 1, wherein forming the first microstructuring, the second microstructuring, and the third microstructuring includes at least one of laser structuring, chemical roughening, mechanical roughening and plasma roughening.

3. The method as claimed in claim 1, wherein forming the sealing ring includes at least one of thermoplastic injection molding, thermoset injection molding, adhesive bonding and filling with an encapsulation compound.

4. The method as claimed in claim 1, wherein forming the sealing ring includes forming the sealing ring without covering the entire upwardly directed surface of the first circuit board element with the sealing ring.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the present invention will be described below with reference to the appended drawings; neither the description nor the drawings are to be interpreted as restricting the invention.

(2) FIGS. 1(a), (b) illustrate a method for producing an electronic module and a finished electronic module according to one embodiment of the present invention.

(3) FIG. 2 illustrates in cross section a form-fit connection with the aid of microstructuring.

(4) FIGS. 3(a), (b) illustrate a method for producing an electronic module and a finished electronic module according to an alternative embodiment of the present invention.

(5) FIG. 4 illustrates an electronic module in a transmission control unit according to one embodiment of the present invention.

(6) FIG. 5 illustrates a transmission having a transmission control unit.

(7) The figures are merely schematic and not true to scale. References which are the same relate to features which are the same or have the same effect in the various figures.

EMBODIMENTS OF THE INVENTION

(8) An embodiment of an electronic module 1 according to the invention and of a method for the production thereof will be described with reference to FIGS. 1(a) and (b).

(9) First, a first circuit board element 3 and a second circuit board element 5, as well as a spacer 7, are provided. The two circuit board elements 3, 5 consist of a thermosetting plastic, for example glass fiber-reinforced epoxy resin. The spacer 7 is arranged as a frame between the two circuit board elements 3, 5, which are arranged parallel to one another, so that the circuit board elements 3, 5 together with the annular spacer 7 fully enclose a central cavity 9. The spacer 7 is in this case dimensioned in relation to its thickness in such a way that the central cavity 9 offers sufficient space for electronic components 11, which are arranged on the first circuit board element 3 on a surface facing toward the central cavity 9.

(10) On an outwardly directed surface 13 of the first circuit board element 3, in the vicinity of the outer circumference 15 of this first circuit board element 3, microstructuring 17 is then formed, for example by laser texturing. Microstructuring 21 is also formed on an adjacent surface 19 of the second circuit board element 5. As represented in FIG. 2, the microstructurings 17, 21 comprise a multiplicity of microscopically small indentations 23 in the form of cavities or undercuts. These indentations generally have dimensions in the submicrometer range, and have for example a depth and/or width of between 10 and 500 nm.

(11) The microstructurings 17, 21 provided on the circuit board elements 3, 5 can subsequently assist with hermetically sealed encapsulation of the two circuit board elements 3, 5 with one another. To this end, a plastic in the form of a subsequently curable liquid is applied, for example by injection molding, in the region of the outer circumference 15 of the first circuit board element 3, while extending around this circumference 15 in a ring. The liquid plastic flows at least partially into the indentations 23 of the microstructurings 17, 21. The spacer 7 in this case prevents the liquid plastic from flowing into the central cavity 9. After curing of the plastic, it forms the sealing ring 25. The plastic which has flowed into the indentations 23 and then been cured in this case forms a hermetically sealed form-fit connection between the sealing ring 25 and the respective surfaces 13, 19 of the first and second circuit board elements 3, 5.

(12) In FIG. 1(b), the sealing ring 25 is formed on the left-hand side in the shape of an injection-molded caterpillar. The plastic applied in the liquid state merges onto the surfaces 13, 19 of the circuit board elements 3, 5 and flows into the microstructurings 17, 21. A shape of an outwardly exposed surface 27 is, however, formed randomly. On the right-hand side in FIG. 1(b), the sealing ring 25 has been applied with the aid of a tool, with the aid of which a cavity was initially formed adjacent to the surfaces 13, 19 to be connected, which was then filled with the liquid plastic for the sealing ring 25, the plastic subsequently having been cured so that a predeterminable external geometry can be produced for the sealing ring 25.

(13) The electronic components 11 provided on the first circuit board element 3 are connected to first electrical terminals 29. On the second circuit board element 3, second electrical terminals 31 are provided, to which the electrical components 47 (not represented in FIG. 1, but see FIG. 4) provided on this second component 5 are electrically connected. By means of press-fit connections 33 or by means of spring contacts, the first electrical terminals 29 are electrically connected to the second electrical terminals 31. In this way, the electronic components 11 provided in the central cavity 9 can be electrically connected electrically to the electrical components 47 provided outside this central cavity 9.

(14) In order to be able to dissipate heat given off during operation of the electronic components 11 better, the central cavity 9 may finally be filled with a thermally conductive gel 49 through an opening 35. The two circuit board elements 3, 5 may have thermal vias which conduct the heat from the components 11 to outer sides of the two circuit board elements 3, 5.

(15) The filling opening 35 as well as a ventilation opening 37 in the two circuit board elements 3, 5 may finally be closed in a leaktight fashion, for example by a solder, adhesive or a pressed-in pin or a pressed-in ball 39.

(16) FIGS. 3(a) and 3(b) represent an alternative embodiment of an electronic module 1. In this embodiment, electrical connection between the electronic components 11 provided on the first circuit board element 3 and the electrical components 47 provided on the second circuit board element 5 is not carried out inside the central cavity 9. Instead, such an electrical connection between externally lying electrical terminals 41 on the first circuit board element 3 and likewise externally lying terminals 43 on the second circuit board element 5 is carried out via electrical lines 45. These electrical lines 45 may, for example, be provided in the form of a bonding wire, a ribbon cable or an SMD jumper. The electrical lines 45 may in this case be arranged close to the circumference of the first circuit board element 3 and subsequently be jointly encapsulated during the injection molding of liquid plastic around this circumference 15 in order to form the sealing ring 25. Such externally lying electrical lines 45, particularly in the form of bonds, may have the advantage over the press contacts represented in FIG. 1 that they function without bores in the circuit board elements 3, and therefore allow simpler preparation of the component parts. In the case of bores for press contacts, a through-hole should be avoided so that no external leaks are formed.

(17) FIG. 4 illustrates a transmission control unit 100 having a plurality of electronic modules 1, an external sensor 101 used as an electrical component 47, and a plurality of jacks 103 likewise used as electrical components 47. The second circuit board element 5 in this case refers to the printed circuit board which undertakes interconnection of the electronics with electrical components 47 of an external circuit. In the transmission control unit 100, these are the sensor 101, the jack 103, further electronics and actuators, etc. The first circuit board element 3 may be a circuit board in the form of an HDI-PCB (high identity interconnect), a DBC (direct bonded copper), or a ceramic substrate (LTCC, HTCC, thick film, etc.), which form for example circuits for electronics of a transmission control unit. Primarily, however, the inventive concept on which the present invention is based may be used in PCB-to-PCB sealing. A carrier plate 105 mechanically supports the electronic module 1.

(18) FIG. 5 shows a vehicle transmission 200 having a transmission control unit 100 formed with the aid of an electronic module according to the invention. The described electronic modules may, however, also be used for other applications, for example in engines or at other places in the vehicle, for example in a fuel tank, cooling water, urea system, electrical drive, in the spray water area, etc.