Method for leak testing a housing

Abstract

A method for testing the tightness of a housing involves providing a pressure sensor in a housing, sealing the housing, and detecting a pressure level in the housing.

Claims

1. A method for testing a tightness of a housing, the method comprising the steps: providing a sensor element in the housing, wherein the sensor element is configured to detect a pressure level in the housing; sealing the housing; positioning the housing within an overpressure or vacuum chamber and setting a predetermined pressure in the overpressure or vacuum chamber; detecting, by the sensor element, a change in pressure level in the housing over a period of time; detecting, by the sensor element, a change in temperature in the housing over the period of time; and determining the tightness of the sealed housing based on said detected change in pressure level taking into account the change in temperature.

2. The method of claim 1, wherein detecting the change in pressure level comprises detecting an equivalent air leak.

3. The method of claim 1, wherein detecting the change in pressure level comprises: detecting a drop in pressure when the housing is arranged in an underpressure or vacuum environment; or detecting an increase in pressure when the housing is arranged in an overpressure environment.

4. The method of claim 1, wherein when a temperature increase in the housing occurs when the housing is sealed, the temperature increase induces a first internal pressure level in the housing, and during a subsequent cooling down process an internal pressure of the housing drops to a second internal pressure level of the housing, wherein said detecting the change in pressure level comprises detecting a pressure drop in the housing from the first internal pressure level in the housing to the second internal pressure level in the housing.

5. The method of claim 4, wherein the detection of the pressure drop in the housing from the first internal pressure level in the housing to the second internal pressure level in the housing is used to determine a working temperature during said sealing of the housing.

6. The method of claim 4, wherein the detection of the pressure drop in the housing from the first internal pressure level in the housing to the second internal pressure level in the housing is used to determine said tightness of the sealed housing.

7. The method of claim 1, wherein the sealing of the housing is performed by laser welding, roller seam welding, or laser soldering.

8. The method of claim 1, wherein detecting the change in pressure level takes place in a controlled overpressure environment for a defined unit of time during a bombing process.

9. The method of claim 1, wherein the sensor element is calibrated using a two point measurement procedure.

10. The method of claim 1, wherein a leak rate of the housing is determined directly using a defined value of the internal volume of the housing and a change in pressure over time.

11. The method of claim 1, wherein the sensor element is temperature-compensated.

12. The method of claim 1, wherein the detection of the pressure level in the internal volume of the housing is carried out during an entire service life of the housing component.

Description

BRIEF DESCRIPTION OF THE DRAWING FIGURES

(1) Some exemplary embodiments of the invention are discussed in detail below with reference to the accompanying drawings, which show in

(2) FIG. 1 an exemplary embodiment of the arrangement of sensor elements in a housing component according to the present invention;

(3) FIG. 2 an exemplary embodiment of an electronic circuit with a sensor element for installation in a housing component according to the present invention;

(4) FIG. 3 an exemplary measurement of a leak rate at a hermetically sealed module with and without temperature compensation of the present invention;

(5) FIG. 4 an exemplary design of a sensor element according to the present invention;

(6) FIG. 5 an exemplary embodiment of an offset and a temperature compensation of the sensor element from FIG. 4; and

(7) FIG. 6 an exemplary embodiment of a method for testing the tightness of a housing according to the present invention.

DETAILED DESCRIPTION

(8) Reference is now made to FIG. 1, where an exemplary embodiment of the arrangement of sensor elements in a housing component according to the present invention is shown.

(9) FIG. 1 shows a housing component 2 or more specifically a portion of a housing component or rather its underside. A plurality of contact elements 6 are provided, which leave the housing component on one side of the housing component 2. In this case the contact elements 6 represent a conductive connection from the interior or rather from the internal volume 8 of the housing component 2 to the external environment. Hence, the contact elements 6 can provide a mechanical attachment and/or an electrical contacting of the housing component 2 with additional electronic components that are located externally.

(10) In FIG. 1 two sensor elements 4 are provided, as examples, in the internal volume 8 of the housing component 2. However, in a deployment scenario only one single sensor element 4 may be provided. In this case the sensor element 4a can be a MEMS chip sensor element, which is bonded in the housing component, while the sensor element 4b may be a capacitive MEMS chip sensor.

(11) Additional electronic components, which may be arranged in the housing component 2 during normal operation, are not shown in more detail in FIG. 1. However, these additional components may also lend themselves to being connected to the outside of the housing component 2 using the contact elements 6.

(12) Next, reference is made to FIG. 2, which shows an exemplary embodiment of an electronic circuit with a sensor element for installation in a housing component according to the present invention.

(13) FIG. 2 shows an exemplary embodiment of a radiometric instrument amplifier. However, the exact configuration or rather the exact field of application of the circuit is not relevant for the inventive concept.

(14) A sensor element 4 is provided, as an example, on a printed circuit board 14 of the circuit 10. Similarly the printed circuit board 14 has contact elements 6, which can penetrate in an appropriate manner the housing wall of the housing component 2 or can be properly attached to the contact elements 6 of FIG. 1. Hence, FIG. 2 shows the integration of a sensor element 4 in a circuit. The needed attachments, such as a power supply or more specifically a voltage supply and measurement outputs for the sensor element 4 may be provided directly on the printed circuit board 14. As a result, the sensor element 4 can be functionally and logically integrated into the circuit 10. Moreover, the circuit behavior of the circuit 10 can also be influenced as a function of a measured value of the sensor element 4.

(15) Next, reference is made to FIG. 3, which shows an exemplary measurement of a leak rate at a hermetically sealed module with and without temperature compensation of the present invention.

(16) The measurement shows a decrease in pressure in the internal volume of a hermetically sealed module or rather a housing component 2. For example, FIG. 3 illustrates a decrease in pressure from the atmospheric ambient pressure 1,000 mbar to a residual pressure of about 975 mbar in the course of 4,000 minutes. The solid line is not temperature compensated, a feature that is depicted by means of the elevations in the curve at 1,500, 1,800 and 3,250 minutes. The dashed line is a temperature-compensated measurement curve. At the same time the comparatively steep drop in pressure to the left side of the curve can also be attributed at least partially to a cooling down process of the housing.

(17) Next, reference is made to FIG. 4, which shows an exemplary design of a sensor element according to the present invention.

(18) FIG. 4 shows an exemplary embodiment of the inventive sensor element 4, constructed as a Wheatstone bridge comprising piezo-sensitive resistors 12 on a silicon diaphragm. The Wheatstone bridge has an input for a supply voltage V.sub.S+, which is connected by way of example directly to the epitaxial layer of the diaphragm of a sealed vacuum reference cavity. Furthermore, piezo-sensitive resistors 12, which are through-connected from the supply voltage V.sub.S+ to ground (GND1 or GND2), are provided. Two resistors 12 are connected in each instance to the positive output Out+ as well as to the negative output Out-.

(19) Next, reference is made to FIG. 5, which shows an exemplary embodiment of an offset and a temperature compensation of the sensor element from FIG. 4.

(20) In this case three resistors R1, R2, and R3 are added to the Wheatstone bridge comprising the piezo-sensitive resistors 12 from FIG. 4, in order to enable, on the one hand, an offset compensation (zero point in the vacuum) by using the resistors R1 and R2 and to enable, on the other hand, a temperature compensation by using the resistor R3.

(21) In this respect the requisite elements for the temperature compensation and the offset compensation can be designed, for example as printed resistors in low temperature co-fired ceramic (LTCC) multilayer technology. These resistors can be adjusted, as required, by means of laser trimming. At the same time a simple resistor R3 parallel to the entire bridge may be sufficient for a temperature compensation. This approach allows the temperature coefficient of the bridge resistor of the Wheatstone bridge, where the temperature compensation is typically in a range of 2,800 ppm/° C., to be reduced to 1,900 ppm/° C. In a specific application such a value may compensate more or less completely a temperature coefficient of the maximum output voltage, which occurs at, for example, 1 bar, with −1,900 ppm/° C. Hence, for a limited temperature window of, for example, ±3° C. for the leak test measurement, the net result is a more or less complete compensation.

(22) An offset voltage of a sensor element 4 due to the tolerances in the Wheatstone bridge on the chip of the sensor element 4 may also be trimmed to zero by means of laserable, printed resistors R1, R2 in LTCC multilayer technology.

(23) In particular, two resistors may be used for this purpose. These resistors are arranged between the terminals GND1 and GND2 in such a way that they are connected in series. The center of both resistors is connected to ground. A laser trimming of at least one of the two resistors R1, R2 may balance the tolerances in the Wheatstone bridge by means of a suitable laser compensation algorithm.

(24) The LTCC multilayer technology provides through its hermeticity from one substrate layer to the next a preferred connectivity for wiring a sensor element from the inner, hermetic chamber or rather from the internal volume 8 of the housing component 2 to the external environment. As a result, no separate connectors for a sensor element 4 have to be provided, but rather conventional, hermetically sealed housings can be used.

(25) Next, reference is made to FIG. 6, which shows an exemplary embodiment of a method for testing the tightness of a housing according to the present invention.

(26) In this case the method 20 for testing the tightness of a housing 2 comprises the following steps: providing 22 a pressure sensor 4 in a housing 2, wherein the pressure sensor 4 is configured to detect a pressure level in the housing 2; sealing 24 the housing 2; and detecting 26 a pressure level in the housing 2.

(27) The present invention can also be used advantageously for multiple chamber designs. In such multiple chamber designs a plurality of hermetically sealed housing chambers that are separated from each other are provided in the same hybrid module. In this case the conventional helium measurement technique fails completely.

(28) The present invention can also be used to switch off high frequency amplifiers or other sensitive electronic components, which are used in the satellite electronics, for example: for in-orbit pressure monitoring with respect to the so-called “multiplication” effect. In this case it involves electron avalanches, triggered by high frequency fields, due to the emission of secondary electrons; and these electron avalanches can cause corona effects or arcing. This happens, in particular, when pressure levels are close to a vacuum (the so-called intermediate pressure range) and can destroy elements of the high frequency power amplifier or its surrounding area. If a high frequency power amplifier is installed in a hermetically sealed housing of the invention, for example, a solid state power amplifier in chip and wire technology, and this solid state power amplifier were to lose its gas pressure (sealing pressure) over its service life, then a situation of “multiplication” could arise. By switching off the devices on the basis of the measurement technique according to the invention, secondary damage to the satellite electronics could be prevented.

(29) Hence, the present invention could be used to “switch on and off,” as a function of the pressure, the measurement devices or components in orbit or during the start phase (intermediate pressure range, protection against “multiplication”).

(30) Finally it must be pointed out that the terms “having” or “comprising” do not exclude other elements or steps and that the terms “a” or “one” do not exclude a plurality. Furthermore, it must be pointed out that the features or the steps that have been described with reference to one of the above exemplary embodiments may also be used in combination with other features or steps of other exemplary embodiments that have been described above. The reference numerals in the claims are not to be regarded in a restrictive sense.