- 1 - 3459325 Method for covering an electric unit, and electric component The invention relates to a method for encasing an electrical unit, and an electrical component which has been produced by means of such a method.
Components, for example in the form of sensors, can be used for measuring ac- celerations or rates of rotation or else other measured variables such as, for ex- ample, rotating magnetic fields or currents, and for forwarding the pre-processed measured signals to higher-order evaluation electronics or a control system.
Components of this type can, for example, have a populated printed circuit board, on which there are diverse electrical or electronic components.
In known production methods, a populated printed circuit board is, for example, pressed into a thermoplastic housing, wherein a cover is then cast and cured or else lasered on.
Different designs and fabrication concepts are known in this re- gard for different types of components, in particular for different types of sensors.
The disadvantage with the known embodiments is in particular that the respective printed circuit board is located in a cavity.
Moisture that diffuses in can lead to migration, corrosion and short-circuits.
It has transpired that customer-specific predefined reguirements with regard to the overall space cannot always be satis- fied.
In addition, a shielding plate can be feasible only with a great deal of effort.
The highest leak-tightness classes can typically not be reached.
A large multiplic- ity of designs and fabrication methods and systems are reguired.
In addition, the known production methods entail a high outlay on design, gualification and sup- port.
US 2013/154626 Al and US 2013/106408 Al disclose housings which each have a first plastic body which encases the printed circuit board and a second plastic body which at least partly encapsulates the first plastic body, wherein the second plastic body can have discontinuities.
In these housings, stresses can occur because of different thermal expansion between materials, which can distort measurements, for example.
- 2 - 3459325 It is therefore an object of the invention to provide a method for encasing an elec- trical unit which, in particular, avoids at least one or more of the aforementioned disadvantages.
It is also an object of the invention to provide an electrical com- ponent which has been produced with a method according to the invention.
According to the invention, this is achieved by a method according to Claim 1 and an electrical component according to Claim 13. Advantageous refinements can be gathered, for example, from the respective sub-claims.
The content of the claims is made the content of the description by explicit reference.
The invention relates to a method for encasing an electrical unit, wherein the method comprises the following steps: = connecting the electrical unit to a leadframe, then - encasing the electrical unit with a first plastic material for forming an inner moulded body, so that a plurality of contacts of the electrical unit project from the inner moulded body, = punching the inner moulded body out of the leadframe, = forming an outer moulded body, which surrounds the inner moulded body, from a second plastic material at least partially in the form of a cage struc-
ture, wherein the outer moulded body rests only partially against the inner mould- ed body and is partially spaced apart from the inner moulded body.
The outer moulded body has a cage region with a number of spaced apart struts or brackets which are each spaced apart from the inner moulded body.
When performing the method according to the invention, the electrical unit is completely enclosed by a typically chemically and mechanically stable plastic material.
No corrosion, migration or short-circuit formation are to be expected.
In addition, ultrasound welding of additional components can be used.
As compared to methods which are known from the prior art, fewer processes overall are need-
ed, which accelerates and simplifies the progress of the method.
As a result of forming the outer moulded body as a cage structure, decoupling between the outer moulded body and the inner moulded body is advantageously
- 3 - 3459325 achieved.
This can help to avoid stressing of the inner moulded body by the outer moulded body.
For instance, protectors against static and dynamic forces can be formed, which protect the entire unit.
As distinct from the full moulding with thermoplastic or more generally the second plastic material, the advantage of de-
coupling the two encasings by a gap is provided here.
Thermomechanical forces, for example of a thermoplastic on a thermoset and from there onto a sensor ele- ment, are largely suppressed.
The spaced design of the outer moulded body from the inner moulded body per- mits advantageous decoupling to avoid the production of stresses which, for ex- ample, can distort measured results from a sensor.
The implementation of the outer moulded body with a cage region permits protec- tion of the inner moulded body similar to a surrounding bicycle helmet.
For ex- ample, should impacts on the outer moulded body occur, these are not passed on directly to the inner moulded body, which likewise helps to avoid stresses and associated measurement errors.
According to a preferred embodiment, a part of the inner moulded body that rests against the outer moulded body is at least partially surface-treated before the out- er moulding body is attached, in particular by means of plasma treatment or laser treatment, in order to achieve leak-tightness against the ingress of liquid.
As a result of such a surface treatment, a leak possibly arising from the implementation with an only partially formed outer moulded body, which could lead to the ingress of liquid, is closed.
A failure of the installed electrical or electronic components as a result of moisture that has diffused in is effectively forestalled in this way.
Furthermore, in the method according to the invention, the integration of a shield- ing plate is particularly simply possible.
In methods known from the prior art, a considerably greater outlay was necessary in order to permit reliable attachment of such a shielding plate.
A shielding plate can in particular improve the immuni- ty of electronics and/or sensors.
The attachment of a shielding plate will be dis-
- 4 - 3459325 cussed in more detail further below.
It should be mentioned that a shielding plate is preferably also encased by the first plastic material.
The connection can be understood in particular as pressing in, soldering and braz- ing or soft soldering, adhesive bonding, welding such as ultrasonic welding, laser welding or resistance welding, or else sintering.
During the connecting step, the electrical unit is typically connected reliably to the leadframe for the remainder of the process, so that it is held in the leadframe.
The leadframe can, for example, have plug or crimp terminals.
Expressed in general terms, metal strips for making external contact can already be part of the leadframe.
The leadframe can have index holes and thus additionally serve as a transport and adjustment aid.
The electrical unit can, for example, be any desired electrical component which is suitable for performing any kind of electrical function.
In addition, a shunt resistor can also be attached which, in particular, can have a section which is formed from manganese.
This is a typically used and tried and tested resistance material which permits reliable measurement of the current flow- ing through by means of tapping off the voltage dropping across it.
Instead of manganese, for example, another resistance material, in particular another copper- nickel-manganese alloy, can also be used.
The shunt resistor can be contacted at two points, for example, or else at more points, for example at four points.
The latter in particular permits four-point measurement which, for example may be advantageous in the case in which a material that is not temperature stable is used.
It should also be mentioned that the electrical unit or a printed circuit board can be enclosed completely by the method according to the invention, specifically by a chemically and mechanically stable thermoset material.
No corrosion, migration or short-circuit formation is to be expected.
This satisfies the highest require-
- 5 - 3459325 ments on mechanical and chemical resistance.
A shielding plate can be constitut- ed without substantial additional outlay.
In addition, it should be mentioned that in the method according to the invention, a design for a neutral part can be defined and only customer-specific overmould- ing variants need to be varied.
This means a significantly lower investment, fewer core processes and higher quantities for the neutral part.
Subassemblies with a lower quantity can be fabricated economically at the same time.
The outlay on qualification, design and support is reduced.
The electrical unit used is preferably a populated printed circuit board.
This can be, in particular, a circuit for measuring currents.
The method has proven to be particularly advantageous for such types of printed circuit boards.
It is also possi- ble, for example, for an integrated circuit (IC) to be used.
In particular, this can be designed for a sensor.
The printed circuit board can be designed, for example, to be rigid, flexible or made of ceramic.
A thermoset material can in particular be used as the first plastic material.
This is in particular chemically and mechanically stable.
A thermoplastic material can in particular be used as the second plastic material.
This can be applied simply and has been tried and tested as an external protector.
If contacts are to be connected during the method, these can be connected to an- other element, in particular a shunt resistor, in particular by welding, brazing, ultrasonic welding, laser welding, adhesive bonding, soft soldering, sintering and/or resistance welding.
Methods of this type have proven worthwhile for typi- cal applications.
According to one embodiment, the step of connecting the contacts to the shunt resistor is carried out after the step of encasing with the first plastic material.
Al-
- 6 - 3459325 ternatively, the step of connecting the contacts to the shunt resistor can also be carried out before the step of encasing with the first plastic material.
According to one development, at least one sensor is attached to the electrical unit and, before the step of encasing the electrical unit and the shielding plate with a first plastic material, the method has the following step:
= covering the sensor with a protective material, in particular with a low-viscosity material, preferably with a glob-top material.
Such an embodiment leads to particularly advantageous further protection of the sensor, which can therefore be protected against chemical and/or mechanical damage.
During the step of encasing with the first plastic material, according to one em-
bodiment the electrical unit is completely encased, possibly with the exception of protruding contacts.
This has proven worthwhile in particular since in this way particularly good chemical and mechanical protection is achieved.
Following the step of encasing with the first plastic material, the inner moulded body is preferably connected to the leadframe with a number of inserted or an- chored supporting struts.
This makes the method easier and ensures a defined po- sition of the inner moulded body.
For example, fixed supporting struts, withdrawable supporting struts and embod-
iments without supporting struts can be used.
This will be discussed in more de- tail further below.
An inserted supporting strut can in particular be understood as a supporting strut which can be removed completely from the moulded body during the punching action.
An anchored supporting strut can be understood in particular as a support- ing strut which is anchored in the moulding body in such a way that part of the supporting strut remains in the moulded body in every case.
- 7 - 3459325 According to one embodiment, a number of convex and/or concave contours is formed in the inner moulded body.
These can be used for the adjustment of fur- ther components or else during the moulding for fixing the first moulded body in a second moulding tool, i.e. a moulding tool for the formation of the outer mould-
ed body.
The contacts can advantageously each have a number of beads.
This facilitates the handling and leads to better retention in surrounding structures.
In addition, a creep path for possibly penetrating liguid is lengthened.
The electrical unit can have a number of holes for anchoring in the first plastic material.
This improves the retention of the electrical unit in the first plastic ma- terial, which forestalls production defects.
During the step of encasing with the second plastic material, a plug is preferably formed, which permits the simple provision of a connecting component.
It is also possible for insert parts to be embedded, so that prefabricated elements can be used and simply co-processed.
During the step of encasing with the second plastic material, a rivet is preferably moulded, specifically in particular for connection to an additional component.
This permits simple fastening and alignment of the additional component.
According to one development, an additional surface activation of the inner moulded body can be carried out, in particular before the step of encasing with the second plastic material.
This leads to improved adhesion of the outer moulded body to the inner moulded body.
The material that can be used for the outer moulded body, that is to say as a sec-
ond plastic material, can in particular be PA (polyamide), PBT (polybutylene ter- ephthalate), hotmelt or PU (polyurethane). The encasing with the second plastic material can in particular be carried out by injection moulding or RIM moulding.
- 8 - 3459325 It should be mentioned that in particular a step of connecting at least a first con- tact and a second contact to a shunt resistor can also be carried out.
This can be done in particular before the encasing with the second plastic material to form an outer moulded body.
For example, a battery sensor can advantageously be formed thereby.
According to a development, before the step of encasing the electrical unit with a first plastic material, the method also has the following step: - attaching a shielding plate associated with the electrical unit.
By means of the shielding plate, in particular improved shielding, for example against electrical or electromagnetic interference, can be achieved.
According to one embodiment, the shielding plate is attached by a step, carried out before the step of connecting the electrical unit to the leadframe, of punching the shielding plate out of the leadframe.
This permits particularly simple provi- sion of the shielding plate which, for example, can be produced as a part of the leadframe.
The shielding plate can be designed as a moulded part and attached by pressing into the electrical unit.
This permits separate production of the shielding plate and greater stylistic freedom.
The shielding plate can in particular be attached parallel to the electrical unit.
This can relate in particular to respective extents of the shielding plate or an elec- trical unit which in particular can be designed as a plate.
Therefore, a particularly advantageous shielding action can be achieved.
According to an advantageous embodiment, the shielding plate can be formed as a trough which accommodates the electrical unit.
Enclosing the electrical unit on multiple sides can thereby be achieved.
The trough can preferably be covered by means of a trough cover.
Therefore, enclosing the electrical unit on all sides can
- 9 - 3459325 particularly advantageously be achieved. This permits particularly advantageous protection against electromagnetic radiation and other comparable influences. The invention also relates to an electrical component which has been produced by means of a method according to the invention. With regard to the method, refer- ence can be made back to all designs and variants described herein. The outer moulded body typically constitutes the component, possibly with protruding con- tacts Further features and advantages can be gathered by those skilled in the art from the exemplary embodiments described below with reference to the appended drawing, in which: Figs 1 to 9 show possible states in a method,
Fig. 10 shows a modification with pins projecting transversely relative to a printed circuit board,
Fig. 11 shows a modification with only partial encapsulation,
Fig. 12 shows a modification with an additionally protected sensor,
Fig. 13 shows the modification from Fig. 12 in a later method step, Figs 14a, 14b show an embodiment according to the invention with only partial encapsulation and formed protectors,
Fig. 15 shows a modification with a covering trough,
Fig. 16 shows the modification from Fig. 15 in a side view,
Fig. 17 shows the modification from Figs 15 and 16 in a later method stage,
Fig. 18 shows the state from Fig. 17 in a side view,
Fig. 19 shows a modification with additional supporting struts,
Fig. 20 shows the state from Fig. 19 in a side view,
Fig. 21 shows a modification with an embedded measuring resistor,
Fig. 22 shows the modification from Fig. 21 in a top view.
Fig. 1 shows an arrangement such as typically occurs at the start of a method ac- cording to the invention. It should be understood that a general method will be described firstly and the cage-like structure will only be described further below with reference to Fig. 14.
- 10 - 3459325 Arranged on the outside is a leadframe 10, in which index holes 11 are formed. The leadframe 10 is used for stabilization and transport, wherein it can be gripped and moved simply by means of the index holes 11. The index holes 11 are used in particular for the transport of the leadframe 10 and for the fine fixing in a mould- ing tool. By means of the index holes, mechanical adjustment of the leadframe 10 and therefore the already assembled component or a sensor in the various devices and/or moulding tools which are used within the context of the method is carried out. The leadframe 10 has dam bars 12, which stabilize the leadframe 10 and in addi- tion are designed for the attachment of further components. Formed in the dam bars 12 are fixing holes 13, which can be used to fix the leadframe 10 or further components. The fixing holes 13 are used in particular for fixing the punched-free part in the overmoulding tool. The leadframe 10 additionally has a number of terminals, three in the present case, in the form of plug terminals 14, which are used as electrical contacts fol- lowing the conclusion of the production process. Furthermore, the leadframe 10 has two shunt connection terminals 15, which are used for the connection of a shunt resistor. In addition, the leadframe 10 has an anchored supporting strut 16 and an inserted supporting strut 18. Their function will be discussed in more de- tail below. It should be understood that, of the supporting struts 16, 18, it is also possible for none or a plurality thereof to be present in each case. Connected to the leadframe 10 is an electrical unit in the form of a printed circuit board 20. The printed circuit board 20 is attached to the plug terminals 14 and the shunt connecting terminals 15, specifically soldered in the present case. However, in principle it is also possible for the other connection technigues described fur- ther above to be used here, for example pressing in. This ensures a fixed connec- tion between the printed circuit board 20 and the leadframe 10.
- 11 - 3459325 To protect the printed circuit board 20 against electromagnetic influences, a shielding plate 45 is attached. This is arranged parallel to and above the printed circuit board 20. Also formed in the printed circuit board 20 are a number of holes 24, which are used for the fixing in a moulded body described further below. In Fig. 1, the populated printed circuit board 20 is illustrated in the leadframe composite. Here, the printed circuit board 20 is used in particular as a circuitry support for sensors and additional circuitry. For example, acceleration sensors and rate-of-rotation sensors in any combination are possible as sensors. Likewise, magnetic field sensors and current sensors can be used or produced. The printed circuit board 20 can be anchored better in the moulded body made of thermoset, described further below, by means of the additional holes 24. In the leadframe 10, the plug terminals 14 are preferably already pre-punched. However, it is also possible to connect the leadframe 10 to the plug terminals 14 in a separate connection process. The shielding plate 45 can be punched directly out of the leadframe 10 or pressed into the printed circuit board 20 as a moulded part. The printed circuit board 20 is preferably pressed into the leadframe 10. Howev- er, other connection technigues, such as soldering and adhesive bonding, are also conceivable. In the case of plug terminals 14 that are not straight, moulded plug terminals 14 can be fixed. The connection of the leadframe 10 to the moulded plug terminals 14 can be produced, inter alia, by welding, soldering, adhesive bonding or splic-
ing.
- 12 - 3459325 In addition to a position of the printed circuit board 20 parallel to the plug termi- nals 14, as illustrated in Fig. 1, a perpendicular position may also be feasible. This will be shown further below in Fig. 10.
Fig. 2 shows the arrangement from Fig. 1 in a side view after the pressing-in. It can also be seen that a sensor 6 and, in addition, a number of electrical compo- nents 9 are arranged on the printed circuit board 20. In the present case, these are attached to the printed circuit board 20 by the SMD technigue. In Fig. 3, a state following the attachment of a first moulded body 30 is illustrat-
ed. The printed circuit board 20 is surrounded by the first moulded body 30, which consists of a thermoset material. The first moulded body 30 can also be designated as an inner moulded body. The first moulded body 30 has been pro- duced by encasing the printed circuit board 20 by means of a thermoset material. As can be seen in Fig. 3, both the anchored supporting strut 16 and the inserted supporting strut 18 project into the first moulded body 30. The anchored support- ing strut 16 is formed in such a way that it has a barb in the first moulded body
20. Therefore, it is also designated as “anchored”. The inserted supporting strut 18 on the other hand has no barb, so that it can be pulled simply and completely out of the first moulded body 30. In any case, on the other hand, the anchored supporting strut 16 remains partly in the first moulded body 30, being able to be broken off with its part located outside the first moulded body 30. The first moulded body 30 ensures in particular by its thermoset material chemi- cal and mechanical protection of the printed circuit board 20, wherein only the plug terminals 14 and the shunt connection terminals 15 project from the first moulded body 30. As will be shown further below, the two shunt connection terminals 15 are U- shaped, so that a connection from the printed circuit board 20 to a region beside the printed circuit board 20 is formed. As will likewise be shown further below, these are used for the connection of a shunt resistor.
- 13 - 3459325 The populated printed circuit board 20 in the state shown has no contact with the exterior. It is surrounded completely by a thermoset material. As a result, the risk that moisture or corrosive media will act on the printed circuit board 20 or the sensor is low. Mechanical stresses on the populated components of the printed circuit board are low or negligible, since the coefficient of expansion of the ther- moset material is approximately egual to that of the printed circuit board 20 and the components located thereon. In addition, the adhesion of the materials to one another is very good. The supporting struts 16, 18 can be designed to be embeddable or anchorable. They are used to support the moulded body, which is held only on one side on the dam bar side, additionally against deflection caused by gravity. These struts have no connection to the printed circuit board 20.
Fig. 4 shows the arrangement from Fig. 3 in a side view. It can further be seen that only the terminals 14, 15 project beyond the first moulded body 30. In principle, it should be mentioned that the shunt connection terminals 15 can also project underneath the first moulded body 30.
Fig. 5 shows the arrangement illustrated in Fig. 4 in a modification. In the present case, two concave fixings 32 and two convex fixings 34 have been formed in the moulded body 30. The fixings 32, 34 are used to anchor or to fix the moulded body 30 in a higher-order structure or else to attach other components to the moulded body 30. In particular, they provide the possibility of forming form- fitting connections to other components or higher-order structures, for example to a moulding tool for a further encasing. For example, they are used for positioning and locking the thermoset moulded body 30 in the thermoplastic overmoulding tool. The fixings 32, 34 can also be designated as contours. It should be men- tioned that the fixings 32, 34 or corresponding elements can also be formed, for example, laterally, that is to say transversely relative to the paper plane of Fig. 5.
- 14 - 3459325
Fig. 6 shows the arrangement from Fig. 3 after the first moulded body 30 has been punched out of the leadframe 10. The printed circuit board 20 with the first moulded body 30 surrounding the same can be seen, wherein the terminals 14, 15 connected thereto, which were originally part of the leadframe 10, project out of the first moulded body 30. As can also be seen, a small part of the anchored sup- porting strut 16 remains in the first moulded body 30. The remainder of the lead- frame 10 is still to be seen on the outside. Formed in the printed circuit board 20, as already described further above, are a number of anchor holes 24, no longer to be seen, which are used for the improved fixing of the printed circuit board 20 in the first moulded body 30. In addition, on the right of the first moulded body 30 there is formed a decoupling zone, not spe- cifically illustrated, in which a certain mobility is provided between the terminals 14, 15 and the printed circuit board 20 or the first moulded body 30. The decou- pling zone has proven to be advantageous in particular during ultrasonic welding of the shunt connection terminal 15 to a shunt resistor, since vibrations possibly leading to delamination are prevented from being coupled into the first moulded body 30. In the punched-free part, the terminals 14, 15 are designed as individual pins. If necessary, a programming pin can be provided, which is no longer accessible af- ter the final moulding. All the terminals 14, 15 can be provided with beads, in order to lengthen the creep path for moisture and to achieve improved anchoring in the overmoulding. According to one possible embodiment, a bead not illustrated in Fig. 6 can be provided, which lengthens a creep path for moisture and permits improved an- choring in a second moulded body to be formed subsequently. Starting from the state illustrated in Fig. 6, a shunt resistor not illustrated in Fig. 6 can be attached, which is shown further below as a shunt resistor 40. The shunt resistor 40 can be fastened to the shunt connection terminals 15 in the present
- 15 - 3459325 case by ultrasonic welding at welding points 42. In principle, other connection technigues can also be used, as described further above. As a result of the ar- rangement shown, it is possible to measure a voltage which drops across the shunt resistor 40 approximately corresponding to a width of the first moulded body 30. This permits the current flowing through to be inferred.
Fig. 7 shows a state of the arrangement from Fig. 6 after the attachment of a sec- ond moulded body 50. The second moulded body 50 can also be designated as an outer moulded body. The second moulded body 50 in the present case consists of a thermoplastic material and surrounds the printed circuit board 20 and the first moulded body 30 and a major part of the shunt connection terminals 15, the plug terminals 14 and, if present, the shunt resistor 40 not shown here. A shunt con- nection terminal 15, which is shown at the top in the image, is designed to be modified somewhat with regard to its making contact with the outside, in particu- lar in comparison with the state illustrated in Fig. 6. The plug terminals 14 project beyond the second moulded body 50, so that mak- ing electrical contact with the printed circuit board 20 is possible. Furthermore, if present, a first contact-making surface and a second contact-making surface of the shunt resistor 40 project beyond the second moulded body 50, in order to permit a connection of external components. For example, other electrical units or an ex- ternal circuit can be connected to these contact-making surfaces, wherein a cur- rent from the printed circuit board 20 flowing through the shunt resistor 40 can be measured. Corresponding signals which are indicative of such a current can be provided to further units via the plug terminals 14. The final overmoulding of the thermoset-moulded printed circuit board 20 is par- ticularly preferably carried out with a thermoplastic material. In this operation, in the present case a plug 56 is also moulded. If necessary, fur- ther inserted parts, such as sleeves, rotary bearings, shunts, etc. can be embedded in the thermoplastic body.
- 16 - 3459325 It should be noted that it can further be seen here that an inserted part in the form of a fastening part 53 is located in the second moulded body 50. This permits, for example, fastening to other components.
Fig. 8 shows the arrangement from Fig. 7 in a side view. With respect to the indi- vidual features, reference should be made to the above description. On the underside of the second moulded body 50, a rivet 52 for heat staking is also formed. In addition, the plug 56 is formed on the right, which permits the simple making of contact with the plug terminals 14 and/or the shunt connection terminals 15. It is also possible for a moulded fixing nipple or fastening dome to be provided. The finished arrangement shown in Figs 7 and 8 following the completion of a possible performance of the method can be designated as an electrical component
5. This can be used in a higher-order component or in a unit such as, for example, a motor vehicle, in particular to measure a current. For the fixing of the thermoset body or first moulded body 30 in the overmould- ing tool, various pin configurations are possible, which are illustrated schemati- cally in Figure 9. A modification of the embodiment according to Figure 8 is shown in Figure 9. Firstly, a withdrawable support pin or supporting strut can be used. After the tool has been closed, said support pin or supporting strut is appropriately withdrawn. A possible result is illustrated by reference symbol 32a in Fig. 9. A fixed support pin or supporting strut can also be used. The support pin forms the contour in the overmoulding. A possible result is illustrated by reference symbol 32b in Fig. 9.
- 17 - 3459325 An embodiment without a support pin or supporting strut can also be used. The elevated contour of the thermoset body is used, for example, as a spacer in the overmoulding tool. A possible result is illustrated by reference symbol 32c in Fig.
9. Likewise, the fixing nipple 52 already mentioned can be used. A modified embodiment, in which the printed circuit board 20 is pressed in at right angles to the plug terminals 14, is illustrated in Fig. 10. As a result, for ex- ample, other sensing directions having sensors with sensing axes orthogonal to the measuring direction can also be implemented. A modification in which the thermoplastic overmoulding or the second moulded body 50 is configured by partial moulding such that the thermomechanical stress on the sensor element is minimized is shown in Fig. 11. The second moulded body does not enclose the first moulded body 30 completely, as shown, but only partially. A modification from a state before the application of the first moulded body 30, in which an overmoulding 7 of a low-viscosity material, in particular glob-top, has been applied over the sensor 6, is shown in Fig. 12. This is used in particular to protect the sensor against thermomechanical stress in a particular way.
Fig. 13 shows the embodiment from Fig. 12 following the overmoulding with the two moulded bodies 30, 50, i.e. in particular as a finished component 5.
Fig. 14a shows the embodiment according to the invention of a finished compo- nent 5, in which the second moulded body 50 does not enclose the first moulded body 30 completely but instead only partly. Fig. 14a shows a top view. Fig. 14b shows the state from Fig. 14a in a side view. This corresponds in particular to a method according to the invention.
- 18 - 3459325 In the respective right-hand part of Figs 14a, 14b, the two moulded bodies 30, 50 are designed to be immediately adjacent to each other.
An interface 59 is formed between the two moulded bodies 30, 50, which must be protected in a particular way against the ingress of moisture.
This will be discussed in more detail further below.
In the respective left-hand part of Figs 14a, 14b, the second moulded body 50 is designed in the form of protectors 58. These enclose the first moulded body 30 only partly, so that the first moulded body 30 can still be seen.
With regard to their action, the protectors 58 are designed to be similar to a bicy- cle helmet, i.e. they keep impacts away from the first moulded body 30 and en- sure mechanical decoupling between the two moulded bodies 30, 50. As a result, the occurrence of mechanical stresses in the first moulded body 30 which, for example, can lead to distorted measured results in sensors, can be effectively pre- vented.
In particular, for example, the occurrence of thermal stresses during tem- perature changes can be prevented.
In general, it should be pointed out that thermoset material is typically hard and brittle.
In order to protect the same against mechanical damage, it can be protect- ed against static and dynamic forces by the protectors 58. These protectors 58 are designed in the form of bows in the present case, for example similar to a bicycle helmet, and keep external forces away from the epoxy moulding or from the first moulded body 30.
As distinct from full overmoulding with thermoplastic, the embodiment according to the invention of Figs 14a, 14b provides the advantage of decoupling the ther- moset from the thermoplastic overmoulding by a gap.
Thermomechanical forces of the thermoplastic on the thermoset and from there on a sensor element are largely suppressed.
- 19 - 3459325 A gap formation between protectors and thermoset housing is produced, for ex- ample, by a specific adjustment of the overmolding process or on the basis of the tool.
In addition, the exposed surfaces of the thermoset can be used to support the thermoset preform in the thermoplastic overmoulding tool.
In an adhesion zone or the interface 59, which is achieved by special surface- processing of the thermoset body, there is intensified adhesion of the thermo- plastic to the thermoset.
This ensures that no corrosive or conductive materials or liguids penetrate into the contact-making region of the thermoset body and dam- age or short-circuit the electric contact there.
The surface treatment or surface processing of a thermoset body or, more generally, of the first moulded body 30 can in particular be carried out by plasma treatment or by laser treatment.
This has proven worthwhile for producing the desired permanent leak-tightness.
It is advantageous if, as illustrated here, the printed circuit board 20 is protected mechanically and chemically in two moulding steps.
In special applications, intensified adhesion of the overmoulding to the thermoset moulding can be achieved by additional surface activation of the thermoset body.
It is advantageous if the fully egualized and checked sensors can be used as BGA or OFN (with and without internal additional circuitry). As a result, customer- specific circuitry on the printed circuit board 20 is possible without increased outlay.
The connection technology is preferably carried out using soldering tech- nology, as was intended in the design of the sensor.
In particular but not only in BGA designs, the thermoset moulding can also be used as an underfiller.
Also advantageous is the production of a neutral part from thermoset, which can then be overmoulded customer-specifically with a thermoplastic or thermoset or elastomer.
- 20 - 3459325 In a special embodiment, the plug can be replaced by a cable.
It is advantageous if the dimension of the printed circuit board is standardized, since then the fabrication of devices can be optimized to this/these format(s). This corresponds to the strategy of the IC manufacturer as a result of defining the housing shape.
In this connection, it is advantageous if the leadframe acts as a holder, adjuster and electrical contact relative to the printed circuit board.
As a result, the printed circuit board 20 itself does not need any direct connection to the outside.
It is en- capsulated completely by the thermoset material which, in its coefficient of ex- pansion, is very close to the printed circuit board material.
The single entry point for contaminations is located in the region of the terminals.
However, these chan- nels are advantageously sealed off, since the thermoset material enters into a con- nection with the leadframe materials.
In a further embodiment, the printed circuit board 20 can be replaced by one or more integrated circuits (IC), which are connected to the leadframe by means of suitable techniques such as, for example, soldering, adhesive bonding or welding.
Additional circuitry such as capacitors can be fitted directly to the leadframe ter- minals within the thermoset.
Typically, PA, PBT, hotmelt or PU are considered as final overmoulding materi- als, generally designated thermoplastics in the text.
The final overmoulding can typically be carried out by injection moulding or RIM moulding.
It should be pointed out generally that mention is frequently made in this descrip- tion of a thermoset or a thermoset material for the inner moulded body and like- wise of a thermoplastic or a thermoplastic material for the outer moulded body.
This refers only to the embodiment currently viewed as most suitable.
It should be understood that these terms can in principle be generalized, in particular to more general plastic materials or generally materials and moulded bodies.
The
- 21 - 3459325 disclosure of this application comprises completely a corresponding modification or widening or generalization. Figure 15 shows an alternative embodiment in a method stage before the applica- tion of the first moulded body 30, wherein a shielding trough 45 is used instead of a plain shielding plate. As illustrated in Fig. 15, the shielding trough 45 can in particular be formed with the leadframe 10, wherein the printed circuit board 20 is inserted into the shielding trough 45 formed or introduced in another way.
Fig. 16 shows a side view of the state illustrated in Fig. 15. The shielding trough 45 can be seen in its trough-like form. The shielding trough 45 is covered with a cover 46. This ensures that the printed circuit board 20 is enclosed on all sides and thus ensures particularly effective protection against electromagnetic interfer- ence. Furthermore, it can be seen that the printed circuit board 20 and the shielding trough 45 are connected to each other by means of a fastening pin 47. A stable mechanical and electrical connection between the shielding trough 45 and the printed circuit board 20 is thereby achieved.
Fig. 17 shows the embodiment from Fig. 15 and Fig. 16 following the application of the first moulded body 30.
Fig. 18 shows the state from Fig. 17 in a side view. It should be noted that the cover 46 is not shown. In general, it should be noted that in an embodiment of the idea of the moulded shielding plate, the shielding plate is formed as a trough or shielding trough. This variant offers the following advantages. In relation to the fabrication seguence, it should be mentioned that the leadframe 10 can be punched and shaped, so that shielding troughs 45 can be fabricated con-
- 22 - 3459325 tinuously in the leadframe composite, in which the finally populated and equal- ized printed circuit board 20 can be inserted and contacted. This intermediate product can then be punched freely or else moulded in the lead- frame composite, which is preferably done with thermoset moulding material. Depending on the design and requirement, the shielding trough 45 can, for exam- ple, be filled with moulding material only on the inside or it can also be over- moulded completely. The shielding trough 45 can contain additional fastening elements. The trough form is advantageous in particular in high-frequency (HF) subassem- blies if effective and efficient protection against interference ingress and interfer- ence emission is required. Practically, this module having the shielding trough 45 on the outer side can be screwed to a metal surface, which performs the shielding of the second half.
Fig. 19 shows a modification of the state from Fig. 3, wherein additional support- ing struts 15b, which support the first moulded body 30, are provided. The stabil- ity can be increased further thereby.
Fig. 20 shows the state from Fig. 19 in a side view. It can be seen that vertical parts of the additional supporting struts 15b, which are designated by the refer- ence symbol 15b, are connected to the shunt connection terminals 15. If these are connected to a shunt resistor, which will be illustrated in more detail further be- low, the vertical parts 15b can thus produce a connection of the shunt resistor to the printed circuit board 20, while the shunt resistor can also be contacted from outside by means of the shunt connection terminals 15. Furthermore, in the embodiment of Fig. 20, components 22 are attached above the printed circuit board 20.
- 23 - 3459325
Fig. 21 shows a side view of a finished component 5 having separate protectors. It can be seen that, in the right-hand part, the first moulded body 30 and the second moulded body 50 adjoin the interface 59 directly, while in the left-hand part a gap 51 is formed between the first moulded body 30 and the second moulded body 50. By means of the gap 51, the formation or transmission of stresses which can dis- tort measurement results is effectively avoided. Furthermore, in the embodiment according to Fig. 21, a shunt resistor 40 can be seen, which, underneath the printed circuit board 20, is embedded in the second moulded body 50 but not in the first moulded body 30. This shunt resistor 40 can in particular be a temperature-independent, for example a temperature-stable and/or long-term stable, reference resistor, which is used for the measurement of a current, in particular a battery current. It is in particular advantageously me- chanically stabilized and protected by the embodiment shown.
Fig. 22 shows a top view of the state illustrated in Fig. 21. It can be seen that a first contact region 44 and a second contact region 46 are formed on the shunt 40 at the side of the first moulded body 30. Therefore, the shunt can be connected to lines or cables which carry a current to be measured. In the finished component, the shunt 40 is in particular connected to the shunt connection terminals 15. In general, the shunt resistor 40 can also be designated as an inserted part with any electrical function, which can be attached to the terminals 15 via the output at the end or to the alternative terminals or vertical parts 15b via the lateral output on the printed circuit board 20. This part can also be omitted and there remains only an overmoulding implemented with a cage structure or a second moulded body 50. The cage structure of the second moulded body 50 is advantageous in stress- sensitive components, such as in sensors, since a force-fitting connection locally in the region of the sensor is prevented. Thrust, tensile or shear stresses caused by
- 24 - 3459325 thermomechanical stressing or by the shrinkage, for example recrystallization of partly crystalline thermoplastics, are not transmitted to the thermoset moulded body 30. The sensor embedded therein is not or barely subjected to the stress act- ing from outside.
It should be understood that this application generally discloses in particular the following combinations: = with a cage and without an electrical inserted part (in particular overmoulding of sensors) - with a cage and with an electrical inserted part (in particular a cur- rent sensor with stress-decoupled overmoulding). The formation of cage structures can be carried out by sliders attached in the tool or else by specific surface activation and non-activation.
The aforementioned steps of the method according to the invention can be per- formed in the order specified.
However, they can also be performed in another order.
The method according to the invention can be performed in one of its em- bodiments, for example with a specific combination of steps, in such a way that no further steps are performed.
However, in principle further steps can also be performed, including those which have not been mentioned.