Abstract:
The present invention refers to a sensor unit ( 10, 10 ′) for an electronic module ( 1 ) which is small and lightweight comprising at least one exposed component ( 5, 5  a,  5   b ) containing a chemical element and/or a chemical compound at its surface which is adapted to undergo a color change observed in visible light due to presence of a corrosive, the exposed component preferably containing elementary copper. The invention further refers to a respective electronic module ( 1 ) and a procedure to calculate the level of corrosive exposure of such an electronic module ( 1 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the United States national phase under 35 U.S.C. §371 of PCT International Patent Application No. PCT/EP2014/059305, filed on May 7, 2014, which claims the benefit of United States Provisional Patent Application No. 61/830,639 filed Jun. 4, 2013, the disclosures of which are hereby incorporated by reference herein in their entireties. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention refers to a sensor unit for an electronic module, a respective electronic module as well as a procedure to calculate the level of corrosive exposure of a respective electronic module. 
       BACKGROUND OF THE INVENTION 
       [0003]    Performance and reliability of electronic modules like printed circuit boards (PCB) of high reliability products can be impaired by corrosion including sulfur (S) and chlorine (Cl) contamination. It is, therefore, necessary to determine the corrosive exposure level of a product while it is being stored, shipped, manufactured or used. 
         [0004]    Presently, it is known to use large sulfur analyzers that sense the level of sulfur in air or other gases, for example the total sulfur analyzer of the company EST analytical TS 3000 based on pulsed UV fluorescence. 
         [0005]    Further, at present the company Techno-Sciences Inc. sells a still large sulfur sensor for hydrogen fuel cell operations which is based on localized surface plasmon resonance capable of detecting parts per billion trace levels of sulfur compounds. The sensor features a nanoparticle decorated thin film technology coupled with a VIS-NIR light source and UV-VIS linear detector. The sensor is based on hybrid plasmon damping that means the damping of the hybrid plasmon mode of nobel metal nanoparticles due to molecular absorption at the nanoparticle surface is observed. Therefore, nanostructured silver is used which detects trace levels of sulfur compounds. This follows from strong interactions of sulfur with silver that distorts the local electric potential at a nanoparticle surface leading to increase electron scattering, and hence increased hybrid plasmon damping. 
         [0006]    Further, the company Plurafil offers a continuous corrosion transmitter that measures in real time the amount of corrosion forming on copper and silver surfaces and transmits this information to a control system. Therefore, the device provides two quartz crystal micro balance sensors, one plated with copper and the other one with silver, wherein each has a natural resonance frequency based on mass. The plating accumulates corrosion films when acid gases react with the base metal. This process results in an increase in sensor mass and a decrease in natural resonance frequency. By applying the proper conversion factors, the sensor correlates the determined mass to corrosion thickness expressed in Ångstroms. 
         [0007]    Considering the above, known possibilities to detect corrosives the problem arises to provide a small and lightweight sensor for corrosives like S and Cl which is feasible to observe the corrosive contamination during the whole lifetime of the electronic module. 
         [0008]    At least the above problem is solved by a sensor unit with the features of claim  1  and by an electronic module with the features of claim  13 . An inventive procedure to calculate the level of corrosive exposure of an electronic module is described in claim  14  solving above problem, too. 
         [0009]    The present invention is directed toward overcoming one or more of the above-mentioned problems. 
       SUMMARY OF THE INVENTION 
       [0010]    The inventive sensor unit for an electronic module in particular comprises at least one exposed component containing a chemical element and/or a chemical compound at its surface which is adapted to undergo a color change observed in visible light due to the presence of a corrosive, preferably containing elementary copper. 
         [0011]    In a preferred embodiment the sensor unit further comprises a light receiving element, for example a spectrophotometer or a camera, operable to receive the visible light reflected by the exposed component. 
         [0012]    In another embodiment the sensor unit comprises processing means operable to determine the color of the visible light reflected by the exposed component, preferably the RGB (Red-Green-Blue) color intensity of the reflected visible light. Therein the RGB color intensity is a well known parameter which is based on the RGB color model and one possibility to describe the color of the reflected visible light. The color spectrum of the light can also be established through use of prisms or diffraction gratings or the like. 
         [0013]    The main advantage of above described inventive sensor unit, in particular according to the above described preferred embodiments, consists therein that this sensor unit can be deployed with the product, i.e. the electronic module or PCB, in a reasonable fashion due to the small instrument size. That means that the sensor unit is so small and lightweight that it can be accommodated at the surface of the substrate of the electronic module (PCB) like any other electronic component. 
         [0014]    The sensor unit is based on the idea that some chemical elements and/or chemical compounds undergo a color change if they are exposed to a corrosive gas or substance and if they are illuminated by visible, preferably by white light. That means the corrosive which reacts with the chemical element and/or chemical compound or is absorbed by either one changes the color of the reflected light. 
         [0015]    Regarding the corrosives sulfur (S) and chlorine (Cl), elementary copper (Cu) changes its color from bright brown (Cu color) to blue as it is exposed to S and to blue-green as it is exposed to Cl and H 2 O. In case Cu is exposed to air containing S at the surface of the exposed Cu, the Cu reacts with S forming copper monosulfide (copper (I) sulfide, CuS) which occurs in nature as a dark indigo blue mineral covellite. The corrosion product of Cl with Cu is Cu(II)chloride (CuCl 2 ), in particular the dihydrate of copper chloride (CuCl 2 *2H 2 O). The color of CuCl 2 *2H 2 O is light blue-green. In order to undergo a color change due to a corrosive reaction at the surface of the exposed component, the exposed component provides a free and exposed surface containing the chemical element or the chemical compound for the reaction with the corrosive or for the adsorption of the corrosive. It is preferred that the exposed surface has a total surface area that can be imaged with a small (&lt;1 mm diameter) lens. In case the exposed component consists preferably of at least two elements or a plurality of elements, each has a surface area which is sized to allow sufficient sensitivity. With present technology the entire assembly is feasible in a size of &lt;1 mm 2 , wherein the elements preferably comprising different surface forms like circles or bars. The above mentioned minimum surface area of the exposed component or its elements allows a reliable detection of color change. 
         [0016]    Either by a spectrophotometer or by taking a picture of the exposed component with a camera and then by using an appropriate imaging software the color of the reflected light by the exposed component may be determined and from that the exposure level of the corrosive, for example of S or Cl, may be calculated based on a respective color calibration done beforehand. Therein the exposure level of the corrosive refers to a certain predefined concentration level of S, Cl or S+Cl in the ambient air. 
         [0017]    In the following, the invention is described using S and Cl as examples of corrosive species but this technique may be applied to other corrosives and other materials of the exposed component beside elementary Cu as well. 
         [0018]    In another embodiment the sensor unit further comprises a light source directed to the exposed component, preferably providing white light, preferably in the 350-800 nm wavelength range. 
         [0019]    As explained above, the sensor unit comprises processing means able to calculate the level of corrosive exposure, for example S/Cl exposure using the determined color of reflected visible light, preferably the RGB color intensity of the reflected visible light. Before the level of corrosive exposure can be determined, one has to correlate the present corrosive amount (such as At % Cl or S) from SEM/EDXS or other analytical methods with the relative intensity of red, green and blue colors in the reflected visible light from the exposed component. 
         [0020]    In particular in order to determine the color of the reflected visible light the sensor unit may comprise at least one optical element, for example a color filter. Thereby, only one color can be determined at one time. In a preferred embodiment a plurality of color filters, for example three color filters for the colors red, green and blue are accommodated side by side so that at the same time the red, green and blue component of the reflected light is received at different areas of the light receiving element, for example of a CCD camera. It is obvious to someone skilled in the art, that any combination of filters spanning the color spectrum could be used to determine the relative color intensities. 
         [0021]    For the installations of high reliability electronics such as telecommunications or military equipment it is of advantage if the sensor unit is operable to receive the reflected light and/or to determine the color of the reflected visible light and/or to calculate the level of corrosive exposure continuously or intermittently. 
         [0022]    For remote access to the data measured, determined or calculated by the sensor unit it is advantageous if the sensor unit further comprises a representation of an individual number of the electronic module, wherein the light receiving element is operable to receive reflected visible light form the representation of the individual number. This representation may be realized for example as a 1D or 2D barcode. Thereby the corrosive contamination may be correlated with the specific electronic module and its specific manufacturing process, transportation way or other characteristics of its lifetime. In case the representation is realized as a 1D or 2D barcode the light receiving element and the processing means preferably work similar to a barcode scanner in order to determine the individual number of the electronic module. 
         [0023]    In another embodiment the sensor unit further comprises a transmitter operable to transmit data from the sensor unit to a remote station, wherein the transmitted data contains data concerning the measured reflected visible light spectrum from the exposed component and/or from the representation of the individual number and/or data concerning the determined color of the reflected visible light and/or data concerning the calculated level of corrosive exposure. By this it is possible to receive data from the electronic module during the whole lifetime of the electronic module without opening the housing of the sensor unit or the electronic module. 
         [0024]    In another embodiment the sensor unit further comprises a temperature sensor. The reaction of the corrosive with the surface of the exposed component depends on the temperature and time duration of the exposure. By considering the ambient temperature of the electronic module the accuracy of the determined level of corrosive exposure can be enhanced. 
         [0025]    In a preferred embodiment the exposed component is surrounded by an area containing no solder mask because this enhances the S sensitivity. The exposed component is an integral part of the sensor unit. The sensor assembly is subsequently attached to the electronic module using standard attachment methods (e.g. surface mount soldering) 
         [0026]    In another embodiment the sensor unit comprises a housing with an opening, wherein the opening is preferably accommodated close to the exposed component. On the one hand the housing protects the interior of the sensor unit and on the other hand the ambient air containing the corrosives reaches the exposed component via the opening. 
         [0027]    The above problem is further solved by an electronic module. The advantage of the inventive electronic module is that the small and lightweight sensor unit is firmly connected with/attached to the electronic module and forms a part of the component set of the electronic module comparable to other electronic components. The outer dimensions of such a sensor unit are for example but not limited to3×3×1 mm (9 mm 3 ). 
         [0028]    The inventive procedure to calculate the level of corrosive exposure of an electronic module with the above described sensor unit contains the following steps. At first the reflected visible light of the exposed component is received by a light receiving element, for example a camera (e.g. a CCD camera) or a spectrophotometer. Then, the color of the received reflected visible light, preferably the RGB color intensity of the reflected visible light is determined, preferably by processing means. Afterwards, by the processing means a level of corrosive exposure is calculated from the determined color of the reflected visible light. 
         [0029]    In one preferred embodiment the level of corrosive exposure is calculated from the determined color of the reflected visible light, preferably from the determined RGB color intensity of the reflected visible light, is based on a mathematical model, for example using a quadratic equation. 
         [0030]    As explained above the calculation of the level of corrosive exposure may be further based on the determined ambient temperature in a preferred embodiment. 
         [0031]    A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art is set forth in the following specification of different embodiments. Thereby, further features and advantages are presented that are part of the present invention independently of the dependent claims. 
         [0032]    Further features, aspects, objects, advantages, and possible applications of the present invention will become apparent from a study of the exemplary embodiments and examples described below, in combination with the figures, and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]    The specification refers to the accompanying figures showing schematically: 
           [0034]      FIG. 1  illustrates an inventive electronic module with an exposure component in a top view, 
           [0035]      FIG. 2  illustrates an example of an exposure component with a representation of an individual number in a top view, 
           [0036]      FIG. 3  illustrates a first embodiment of a sensor unit accommodated at an inventive electronic module in a side view, 
           [0037]      FIG. 4  illustrates another embodiment of a sensor unit accommodated at an inventive electronic module in a side view, 
           [0038]      FIG. 5  illustrates the relationship of red color percentage intensity and S concentration in ambient air (in at %) as determined by experiment (see square dots) and fitted with a quadratic equation, 
           [0039]      FIG. 6  illustrates the relationship of blue color percentage intensity and S concentration in ambient air (in at %) as determined by experiment (see square dots) and fitted with a quadratic equation (see line), 
           [0040]      FIG. 7  illustrates the relationship of red color percentage intensity and S+Cl concentration in ambient air (in at %) as determined by experiment (see square dots) and fitted with a quadratic equation (see line), and 
           [0041]      FIG. 8  illustrates the relationship of blue color percentage intensity and S+Cl concentration in ambient air (in at %) as determined by experiment (see square dots) and fitted with a quadratic equation (see line). 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0042]    In the following embodiments of the present invention are explained with regard to the corrosives S and Cl and the exposure component elementary Cu. The present invention may be realized with regard to other corrosives and exposure components containing other chemical elements or chemical compounds as well. 
         [0043]      FIG. 1  depicts the inventive electronic module (PCB)  1  containing different electronic components  3  at its surface. The conductive copper traces are not shown. The electronic module  1  further comprises an electrically isolating substrate  2  (for example a resin is impregnated B-stage cloth, pre-prec) at which surface the copper traces and the electronic components  3  are accommodated. In the right corner of the electronic module  1  an inventive sensor unit  10  with an exposure component  5  is provided. 
         [0044]    One example of such an exposure component  5  consists of nine layer like elements whose surface is formed either as a circle  5   a  accommodated in a horizontal row or as a bar  5   b  accommodated in a vertical row as shown in  FIG. 2 . Beside the exposure component  5  a representation of an individual number of the electronic module  1  is provided as a 2D barcode  7 . 
         [0045]    The area  9  of the exposed component  5  is not covered with solder mask (solder resist), a thin lacquer-like film of polymer that is applied to the copper traces of the PCB  1  to the remaining area of the electronic module  1  for protection against oxidation and to prevent solder bridges from forming between closely spaced solder pads. Further, the electronic components  3  and the solder pads (not shown in  FIG. 1 ) are not covered with the solder mask. 
         [0046]    As shown in  FIG. 3  the sensor unit  10  further comprises a housing  11  which has an opening  12  close to the exposed component  5  and a light source  13 , containing for example at least one LED. The light source  13  provides light in the visible wavelength range which passes an optical component  15 , for example containing lenses, and illuminates the surface of the exposed component  5  and the 2D barcode  7 . The visible light reflected from the exposed component  5  and from the 2D barcode  7  passes the optical component  15  and is received by a receiving element  17 , for example a spectrophotometer or a camera (e.g. a CCD camera). The receiving element  17  converts the light signals from the exposed component  5  and the 2D barcode  7  into electrical signals. The housing  11  is fixed at the surface of the substrate  2  using an SMT solder joint  14 . 
         [0047]    The receiving element  17  is connected to the processing integrated circuit (IC)  19  which as processing means to process the electrical signals transmitted from the receiving element  17  as explained in detail below. 
         [0048]    In the embodiment of the inventive sensor unit  10  as shown in  FIG. 3  the light reflected from the exposed component  5  passes three filters  21  accommodated side by side, for example a red filter, a blue filter and a green filter. Accordingly, the receiving element  17 , for example provided as a CCD camera receives the filtered reflected light at three corresponding different areas in the camera. 
         [0049]    In the embodiment as shown in  FIG. 4  the sensor unit  10 ′ additionally comprises a ASIC control unit  23  as another processing means, a power supply unit  25 , for example a battery, and a transmitter  27 , for example a radio frequency transmitter, e.g. a Bluetooth transmitter according to the IEEE standard. The ASIC control unit  23 , the power supply unit  25  and the transmitter  27  are connected to each other and to the imaging unit  29  containing the light source  13 , the optical component  15 , the filter  21 , the receiving element  17  and the processing IC  19 . The mentioned components and elements are capable of transmit electric signals and electric energy via the connection. 
         [0050]    The data processed in the imaging unit  29  and the ASIC control unit are transmitted to a remote station using the transmitter  27 . 
         [0051]    The electrical signals representing the color of the reflected visible light of the exposed component and the content of the 2D barcode provided by the receiving element  17  are processed in the processing IC  19  and, if applicable, additionally in the ASIC control unit  23 . Therein, the color information is extracted from the signals and, for example, the color intensity of red, green and blue visible light, in particular the respective percentage intensity (please explain this value) is determined. Using a respective calibration which is shown for example by means of the diagrams of  FIGS. 5 to 8  the S concentration, Cl concentration or S+Cl concentration in atomic percent within the ambient air and the respective corrosive exposure level of S, Cl or S+Cl corrosive is determined. Additionally, from the picture of the 2D Barcode the individual number of the electronic module  1  is determined by the processing means  19 ,  23 . 
         [0052]    In a further embodiment the sensor unit  10 ′ may further comprise a temperature sensor  31  measuring the ambient temperature. The information about the ambient temperature which is provided to the ASIC control unit  23  as well is further used to determine the correct corrosive exposure level of S, Cl or S+Cl. 
         [0053]    If the corrosive exposure level determined by the sensor unit  10 ,  10 ′ passes a certain predefined maximum value an alarm (e.g. an audible alarm or a visible alarm) may be activated. 
         [0054]    For calibration of the sensor unit  10 ,  10 ′ experiments have to be conducted to determine the correlation between the color of the visible light reflected by the exposed component and the corrosive exposure level or the corrosive concentration in the ambient air. Therefore, in a vacuum jar a copper exposed component, a S and/or Cl source and 1 drop of DI water is provided. Then, the air is pumped out of the vacuum jar. Afterwards the vacuum jar is placed in an oven or air to air temperature cycles chambers for various temperature and time duration exposure. Then, an optical image of the copper exposed component is obtained and an analysis of the RGB intensity is conducted. At the same time SEM/EDXS element analysis is performed to obtain the S and Cl concentration within the jar. The following table 1 shows the copper exposure component SEM/EDXS and optical RGB color intensity test results. 
         [0000]    
       
         
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 S 
                 Cl 
                 S + Cl 
                 Red 
                 Green 
                 Blue 
                 Red 
                 Green 
                 Blue 
                 1-Red 
               
               
                   
                 concentation 
                 concentation 
                 concentation 
                 Average 
                 average 
                 average 
                 percentage 
                 percentage 
                 percentage  
                 percentage 
               
               
                   
                 (at %) 
                 (at %) 
                 (at %) 
                 (0-255)  
                 (0-255) 
                 (0-255) 
                 (%) 
                 (%) 
                 (%) 
                 % 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 A5-1c 
                 0.0 
                 0.0 
                 0.0 
                 157.2 
                 109.4 
                 100.0 
                 42.9 
                 29.9 
                 27.3 
                 57.1 
               
               
                 B48-1c 
                 0.0 
                 0.0 
                 0.0 
                 152.0 
                 101.4 
                 104.1 
                 42.5 
                 28.4 
                 29.1 
                 57.5 
               
               
                 B240-1c 
                 0.0 
                 0.1 
                 0.1 
                 148.8 
                 98.7 
                 102.6 
                 42.5 
                 28.2 
                 29.3 
                 57.5 
               
               
                 A1-12C-trace 
                 0.2 
                 0.0 
                 0.3 
                 122.5 
                 85.9 
                 111.7 
                 38.3 
                 26.8 
                 34.9 
                 61.7 
               
               
                 A1-12C-circle 
                 0.3 
                 0.1 
                 0.3 
                 127.1 
                 82.5 
                 98.5 
                 41.3 
                 26.8 
                 32.0 
                 58.7 
               
               
                 A1-11C-circle 
                 0.6 
                 0.2 
                 0.9 
                 116.7 
                 95.7 
                 135.8 
                 33.5 
                 27.5 
                 39.0 
                 66.5 
               
               
                 A1-11C-trace 
                 0.7 
                 0.2 
                 0.9 
                 118.8 
                 98.2 
                 142.4 
                 33.1 
                 27.3 
                 39.6 
                 66.9 
               
               
                 A2-12C-trace 
                 0.8 
                 0.1 
                 0.9 
                 125.8 
                 94.7 
                 133.8 
                 35.5 
                 26.7 
                 37.8 
                 64.5 
               
               
                 A2-7c 
                 0.8 
                 0.0 
                 0.9 
                 119.9 
                 119.4 
                 166.0 
                 29.6 
                 29.5 
                 41.0 
                 70.4 
               
               
                 A2-12C-circle 
                 0.9 
                 0.1 
                 1.0 
                 129.7 
                 96.0 
                 120.9 
                 37.4 
                 27.7 
                 34.9 
                 62.6 
               
               
                 A2-10c 
                 1.1 
                 0.1 
                 1.2 
                 127.0 
                 102.0 
                 142.0 
                 34.2 
                 27.6 
                 38.2 
                 65.8 
               
               
                 A2-4c 
                 1.5 
                 1.9 
                 3.4 
                 77.8 
                 75.1 
                 134.0 
                 27.1 
                 26.2 
                 46.7 
                 72.9 
               
               
                 A2-11C-trace 
                 1.5 
                 0.2 
                 1.7 
                 83.3 
                 68.5 
                 111.5 
                 31.6 
                 26.0 
                 42.4 
                 68.4 
               
               
                 A2-11C-circle 
                 1.6 
                 0.2 
                 1.8 
                 97.9 
                 80.7 
                 125.5 
                 32.2 
                 26.5 
                 41.3 
                 67.8 
               
               
                 A5-10c 
                 2.3 
                 0.3 
                 2.6 
                 104.3 
                 103.8 
                 167.1 
                 27.8 
                 27.7 
                 44.5 
                 72.2 
               
               
                 A2-9c 
                 2.5 
                 0.3 
                 2.8 
                 105.2 
                 98.8 
                 172.4 
                 28.0 
                 26.3 
                 45.8 
                 72.0 
               
               
                 B48-7c 
                 4.0 
                 0.0 
                 4.0 
                 42.0 
                 41.5 
                 100.3 
                 22.8 
                 22.6 
                 54.6 
                 77.2 
               
               
                 B120-7c 
                 5.5 
                 0.1 
                 5.7 
                 26.6 
                 28.2 
                 62.5 
                 22.7 
                 24.0 
                 53.3 
                 77.3 
               
               
                 A5-9c 
                 5.6 
                 0.3 
                 5.8 
                 20.3 
                 20.6 
                 60.6 
                 20.0 
                 20.3 
                 59.7 
                 80.0 
               
               
                   
               
             
          
         
       
     
         [0055]    As depicted in the diagrams of  FIGS. 5 to 8  a good correlation between the ration of the red and blue color of the reflected light and the S concentration or the S+Cl concentration determined by SEM/EDXS analysis is observed.  FIGS. 5 and 7  show that red color percentage intensity decreases as S and Cl level increases. Further, according to the diagrams in  FIGS. 6 and 8 , the blue color percentage intensity increases as S and Cl level increases. 
         [0056]    The correlation can be determined as a quadratic equation (see fitted curve in  FIGS. 5 to 8 ), in particular
       for  FIG. 5 : y=0.0126x 2 −1.035x+21.341, wherein x is the red percentage intensity (in %) and y the S concentration (in at %),   for  FIG. 6 : y=0.0047x 2 −0.2242x+2.5257, wherein x is the blue percentage intensity (in %) and y the S concentration (in at %),   for  FIG. 7 : y=0.0112x 2 −0.9597x+20.713, wherein x is the red percentage intensity (in %) and y the S+Cl concentration (in at %) and   for  FIG. 8 : y=0.0036x 2 −0.1147x+0.2473, wherein x is the blue percentage intensity (in %) and y the S+Cl concentration (in at%).       
 
         [0061]    The present inventive solution uses the simple concept of color change of an exposure component surface in order to detect corrosive presence and thereby to determine the level of corrosive exposure as a measure of the probability of failure of a high reliability board or product containing such board. This solution can be implemented easily and cost effectively. Further it is possible to determine the level of corrosive exposure for each individual board or product separately. The sensor unit may be implemented with instrumentation during manufacturing of the electronic module  1  or as an integrated component which stays with the is electronic assembly and which can issue alarms allowing preventative maintenance in the case of high reliability, maintainable systems. The inventive sensor unit  10 ,  10 ′ is able to constantly monitor the corrosive exposure level and even transmit these data to a remote station including the individual number of the electronic module. 
         [0062]    It will be apparent to those skilled in the art that numerous modifications and variations of the described examples and embodiments are possible in light of the above teachings of the disclosure. The disclosed examples and embodiments are presented for purposes of illustration only. Other alternate embodiments may include some or all of the features disclosed herein. Therefore, it is the intent to cover all such modifications and alternate embodiments as may come within the true scope of this invention, which is to be given the full breadth thereof. 
       LIST OF REFERENCE NUMBERS 
       [0063]      1  electronic module 
         [0064]      2  substrate 
         [0065]      3  electronic component 
         [0066]      5  exposure component 
         [0067]      5   a,    5   b  element of exposure component  5   
         [0068]      7  2D barcode 
         [0069]      9  area with no solder mask 
         [0070]      10 ,  10 ′ sensor unit 
         [0071]      11  housing 
         [0072]      12  opening of housing 
         [0073]      13  light source 
         [0074]      14  SMT solder joint 
         [0075]      15  optical component 
         [0076]      17  light receiving element 
         [0077]      19  processing IC 
         [0078]      21  filter 
         [0079]      23  ASIC control unit 
         [0080]      25  power supply unit 
         [0081]      27  transmitter 
         [0082]      29  imaging unit 
         [0083]      31  temperature sensor