Patent Publication Number: US-2010108205-A1

Title: Method and device for tempering electronic components

Description:
The invention relates to a method and a device for tempering electronic components within a handler for a functional test in accordance with the preamble of claim  1  or  4 . 
     Electronic components in the form of semiconductor components are usually submitted to a special functional test under certain temperatures during or after their production. The temperature range, in which the components are tested, can be −60° C. to +170° C. for example. It is thus necessary to cool down or heat up the components accordingly. The components can be present in the form of single pieces or a group (strips, lead frames) during the test procedure. 
     Tempering of components is usually performed in a so-called handler, that is to say an automatic handling device for electronic components, which for this purpose has a temperature chamber, wherein the components are pre-tempered to the desired temperature, as well as a test chamber, provided with a chuck, which holds the components while a contact device, introduced from the outside, is placed on the latter in the desired contact position. The components in this case are transported from the temperature chamber to the chuck by means of a special transport device (pick and place unit). 
     It is known to temper the components in the temperature chamber in the vicinity of the transport device as well as in the test chamber in a purely convective manner in the air circulating and swirling process, wherein a gas heated accordingly is fed into the temperature and test chamber. This can take place in low-temperature tests either by evaporating liquid nitrogen in the temperature chamber, by way of evaporation enthalpy or by means of external cooling units, wherein in the closed re-circulation process an air stream is swirled through the temperature chamber and cooled down in the external cooling unit by means of a heat pump. Both cases concern flow rates in the low-pressure range. 
     This known method however has the disadvantage that all tempered areas of the handler must be insulated in a costly way, in order on the one hand to achieve exact tempering of the components and on the other hand to prevent damage to the machine components during hot or cold operation. A special problem in particular is caused by condensation on the chamber walls as well as by freezing up of critical places, the contact points for example, during cold tests. Furthermore systems with purely convective tempering are relatively sluggish so that the tempering speeds frequently leave a great deal to be desired. 
     In order to avoid these disadvantages, in some cases a change has been made to stop working with temperature chambers but only to heat or cool a few crucial places in the handler (hot/cold spot tempering). Thus it is known to place components, which are still grouped together in the strip group, on a chuck heated accordingly and the components are tempered in a purely conductive manner. Also here tempering times however are not insignificant. In order to shorten these, “soak stations”, which are designed as heating or cooling plates, are used beforehand in the known way and likewise the components are pre-tempered purely by transfer of conductive heat. The plates in this case are heated in the known way by means of electrical heaters or by means of a liquid medium, which is cooled down or heated up by an external cooling or heating unit accordingly. 
     Although in the case of conductive tempering more effective heat transfer to the electronic component is necessary than is possible with convective tempering and at a far lower cost of insulation, conductive tempering in particular has the disadvantage that heat transfer from the plates to the components is inhomogeneous and varied, therefore the temperature distribution over the components is sometimes very inhomogeneous and inexact. Furthermore conductive tempering of several strips in parallel is very costly. In the case of tempering with a liquid medium, wherein special oils are usually used, there is a risk of leakage and the problem that suitable oils are usually only available down to −40° C. In addition the components are subject to a sharp change in temperature, which can lead to unusually high thermal loading of the components in a very short time. 
     American Patent U.S. Pat. No. 4,918,928 A discloses a method and a device in accordance with the preamble of claim  1  or  4 , wherein for example the semiconductor components are pre-tempered in a convective manner in a pre-treatment chamber and a subsequent treatment chamber. The components are directly brought in a test chamber to the desired test temperature both in a conductive as well as in a convective manner. Furthermore there the gas pressure in the pre-treatment and post-treatment chambers as well as in the test chamber is maintained slightly above the ambient pressure, as a result of which ingress of ambient air into these chambers is to be prevented. Through such a measure however in the case of automatic handling devices, which are optimised for speed and throughput into the treatment chambers and into the test chamber, ingress of humid or contaminated ambient air into the treatment chambers and test chamber is not adequately avoided, because of entrainment effects due to the components being handled. 
     Furthermore a method and a device for tempering electronic semiconductor components for a functional test are disclosed by German Patent DE 10 2004 002 707 A1, wherein the components to be tested are pre-tempered by means of a gas and brought to test temperature by heated gas flowing in a controlled way in the opposite direction. 
     The object of the invention is to create a method and a device of the kind initially specified with which it is possible to carry out tempering of electronic components in a simple, economic, fast and exact way as possible and ingress of ambient air into the temperature and test chamber can be prevented particularly reliably even with fast operating automatic handling devices. 
     This object is achieved according to the invention by a method with the features of claim  1  and with a device in accordance with the features of claim  4 . Advantageous embodiments of the invention are described in further claims. 
     In the method according to the invention the gas pressure inside the test chamber is maintained greater than the gas pressure in the temperature chamber. Furthermore the inlet and the outlet of the temperature chamber are alternately opened and closed so that the gas flows uni-directionally from the test chamber into the temperature chamber and from this into the atmosphere. 
     Because the gas pressure inside the test chamber is maintained at a greater level than the gas pressure in the temperature chamber and the gas pressure inside the temperature chamber at a greater level than the ambient pressure, it is ensured that the gas flows uni-directionally from the test chamber into the temperature chamber and from this into the atmosphere in a particularly reliable way even when fast operating automatic handling devices with high throughput are used. Uni-directionally here means that the gas flows exclusively from the test chamber into the temperature chamber and from there into the atmosphere, and not in the reverse direction. The continuous flow of dry gas prevents freezing up of the contact areas as well as preventing condensation from forming on the chamber walls in low-temperature tests. 
     The inlet and outlet of the temperature chamber are alternately opened and closed, that is to say the inlet and outlet, via which the components are introduced into the temperature chamber or removed from this, are not opened at the same time. Thereby it is guaranteed that dry gas always flows from the temperature chamber to the outside and humid air can never ingress into the temperature chamber and from there into the test chamber. 
     Furthermore a special combination of convective tempering of the components in a temperature chamber and hot/cold spot tempering in the test chamber is used, wherein the components there are brought to the desired test temperature and maintained at this in a conductive manner or by heated gas flowing in a controlled way directly in the opposite direction. 
     In contrast to purely convective tempering the method according to the invention in particular offers the advantage that the insulation cost is substantially reduced, since only the temperature chamber, but not the test chamber must be extensively insulated. The space required for the test chamber is therefore substantially less. Furthermore a modular concept is easier to implement than a purely convective method since when using a purely convective method the machines must be newly designed over and over again depending on each application. The possibility of the modular concept leads to advantages in planning, extending and re-jigging the system. 
     Compared to the purely conductive process, the method according to the invention offers the advantage that the components are already really well pre-tempered when they arrive at the test chamber. No extremely sharp or rapid changes in temperature occur, so that thermal loading on the components is substantially less. The temperature transition and temperature distribution over several components of a strip is substantially more homogeneous and uniform. Distortions of the strips containing the components can therefore be avoided. Furthermore the method according to the invention renders the possibility of very fast and exact tempering of the components. 
     In accordance with an advantageous embodiment additional dry gas, which expediently consists of dried ambient air, is fed into the test chamber. As a result the risk of condensation in the test chamber area is avoided or at least substantially reduced. Since the dry gas fed into the test chamber is at ambient temperature, in addition the drive mechanism for the chuck and the transport device for the components are not exposed to any thermal loads. 
     The device according to the invention offers the same advantages, as described with respect to the method. 
    
    
     
       The invention is described by way of example below in detail on the basis of the drawings, wherein: 
         FIG. 1  is a schematic plan view onto the device according to the invention, and 
         FIG. 2  is a schematic illustration for clarification of the chuck. 
     
    
    
       FIG. 1  shows a handler  1  with a temperature chamber  2  and a test chamber  3 . The temperature chamber  2  has an inlet  4  via which a strip  6  with several components  5  arranged next to one another can be introduced into the temperature chamber  2 . The strips  6  are transferred to the handler  1  by a loader  7 . 
     The device shown in  FIG. 1  and  FIG. 2  is described below on the basis of an example, wherein the components are maintained at low temperature. The inventive concept however can be applied analogously if components are to be heated up. 
     The temperature chamber  2  has a tempering (soak area) area  8  and a transfer area  9 . Tempering the components  5  in the temperature chamber  2  is performed in a convective manner by means of a cold gas  10 , which is produced by a tempering device  11  and fed into the tempering area  8  of the temperature chamber  2 . The tempering device  11  may be a separate unit arranged externally to the handler  1 , as illustrated. Alternatively it is also possible for the tempering device  11  to be integrated with the handler  1 . Liquid nitrogen  12  evaporates in the tempering device  11 , brought to the desired temperature by means of a heater  13  and fed in gaseous form to the tempering area  8  of the temperature chamber  2 . The cold gas  10 , as illustrated by the arrow  14 , is returned in the re-circulation process through the temperature chamber  2  to the transfer area  9  and from there again from the temperature chamber  2  into the tempering device  11 , as illustrated by the arrow  15 . In the tempering device  11 , as illustrated by the arrow  16 , the cold gas  10 , after mixing with the liquid nitrogen  12 , is again returned to the heater  13  and from there fed into the tempering area  8 . 
     After the strip  6  with the components  5  has been brought to the desired temperature in the tempering area  8 , it is transported to the transfer area  9 . Afterwards the strip  6  can be transported from there by means of transport device  17  (pick and place unit) to a chuck  18 , which is provided in the test chamber  3 . Such a transport device is known, so that it does not need to be discussed further. 
     The chuck  18  as shown in detail in  FIG. 2 , is usually located on a lifting plate  19 , in order to raise the chuck  18  and thus the strips  6  with the components  5  resting on the chuck  18  to a height, at which a contact device  20  can be placed on the electrical contacts of the components  5 . Evenly heated gas at a temperature corresponding to the test temperature is fed into the chuck  18  via a pipe  21 . A plurality of outlet pipes  22  branches off from pipe  21 , in order to subject all components  5  of the strip  6  with evenly heated gas from below. The components  5  are thus brought to the desired temperature in the chuck  18  in a conductive manner by means of the chuck  18  and/or by direct contact with a gas heated accordingly. 
     In addition it is also possible for the lifting plate  19  to have a heating device  23 , for example a heating foil, with which the temperature of the lifting plate  19  and thus that of the chuck  18  can be adjusted as desired. 
     The direct contact of the components  5  in the chuck  18  with heated gas is indicated in  FIG. 1  with the arrow  24 . Additional or alternative conductive tempering of the chuck  18 , which can be carried out in particular by the lifting plate  19 , is indicated with the arrow  25 . 
     In addition, as illustrated by the arrow  26 , a dry gas can be fed into the test chamber  3 , in particular in the form of dried ambient air. This dry gas in particular serves to prevent condensation forming on the wall of the test chamber  3 . 
     Optionally it is also possible, as indicated by the arrows  27 ,  28 , to temper the components  5  in the transport device  17  indirectly and/or directly. 
     After testing the strip  6  with the components  5  is returned by means of the transport device  17  from the chuck  18  back into the transfer area  9  of the temperature chamber  2  and can then be removed from the temperature chamber  2  by means of a suitable transport device via an outlet  29 . Expediently in this case the components  5  are first transported into a temperature adapting area (de-soak area)  30 , which is located inside the handler  1  and enables the components to be heated up or cooled down to ambient temperature. From there the components  5  can be removed from the handler  1 . 
     The dry gas indicated by the arrow  26  is fed to the test chamber  3  in such a way that the pressure P 1  inside the test chamber  3  is greater than the pressure P 2  in the temperature chamber  2 . The pressure P 2  inside the temperature chamber  2  is again greater than the ambient pressure P a , which prevails in the loader  7  and in the temperature adapting area  30 . In this way it guaranteed that the dry gas fed into the test chamber  3  (arrow  26 ) flows uni-directionally from the test chamber  3  into the temperature chamber  2  and from there either into the loader  7  or into the temperature adapting area  30 , as indicated by the arrows  31 ,  32 . In order at all times to prevent ingress of humid ambient air into the temperature chamber  2 , inlet  4  and outlet  29  of the temperature chamber  2  are alternately opened and/or closed, but not at the same time. 
     As indicated in  FIG. 1 , the temperature chamber  2  and the test chamber  3  are of modular construction and arranged directly next to one another. Since just in the temperature chamber  2  tempering of the components  5  is performed in a convective manner, it is only necessary to insulate the temperature chamber  2  extensively while the test chamber  3  only has to be insulated to a minimum or not at all.