APPARATUS FOR TESTING SEMICONDUCTOR DEVICES

Abstract: An apparatus (201) for testing a semiconductor device including a dielectric package (202) and a lead (202a) with respect to withstand voltage thereof against electrostatic charges existing on the dielectric package (202). The apparatus comprises charging means having a metal plate (203) connected to an output terminal of a DC power source (206) for charging the dielectric package by bringing the metal plate (203) into contact with the surface of the package (202) when voltage is supplied from the DC power source (206) thereto, first discharge means having a metal bar (204) connected to ground potential via load impedance for discharging charges on the package (202) by selectively bringing the metal bar (204) into contact with the lead in (202a) said successive charging of the package (202), and second discharge means having a terminal (205a) connected to the ground potential via a resistor (211) for discharging charges remaining in a circuit of the semiconductor device by bringing the terminal into contact with the lead (202a) after stopping the supply of the voltage in succession to the discharging by the first discharge means.

Description: The present invention relates to an apparatus for testing electrostatic breakdown in a semiconductor device and for thereby securely and stably monitoring electrostatic breakdown with use of a charged device model damaged due to electrostatic charges stored on a dielectric package of the semiconductor device. A MOS IC, being highly integrated and of miniature size, is likely to be subject to electrostatic breakdown since inter-electrode distance has been made fine at present, e.g. typically less than 2 µm in its designed pattern and as less than 35 µm in its gate oxide film. In addition, such electrostatic breakdown may also originate from diversified packagings thereof. A flat package as an example tends to have a higher electrostatic capacity due to mold resin thereof being made thinner, and hence to have more electric charges impressed thereon. Moreover a chip-on board IC allows the chip to be charged with electrostatic charges directly thereon. The electrostatic charge so impressed may damage the gate oxide film and the junction thereof. The mechanism of this electrostatic breakdown phenomenon can be caused by allowing the package surface to be charged with static electricity, which static electricity is then discharged through a lead. The present applicant has proposed "the charged package method", as a method of testing electrostatic breakdown of a semiconductor device of charging a package thereof with electricity, which has been described in detail in Japanese Laid-Open Patent Publication No.60-73375. This charged package breakdown testing method facilitates the determination of equivalent parameters of an electrostatic breakdown phenomenon caused due to charges stored on a package, and assist the design of the circuit concerned, the shape of its package, and the like. It is necessary to effect the steps of charging an IC to be tested with electricity and of discharging it from the leads of the IC in repetition for each lead and for each voltage due to charge electricity onto a package. For example, in testing an IC with 64 pins, 64 x several times or several tens of times repetition are needed Furthermore, it takes several seconds to lower the voltage of the power source to zero, owing to the internal capacitance of the power source. Thus, after a test on one lead, it is impossible to start a test on the next lead instantly. The present invention seeks to provide an apparatus for testing the electrostatic withstand voltage of an IC and for testing the electrostatic withstand voltage of an IC by the charged package method with ease and rapidity. In accordance with the present invention there is provided an apparatus for testing a semiconconductor device including a dielectric package and a lead with respect to withstand voltage thereof against electrostatic charges existing on said dielectric package, said apparatus comprising:- (a) charging means having a metal plate connected to an output terminal of a DC power source for charging said dielectric package by bringing said metal plate into contact with the surface of said package when voltage is supplied from said DC power source thereto; (b) first discharge means having a metal bar connected to ground potential via a load impedance for discharging charges on said package; said apparatus being characterised in that said first discharge means is operable to discharge charges on said package by selectively bringing said metal bar into contact with said lead in said successive charging of said package; and further comprising a second discharge means having a terminal connected to ground potential via a resistor for discharging charges remaining in a circuit of said semiconductor device by bringing said terminal into contact with said lead after stopping the supply of the voltage in succession to said discharging by said first discharge means. In order that the invention may be better understood, an embodiment thereof will now be described by way of example only and with reference to the accompanying drawings in which:- Figure 1 is a schematic view illustrating an embodiment of an electrostatic withstand voltage test apparatus according to the present invention; Figure 2 is a flowchart illustrating the test steps of Figure 1; Figure 3 is a perspective view illustrating the whole electrostatic withstand voltage test apparatus; Figure 4 is a perspective view illustrating a combination of a test table unit and a test table base; Figure 5 is a perspective view illustrating a drive part; and Figure 6 is a block diagram illustrating an electrostatic withstand voltage testing apparatus having a circuit for lowering the voltage of a power source according to the present invention. An embodiment of electrostatic breakdown testing apparatus for a semiconductor device according to the present invention will be described with reference to the accompanying drawings. As shown in Figure 1 schematically illustrating the present embodiment of the electrostatic withstand voltage testing apparatus, the electrostatic withstand voltage testing apparatus 201 consists of a metal plate 203 for applying high DC voltage to the package of an IC 202 to be tested and for thereby charging it with electricity, a metal bar 204 for producing an electrical discharge by making contact with a prescribed lead 202a, and a terminal 205a for contacting with all leads 202a of the IC 202 to completely eliminate electric charges left behind in the circuit of the IC 202 after the electrical discharge. The metal plate 203 is connected with a high DC voltage power source 206, which can preferably generate voltage arbitrarily from about 0V to about 3kV. The metal bar 204 has a sliding mechanism, etc., driven by a motor, whereby it is made movable onto an arbitrary lead 202a by allowing the sliding mechanism to be operated in the X - Y directions while it is brought into contact with and separated from a prescribed lead 202a by allowing the sliding mechanism to be operated in the z direction (vertically). Moreover, the bar 204 is connected with equivalent impedance means 207, whereby it can adjust discharge from the IC 202. Hereupon, the bar 204 is shown in the figure so as to be movable in the X - Y - Z directions, but it may be adapted to have a function of moving only vertically, and adapted to be movable in the X - Y directions with the aid of the motion of a table including the metal plate 203. Furthermore, for the driving source described above, not only a motor but also pneumatic pressure or hydraulic pressure means may be used. The metal bar 204 has a rounded cross section and a tapered end part thereof in contact with the lead. The length of the cylindrical part of the metal bar 204 is more than 10 mm with a diameter thereof being more than 5 mm. The length of the tapered part is less than 10 mm with the diameter of the tip end surface thereof being more than 0.5 mm. The terminal 205a is fixedly mounted on a terminal base 205b, and movable therewith. In addition, the terminals 205a are connected to ground potential, the number of which terminals is at least the same as that of the leads 202a of the IC 202. The terminals 205a are made free to make contact with all the leads 202a by their movements toward the IC 202. When the IC 202 has its leads guided bidirectionally as in a dual in line package IC, it is prepared to have a set of right and left terminals 205a. On the other hand, when it has its leads 202a guided in four directions as in a chip carrier, etc., it is prepared to have a set of terminals 205a for the four directions. It is here obvious in case of the set of leads 202a guided in four directions that the number of terminals 205a should be the same as that of the leads 202a, otherwise it is difficult to make contact with any of the leads 202a. The terminals 205 may preferably be arranged so as to be switchable also to a tester 209 in addition to ground potential by means of a switch 208 such as a relay, etc. If this is done, it can immediately be judged whether or not any electrostatic breakdown is produced in the IC 202 in addition to the function of the terminal 205a of eliminating stored electric charges, and furthermore a space to provide a terminal of the tester can be saved. However, it is also possible to provide a terminal for the tester independently of the terminal 205a and thereby judge whether or not any electrostatic breakdown is produced. Although one connection of the terminal 205a is not shown in the figure, it can be conducted in the same manner as that of the other thereof. A test step of the electrostatic withstand voltage testing apparatus 201 will be described with reference to Figure 2. (A) The IC 202 is mounted on the metal plate 203. The metal plate 203 preferably has a frame into which the IC 202 is securely fitted for facilitating positioning thereof. The following steps are of those of the electrostatic withstand voltage testing for each lead 202a. (B) High voltage is applied to the metal plate 203 for charging a package of the IC 202 with electricity. (C) The metal bar 204 is then lowered to a prescribed lead 202a for producing electrical discharge, and thereafter the high voltage is cut off. (D) Electric charges left behind in the IC 202 are discharged by pushing the terminal 205a against the lead 202a while keeping the lead 202a and the metal bar 204 in contact. The contact between the lead 202a and the metal bar 204 kept as such is to prevent electrostatic breakdown from being produced at portions other than the discharged lead 202a due to inverse voltage induced as electric charges are discharged from the terminal 205a since electric charges are stored in the circuit of the IC 202 owing to penetration of the electric charges through the package due to high voltage. After discharging the electric charges in the circuit, the switch 208 is switched for connection with the tester 209, which tester 209 then checks that electrostatic breakdown is produced. This is done after discharging the electric charges remaining in the circuit. Otherwise, the tester is erroneously operated, or in the worst case it may be destroyed. (E) The metal bar 204 and the terminal 205a are separated away from the lead 202a. Hereby, the step of the electrostatic withstand voltage testing at the first time for a prescribed lead 202a is finished. These steps from (B) to (E) are repeated for each leads 202a. In addition, the voltage to be applied to the metal plate 203 is changed and these steps are repeated. (F) When the electrostatic withstand voltage testing for each lead 202a is finished, the IC 202 is disconnected from the metal plate 203. Any electrostatic withstand voltage testing can be effected by making use of such steps. In succession, the whole of the embodiment of the electrostatic withstand voltage testing apparatus will be described with reference to Figure 3. As shown in the figure, the electrostatic withstand testing apparatus 201 has a test table unit 231 including the metal plate 203 and the terminal base 205b illustrated in Figure 1, a test table base 232, a drive unit 233 for transmitting power to the test table unit 231, and a bar drive base 234 for moving the metal bar 204 onto the arbitrary lead 202a of the IC 202. The test table unit 231 and the test table base 232 are arranged as shown in Figure 4. Figure 4(a) shows the test table base 232, whereon levels L1 through L8 being part of the drive unit 233 are exposed. In addition, a connector 241 is provided on the side of the test table 232 for electrically connecting the test table 232 with the table unit 231. Figures 4(b) and 4(c) show the test table units 231 respectively for PLCC and DIP. The test table unit 231 having four holes 242 is guided for mounting by corresponding projections 243 provided on the test table base 232. Moreover, another connector fitting to the connector 241 is provided downwardly of the test table unit 231, and connection between these connectors is simultaneously completed by fitting of the hole 242 to the projection 243. Furthermore, cams are projected at positions corresponding to the levers L1 through L8 downwardly of the terminal base 205 provided on the test table unit and the chuck 244 for pressing the IC, and pushed and driven by movements of the levers L1 through L8 in a direction of the centre of the test table unit. The test table unit 231 (Figure 4(b)) for PLCC has eight, in total, slide parts for the four terminal bases 205b so as to make contact with leads of the PLCC derived in four directions, and for four chucks 244 so as to push four corners of the package. These slide parts are resiliently supported in the opposite direction to the outer, and adapted to slide in this opposite direction owing to the movement of the levers toward the outer. The test table unit 231 (Figure 4(c)) for DIP has four, in total, slide parts for a set of the terminal bases 205b in contact with the leads disposed along a long side of the IC, and for a set of chucks 244 each serving to push a short side of the IC. These slide parts are also adapted to slide toward the centre, but upon operation thereof any lever among the levers L1 through L8 has not a corresponding slide, which lever may not be driven. The drive unit 233 has three sheets of plate cams C1 through C3 as shown in Figure 5, which are arranged so as to be rotatable respectively independently around the same shaft, and driven respectively by motors M1 through M3 via respective timing belts. Eight shafts are arranged in the neighbourhood of the cams C in an equal interval around a concentric circuit taking the shaft described previously as a centre, each of which is supported to be rotatable with the aid of bearings. The levers L1 through L8 are provided on the upper end of each of the respective shafts and the cams L1 and L5 thereamong are arranged so as to follow the cam C3 while the levers L2, L4, L6 and L8 are arranged to follow the cam C1 and the levers L3 and L7 are arranged to follow the cam C2. Driven levers following the cam C are provided downwardly of the levers L1 through L8. These levers, since each fixedly mounted on the shaft, can transmit the motion of the motor M transmitted via the cam C to the levers L1 through L8. The present embodiment of the electrostatic withstand voltage testing apparatus can exchange the test table unit 231 with ease depending on the kind and shape of an IC to be tested, so that it can easily inspect a plurality of ICs having different shaped packages. A modification of this embodiment will now be described. In the above embodiment, any IC was fixed on the metal plate 203 with use of chuck means. Instead of this, a vacuum chuck may be employed by making a small hole in the metal plate 203 and then applying a vacuum through the hole. Moreover, the terminal 205a was divided for each lead to serve also as a terminal of the tester, but it may be plate-shaped over all leads provided a tester terminal is provided independently. Hereby, electric charges existent in the IC can be removed. A further embodiment of the electrostatic withstand voltage testing apparatus of the present invention will now be described. The apparatus in the present embodiment has a circuit for lowering the voltage of the power source. As shown in Figure 6 illustrating the electrostatic withstand voltage testing apparatus for the IC 202 of the present invention, the metal plate 203 is connected with the high DC voltage power source 206, on which the IC 202 to be tested is mounted. The metal plate 203 is further connected with one end of a switch means such as relay 301, the other end of which relay 301 is grounded via a resistor 302. The terminal 205a is grounded via a resistor 211. The metal bar 204 and the terminal 205a are brought into contact with the lead 202a of the IC 202 upon testing. First, in a state of the apparatus where the relay 301 is opened, the metal bar 204 off, and the terminal 205a off, voltage is applied from the power source 206 to the IC 202 mounted on the metal plate 203. When the voltage of the IC 202 reaches a prescribed value, the metal bar 204 is brought into contact with the lead 202a of the IC 202 for producing discharge. Thereafter, the terminal 205a is brought into contact with the lead 202a for removing electric charges left behind in the IC 202. The testing so effected for the lead 202a is finished with a series of the operations described above, and to be ready for the next lead 202a, the power source 206 is dropped with the relay 301 being closed, and thereafter the metal bar 204 and the terminal 205a are separated from the lead 202a. In the present invention, as described in detail in the first embodiment, the electrostatic withstand voltage testing apparatus has a metal plate capable of charging an IC to be tested with electric charges, and a metal bar and terminal capable of making contact with and separating from the leads of the IC. Accordingly, the charged package breakdown testing method can be executed with ease. In particular, it is effective in shipping and acceptance inspections. Furthermore, as described in detail in the second embodiment, the electrostatic withstand voltage testing apparatus is adapted to have the relay and the resistor provided in the output of the power source, whereby the potential of the metal plate can rapidly be lowered by closing the relay. Accordingly, it can be anticipated to shorten the cycle time from the finish of a test at a certain lead to the start thereof at the next lead. Furthermore, the present apparatus can also be employed as a safety devide in case where an IC to be tested is mounted on the metal plate, by keeping the relay closed.

Claims: An apparatus (201) for testing a semiconductor device including a dielectric package (202) and a lead (202a) with respect to withstand voltage thereof against electrostatic charges existing on said dielectric package (202), said apparatus comprising:- (a) charging means having a metal plate (203) connected to an output terminal of a DC power source (206) for charging said dielectric package (202) by bringing said metal plate (203) into contact with the surface of said package (202) when voltage is supplied from said DC power source (206) thereto; (b) first discharge means having a metal bar (204) connected to ground potential via a load impedance (207) for discharging charges on said package (202); said apparatus being characterised in that said first discharge means is operable to discharge charges on said package (202) by selectively bringing said metal bar (204) into contact with said lead (202a) in said successive charging of said package (202); and further comprising a second discharge means having a terminal (205a) connected to ground potential via a resistor (211) for discharging charges remaining in a circuit of said semiconductor device by bringing said terminal (205a) into contact with said lead (202a) after stopping the supply of the voltage in succession to said discharging by said first discharge means. An apparatus (201) for testing a semiconductor device with respect to withstand voltage according to claim 1, wherein said apparatus (201) further includes means to connect said output terminal of said DC power source (206) to ground potential after said discharging by said second discharge means.

Inventors: INAMURA, KAZUHIKO, TASHITA, YOJI
Applicants: OKI ELECTRIC INDUSTRY COMPANY, LIMITED
Application year: 1987
Main classification: G01R31
IPC codes: G01R31