SENSOR MODULE FOR AIR QUALITY MEASUREMENT

Abstract

A sensor module as well as a method for manufacturing a sensor module for determining a property of a fluid, in particular for measuring air quality, comprises a printed circuit board, at least one sensor on the printed circuit board for measuring a parameter of the surrounding air and a housing for the printed circuit board. A part of the printed circuit board protrudes from an opening in the housing (10), wherein the at least one sensor (21, 22) is located on a front side of the protruding part of the printed circuit board. In addition, at least the front side of the protruding part of the printed circuit board, with the exception of a recess for the at least one sensor, is encapsulated with a filling compound. The sensor module can be used in an interior or an air duct of motor vehicles or buildings. In one embodiment, the sensor module measures temperature, relative humidity and gas concentration in a fluid, especially in the surrounding air.

Claims

1. Sensor module for determining a property of a fluid, in particular for measuring air quality, comprising a printed circuit board, at least one sensor on the printed circuit board for recording a parameter of the fluid, in particular of the surrounding air, and a housing for the circuit board, wherein a part of the circuit board protrudes from an opening in the housing, wherein the at least one sensor is located on a front side of the protruding part of the printed circuit board, wherein at least the front side of the protruding part of the printed circuit board, with the exception of a recess for the at least one sensor, is encapsulated with a filling compound.

2. Sensor module according to claim 1, wherein at least a back side of the protruding part of the printed circuit board, with the exception of a further recess which is opposite the at least one sensor, is encapsulated with filling compound.

3. Sensor module according to claim 1, wherein at least the opening in the housing is encapsulated with filling compound.

4. Sensor module according to claim 1, the housing being of plastic material.

5. Sensor module according to claim 1, wherein a base shape of the housing is cuboidal.

6. Sensor module according to claim 1, the housing comprising a connector for electrically contacting the printed circuit board from outside the sensor module.

7. Sensor module according to claim 6, wherein the connector is located on a side of the housing adjacent to or opposite the side with the opening.

8. Sensor module according to claim 1, the housing comprising a fastener for mounting on an air duct or in a water tank.

9. Sensor module according to claim 8, wherein the fastener is located on the side of the housing with the opening.

10. Sensor module according to claim 8, the fastener comprising a bayonet lock.

11. Sensor module according to claim 1, the housing comprising a further opening on a side adjacent to or opposite the side with the opening.

12. Sensor module according to claim 11, wherein the further opening is encapsulated with filling compound.

13. Sensor module according to claim 1, wherein the printed circuit board, with the exception of a recess for the at least one sensor and a further recess opposite the at least one sensor, is encapsulated with filling compound.

14. Sensor module according to claim 11, the housing comprising guiding means for inserting the printed circuit board through the further opening into the housing.

15. Sensor module according to claim 14, the guiding means comprising a chamfer in the housing, which is arranged obliquely to the side with the further opening.

16. Sensor module according to claim 1, the housing comprising locking means for locking the circuit board after insertion.

17. Sensor module according to claim 1, wherein the at least one sensor is in direct contact with the surrounding air.

18. Sensor module according to claim 1, wherein the at least one sensor comprises a temperature sensor.

19. Sensor module according to claim 1, wherein the at least one sensor comprises a humidity sensor.

20. Sensor module according to claims 18 and 19, wherein the temperature sensor and the humidity sensor are integrated in a single chip.

21. Sensor module according to claim 1, wherein the at least one sensor comprises a gas sensor.

22. Sensor module according to claim 21, wherein the gas sensor measures a concentration of a gas in the surrounding air.

23. Sensor module according to claim 21 or 22, wherein the gas sensor is a MOX sensor.

24. Sensor module according to claim 1, wherein the protruding part of the printed circuit board is step-shaped and comprises two steps, wherein the two steps protrude from the housing by the lengths l1 and l2, where l1>l2.

25. Sensor module according to claim 18, wherein a distance of the gas sensor from the opening in the housing is at most 25% of l1, and wherein a distance of the temperature sensor and/or the humidity sensor from the opening in the housing is at least 75% of l1.

26. Sensor module according to claim 1, comprising processing means for measured values from the at least one sensor on the printed circuit board.

27. Sensor module according to claim 1, comprising at least one ESD bracket made of an electrically conductive material on the printed circuit board, which at least partially spatially bridges the at least one sensor and is connected to a ground connection of the printed circuit board, for protecting the sensor from damage by electrostatic discharge.

28. Sensor module according to claim 27, wherein the ESD bracket is partially encapsulated with filling compound.

29. Sensor module according to claim 1, where the filling compound is a hot melt or UV curable adhesive.

30. Method of manufacturing a sensor module for determining a property of a fluid, for example for air quality measurement, comprising the following steps: a. Providing a printed circuit board with at least one sensor, which measures a parameter of the surrounding fluid, for example of the surrounding air, and a housing for the printed circuit board, which has an opening for a protruding part of the printed circuit board at least on one side, b. Inserting the printed circuit board into the housing, c. Encapsulating a front side, on which the at least one sensor is located, of the protruding part of the printed circuit board, with the exception of a recess for the at least one sensor, with a filling compound.

31. Method according to claim 30, wherein the printed circuit board is inserted in step b through a further opening of the housing.

32. Method according to claim 30, wherein the insertion of the printed circuit board in step b is assisted by guiding means and/or a chamfer in the housing.

33. Method according to claim 30, wherein step b comprises the following steps: Oblique inserting of the printed circuit board into the housing through the further opening, wherein a distance of the printed circuit board from the chamfer in the housing is kept greater than a height of the at least one sensor together with an ESD bracket above the printed circuit board, preferably supported by the guiding means, When the part of the printed circuit board with the at least one sensor protrudes from the housing through the opening, pressing the printed circuit board onto the chamfer, preferably assisted by the guiding means, Tilting the printed circuit board over the chamfer into a final position where it is preferably locked in the housing by locking means.

34. Method according to claim 30, wherein in step c, additionally a back side of the protruding part of the printed circuit board opposite the front side, with the exception of a further recess opposite the at least one sensor, is encapsulated with filling compound.

35. Method according to claim 30, wherein in step c, the opening in the housing is additionally encapsulated with filling compound.

36. Method according to claim 30, wherein in step c, additionally cavities in the housing and in the printed circuit board are encapsulated together with the at least one sensor, such that only one recess and one further recess for the at least one sensor and possible cavities in the at least one sensor remain.

37. Method according to claim 30, wherein the housing together with the inserted printed circuit board is transferred in step c for encapsulating into a mould which has a punch for the recess for the at least one sensor.

38. Method according to claim 37, wherein the punch exerts a force on an ESD bracket above the at least one sensor and deforms it before encapsulating.

39. Method according to claim 37, wherein a further punch exerts a counterforce on the back side of the printed circuit board opposite the ESD bracket.

40. Method according to claim 30, wherein the filling compound is a hot melt or UV curable adhesive.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Further advantageous embodiments of the invention result from the dependent claims and the modes for carrying out the invention shown below on the basis of the drawings, which show:

[0036] FIG. 1 a top view of a sensor module for determining a property of a fluid, for example for air quality measurement, with a temperature/humidity and a gas sensor on the front side of a printed circuit board according to a first embodiment of the invention,

[0037] FIG. 2 a side view of the sensor module according to the first embodiment,

[0038] FIG. 3 a front view of the sensor module according to the first embodiment,

[0039] FIG. 4 a view from behind on the sensor module according to the first embodiment,

[0040] FIGS. 5 and 6 two perspective views of the sensor module according to the first embodiment from different angles,

[0041] FIG. 7 a top view of a sensor module for determining a property of a fluid, for example for air quality measurement, with a temperature/humidity sensor on the front side of a printed circuit board according to a second embodiment of the invention,

[0042] FIG. 8 a top view of a sensor module for determining a property of a fluid, for example for air quality measurement, with a temperature/humidity sensor on the front side of a printed circuit board according to a third embodiment of the invention,

[0043] FIGS. 9 and 10 a side view of a vertical cut through the housing of the sensor module, while a printed circuit board with a sensor is inserted at an angle during manufacture according to an embodiment,

[0044] FIG. 11 shows a vertical cut through the housing, while the printed circuit board with the sensor is pressed onto a chamfer during manufacture according to an embodiment,

[0045] FIG. 12 shows a vertical cut through the housing, while the printed circuit board with the sensor is tilted over the chamfer into its final position during manufacture according to an embodiment,

[0046] FIG. 13 a view from below onto a horizontally cut sensor module for determining a property of a fluid, e.g. for air quality measurement, with guiding means and alignment pins for the circuit board,

[0047] FIGS. 14, 15 and 16 a vertical cut through the housing with different embodiments of locking means for the printed circuit board,

[0048] FIGS. 17 and 18 a vertical cut through the housing with two variants of mounting a connector,

[0049] FIG. 19 a top view of the sensor module with marking of a vertical cut A-B through the circuit board for the following Figs.,

[0050] FIGS. 20, 21 and 22 the vertical cut A-B through the printed circuit board.

MODES FOR CARRYING OUT THE INVENTION

[0051] FIG. 1 shows a top view of a sensor module for determining a property of a fluid, for example for air quality measurement, with a temperature/humidity sensor 21 and a gas sensor 22 on the front side of a printed circuit board 20 according to a first embodiment of the invention. The sensor 21 is an integrated sensor for measuring the temperature and relative humidity in the surrounding air. The gas sensor 22 is a MOX (metal oxide) sensor which preferably measures the concentration of a gas, e.g. of NO2, SO2, O3, CO, VOC (volatile organic compounds), in the surrounding air.

[0052] The two sensors 21 and 22 are mounted on a printed circuit board 20 and are supplied with power via this board. The printed circuit board 20 is encapsulated with a filling compound for reinforcement and sealing, preferably with a hot melt, e.g. Henkel Technomelt PA 6771 or Bostik Thermelt 181. The encapsulation has recesses in the sensors 21 and 22 so that the surrounding air can come into contact with the sensitive elements. It can be seen from FIG. 1 that the sensors 21 and 22 are not surrounded by measuring chambers, but are directly exposed to the surrounding fluid, e.g. the surrounding air, e.g. the air flow in an air supply duct. This has the advantages that the measurement is not delayed by a sluggish fluid/air exchange in the chamber, and that the measurement is not distorted by outgassing that could accumulate in a chamber.

[0053] In the embodiment shown, the temperature/humidity sensor 21 is positioned near the tip of the PCB, while the gas sensor 22 is located near the housing 10. Thus, the two sensors 21 and 22 are clearly separated from each other, which prevents mutual interference, in particular a tampering of the temperature measurement by a heating element in the gas sensor 22.

[0054] A power supply and a data processing unit for the measured values are also mounted on circuit board 20 (both not shown because they are located inside housing 10). These are located on that part of the printed circuit board 20 which does not protrude from the housing 10. The housing is made of plastic, e.g. PP or PBT, and protects the sensor module from mechanical damage. The connection of the sensor module to an external power supply and further processing of the data is done via electrical contacts in a connector 11. In the embodiment shown in FIG. 1, the connector 11 is formed on a side of the housing 10 defined as top side, while the printed circuit board 20 protrudes from the housing 10 on a side defined as front side. Different arrangements are possible, e.g. the connector 11 is located on a back side of housing 10 opposite the front side.

[0055] Another part of the housing 10 in FIG. 1 is the bayonet lock 12 for mounting the sensor module on a carrier, e.g. for attachment to an air supply duct for the interior of a motor vehicle or building. By fastening with a bayonet lock 12, an airtight connection can be established with simultaneous locking of the sensor module in the carrier. However, other forms of fastening are also possible, e.g. via a thread.

[0056] FIG. 2 shows a side view of the sensor module according to the first embodiment, while FIG. 3 illustrates a front view and FIG. 4 a back view. FIG. 2 shows how the printed circuit board 20 with the sensors at the front protrudes from the housing 10. In addition, the bayonet lock 12 with two pins 13 for locking is illustrated. The view of FIG. 4 from the back is the view of a viewer looking at the mounted sensor module from outside the air supply duct.

[0057] FIG. 5 shows a perspective view of the sensor module with housing 10 and encapsulated circuit board 20 from diagonally below according to the first embodiment of FIGS. 1-4, with the pin 13 of the bayonet connection 12 clearly visible.

[0058] FIG. 6 supplements this with a perspective view from an oblique angle. In this view, the recess can be seen, which is located in the encapsulation around the circuit board 20 above the sensor 21 and allows direct contact of a sensitive element of the sensor 21 with the surrounding fluid, for example the surrounding air.

[0059] FIG. 7 shows a top view of a sensor module for determining a property of a fluid, for example for air quality measurement, with a temperature/humidity sensor on the front side of a printed circuit board 20 according to a second embodiment of the invention. The second embodiment comprises to a large extent the same components as the first embodiment in FIGS. 1-6, i.e. a housing 10 with protrusions for a connector 11 and a bayonet lock 12, and an encapsulated printed circuit board 20. In contrast to FIGS. 1-6, FIG. 7 shows only one sensor 21. In one embodiment, this is again an integrated temperature/humidity sensor.

[0060] FIG. 8 illustrates a top view of a sensor module for determining a property of a fluid, for example for air quality measurement, with a temperature/humidity sensor on the front side of a printed circuit board 20 according to a third embodiment of the invention. The difference to the first two embodiments in FIGS. 1-6 and 7 is the shape of the encapsulated printed circuit board 20. The part of the printed circuit board 20 which protrudes from the housing and thus into the air supply duct in the assembled state is less wide in FIG. 8. This leads to a lower influence on the air flow in the duct or the fluid to be measured. As in the second embodiment, an integrated temperature/humidity sensor is preferably mounted on PCB 20. However, it is also conceivable for all embodiments to use only a single temperature sensor if the relative humidity values are not of interest.

[0061] FIGS. 9-12 show a side view of a housing 10 of the sensor module during manufacture, while a printed circuit board 20 with a sensor 23 is inserted before encapsulation according to an embodiment. The housing 10 with protrusions for connector 11 and bayonet lock 12 including pin 13 corresponds largely to that shown in FIG. 2. In addition, FIGS. 9-12 shows a chamfer 14, the purpose of which is explained in the following.

[0062] The circuit board 20 is not yet encapsulated in FIGS. 9-12. Therefore, the sensor 23 is visible as an attached chip. Furthermore, the sensor 23 is spanned by an ESD bracket 24 (electrostatic discharge) which protects it from damage by electrostatic discharge. The ESD bracket 23 is also largely encapsulated after encapsulation, which increases the mechanical stability of the sensor module.

[0063] As the sensor 23 and the ESD bracket 24 can easily be damaged before encapsulation, the printed circuit board 20 is inserted at an angle and with sufficient distance to the chamfer 14 in the first assembly step in FIG. 9, so that the sensor 23 and the ESD bracket 24 do not touch the chamfer 14. In FIG. 10, it is shown how the printed circuit board 20 is pushed out of the opening 16 in the front of the housing 10 such that the part of the printed circuit board 20 with the sensor 23 in FIG. 11 protrudes from the housing 10. The printed circuit board 20 is guided by guiding means 15, which is shown in FIG. 13. In FIG. 11, the printed circuit board is then pressed against the chamfer 14. The insertion of the printed circuit board 20 is completed in FIG. 12 by tilting it over the chamfer 14 and thus, with the exception of the part with the sensor 23 protruding at the front, it is situated completely in the housing 10.

[0064] Finally, the arrangement shown in FIG. 12 is encapsulated. For this purpose, the entire arrangement is placed in a mould in vertical orientation as shown in FIG. 1. The mould includes a punch for each sensor, which keeps the recess for the sensor free. Now the further opening 17 of the housing 10, through which the PCB 20 in FIGS. 9-11 was inserted, is filled and the part of the PCB 20 protruding from the opening 16 is encapsulated with the sensor 23 and the ESD bracket 24 with the exception of the recess.

[0065] Various materials can be used as filling material, but a hot melt is preferred. The advantage of a hot melt is that lower pressures have to be applied during encapsulation than with other methods such as injection moulding. However, UV-curable resins are also conceivable as a filling material. At the end of the production process, a compact and robust sensor module is produced.

[0066] FIG. 13 shows a view from below onto a horizontally cut sensor module for determining a property of a fluid, for example for air quality measurement. The printed circuit board 20 is secured against lateral displacement in the housing 10 by the guiding means 15. In addition, the guiding means 15 support the insertion process described above. Furthermore, two alignment pins 28 help to align the PCB 20 correctly and clamps 25 serve as locking device for the PCB 20 in the desired position.

[0067] FIGS. 14, 15 and 16 illustrate a vertical cut through the housing 10 with different embodiments of the locking means for the printed circuit board 20, with the printed circuit board 20 being supported vertically by supports 23. Towards the bottom, the clamps 25 are used to hold the PCB 20, see FIG. 14. In FIG. 15, a pin 26 is used to lock the PCB 20 at the bottom. In FIG. 16, the locking downwards is achieved by soldering or pressing a pin 27 of the connector 11, which is fixed in the housing 10, to the printed circuit board 20.

[0068] FIGS. 17 and 18 show a vertical cut through the housing with two variants for attaching pins 27 of a connector 11. In FIG. 17, the pins 27 are already firmly mounted in the housing 10 before the PCB 20 is inserted into the housing 10. When tilting the PCB over the chamfer 14, the pins 27 then pierce the PCB 20 in holes provided for this purpose in the PCB 20. Finally, the pins 27 are soldered to the PCB 20 or already fixed by pressing them in.

[0069] In FIG. 18, the pins 27 are already soldered to the PCB 20 or pressed into the PCB 20 before the PCB 20 is inserted into the housing 10. When tilting the printed circuit board 20 over the chamfer 14, they are inserted into the connector 11 up to their desired position.

[0070] FIG. 19 shows a top view of the sensor module with housing 10 and printed circuit board 20 as well as marking of a vertical section A-B through the printed circuit board 20. FIGS. 20, 21 and 22 show different embodiments of encapsulating the printed circuit board 20 with the filling compound 29 by vertical sections A-B through the printed circuit board 20. In the embodiment of FIG. 20, the complete circuit board 20 is encapsulated with filling compound 29 with the exception of a recess for the sensor 21 on the front side and a further recess 30 on the back side. The further recess is opposite the sensor 21 and comes from a further punch which exerts a counterpressure on the back side of the circuit board 20 when the circuit board 20 is encapsulated with the filling compound 29, while on the front side a punch exerts pressure on the ESD bracket 24.

[0071] In the embodiments of FIGS. 21 and 22, there is no further recess opposite the sensor 21 on the back side of the printed circuit board 20, but part of the housing 10 is continuous along the printed circuit board 20 all the way up to this point. This part of the housing supports the protruding part of the printed circuit board 20 and thus makes the sensor module more robust. In FIG. 21, the lateral extension of this housing part along the section A-B is limited to the width of the opposite sensor 21. In FIG. 22, the housing part in section A-B has the shape of an upside down T whose width exceeds the width of the printed circuit board 20. The cavity between the cross line of the T and the printed circuit board 20 is filled with filling compound 29 during encapsulation. This arrangement makes the protruding part of the PCB 20 even less sensitive to mechanical influences.