DE10321640B4 - Infrared sensor with improved radiation efficiency - Google Patents

Abstract

Radiation sensor, z. B. for non-contact temperature measurement or infrared gas spectroscopy, a detector chip (2) consisting of a support body (17) having a recess (18) and an absorber element (19) which absorbs radiation and thereby heated, 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), wherein at least the base or the bottom surface 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, wherein a housing (1, 9) consisting of a carrier substrate (1) and a cap (9) having an opening (21) which is formed such that the radiation to be detected can pass through the opening (21) is provided, wherein the detector (2) in such a manner in the housing (1, 9) is ordered that the through the opening (21) passing radiation at least partially on the absorber element (19) and wherein the carrier substrate (1) consists of a base material that is not electrically conductive, characterized in that the carrier substrate (1) a metallic line or layer (11) extending over the carrier substrate (1) at least to the portion (17) on which the cap (9) contacts the carrier substrate (1), and wherein the carrier substrate (1 ) consists of a ceramic base material, or an organic material and the metal line or metal layer (11) by printed conductive and insulating tracks, preferably of silver-palladium or silver-platinum is formed, wherein terminal contacts (14) for the transmission of the detector signal from the Housing (2, 9) on the underside of the carrier substrate (1) are provided.

Description

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

There are a variety of techniques for measuring temperatures known that exploit a large number of effects metrologically, in which physical or chemical properties show a temperature dependence. Almost all methods rely on a heat transfer to the sensor or sensor. In so-called contact thermometers, this heat transfer occurs by heat conduction and convection, in the non-contact thermometers (radiation thermometers) by thermal radiation.

Although the touch thermometers generally work very reliable and are usually easy and inexpensive to manufacture, their application is still limited. 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 to measure the temperature of fast moving or hard to reach objects.

Therefore, non-contact measuring methods based on the temperature radiation are used in many fields of application. Each surface with a temperature T> 0 K emits electromagnetic radiation, the so-called temperature radiation. If a radiation emanating from one surface strikes another surface, it is partially reflected, absorbed or transmitted. Therefore, in radiation thermometers absorption elements are used which ideally have a non-wavelength-independent absorption capacity and which heat when the radiation (infrared radiation), 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 an optical system, a detector with an absorption element and a housing which protects the optics and detector mechanically and thermally. In these sensors, the infrared radiation emitted by the test object is imaged on an absorbing surface by suitable windows or optical components, this surface undergoing an increase in temperature due to the absorption. It will be understood that, in principle, temperatures lower than the temperature can also be measured with this method of the detector. In this case, however, the temperature reduction, due to the self-emission of the absorption element is greater than the temperature increase due to the absorption of the detected radiation, so that overall a temperature decrease of the absorber element occurs.

The temperature increase or temperature difference can then be measured in different ways. In the case of the thermistor bolometers, the change in the electrical resistance, in the case of the thermocouples, the voltage at the point of contact between two metal wires, and in the pyroelectric detectors, a charge shift, which results from a temperature change of special isolator crystals.

The thermocouples use the so-called Seebeck effect to detect the elevated temperature. In this case, the connection point of a thermocouple made of two different thermoeleketrischen materials is brought into contact with the absorber region, 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 plurality 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, where possible to be produced inexpensively with known standardizable processes. The increasing miniaturization leads to a smaller absorber surface in the radiation sensors and thus to a lower temperature increase, which in turn leads to a lower signal and thus to a reduced resolution.

Therefore, it is particularly important in 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 environment in order to produce the largest possible increase in temperature and thus a large sensor output signal.

Radiation sensors are therefore already known having a detector formed as a chip, which consists of a support body with a recess and an absorber element which absorbs radiation and thereby heated, wherein the absorber element is disposed above the recess, so that at least one section of the absorber element, the support body not touched. For this purpose is often a membrane with very low thermal conductivity, the recess substantially concealing, arranged and the absorber element positioned on the membrane. This ensures that the absorber element is largely thermally decoupled from the support body.

The known infrared sensors are mainly produced by means of silicon micromechanics and mounted in standard housings of electrical engineering. For example, in the EP 0 699 364 An infrared radiation detector is described, in which the various chips, for example a thermopile array with an ASIC (application-specific circuit) for signal preprocessing and a memory IC are mounted on the bottom plate of a TO (transistor outline) housing floor. The known TO housing, however, have cast pins for contacting and can therefore be mounted only in Durchsteckkontaktierung on printed circuit boards. A modern SMD (Surface Mounted Device) assembly technology is not possible.

Also in the US 5,693,942 described infrared detector is arranged in a TO-housing, which must be mounted by means of Durchsteckkontaktierung on printed circuit boards. The embodiment shown here occupies an additional recess below the sensitive surface of the sensor chip in the housing bottom plate. The recess, which may also be designed to be reflective, serves to increase the distance between absorber element and 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 metallic cap. In this case, 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 on 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 via multiple reflection on the housing wall or the metallic cap. These multiple reflections lead to a Meßfleckvergrößerung, which is undesirable in those measuring arrangements, which have the radiation or temperature measurement of a spatially limited object to be measured. This is the normal case with non-contact temperature measurement. The known solutions with metal pin housing can only be contacted by means of a through-hole contact on the next wiring level. This can be done for example by soldering. In the known solutions, SMD mounting techniques can not be implemented.

The DE 42 44 607 , the US 5,693,942 , the WO 95/18961 and the EP 0 599 364 also show infrared sensors.

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

According to the invention, this object is achieved by a radiation sensor having all the features of claim 1.

This material, which is preferably selected so that it has virtually no inherent absorption and almost no transmission, reflects the portion of the radiation that has passed through the absorber element back to it, to ensure that the reflected radiation transmitted through the absorber element is also used to increase the temperature of the Absorber element contributes. In several experiments, it has surprisingly been found that it is not necessary to provide an additional recess in the bottom plate or the carrier substrate. The reflective layer or the reflective material may instead be arranged directly on or at the base or the bottom surface of the recess. Advantageously, the recess in the support body is designed to be continuous, so that the absorber element is arranged directly above the material arranged under the support body.

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, wherein the detector chip is arranged in the housing, that the radiation passing through the opening at least partially meets the absorber element.

This allows a simple realization of the radiation sensor.

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

In order to allow the most uniform possible temperature distribution in the carrier substrate, this has in a further particularly preferred embodiment, a metallic layer which extends over or in the carrier substrate, at least up to the portion on which the cap with the Carrier substrate connects, and wherein the metallic layer covers most of the carrier substrate surface disposed within the cap. By this measure, a good thermal coupling of the cap with the carrier substrate is also possible.

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 be advantageously formed by printed conductive and insulating tracks, preferably of silver-palladium or silver-platinum.

Alternatively, the carrier substrate can also consist of an organic material, for example of epoxide, pertinax or polyimide, preferably of FR2, FR3 or FR4. In this case, the metal layer is expediently composed of a laminated or additively applied metal layer having a thickness of preferably between about 20 and 150 μm, wherein the metal layer is preferably made of copper.

Furthermore, it has been shown that it is particularly expedient if the carrier substrate has a radiation-absorbing layer as the topmost layer around the carrier body, wherein the radiation-absorbing layer can be, for example, an organic lacquer, a photoresist or a solder stopper. By this measure, radiation components that do not fall on the Absorberrelement not reflected, so that the measurement spot is not increased. Alternatively, the metallic layer may also be roughened to increase 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, wherein the marking is designed such that automatic positioning systems based on the marking an orientation and / or Positioning of the sensor can perform.

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

In order to enable an SMD mounting of the radiation sensor according to the invention, the connection contacts for the transmission of the detector signal from the housing at the bottom of the carrier substrate, d. H. on the side facing away from the cap, provided. The connection of the detector element with the terminal contacts is then advantageously via metallized through holes, so-called VIAs, through the carrier substrate, wherein the terminal contacts are then preferably formed as a solder bump. Thus, an automatic assembly of the radiation sensor with known SMD techniques is possible.

Furthermore, it has been shown that advantageously the metallic layer and / or the radiation-absorbing layer, if present, is interrupted in the immediate vicinity of the through-holes. This establishes a defined contact between the detector chip and the terminal contact.

Advantageously, the through holes are sealed gas-tight and preferably filled with a sealant.

Further advantages, features and possible applications of the present invention will become apparent from the following description of preferred embodiments and the accompanying figures. Show it:

1 a radiation sensor according to the invention in a plan view from above with the cap removed,

2 a sectional view through the radiation sensor of 1 .

3 an alternative embodiment of the inventive radiation sensor, in which the carrier substrate is designed as a direct connector,

4 a further alternative embodiment of the radiation sensor according to the invention, in which a connector is arranged on the upper side of the carrier substrate, and

5 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 the 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 in the 1 and 2 shown. A detector chip 2 having a thermopile element here, a silicon circuit 3 and a temperature reference 4 for measuring the ambient temperature are with good thermal contact on a carrier substrate 1 attached, either from an organic circuit board material or a ceramic, such as oxide ceramic or AIN ceramic. It is understood that the temperature reference 4 optionally also in the silicon circuit 3 , which may be formed, for example, as an application-specific integrated circuit with amplifier and compensation circuit, as a so-called ASIC, integrated. This sound circuit represents the first stage for signal conditioning. In addition, it is understood that the detector chip also several elements, the z. B. in the form of a cell or matrix may contain.

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

The detector chip 2 , the temperature reference element 4 and the silicon circuit 3 are through thin bonding wires 5 with the terminal contact surfaces 6 of the carrier substrate 1 electrically connected.

The carrier substrate 1 has a metallization 11 on. The detector chip 2 is on a support body 17 mounted, a recess 18 having. The absorber element 19 of the detector chip 2 is so over the recess 18 of the supporting body 17 arranged that the absorber element 19 at least in some areas no contact with the support body 17 Has. Below the absorber element 19 is the metallization 11 with a very good reflective coating 7 equipped, for example, can be designed as a thin, galvanically or chemically applied gold layer. Such a coating is inexpensive to implement because it is one of the standard processes in the manufacture of printed circuit boards. If the carrier substrate 1 of an organic carrier substrate material, such as FR2, FR3, FR4 or polyimide, becomes a laminated or additively deposited metal layer 11 preferably between about 20 and 150 microns thick under the detector chip 2 , below the temperature reference 4 or under the silicon circuit 3 arranged as far as the cap support surface The metal layer which can be used, for example, is the copper layer which is usually present in printed circuit boards.

Is used as a carrier substrate 1 uses a ceramic substrate, then there is the metal layer 11 with advantage of a printed conductor, for example of silver-palladium or silver-platinum.

The metal layer 11 is about the chip elements 2 . 3 and 4 as well as the contact surfaces 6 and the circular segment area for cap mounting with an absorbent layer 8th overdrawn. The absorbing layer 8th may for example consist of a Lötstoplack, preferably in organic substrate material or a printed insulating layer, preferably in ceramic substrates. This ensures that unwanted radiation components, in addition to the absorber element 19 fall on the substrate surface, are not reflected, but through the absorption layer 8th be absorbed. By this measure, an increase in the Meßfleckgröße is counteracted.

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

The connection pads 6 are, as in 2 can be clearly seen through implementation holes 13 , which are also referred to as vias, in the carrier substrate 1 with the connection contacts 14 , which are designed here as a soldering hole, connect. The passage holes 13 are metallised on the walls and become, for example, with the help of a drop of glue 15 or a Lotverschlusses with solder ball sealed from the bottom after completion of installation gas-tight. This closure ensures that the sensor and thus the detector element 2 against environmental influences, such as moisture, aggressive gases, etc. is protected.

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

By on the underside of the carrier substrate 1 arranged solder balls 14 is easy contact of the sensor element with the next wiring level or with a connector or with a flexible circuit board, which acts as an intermediate wiring possible.

For this purpose, the metallizations of the Durchführngslöcher 13 to the printed soldering holes 14 guided.

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

The most permanent contacting of the sensor element with the next wiring level, which consists in most cases of a printed circuit board can after the automatic assembly of the circuit board with the BGA by the remelting of the solder bumps, d. H. done by the so-called reflow soldering. Of course, Ball Grid Array sockets could be used for contacting for the sensor test or even for final assembly.

Clearly visible in 1 the asymmetric marker 16 for example, using metallization 11 will be produced. By this asymmetric marking 16 is an automatic detection and positioning of the sensor by standard assembly and testing machines possible. In principle, the marking may be on the upper side, ie on the cap side of the carrier substrate, as well as on the underside on the carrier substrate 1 be executed, wherein the arrangement of the marking on the upper side of the carrier substrate 1 On the whole, the sensor element according to the invention fulfills all requirements which are admits to an SMD component.

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

• – Das Trägersubstrat 1 kann als Leiterplatte mit Kontakten 23 für Direktsteckverbinder 22 ausgestattet sein (siehe 3),
• – das Trägersubstrat 1 kann als Leiterplatte mit einem Steckverbinder 24, der sich auf der Trägersubstratober- oder -unterseite befinden kann, ausgestattet sein (siehe 4),
• – das Trägersubstrat 1 kann als Leiterplatte, die als Flex- oder Starr-Flex-Leiterplatte ausgeführt ist und wobei das Ende der Leiterplatte als Direktsteckverbinder 22 mit Direktsteckverbinderkontakten 23 ausgeführt ist, ausgebildet sein (siehe 5).

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

• - The carrier substrate 1 can be used as a printed circuit board with contacts 23 for direct connectors 22 be equipped (see 3 )
• - The carrier substrate 1 can be used as a printed circuit board with a connector 24 , which may be located on the carrier substrate top or bottom, be equipped (see 4 )
• - The carrier substrate 1 can be used as a printed circuit board, which is designed as a flex or rigid-flex circuit board and wherein the end of the circuit board as a direct connector 22 with direct connector contacts 23 is executed, be formed (see 5 ).

LIST OF REFERENCE NUMBERS

1

carrier substrate

2

detector chip

3

Silicon circuit

4

temperature reference

5

Bond wires

6

Terminal contact surface

7

reflective material

8th

radiation-absorbing layer

9

cap

10

filter

11

metallic pipe / layer

12

Connection between cap and carrier substrate

13

Through holes

14

Connecting contacts / solder balls

15

sealant

16

mark

17

supporting body

18

recess

19

absorber element

20

Cap bearing surface

21

cap opening

22

Backplane

23

Backplane Contact

24

Connectors

25

Connector pin

Claims (16)

Radiation sensor, z. B. for non-contact temperature measurement or infrared gas spectroscopy, a detector chip ( 2 ) consisting of a supporting body ( 17 ) with a recess ( 18 ) and an absorber element ( 19 ), which absorbs radiation and thereby heats up, wherein the absorber element ( 19 ) over the recess ( 18 ) is arranged so that at least a portion of the absorber element ( 19 ) the supporting body ( 17 ) and the supporting body on a carrier substrate ( 1 ), wherein at least the base or the bottom surface of the recess ( 18 ) at least partially made of a material ( 7 ), which reflects the radiation to be detected and under which the carrier substrate ( 1 ), wherein 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 through the opening ( 21 ) is provided, the detector ( 2 ) in the housing ( 1 . 9 ) is arranged, that through the opening ( 21 ) passing radiation at least partially on the absorber element ( 19 ) and wherein the carrier substrate ( 1 ) consists of a base material that is not electrically conductive, characterized in that the carrier substrate ( 1 ) 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 ), and wherein the carrier substrate ( 1 ) consists of a ceramic base material, or an organic material and the metal line or metal layer ( 11 ) is formed by printed conductive and insulating tracks, preferably of silver-palladium or silver-platinum, wherein terminal contacts ( 14 ) for the transmission of the detector signal from the housing ( 2 . 9 ) on the underside of the carrier substrate ( 1 ) are provided. Radiation sensor according to claim 1, characterized in that at least the base or the bottom surface of the recess ( 18 ) at least partially made of a metallic material ( 7 ), preferably made of gold, wherein the material is preferably formed as a layer and preferably has a thickness of less than 1 micron. Radiation sensor according to Claim 1 or 2, characterized in that the carrier substrate ( 1 ) of epoxy, pertinax or polyimide, and more preferably FR2, FR3 or FR4. Radiation sensor according to claim 1 or 2, characterized in that the carrier substrate consists of oxide ceramic or AIN ceramic. Radiation sensor according to one of Claims 1 to 4, characterized in that the carrier substrate ( 1 ) as the uppermost layer around the supporting body ( 17 ) a radiation-absorbing layer ( 8th ), wherein the radiation-absorbing layer ( 8th ) is an organic paint, a photoresist or a solder resist. Radiation sensor according to one of Claims 1 to 5, characterized in that the carrier substrate ( 1 ) at least one mark ( 16 ), which outside the cap ( 9 ), the marking ( 16 ) is designed so that automatic positioning systems based on the marking ( 16 ) can perform an orientation and / or positioning of the sensor. Radiation sensor according to Claim 6, characterized in that the marking ( 16 ) in the metallic layer ( 11 ) is arranged. Radiation sensor according to one of Claims 1 to 7, characterized in that a temperature reference ( 4 ) provided by the detector ( 2 ) is disconnected. Radiation sensor according to one of Claims 1 to 8, characterized in that a circuit ( 8th ), preferably a silicon circuit for processing the detector signal is provided. Radiation sensor according to Claim 9, characterized in that the detector element has metallized through holes ( 13 ) through the carrier substrate ( 1 ) with the connection contacts ( 14 ), the terminal contacts ( 14 ) are preferably formed as solder bumps. Radiation sensor according to Claim 9 or 10, as far as dependent on Claim 5, characterized in that the metallic layer ( 11 ) in the immediate vicinity of the through holes ( 13 ) is interrupted. Radiation sensor according to one of Claims 9 to 11, as far as dependent on Claim 10, characterized in that the radiation-absorbing layer ( 8th ) in the immediate vicinity of the through holes ( 13 ) is interrupted. Radiation sensor according to one of Claims 9 to 12, characterized in that the through-holes ( 13 ) are sealed gas-tight and preferably with a sealant ( 15 ) are filled. Radiation sensor according to one of Claims 1 to 13, characterized in that the carrier substrate ( 1 ) as a direct connector ( 22 ) is trained. Radiation sensor according to one of claims 1 to 13, characterized in that on the upper or lower side of the carrier substrate ( 1 ) a connector ( 24 ) is preferably fixed by soldering or gluing. Radiation sensor according to one of Claims 1 to 13, 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 at one end as a direct connector structure ( 22 ) is trained.

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