AN APPARATUS FOR PERFORMING ELECTRICAL AND ENVIRONMENTAL TESTS ON ELECTRONIC SEMICONDUCTOR DEVICES

Abstract: An apparatus for performing electrical and environmental tests on electronic semiconductor devices, which apparatus has an operating region (105) for accommodating the electronic devices, means for driving the electronic devices and that are arranged outside the operating region (105), a plurality of resiliently yielding terminals (250), connected electrically to the driving means, for contacting the electronic devices electrically, and in which apparatus a plurality of support elements (245) for at least one of the resiliently yielding terminals (250) are provided, each support element (245) being removable from the test apparatus.

Description: AN APPARATUS FOR PERFORMING ELECTRICAL AND ENVIRONMENTAL TESTS ON ELECTRONIC SEMICONDUCTOR DEVICES The present invention relates to an apparatus for performing electrical and environmental tests on electronic semiconductor devices. After the production process, electronic semiconductor devices are generally subjected to a test which enables their functional parameters to be checked and which, by applying to the electronic devices a series of electrical and environmental stresses, enables devices that have immediately identifiable defects or that are potentially defective to be eliminated. In particular, electronic devices are subjected to a burn-in test which consists in causing the electronic devices to function for some tens of hours at a very low or very high temperature (for example, from -50° to +300°C) in order to simulate a long period of operation of the electronic devices at ambient temperature (25° - 50 °C) . During the performance of the test, the electronic devices (typically accommodated on a test board) are inserted into a thermal chamber maintained at high (or very low) temperature. The test board is then connected electrically to a driver module which manages the performance of the test . Typically, the test board is connected to the driver module by means of a connector which is press-fitted onto corresponding contacts of the test board. Such a structure has, however, a limited number of contact lines. In addition, the connection of the connector requires a fairly high pressing force which does not enable the board to be loaded and unloaded from the test apparatus automatically. A different solution, which is used, for example, to perform electrical tests on printed circuit boards, consists in using resiliently yielding terminals, each of which contacts transversely a corresponding conductive pad of the test board. However, those resilient terminals have a rather complex structure and are therefore very expensive, which is reflected in the overall cost of the complete test apparatus. In addition, the resilient terminals are subjected to intense and repeated mechanical and thermal stresses, which means that they become worn over time and they therefore have to be completely replaced at extremely high cost, All of the above greatly limits the use of the test process and prevents it from being used on a large scale, with a consequent reduction in the level of quality and reliability in the production of the electronic semiconductor devices. The object of the present invention is to overcome the above-mentioned disadvantages. To that end, an apparatus is proposed for performing electrical and environmental tests on electronic semiconductor devices as described in claim 1. Briefly, an apparatus is provided for performing electrical and environmental tests on electronic semiconductor devices, which apparatus has an operating region for accommodating the electronic devices, means for driving the electronic devices and that are arranged outside the operating region, a plurality of resiliently yielding terminals, connected electrically to the driving means, for contacting the electronic devices electrically, and in which apparatus a plurality of support elements for at least one of the resiliently yielding terminals are provided, each support element being removable from the test apparatus. In addition, the present invention also proposes a connecting block for use in the test apparatus. Further characteristics and the advantages of the test apparatus according to the present invention will become clear from the following description of a preferred embodiment thereof which is given by way of non-limiting example with reference to the appended drawings, in which: Figure 1 illustrates the test apparatus schematically; Figure 2 shows a detail of the test apparatus with various blocks for connection to the electronic devices; Figure 3 is a sectioned partial view of the connecting block. Referring in particular to Figure 1, an apparatus 100 for performing burn-in tests on electronic semiconductor devices is illustrated. The test apparatus 100 comprises an operating region 105 (constituted by a thermal chamber maintained at high temperature or at very low temperature) and an external region at ambient temperature 110. A plate 115 acts as an insulating wall between the thermal chamber 105 and the ambient temperature region 110. A test board 120, or BIB (Burn-in Board) , is accommodated in the thermal chamber 105. Connecting sockets 125 (for example a few tens) are provided on a rear surface of the test board 120 and each of them accommodates removably an electronic device to be tested (not shown in the drawing) ; the socket 125 holds the electronic device in position for the period of time necessary to perform the test and at the same time enables the electronic device to be removed at the end of the test process without damaging it. A set of conductive contact pads 130 is provided on a front surface of the test board 120 for each socket 125; the contact pads 130 of each set are connected electrically (by metal strips and metallised through-holes) to the corresponding socket 125 and thus to the electronic device accommodated therein. The test board 120 slides horizontally in a lower guide 135a and in an upper guide 135b (parallel to the insulating plate 115) . The guides 135a and 135b are mounted on sliding pins 137a and 137b, respectively, (around each of which a spring is arranged) . The sliding pins 137a, 137b extend perpendicularly from a front surface of a pressure frame 140, facing the test board 120 (on the side opposite the insulating plate 115) . The front surface of the pressure frame 140 is also provided with thrust fingers 145, each of which acts in the region of a set of contact pads 130 of the test board 120. Secured in the vicinity of each corner of a front wall of the insulating plate 115 (for example, by means of a ring nut) is an electrical motor 150 (only two of which are shown in the drawing) ; the electrical motor 150 operates an endless screw 155 which moves the pressure frame 140. A bus board 157 is secured to the front surface of the insulating plate 115 by lag screws 159 (only one of which is shown in the drawing) . The bus board 157 is provided with expansion slots 160a and 160b (three of which are shown in the drawing) , in each of which an electronic printed circuit board provided with edge connectors is inserted perpendicularly. In particular, the slot 160a accommodates a configuration board 165 on which circuit elements simulating an operating state of the electronic devices are arranged; the slot 160b accommodates a driver board 170 on which circuit elements managing the performance of the test are arranged. Referring now to Figure 2, the insulating plate 115 is secured to a bearing frame 205 of the test apparatus by means of lag screws 210 (only one of which is shown in the drawing) . In the region of each socket of the test board, the insulating plate 115 has openings 225 for access to conductive contact pads 230 of the bus board 157. The opening 225 has a rectangular cross-section and has a widened rear portion and a narrowed front portion which define a stop. A block 233 for connection to the electronic devices to be tested is inserted in each opening 225. In particular, the connecting block 233 is constituted by a base 235 having dimensions matching the widened portion of the opening 225. The base 235 acts as a support element for rigid terminals 240 (for example, a few tens) which project towards the outside of the thermal chamber 105. The base 235 is provided with a further support element 245 having dimensions matching the narrowed portion of the opening 225. Resiliently yielding terminals 250 (for example, a few tens) project from the support element 245 towards the interior of the thermal chamber 105; each resilient terminal 250 is connected electrically to a corresponding rigid terminal 240. The connecting block 233 is inserted from the rear into the opening 225 (with the resilient terminals 250 facing forwards) until the base 235 abuts the stop defined by the narrowed portion of the opening 225, so that the resilient terminals 255 project from the insulating plate 115. The bus board 157 is thus secured to the insulating plate 115 and each rigid terminal 240 is soldered to a corresponding contact pad 230. Referring to Figure 1 and Figure 2 together, in the course of the test process, the board 120 is inserted into the sliding guides 135a and 135b, for example by means of an automatic loading/unloading robot . The electrical motors 150 operate the endless screws 155 which pull the pressure frame 140 towards the insulating plate 115; during its movement, the pressure frame 140 entrains the sliding guides 135a, 135b and thus also the test board 120. Thus, each thrust finger 145 acts on the corresponding set of contact pads 130, which are pressed against the resilient terminals 250. The pressure brings about the resilient yielding of the terminals 250 which are thus kept pressed against the contact pads 130 in such a manner as to ensure good electrical contact (between the bus board 157, and thus the configuration boards 165 and the driver board 170, and the electronic devices accommodated in the sockets 125) . At the end of the test process, the operations described above are carried out in reverse order in order to extract the board 120 from the thermal chamber 105. Analogous considerations apply where the test apparatus has a different structure, is used for performing different electrical and environmental tests (for example pressure or humidity tests), the sockets are replaced by other equivalent supports, a test board is not used and the electronic devices, joined to one another by means of a lead frame, are accommodated directly in the thermal chamber (with the resilient terminals contacting the terminals of the electronic devices directly) , the number of configuration and driver boards differs, or other equivalent elements are provided, the support elements for the resilient terminals have a different form, and so on. As described in detail hereinafter, each support element 245 is connected removably to the corresponding base 235. Alternatively, all of the support elements 245 are connected to a single plate (in which the connections to the bus board 157 are provided) , the base 235 and the support element 245 are produced in a single piece which is connected removably to the bus board 157, and so on. More generally, the test apparatus according to the present invention is provided with a plurality of elements for supporting one or more resiliently yielding terminals, each support element being removable from the test apparatus . That solution permits simple replacement of a single support element (with the associated resilient terminals), for example, for maintenance operations, without requiring complete replacement of all the resilient terminals of the thermal chamber (which are extremely expensive) . The test apparatus of the invention is inexpensive to maintain, which enables the test process to be used on a large scale, consequently increasing the level of quality and reliability in the production of the electronic semiconductor devices. In the particular embodiment of the present invention described above, each support element 245 (provided with some tens of resilient terminals, for example 48) is associated with a socket 125; that solution is an optimum compromise between the opposing requirements of flexibility and structural simplicity of the test apparatus. Preferably, the configuration boards 165 enable just a few of the resilient terminals 250 of each support element 245 to be operated selectively, in accordance with the number and the arrangement of the contact pads 130 on the test board 120. The same test apparatus can therefore be used for any type of test board having contact pads compatible with the resilient terminals 250. The particular structure of the insulating plate 115 enables the arrangement of the contact pads 230 of the bus board 157 to be modified very economically. Once the insulating plate 115 (with the connecting blocks 233) has been removed from the bearing frame 205 (by unscrewing the screws 210) , it is necessary only to detach the rigid terminals 240 of each base 235 from the contact pads 230 by heating the corresponding solders until they melt. At that point, the bus board 157 is detached from the insulating plate 115 (by unscrewing the screws 159) . The connecting blocks 233 (removed from the insulating plate 115) are inserted into the openings of a fresh insulating plate, with the openings positioned in the region of the contact pads of a fresh bus board. The fresh bus board is mounted on the fresh insulating plate and the rigid terminals 240 are then soldered to the corresponding contact pads. Furthermore, the configuration boards 165 arranged outside the thermal chamber 105 make it possible to use active electronic components (such as transistors) and complex simulation circuits, such as, for example, clock signal generators, in addition to passive electronic components (such as resistors and capacitors) . The slots 160a enable the configuration boards 165 to be replaced extremely simply and rapidly, which makes the test apparatus 100 particularly flexible because it is possible to test various types of electronic device simply by replacing the configuration boards 165. That solution also reduces the waiting times for setting up a fresh test process because only the configuration boards 165, which require a very short manufacturing time, have to be produced. Moreover, should the configuration boards 165 present problems, they can be replaced by other reserve boards at little cost and without interrupting the test process. In general, the various characteristics of the structure described above enable the test apparatus 100 to be readily configured for different types of electronic device. Analogous considerations apply where each support element is provided with a different number of resilient terminals (with each support element associated with two or more sockets or, conversely, with each socket associated with two or more support elements) , the rigid terminals are press-fitted into resilient holes provided in the bus board, the openings formed in the insulating plate are in a different form, the insulating plate is secured in a different manner, other equivalent means are used for removably connecting the configuration boards to the bus board, and so on. The test apparatus of the present invention in any case also lends itself to being produced in a form where the resilient terminals are not selectively activatable, the rigid terminals are secured irreversibly to the bus board, the insulating plate is not removable, the configuration boards are fixed, or the simulation circuit elements are arranged on the test board. Referring now to Figure 3, the base 235 is constituted by a plate of insulating material (for example, plastics material) . The support element 245 is formed by a metal plate 305 (for example of aluminium) resting on the base 235; a thin insulating plate 310 and a further insulating plate 315 (resistant to high temperature) rest on the metal plate 305. Three (mutually coaxial) through-holes having a circular cross-section 320, 325 and 330 are formed in the support element 245 for each resilient terminal 250; in particular, the hole 320 is formed in the metal plate 305, the hole 325 is formed in the insulating plate 310 and the hole 325 is formed in the insulating plate 315. The hole 320 has a larger diameter than that of the hole 325; the hole 330 has a predominantly widened lower portion (having a diameter larger than that of the hole 325) and a narrowed upper portion which define a stop. A metal bush 333 is embedded into the insulating plates 310, 315, around the holes 325 and 330; the metal bush 333 extends through the entire thickness of the insulating plates 310 and 315 (from an upper surface of the insulating plate 315 to a lower surface of the insulating plate 310) . The resilient terminal 250 is constituted by a metal needle (for example of copper) divided into two portions by a collar 335 having a diameter matching that of the widened portion of the hole 330; in particular, an upper portion (having a length greater than the height of the insulating plate 315) has a diameter matching that of the narrowed portion of the hole 330, and a lower portion (having a length greater than that of the metal plate 305) has a diameter matching that of the hole 325. The upper portion of the resilient terminal 250 is inserted into the hole 330 until the collar 335 abuts the stop defined by the narrowed portion of the hole 330, so that an upper end of the resilient terminal 250 projects from the upper surface of the insulating plate 315. A spring 345 is inserted in the widened portion of the hole 330, around the resilient terminal 250. The insulating plate 310 is fitted (by means of the hole 325) onto the resilient terminal 250 so that the spring 345 is restrained inside the widened portion of the hole 330. The metal plate 305 is then fitted in an analogous manner (by means of the hole 320) onto the resilient terminal 250 so that a lower end of the resilient terminal 250 projects from a lower surface of the metal plate 305. The lower portion of the resilient terminal 250 is free to slide without contact in the hole 320 and therefore the resilient terminal 250 is insulated electrically from the metal plate 305. A through-hole 355 having a circular cross-section is formed in the base 235 for each rigid terminal 240; the hole 355 has a widened upper portion and a narrowed lower portion which define a stop. The rigid terminal 240 (produced, for example, from copper) has a generally cylindrical shape and is constituted by a main body from which a tip extends; the main body of the rigid terminal 240 has a diameter matching that of the widened portion of the hole 355, while the tip of the rigid terminal 240 has a diameter matching that of the narrowed portion of the hole 355 and a height greater than that of the narrowed portion. The main body of the rigid terminal 240 generally has a smaller height than that of the widened portion of the hole 355 and has a blind longitudinal hole 360 matching the lower end of the corresponding resilient terminal 250. The main body of one of the rigid terminals, indicated 240g in the drawing, has a larger height than that of the widened portion of the hole 355 (and does not have any blind hole) ; the rigid terminal 24 Og is connected to a reference (or ground) terminal of the bus board. A blind hole 365 (matching the main body of the rigid terminal 240g) is formed in the metal plate 305. The rigid terminal 240, 24 Og is inserted into the hole 355 (with the tip facing downwards) until the main body abuts the stop defined by the narrowed portion of the hole 355 so that the tip projects from a lower surface of the base 235. The main body of the rigid terminal 240 does not reach an upper surface of the base 235 and therefore the rigid terminal 240 is insulated from the metal plate 305, while an upper end of the main body of the rigid terminal 24 Og projects from the upper surface of the base 235. The support element 245 is pushed against the base 235 so that the lower end of the resilient terminal 250 is received in sliding contact in the hole 360 of the corresponding rigid terminal 240. At the same time, the upper end of the main body of the rigid terminal 24Og is press-fitted into the hole 365. The support element 245 is secured to the base 235 by a pair of lag screws 370 (only one of which is shown in the drawing) which are arranged in the vicinity of opposite corners of the connecting block 233. In particular, the screw 370 is inserted into a through-hole 375 formed in the insulating plate 315, into a through- hole 380 formed in the insulating plate 310 and into a through-hole 385 formed in the metal plate 305; the screw 370 engages in a threaded blind hole 390 formed in the base 235. In a rest state (as shown on the left in the drawing) , the spring 345 pushes the resilient terminal 250 towards the outside of the support element 245, in such a manner as to move the upper end of the resilient terminal 250 away from the upper surface of the insulating plate 315. In an operating state (as shown on the right in the drawing) , the resilient terminal 250 moves back (under the action of the thrust exerted by the test board) against the action of the spring 345. In both cases, the resilient terminal 250 is in electrical contact (in the hole 360) with the corresponding rigid terminal 240. The structure described above is particularly advantageous because the electrical contact between the resilient terminal 250 and the rigid terminal 240 is not produced by means of the spring 345 (as is the case in known structures) . The spring 345 is therefore prevented from becoming heated by the Joule effect, with consequent degradation of its resilient characteristics. That solution enables less expensive springs to be used, thus reducing the cost of the entire connecting block; at the same time, the service life of the spring is increased, thus reducing the maintenance operations carried out on the test apparatus. The solution enables a very long travel to be obtained for the resilient terminal (for example up to a few centimetres) which ensures improved electrical connection between the resilient terminals and the contact pads of the test board. In addition, the fact that each support element 245 is removable from the corresponding base 235 enables the cost of the part to be replaced during maintenance operations to be contained. In particular, the structure described above is completely dismountable (by carrying out the operations described above in reverse order) , which also enables, for example, just one spring to be replaced, thus minimising maintenance costs. The metal plate 305 and the metal bushes 333 (connected to ground by means of the rigid terminal 240g) act as an electromagnetic shield for each resilient terminal 250. Any electromagnetic interference, even at very high operating frequencies, can therefore be reduced. This result is obtained with a structure which in any case ensures optimum insulation from the thermal chamber (by means of the plates 310, 315) . Analogous considerations apply where the resilient terminals and the rigid terminals are produced from different materials, the spring is replaced by other equivalent resilient elements, the metal bushes do not extend through the entire thickness of the insulating plates, the metal plate and the metal bushes are replaced by corresponding elements produced from another conductive material, the metal plate and the metal bushes are connected to earth in a different manner (optionally independently of one another) , only the metal plate or only the metal bushes is/are provided, there is a different number of lag screws, the support element and the base are in snap-connection with one another, or more generally other equivalent means of releasable connection are provided, and so on. The test apparatus of the present invention in any case also lends itself to being produced with resilient terminals having a different structure (for example, having telescopic pins) , with the resilient terminals connected to the rigid terminals in another manner, without the metal plate and the metal bushes (where low frequencies are used) , and so on. Naturally, in order to satisfy contingent and specific requirements, an expert in the art may apply to the apparatus described above for performing electrical and environmental tests on electronic semiconductor devices many modifications and variations, all of which, however, are included within the scope of protection of the invention as defined by the following claims.

Claims: CLAIMS 1. An apparatus (100) for performing electrical and environmental tests on electronic semiconductor devices having an operating region (105) for accommodating the electronic devices, means (170) for driving the electronic devices arranged outside the operating region (105) , a plurality of resiliently yielding terminals (250) , connected electrically to the driving means (170) , for contacting the electronic devices electrically, characterized in that it comprises a plurality of support elements (245) for at least one of the resiliently yielding terminals (250) , each support element (245) being removable from the test apparatus (100) . 2. A test apparatus (100) according to claim 1, further comprising means (115, 235) for insulating the operating region (105) , a plurality of rigid terminals (240) projecting from the insulating means (115, 235) towards the outside of the operating region (105) , the rigid terminals (240) being connected to the driving means (170) , means (370) for removably connecting each support element (245) to the insulating means (115, 235), each resiliently yielding terminal (250) being connected electrically in sliding contact to a corresponding one of the rigid terminals (240) . 3. A test apparatus (100) according to claim 2, wherein each resiliently yielding terminal (250) has a first and a second end projecting, respectively, from a surface of the support element (245) bearing against the insulating means (115, 235) and from a free surface of the support element (245) remote from the bearing surface, the support element (245) comprising resilient means (345) for pushing the resiliently yielding terminal (250) towards the outside of the support element (245) in order to move the second end of the resiliently yielding terminal (250) away from the free surface, each rigid terminal (240) being provided with a seat (360) for receiving in sliding contact the first end of the corresponding resiliently yielding terminal (250) . 4. A test apparatus (100) according to claim 3, in which the insulating means (115, 235) comprise a plurality of further support elements (235) for at least one of the rigid terminals (240) , each support element (245) being removably connected to a corresponding one of the further support elements (235) in order to define a connecting block (233), and an insulating plate (115) provided with a plurality of openings (225) in each of which one of the connecting blocks (233) is inserted, the test apparatus (100) further comprising a bearing frame (205) and means (210) for removably securing the insulating plate (115) to the bearing frame (205) . 5. A test apparatus (100) according to claim 4, wherein each support element (245) comprises an insulating portion (310, 315) and an electromagnetic shield portion (305) produced from conductive material and arranged between the insulating portion (310, 315) and the further support element (235) , the rigid terminals (240) being insulated by the shield portion (305) , and wherein each resiliently yielding terminal (250) is inserted in a corresponding through-hole (325, 330) and into a corresponding further through-hole (320) which are formed in the insulating portion (310, 315) and in the shield portion (305) , respectively, the resilient means comprising a spring (345) accommodated in the through-hole (325, 330) and the resiliently yielding terminal (250) being slidable without contact in the further through-hole (320) . 6. A test apparatus (100) according to claim 5, wherein the further support element (235) is provided with a further rigid terminal (240g) connected electrically to a reference terminal, the shield portion (305) being connected electrically to the further rigid terminal (240g) . 7. A test apparatus (100) according to claim 5 or 6, wherein the insulating portion (310, 315) comprises a plurality of electromagnetic shield bushes (333) produced from conductive material in contact with the shield portion (305), each shield bush (333) being arranged around one of the through-holes (325, 330) . 8. A test apparatus (100) according to any one of claims 1 to 7, further comprising means (165) for simulating an operating state of the electronic devices, the simulation means (165) being arranged outside the operating region (105) . 9. A test apparatus (100) according to claim 8, furhter comprising a bus (157) for connection to the resiliently yielding terminals (250) which is arranged outside the operating region (105) and means (160a) for removably connecting the simulation means (165) to the connecting bus (157) . 10. A test apparatus (100) according to any one of claims 1 to 9, wherein the operating region (105) is suitable for accommodating a test board (120) having a plurality of sockets (125) , each of which removably accommodates one of the electronic devices, and having a plurality of sets of contact pads (130) , the contact pads (130) of each set being connected electrically to a corresponding one of the sockets (125), and wherein the resiliently yielding terminals (250) of each support element (245) are associated with a corresponding one of the sets of contact pads (130) . 11. A connecting block (233) for use in the test apparatus (100) according to any one of claims 4 to 10.

Inventors: ZAFFARAMI ANTONIO, ZAFFARAMI, ANTONIO
Applicants: ELES EQUIPMENT S R L, ZAFFARAMI ANTONIO, ELES EQUIPMENT S.R.L., ZAFFARAMI, ANTONIO
Application year: 1999
Main classification: G01R31
IPC codes: G01R31