Abstract:
A testing method for a micro electro-mechanical system is described, comprising the steps of: i) feeding a system to be tested on a first tray; ii) collecting the system from the first tray; and iii) verifying correct operation of the system collected from the first tray; the method further comprises step iv) of acquiring at least one parameter associated with the presence or otherwise of the system on the first tray; and/or with the fact that the system matches or otherwise a correct identification code; and/or with correct or incorrect orientation and/or position of the system on the first tray; step iv) being performed prior to step ii).

Description:
[0001]    The present invention concerns a testing method and unit for micro electro-mechanical systems, also known as MEMS. 
         [0002]    In particular, the term micro electro-mechanical systems indicates in a non-limiting manner systems having a square or rectangular form with sides ranging from 1 mm to 6 mm and thickness in the order of 1 mm. 
       BACKGROUND OF THE INVENTION 
       [0003]    Testing units for micro electro-mechanical systems are known, essentially comprising:
       a plurality of trays, each of which can be fed with a respective plurality of micro electro-mechanical systems;   a testing device for the micro electro-mechanical systems, which electrically communicates with the above-mentioned systems and verifies that the systems themselves are able to correctly respond to a plurality of external stimuli, for example correct transmission of the electrical signal, variations in temperature levels, humidity, noise, acceleration and vibration and magnetic fields; and   a collecting device, which collects the micro electro-mechanical systems from one of the trays and makes them available to the testing unit.       
 
         [0007]    More precisely, each tray comprises a plurality of chambers, for example a few hundred, within which the micro electro-mechanical systems to be tested are housed. 
         [0008]    The trays enter the testing unit one after the other, stop, and the collecting device collects the micro electro-mechanical systems from the tray inside the testing unit. 
         [0009]    The testing device comprises, in turn, a chamber provided with a plurality of seats, within which the micro electro-mechanical systems are housed and where their respective functions are tested by means of connection to electrical terminals. 
         [0010]    Each micro electro-mechanical system further comprises, on its surface, a two-dimensional identification code, which contains numerous first pieces of information and can be associated with further second pieces of information contained in an external database, including the relative batch. 
         [0011]    The Applicant has observed that the above-mentioned testing units, although they function correctly, could be improved, in particular as regards the rapidity and optimisation of the testing process. 
         [0012]    More precisely, if the micro electro-mechanical systems are not correctly housed in the tray, there is the risk of the systems being positioned incorrectly within the respective seats of the testing device and consequently interrupting operation of the testing unit. 
         [0013]    Furthermore, if the micro electro-mechanical systems are not correctly housed in the tray present inside the machine, there is the risk of interaction with the collecting device causing the micro electro-mechanical systems to come off the tray. This would cause non-collection of said systems or the generation of noise and vibration inside the testing unit. 
         [0014]    Moreover, it is important to note that the micro electro-mechanical system must be correctly positioned in the seats of the testing device chamber, in order that said systems can be correctly connected to the electrical terminals. 
         [0015]    If the micro electro-mechanical system is incorrectly positioned on the tray, it is nevertheless positioned by the collecting device inside the relative seat of the testing device and testing is performed, albeit ineffectively. 
         [0016]    Lastly, if the micro electro-mechanical system is not present on the tray, due to an error, the collecting device detects this and collects another system, reducing the efficiency and rapidity of the testing operation. 
         [0017]    U.S. Pat. No. 5,805,472 discloses a testing method comprising reading means for reading an identification code of test trays. 
         [0018]    U.S. Pat. No. 5,865,319 discloses an automatic test handler. 
         [0019]    The need is felt in the sector to optimise operation of the testing unit, in particular in terms of rapidity and optimisation of the testing operations of the micro electro-mechanical systems. 
       SUMMARY OF THE INVENTION 
       [0020]    The object of the present invention is to provide a testing method for a micro electro-mechanical system which simply and inexpensively meets the above-mentioned need. 
         [0021]    The above object is achieved by the present invention since it relates to a testing method for a micro electro-mechanical system, as defined in claim  1 . 
         [0022]    The present invention further relates to a testing unit for a micro electro-mechanical system, as defined in claim  8 . 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    For a better understanding of the present invention a preferred embodiment is described below, purely by way of non-limiting example and with reference to the accompanying drawings, in which  FIGS. 1 to 6  are perspective views of a testing system for micro electro-mechanical systems produced according to the teachings of the present invention and in respective successive steps of a testing method according to the teachings of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    With reference to  FIGS. 1 to 6 , the number  1  indicates a testing unit for micro electro-mechanical systems  2 , also known as MEMS. 
         [0025]    In the case illustrated and merely by way of non-limiting example, the systems  2  (only two of which are illustrated in  FIGS. 1 to 6 ) each have a square or rectangular form with sides ranging from 1 mm to 6 mm and thickness in the order of 1 mm. 
         [0026]    The systems  2  further comprise respective identification codes, a two-dimensional graphic sign in the case illustrated. 
         [0027]    The identification codes contain first pieces of information relative to the systems  2  and furthermore can be associated with further second pieces of information contained in an external database. The first and/or second pieces of information contain, in particular, the batches to which the relative systems  2  belong. 
         [0028]    Each system  2  further comprises a sign  19  positioned at one of its vertexes to uniquely identify the orientation of the system  2 . 
         [0029]    The unit  1  essentially comprises:
       a magazine  3  containing a plurality of trays  4 ,  4   a  each loaded with a plurality of systems  2 ;   a frame  5 ;   a feeding device  6 , which collects, one after the other, the trays  4   a  one at a time from the magazine  3 ;   a collecting device  7 , which is adapted to collect the systems  2  from the tray  4 ,  4   a;  and   a testing device  8 , which comprises a plurality of seats  9  (only one of which is illustrated) for receiving respective systems  2 .       
 
         [0035]    The frame  5  supports the feeding device  6 , the collecting device  7  and the testing device  8 . 
         [0036]    More precisely, the trays  4  are stacked on top of one another inside the magazine  3  and access in sequence, one after the other, the unit  1 . 
         [0037]    The trays  4  are stacked inside the magazine  3  in a direction Z, vertical in the case illustrated. 
         [0038]    The testing device  8  is adapted to verify the quality and functionality characteristics of the systems  2 . 
         [0039]    In particular, the testing device  8  comprises, for each seat  9  and therefore for each system  2  to be tested:
       an electrical circuit (not illustrated) for dialoguing with the system  2 ; and   a plurality of sub-devices (not illustrated), which can be activated to expose the system  2  to a plurality of external stimuli, for example variations in temperature levels, humidity, noise, acceleration, vibration and magnetic fields applied.       
 
         [0042]    The feeding device  6  can be fed with the tray  4   a  arranged at the top within the magazine  3  and moves it in the direction Y on the frame  5 . 
         [0043]    The trays  4 ,  4   a  are also elongated parallel to the direction Y. 
         [0044]    The systems  2  to be tested are arranged on the tray  4  in rows (only two of which are illustrated in the attached figures) parallel to the direction X and in columns parallel to the direction Y (only one of which is illustrated in the attached Figures). 
         [0045]    The collecting device  7  moves in directions X, Y and Z to position itself at the top and collect the systems  2 . 
         [0046]    Advantageously, the unit  1  comprises an acquisition device  10 , which is configured to acquire at least one parameter associated:
       with the presence or otherwise of the systems  2  on the tray  4   a;  and/or   with the fact that the systems  2  to be tested correspond or otherwise to the correct respective identification codes; and/or   with the correct or incorrect position/orientation of the systems  2  to be tested on the tray  4   a.          
 
         [0050]    In greater detail, the acquisition device  10  acquires an optical parameter. 
         [0051]    In the case illustrated, the acquisition device  10  comprises:
       two pairs of high-resolution cameras  11  (only one camera  11  of which is indicated in the attached Figures), which acquire an image of the systems  2  arranged on the tray  4   a;  and   a lighting device not illustrated.       
 
         [0054]    Said image contains the sign  19  and, therefore, is also representative of the orientation of the systems  2 . 
         [0055]    The acquisition device  10  moves in the direction Y and remains at a fixed distance in the direction Z from the tray  4   a.    
         [0056]    Preferably, the unit  1  supports a support  12  in a movable manner in the direction Y and in a fixed manner in the direction Z. 
         [0057]    The support  12  is integral in the direction Y with the acquisition device  10  and with the collecting device  7  and allows movement thereof in the direction Y. 
         [0058]    The collecting device  7  is, furthermore, movable in the directions X, Z with respect to the support  12 , so as to collect the systems  2  to be tested present on the tray  4   a.    
         [0059]    More precisely, the tray  4   a  is stopped inside the unit  1  and the cameras  11  acquire one or more two-dimensional images of the system  2  for a maximum time of three seconds. 
         [0060]    More precisely, in order to acquire the entire surface of the tray  4   a,  the cameras  11  acquire a plurality of images of the system  2 , varying the position acquired by means of a movement of the cameras  11  in the direction Y. 
         [0061]    The unit  1  further comprises a control unit  15  functionally connected to the camera  11  and to the collecting device  7 . 
         [0062]    The control unit  15  is programmed to:
       identify, on the basis of the image acquired by the camera  11 , whether the system  2  should be accepted or discarded or whether it is absent; and   generate a control signal for the collecting device  7 .
 
The control signal is generated so that the collecting device  7 :
   leaves the system  2  on the tray  4   a,  if the system  2  is to be discarded or is absent; or   collects the system  2  from the tray  4   a  and arranges it in a seat of the testing device  8 , if the system  2  is to be tested.       
 
         [0067]    In the case illustrated, the acquisition device  10  is positioned, in direction Y, on the opposite side of the collecting device  7  with respect to the testing device  8 . 
         [0068]    The unit  1  further comprises:
       a collecting device  20 , which is adapted to collect the tested systems  2  from the testing device  8 ;   a magazine  21  containing a plurality of trays  22 ,  22   a  overlapping in the direction Z and which have received the tested systems  2  from the collecting device  20 ; and   a feeding device  23 , which moves one tray  22   a  at a time with the tested systems  2  towards the magazine  21 .       
 
         [0072]    The collecting device  20  is fixed to the support  12  in the direction Y and is movable with respect to the support  12  in the directions X, Z to arrange the tested systems  2  on the tray  22   a.    
         [0073]    The tray  22   a  is moved by the feeding device  23  in the direction Y with respect to the frame  5 . 
         [0074]    The trays  22 ,  22   a  are elongated in the direction Y, lie on a plane defined by the directions X, Y and are arranged horizontally in use. 
         [0075]    Below, operation of the unit  1  is described with reference to a group of systems  2  to be tested. 
         [0076]    More in particular, operation of the unit  1  is described starting from a condition in which a tray  4   a  is arranged on the feeding device  6 , the systems  2  to be tested are arranged on the tray  4   a  ( FIG. 1 ) and the tray  22   a  is arranged on the feeding device  23 . 
         [0077]    The tray  4   a  is moved forward by the conveyor  6  in the direction Y towards the testing device  8  and stops. 
         [0078]    At this point ( FIG. 2 ), the cameras  11  move in the direction Y, remain at a fixed distance in the direction Z from the tray  4   a  and scan the system  2 . 
         [0079]    More specifically, the scanning time is less than 3 seconds. 
         [0080]    The cameras  11  acquire an image representing:
       the presence or otherwise of the systems  2  on the tray  4 ; and/or   matching or otherwise of the systems  2  to be tested with the correct respective identification codes; and/or   the correct or incorrect position/orientation of the system  2  to be tested on the tray  4   a.          
 
         [0084]    The cameras  11  furthermore acquire the position of the sign  19 , so that the image acquired also represents the orientation of the system  2 . 
         [0085]    The control unit  15  generates, on the basis of the image acquired by the cameras  11 , a control signal for the collecting device  7 . 
         [0086]    More specifically, if the image acquired detects that the systems  2  should be discarded or are absent, the control signal is such that the collecting device  7  leaves the systems  2  on the tray  4   a.    
         [0087]    If the image acquired detects that the system  2  is to be tested, the control signal is such that the collecting device moves in the directions X, Z, collects ( FIG. 3 ) the systems  2  from the tray  4   a  and houses them in the seat  9  of the testing device  8 . 
         [0088]    Alternatively, the collecting device  7  can perform repositioning of the systems  2  to be tested on the tray  4   a  before moving them into the seats  9  of the testing device  8 . 
         [0089]    Once all the systems  2  to be tested have been collected, in one or more operations, by the collecting device  7  from the tray  4   a,  the latter is returned to the magazine  3 . 
         [0090]    Simultaneously ( FIG. 4 ), the testing device  8  verifies the quality and functionality characteristics of the system  2  housed in the seat  9 . 
         [0091]    More specifically, the testing device  8  dialogues by means of electrical connection with the systems  2  to be tested and subjects them, by means of the sub-devices, to a plurality of external stimuli, for example variations in temperature levels, humidity, noise, acceleration and vibration and magnetic field applied. 
         [0092]    Once the testing has been performed, the collecting device  20  collects ( FIG. 5 ) the tested systems  2  from the seat  9  of the testing device  8  and arranges them on the tray  22   a  which is positioned at a standstill on the feeding device  23  ( FIG. 6 ). 
         [0093]    The tray  22   a  moves forward in the direction Y on the opposite side of the testing device  8  and reaches the magazine  21 . 
         [0094]    The magazine  21  contains the tested systems  2 , which can be made available at an outlet of the unit  1 . 
         [0095]    The systems  2  which have not passed the testing in the testing device  8  are collected by the collecting device  20  and conveyed to waste containers not illustrated. 
         [0096]    From an examination of the method and the testing unit  1  according to the present invention, the advantages it offers are evident. 
         [0097]    In particular, the unit  1  comprises an acquisition device  10 , which is configured to acquire a parameter associated with:
       the presence or otherwise of the systems  2  on the tray  4   a;  and/or   matching or otherwise of the systems  2  to be tested with the correct identification code; and/or   correct or incorrect position/orientation of the systems  2  to be tested on the tray  4   a.          
 
         [0101]    In this way, the presence of the systems  2  on the tray  4   a  and/or correct matching of the identification code and/or correct orientation/position on the tray  4   a  are verified before the collecting device  7  collects the systems  2  and the testing device  8  tests the systems  2 . 
         [0102]    Consequently, unlike what is described in the introductory part of the present description with reference to the known solutions, the systems  2  to be discarded or not present are not unnecessarily tested by the testing device  8 . 
         [0103]    This drastically reduces the risk, in the case of incorrect positioning of the systems  2  on the tray  4   a,  of the collecting device  7  inaccurately positioning the systems  2  inside the respective seats  9  of the testing device  8  and undesired stoppage of the operation of unit  1 . 
         [0104]    Furthermore, in the event of incorrect positioning of the systems  2  on the tray  4   a,  there is a reduced risk of the collecting device  7  having to recognise the incorrect positioning or causing the systems  2  to come off the tray  4   a  with the consequent generation of noise and vibration inside the unit  1 , thus reducing the testing efficiency and rapidity of the unit  1 . 
         [0105]    Moreover, if the systems  2  are not correctly oriented on the tray  4   a,  the systems  2  are not unnecessarily collected by the collecting device  7  and, therefore, are not tested by the testing device  8 . 
         [0106]    Lastly, if the image of the identification code acquired by the camera  11  reveals that the relative system  2  does not belong to the correct production batch, the relative system  2  is not collected by the collecting device  7  and, consequently, is not tested by the testing device  8 . 
         [0107]    The Applicant has observed that as a result of the above-listed advantages, the time necessary to test a given number of systems  2  is substantially reduced compared to the solutions known and described in the introductory part of the present description. 
         [0108]    Lastly it is clear that modifications and variations can be made to the unit  1  and the testing method described and illustrated here which do not depart from the protective scope defined by the claims. 
         [0109]    In particular, the unit  1  could comprise one single camera  11 . In this case, the camera  11  would be movable in both direction Y and direction X.