WO2004102139A1

WO2004102139A1 - Infrared sensor with improved radiant yield

Info

Publication number: WO2004102139A1
Application number: PCT/DE2004/000971
Authority: WO
Inventors: Marion Simon; Wilhelm Leneke; Mischa Schulze; Karlheinz Storck; Jörg SCHIEFERDECKER; Stephan Karl
Original assignee: Heimann Sensor Gmbh
Priority date: 2003-05-13
Filing date: 2004-05-10
Publication date: 2004-11-25
Also published as: JP2007503586A; JP4685019B2; DE10321640B4; DE10321640A1

Abstract

The invention relates to a radiation sensor, for example for the non-contact temperature measurement or infrared gas spectroscopy, comprising a detector chip (2), with a support body (17) which has a recess (18) and an absorber element (19) which absorbs radiation and is thus heated, whereby the absorber element (19) is arranged over the recess (18), such that at least a section of the absorber element (19) is not in contact with the support body (17) and the support body (17) is mounted on a support substrate (1). According to the invention, a radiation sensor, comprising a detector, preferably a detector chip, with a support body which has a recess and an absorber element which absorbs radiation and is thus heated, whereby the absorber element is arranged over the recess, such that at least a section of the absorber element is not in contact with the support body and whereby at least the base or the floor surface of the recess in the support body at least partly comprises a material which reflects the radiation for detection, can be provided, whereby at least the base or the floor surface of the recess (18) at least partly comprises a material (7) which reflects the radiation for detection and under which the support substrate (1) is located.

Description

Infrared sensor with improved radiation yield

The present invention relates to a radiation sensor, for example for non-contact temperature measurement or infrared gas spectroscopy.

A large number of techniques for measuring temperatures are known which take advantage of a large number of effects in measurement, in which physical or chemical substance properties show a temperature dependence. Almost all processes are based on heat transfer to the sensor or sensor. In the case of so-called touch thermometers, this heat transport takes place by conduction and convection, in the case of non-contact thermometers (radiation thermometers) by heat radiation.

Even though the contact thermometers generally work very reliably and are usually simple and inexpensive to manufacture, their area of use is nevertheless restricted. For example, due to the material properties of the sensor, there is an upper temperature limit above which the sensor can no longer be operated. In addition, the contact thermometers are unsuitable for measuring the temperature of quickly moving or difficult to access objects.

For this reason, non-contact measurement methods based on thermal radiation are used in many areas of application. Every surface with a temperature T> 0 K emits electromagnetic radiation, the so-called temperature radiation. If radiation emanating from one surface strikes another surface, it is partially reflected, absorbed or transmitted. For this reason, absorption elements are used in radiation thermometers, which ideally have an absorption capacity that is independent of the wavelength and which heat up when the radiation (infrared radiation) strikes it, so that the heating of the adsorption element can serve as evidence of the emitted infrared radiation.

Radiation thermometers or so-called radiation pyrometers generally have optics, a detector with an absorption element and a housing which mechanically and thermally protects the optics and detector. In these sensors, the infrared radiation emitted by the measurement object is imaged on an absorbing surface by suitable windows or optical components, this surface experiencing a temperature increase due to the absorption. It goes without saying that this method can in principle also be used to measure temperatures which are below the temperature of the detector. In this case, however, the temperature drop is greater than the temperature due to the self-radiation of the absorption element. increase due to the absorption of the detected radiation, so that a total decrease in temperature of the absorber element occurs.

The temperature increase or temperature difference can then be measured in different ways. With the thermistor Bolornetem one measures the change of the electrical resistance, with the thermocouples the voltage at the contact point of two metal wires, with the pyroelectric detectors a charge shift which arises with a temperature change of special insulator crystals.

The thermocouples use the so-called Seebeck effect to detect the elevated temperature. The connection point of a thermocouple made of two different thermoelectric materials is brought into contact with the absorber area, while the reference contact is generally at the temperature of the sensor housing. Since the sensor output voltages of such thermocouples are very low, many such thermocouples are often connected in series. Such a series connection of a large number of thermocouples is also referred to as a thermopile or thermopile.

In recent years, great efforts have been made in many technological fields to miniaturize electrical and electronic components, whereby they should be inexpensive to manufacture as far as possible using known standardized processes. The increasing miniaturization of the radiation sensors leads to a smaller absorber area and thus to a lower temperature increase, which in turn leads to a lower signal and thus to a reduced resolution.

It is therefore particularly important for the miniaturized radiation sensors to achieve the highest possible absorption of the infrared radiation in the absorber system and to isolate the absorber surface thermally as well as possible from the surroundings in order to generate the greatest possible temperature increase and thus a large sensor output signal.

Radiation sensors are therefore already known with a detector designed as a chip, which consists of a support body with a recess and an absorber element, which absorbs radiation and is thereby heated, the absorber element being arranged above the recess, so that at least a section of the absorber element supports the support body not touched. For this purpose, a membrane with very low thermal conductivity, which essentially conceals the recess, is often arranged and the absorber element is positioned on the membrane. This ensures that the absorber element is largely thermally decoupled from the support body. The known infrared sensors are mainly manufactured using silicon micromechanics and mounted in standard housings in electrical engineering. For example, EP 0 599 364 describes an infrared radiation detector in which the various chips, for example a thermopile array with an ASIC (application-specific circuit) for signal preprocessing and a memory IC on the base plate of a TO (transistor Outline) housing base are mounted. However, the known TO housings have glazed pins for contacting and can therefore only be mounted on printed circuit boards in push-through contacting. Modern SMD (Surface Mounted Device) mounting technology is not possible with this.

The infrared detector described in US Pat. No. 5,693,942 is also arranged in a TO housing, which must be mounted on printed circuit boards by means of push-through contacting. The embodiment shown here has an additional recess in the housing base plate below the sensitive surface of the sensor chip. The cutout, which can also be designed to be reflective, serves to increase the distance between the absorber element and the carrier substrate in order to increase the sensitivity of the infrared sensor.

The thermopile sensors available on the market each use a metal pin housing with a metal cap. An optical element, for example an infrared filter, is provided in the cap. Part of the infrared radiation falls through the infrared filter in the cap onto the area next to the sensor element, which usually consists of a metallic and thus also reflective TO bottom plate. These radiation components are reflected back to the absorber by multiple reflection on the housing wall or the metallic cap. These multiple reflections lead to an enlargement of the measuring spot, which is undesirable in those measuring arrangements which aim at the radiation or temperature measurement of a spatially limited measurement object. This is the normal case for non-contact temperature measurement. The known solutions with a metal pin housing can only be contacted by means of a push-through contact on the next wiring level. This can be done, for example, by soft soldering. With the known solutions, SMD assembly techniques cannot be implemented.

Compared to this prior art, it is an object of the invention to provide a radiation sensor which is fundamentally suitable for SMD assembly technology, which has a high sensitivity to infrared radiation and is nevertheless inexpensive to manufacture.

According to the invention, this object is achieved by a radiation sensor which has a detector, preferably a detector chip, consisting of a support body with a recess and an absorber element which absorbs radiation and is thereby heated, the absorber element being arranged above the recess, so that at least a section of the absorber element does not touch the support body and at least the base or the bottom surface the recess in the support body consists at least partially of a material which reflects the radiation to be detected.

This material, which is preferably selected in such a way that it has practically no self-absorption and almost no transmission, reflects the radiation component that has passed through the absorber element back to the latter, in order to ensure that the reflected radiation component transmitted by the absorber element also increases the temperature of the Absorber element contributes. Surprisingly, several experiments have shown that it is not necessary to provide an additional cutout in the base plate or the carrier substrate. Instead, the reflective layer or the reflective material can be arranged directly on or on the base or the bottom surface of the recess. Advantageously, the recess in the support body is continuous, so that the absorber element is arranged directly above the material arranged under the support body.

In a particularly preferred embodiment, at least the base or the bottom surface of the recess consists at least partially of a metallic material, preferably of gold. The layer reflecting the radiation to be detected is advantageously designed as a layer and has a thickness of less than 2 μm.

In a particularly expedient embodiment, the radiation sensor has a housing which consists of a carrier substrate and a cap with an opening which is designed such that the radiation to be detected can pass through the opening, the detector chip being arranged in the housing in this way, that the radiation passing through the opening at least partially strikes the absorber element.

This allows the radiation sensor to be easily implemented.

In a particularly preferred embodiment, the carrier substrate consists of a base material that is not electrically conductive. This feature in particular makes it possible to design the radiation sensor as an SMD (Surface Mounted Device).

In order to enable a temperature distribution in the carrier substrate that is as uniform as possible, in a further particularly preferred embodiment the latter has a metallic layer which extends over or in the carrier substrate, at least up to the section on which the cap comes into contact with the carrier substrate and wherein the metallic layer covers most of the carrier substrate surface arranged within the cap. This measure additionally enables a good thermal coupling of the cap to the carrier substrate. It has been shown that the carrier substrate advantageously consists of a ceramic base material, preferably of oxide ceramic or AIN ceramic. The metal layer can then advantageously be formed by printed conductor and insulation tracks, preferably made of silver-palladium or silver-platinum.

Alternatively, the carrier substrate can also consist of an organic material, for example epoxy, Pertinax or polyimide, preferably FR2, FR3 or FR4. In this case, the metal layer expediently consists of a metal layer laminated or additively applied with a thickness of preferably between approximately 20 and 150 μm, the metal layer preferably consisting of copper.

Furthermore, it has been shown that it is particularly expedient if the carrier substrate has a radiation-absorbing layer as the uppermost layer around the support body, the radiation-absorbing layer being, for example, an organic lacquer, a photoresist or a solder resist. By this measure, radiation components that do not fall on the absorber element are not reflected, so that the measurement spot is not enlarged. Alternatively, the metallic layer can also be roughened to increase the absorption.

In order to enable automatic mounting of the radiation sensor, it is provided in a further particularly preferred embodiment that the carrier substrate has a marking which is arranged outside the cap, the marking being designed such that automatic positioning systems use the marking to provide orientation and / or can position the sensor.

It has been shown that the marking is advantageously arranged in the metallic layer. In other words, the radiation-absorbing layer, if it is present, does not extend over the entire carrier substrate, but rather leaves the metallic layer outside the cap at least partially uncovered, so that the marking can be arranged in the metallic layer.

In order to enable SMD mounting of the radiation sensor according to the invention, it is provided in a further advantageous embodiment that the connection contacts for the transmission of the detector signal from the housing are provided on the underside of the carrier substrate, ie on the side facing away from the cap. The detector element is then advantageously connected to the connection contacts via metallized through-holes, so-called VIAs, through the carrier substrate, the connection contacts then preferably being designed as solder bumps. This makes it possible to automatically equip the radiation sensor with known SMD techniques. Furthermore, it has been shown that the metallic layer and / or the radiation-absorbing layer, if these are present, is advantageously interrupted in the immediate vicinity of the through holes. This creates a defined contact between the detector chip and the connection contact.

The through holes are advantageously closed gas-tight and preferably with a

Sealant filled.

Further advantages, features and possible uses of the present invention will become clear from the following description of preferred embodiments and the associated figures. Show it:

1 shows a radiation sensor according to the invention in a top view from above with the cap removed, FIG. 2 shows a sectional view through the radiation sensor from FIG. 1,

FIG. 3 shows an alternative embodiment of the radiation sensor according to the invention, in which the carrier substrate is designed as a direct plug connector,

Figure 4 shows a further alternative embodiment of the radiation sensor according to the invention, in which a plug connector is arranged on the top of the carrier substrate, and Figure 5 shows a further alternative embodiment of the radiation sensor according to the invention, in which the carrier substrate is designed as a flex or rigid-flex circuit board, and that End of the circuit board is designed as a direct connector with direct connector contacts.

The basic structure of the temperature sensor according to the invention is shown in FIGS. 1 and 2. A detector chip 2, which here has a thermopile element, a silicon circuit 3 and a temperature reference 4 for measuring the ambient temperature are fastened with good thermal contact to a carrier substrate 1, which is either made of an organic circuit board material or a ceramic, such as oxide ceramic or AIN -Ceramic, exists. It goes without saying that the temperature reference 4 can optionally also be integrated in the silicon circuit 3, which can be designed, for example, as an application-specific integrated circuit with an amplifier and compensation circuit, as a so-called ASIC. This circuit represents the first stage for signal conditioning. In addition, it goes without saying that the detector chip also has several elements which, for. B. are arranged in the form of a line or matrix.

The individual components 2, 3 and 4 are preferably mounted on the carrier substrate 1 with the aid of a conductive adhesive, for example a silver-filled epoxy adhesive. Alternative is however, soldering the chip components with a tin-lead solder or with a lead-free solder is also possible.

The detector chip 2, the temperature reference element 4 and the silicon circuit 3 are electrically conductively connected to the connection contact surfaces 6 of the carrier substrate 1 by means of thin bond wires 5.

The carrier substrate 1 has a metallization 11. The detector chip 2 is mounted on a support body 17 which has a recess 18. The absorber element 19 of the detector chip 2 is arranged above the recess 18 of the support body 17 such that the absorber element 19 has no contact with the support body 17, at least in some areas. Below the absorber element 19, the metallization 11 is equipped with a very well reflective coating 7, which can be designed, for example, as a thin, galvanically or chemically applied gold layer. Such a coating can be implemented inexpensively, since it is one of the standard processes in the production of printed circuit boards.

If the carrier substrate 1 consists of an organic carrier substrate material, such as FR2, FR3, FR4 or polyimide, a laminated or additively applied metal layer 11, preferably between about 20 and 150 μm thick, is placed under the detector chip 2, under the temperature reference 4 or arranged under the silicon circuit 3 up to the cap contact surface. For example, the copper layer usually present in printed circuit boards can be used as the metal layer.

If a ceramic substrate is used as the carrier substrate 1, then the metal layer 11 advantageously consists of a printed conductor track, for example of silver-palladium or silver-platinum.

The metal layer 11 is coated with an absorbent layer 8 around the chip elements 2, 3 and 4 as well as around the contact surfaces 6 and the circular segment surface for the cap assembly. The absorbent layer 8 can, for example, consist of a solder resist, preferably in the case of organic substrate material or a printed insulation layer, preferably in the case of ceramic substrates. This ensures that undesired radiation components that fall next to the absorber element 19 on the substrate surface are not reflected, but are absorbed by the absorption layer 8. This measure counteracts an increase in the size of the measuring spot.

As can be seen in FIG. 2, a metallic cap 9, which consists for example of steel, nickel, measurement or copper, is mounted on the carrier substrate 1 in a gas-tight manner. The metallic cap 9 has an opening 21 with an infrared filter 10 is covered, which is preferably optically coated. The filter 10 can be installed in the cap 9, for example by gluing, soft soldering or diffusion welding. The connection 12 between the cap 9 on the one hand and the carrier substrate 1 on the other hand can advantageously be made by soft soldering or by gluing. The connection medium 12 between the cap 9 and the carrier substrate 1 is preferably selected depending on the application in such a way that either an electrical contact and thus a good thermal connection between the cap 9 and the metal layer 11 or an electrically insulated assembly is realized. In the first case metallic soft solder is advantageously used and in the second case dielectric filled epoxy resin adhesive is used.

The connection contact surfaces 6, as can be clearly seen in FIG. 2, are connected through lead-through holes 13, which are also referred to as vias, in the carrier substrate 1 to the connection contacts 14, which are designed here as solder bumps. The through holes 13 are metallized on the walls and are sealed gas-tight from the bottom, for example with the aid of a drop of adhesive 15 or a solder seal with a solder ball, after completion of the assembly. This closure ensures that the sensor and thus the detector element 2 is protected against environmental influences, such as moisture, aggressive gases, etc.

In a particularly preferred embodiment, the closure takes place under a defined gas atmosphere, for example in the case of a dry nitrogen atmosphere or noble gas atmosphere, in order to ensure a defined gas and moisture ratio in the interior.

The solder balls 14 arranged on the underside of the carrier substrate 1 make it easy to make contact with the sensor element with the next wiring level or with a plug connector or with a flexible printed circuit board which acts as intermediate wiring.

For this purpose, the metallizations of the through holes 13 are guided to the solder bumps 14 printed on.

As a result, a surface mount device (SMD) has been realized. This is also known as a ball grid array (BGA). When using circuit board material, for example FR4, FR3, FR2 or polyimide as the carrier substrate, such a component is also referred to as a plastic ball grid array (PBGA).

The most permanent contact of the sensor element with the next wiring level, which in most applications consists of a printed circuit board, can be achieved by automatically re-melting the solder bump, ie by re-melting the printed circuit board with the BGA the so-called reflow soldering. Of course, ball grid array bases could also be used for contacting for the sensor test or even for final assembly.

The asymmetrical marking 16, which is produced, for example, using the metallization 11, can be clearly seen in FIG. This asymmetrical marking 16 enables automatic detection and positioning of the sensor by means of commercially available placement and test machines. In principle, the marking can be on the top, i.e. on the cap side of the carrier substrate and also on the underside on the carrier substrate 1, the arrangement of the marking on the top of the carrier substrate 1 being particularly preferred.

Overall, the sensor element according to the invention fulfills all the requirements that are placed on an SMD component.

In particular, if a standardized printed circuit board is selected as the carrier substrate 1, for example, further external components can also be applied to the front or the back of the carrier substrate 1. This can be particularly advantageous if the additional components have a high electrical power loss, which can lead to thermal influencing of the infrared sensor chip.

Alternatively, the carrier substrate 1 designed as a printed circuit board can also be designed in such a way that other contacts to the next wiring level are possible. These can be the following embodiments:

- The carrier substrate 1 can be equipped as a printed circuit board with contacts 23 for direct plug connectors 22 (see FIG. 3), - the carrier substrate 1 can be equipped as a printed circuit board with a plug connector 24, which can be located on the upper or lower side of the carrier substrate (see FIG 4)

- The carrier substrate 1 can be designed as a printed circuit board, which is designed as a flex or rigid-flex printed circuit board and the end of the printed circuit board is designed as a direct connector 22 with direct connector contacts 23 (see FIG. 5). LIST OF REFERENCES

1 carrier substrate 2 detector chip 3 silicon circuit

4 temperature reference

5 bond wires

6 connection contact surface

7 reflective material

8 radiation absorbing layer 9 cap 10 filter

11 metallic line / layer 12 connection between cap and carrier substrate 13 through holes 14 connecting contacts / solder balls 15 sealant

16 marking 17 support body 18 recess 19 absorber element

20 cap contact surface 21 cap opening 22 direct plug connector

23 Direct connector contact

24 connectors

25 connector contact pin

Claims

Patent claims

1. radiation sensor, e.g. B. for non-contact temperature measurement or infrared gas spectroscopy, which has a detector chip (2) consisting of a support body (17) with a recess (18) and an absorber element (19) which absorbs radiation and thereby heats up, wherein the absorber element (19) is arranged above the recess (18) so that at least a portion of the absorber element (19) does not touch the support body (17) and the support body is mounted on a carrier substrate (1), characterized in that at least the The base or the bottom surface of the recess (18) consists at least partially of a material (7) which reflects the radiation to be detected and under which the carrier substrate (1) is located.

2. Radiation sensor according to claim 1, characterized in that at least the base or the bottom surface of the recess (18) at least partially consists of a metallic material (7), preferably of gold, the material preferably being formed as a layer and preferably a thickness less than 1 μm.

3. Radiation sensor according to claim 1 or 2, characterized in that a housing (1,

9) consisting of a carrier substrate (1) and a cap (9) with an opening (21), which is designed such that the radiation to be detected can pass through the opening (21), the detector (2) is arranged in the housing (1, 9) in such a way that the radiation passing through the opening (21) at least partially strikes the absorber element (19).

4. Radiation sensor according to claim 3, characterized in that the carrier substrate (1) consists of a base material that is not electrically conductive.

5. Radiation sensor according to claim 3 or 4, characterized in that the carrier substrate (1) has a metallic line or layer (11) which extends over the carrier substrate (1) at least up to the section (17) on which the Cap (9) with the carrier substrate (1) extends extends and covers most of the carrier substrate surface arranged within the cap (9).

6. Radiation sensor according to claim 4 or 5, characterized in that the carrier substrate (1) consists of a ceramic base material, preferably of oxide ceramic or AIN ceramic.

7. Radiation sensor according to claim 6 as far as dependent on claim 5, characterized in that the metal line or metal layer (11) is formed by printed conductive and insulating tracks, preferably made of silver-palladium or silver-platinum.

8. Radiation sensor according to claim 4 or 5, characterized in that the carrier substrate (1) consists of an organic material, preferably epoxy, Pertinax or polyimide, particularly preferably FR2, FR3 or FR4.

9. Radiation sensor according to claim 8 as far as dependent on claim 7, characterized in that the metal layer (11) is a laminated or additively applied metal layer with a thickness of preferably between about 20 and 150 microns, wherein the metal layer (11) is preferably made of Copper exists.

10. Radiation sensor according to one of claims 3 to 9, characterized in that the carrier substrate (1) as the uppermost layer around the support body (17) has a radiation-absorbing layer (8), the radiation-absorbing layer (8) being an organic lacquer , a photoresist or a solder mask.

11. Radiation sensor according to one of claims 3 to 10, characterized in that the carrier substrate (1) has at least one marking (16) which is arranged outside the cap (9), the marking (16) being designed such that automatic Positioning systems can perform an orientation and / or positioning of the sensor on the basis of the marking (16).

12. Radiation sensor according to claim 11, characterized in that the marking (16) is arranged in the metallic layer (11).

13. Radiation sensor according to one of claims 1 to 12, characterized in that a temperature reference (4) is provided which is separate from the detector (2).

14. Radiation sensor according to one of claims 1 to 13, characterized in that a circuit (8), preferably a silicon circuit is provided for processing the detector signal.

15. Radiation sensor according to one of claims 3 to 14, characterized in that connection contacts (14) for the transmission of the detector signal from the housing (2, 9) on the underside of the carrier substrate (1) are provided.

16. Radiation sensor according to claim 15, characterized in that the detector element is connected via metallized through holes (13) through the carrier substrate (1) to the connection contacts (14), the connection contacts (14) preferably being designed as solder bumps.

17. Radiation sensor according to claim 15 or 16, insofar as related to claim 5, characterized in that the metallic layer (11) is interrupted in the immediate vicinity of the through holes (13).

18. Radiation sensor according to one of claims 15 to 17, insofar as referred to claim 10, characterized in that the radiation-absorbing layer (8) is interrupted in the immediate vicinity of the through holes (13).

19. Radiation sensor according to one of claims 15 to 18, characterized in that the through holes (13) are closed gas-tight and are preferably filled with a sealant (15).

20. Radiation sensor according to one of claims 1 to 19, characterized in that the carrier substrate (1) is designed as a direct connector (22).

21. Radiation sensor according to one of claims 1 to 19, characterized in that on the top or bottom of the carrier substrate (1), a connector (24) preferably through

Soldering or gluing is attached.

2. Radiation sensor according to one of claims 1 to 19, characterized in that the

Carrier substrate (1) is designed as a flexible printed circuit board or as a rigid-flex printed circuit board and this is formed at one end as a direct connector structure (22).