Abstract:
A high permeability magnetic core structure introduces a magnetic field to an intergrated circuit during testing. The magnetic core is mounted in an automatic tester and is integrated into the mechanical test site assembly that holds the integrated circuit in place during testing. Wound wire coils, mounted on the core structure, generate the magnetic field that is used for the test.

Description:
BACKGROUND OF THE INVENTION 
     Devices such as integrated circuits that have circuitry and/or structures for sensing a magnetic field should be tested by applying a known magnetic field and measuring an output signal to determine whether an actual output signal is sufficiently close to an expected output signal. One way to perform such testing is to use a coil in a bench test. This process allows testing in a carefully controlled testing environment, but is labor intensive and not suitable for testing large numbers of devices. It would be desirable to have a system that could automatically and controllably test large numbers of devices designed to sense magnetic fields, and more desirable to further be able to control for electrical and temperature effects. 
     SUMMARY OF THE INVENTION 
     A testing system according to the present invention tests devices in the presence of a magnetic field repeatably and quickly so that production runs of devices can be tested. 
     The testing system preferably also includes equipment for performing electrical testing, and is configured so that both electrical input and magnetic input can be provided at one testing location. A magnetic field source, preferably an electromagnetic coil that allows the magnetic field to be controlled and varied to test at multiple known magnitudes, provides a known magnetic field to a device with a magnetic core assembly. The core assembly is integrated into the testing machine in such a way that the magnetic flux is contained but can be passed directly through the device being tested. This containment is accomplished by the configuration of the core assembly and the selection of materials, depending on whether those materials have high permeability or low permeability. 
     Because of the use of a magnetic field, components of the core assembly should have high permeability, e.g., a maximum D.C. permeability at least on the order of 10 5 , while other components near the device and the core should have permeability close to one (1). Such low permeability materials include plastic and certain types of stainless steel (e.g., the 300 series). In addition, it is desirable for the track or conveyor to have a slit at a location near the device to minimize Lorentz forces that may be induced near the device when the magnetic field changes. This slit is particularly desirable if the magnetic generator is a coil and the magnetic field varies. 
     The system is preferably configured for surface mount SOIC packages or for dual in-line packages (DIPs). 
     In a method according to the present invention, a device is brought to a testing location, and electrical conductors are brought into contact with pins from the device to sense output signals in response to input conditions. One or more electrical signals are provided from the conductors to one or more of the pins, and a resulting signal or signals is/are sensed with the conductors in response to the electrical input. One or more known magnetic fields are applied to the device and a resulting signal or signals is/are sensed in response to the magnetic field input. These electrical and magnetic tests are performed sequentially in either order (although preferably magnetic last) while the device is held in one testing location. The method thus allows multiple tests to be performed without moving the device to another location between tests. 
     The testing system of the present invention can thus provide a controllable and variable magnetic field directly through the device and can contain the generated magnetic field over a wide range of field strengths. The testing system of the present invention can perform electrical and magnetic tests of integrated circuits quickly and at a single location, thus speeding the process per device. The testing system preferably also controls temperature, so the device can be characterized in a uniform temperature environment and over the full temperature range if desired. Other features and advantages will become apparent from the following detailed descriptions, drawings, and claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block and pictorial view of a known testing device. 
     FIG. 2 is a front view of a portion of a testing assembly according to the present invention. 
     FIG. 3 is a part cross-sectional, part side view of the portion of the testing assembly of FIG.  2 . 
     FIG. 4 is a perspective view of a magnetic core assembly. 
     FIG. 5 is a front view of a track, illustrating the use of a slit for preventing Lorenz forces. 
    
    
     DETAILED DESCRIPTION 
     A known type of testing system  10  for testing packaged integrated circuits (ICs) is represented in FIG.  1 . Testing systems of this general type are commercially available from Aseco Corporation of Marlboro, Mass., e.g., an Aseco S170 model. Devices  14  that are to be tested are held in a hopper  12 . A track  16  carries devices  14  from hopper  12  to a testing area  20 . At this testing area, a pin (not shown) holds the device in place. While not shown in FIG. 1, track  16  is actually bowed outwardly at the testing area and curves away in the same direction above and below the testing area. The devices that are represented here are surface mount 8-pin SOIC devices (four pins on each side), although the testing system can be adapted to other types of packaged devices, such as dual in-line packages (DIPs). 
     Testing area  20  is covered with a track cover  18  that has two vertically elongated slots  22 ,  24 . Testing paddles  26 ,  28  extend through slots  22 ,  24  and orthogonally away from track  16 . Paddles  26 ,  28  have conductors (test pads)  32 ,  34  used to make an electrical connection with pins  30  that extend from device  15 . A spring loaded pair of metal bellows (not shown) pushes paddles  26 ,  28  into and out of contact with pins  30 . Electrical testing is performed by providing input signals through conductors  32 ,  34  to selected ones of pins  30  and receiving output signals from selected ones of pins  30  through conductors  32 ,  34 . 
     In such devices, testing is performed in an enclosed temperature-controlled chamber that has sensors for sensing the temperature within the chamber and a heating mechanism for providing heat. The device can thus be characterized over a desired temperature range. 
     The mechanical, electrical, and temperature control are represented generally here as “control”  40 , and each of these control functions is generally known. Control  40  can include a programmed microprocessor, general purpose computer, one or more ASICs, or some combination of these components. Control  40  controls the metal bellows to move the test paddles, the heater to control the temperature in response to a temperature sensor, and circuitry for providing input signals and detecting output signals. With appropriate modifications, the control functions can be modified for other types of devices, such as DIPs. 
     After a device is tested in testing area  20 , the pin (not shown) that holds the device is retracted to release the device down track  16  to a sorter  42 . Sorter  42  causes the tested devices to be sorted into a number of bins  42 - 44  (three bins are shown, but there can be more). These bins allow sorting into pass and fail devices, and allow the failed devices to be further subdivided. 
     Referring also to FIGS. 2 and 3, the testing system of the present invention is designed to test devices in the presence of a known magnetic field. Consequently, it is particularly useful for testing devices that sense magnetic fields. The testing system is preferably a modified version of the general type of testing device described above in connection with FIG. 1, to keep the features of electrical testing and temperature control. Like the known system, the testing system of the present invention preferably has a hopper or some other storage for keeping a large number of devices, a track or some other type of conveyor or transporter for providing one or more devices to a testing location, testing paddles or some other set of electrical conductors for making contact with the device to provide and/or receive signals, a sorter for sorting devices after testing, and bins. The principles and features of the present invention are not necessarily limited, however, to any particular type of testing system or packaged device. 
     In a manner similar to that shown in FIG. 1, the devices to be tested are provided from a hopper along a track  50  in a line so that multiple devices are on track  50  at the same time. Referring particularly to FIG. 3, before reaching the testing location, a device is physically stopped by a series of pins  52 ,  54 , and  56  (FIG.  3 ). Pins  52 ,  54 , and  56  each stop the devices, thereby effectively pipelining the devices to the testing area. Pins  52  and  54  are moved with springs  58 ,  60  and metal bellows  62 ,  64  under control from a controller over electrical lines  66 ,  68 . Pin  56  is also controlled with an actuator  70  that is pushed forward and drawn back with bellows  72  and spring  74  under control over line  76 . 
     Underneath the testing area is a stop pin  80  that stops the device after pin  56 , the last pin before the testing location, releases the device. The device hits stop pin  80  and may bounce somewhat before coming to rest, at which time an actuating pin  82  is operated to contact the device to hold the device against a track cover  84  at a testing location  85 . Pin  82  is extended and retracted with a bellows  86  and a spring  88 . 
     After the device is thus secured between pin  82  and cover  84  at testing location  85 , electrical conductors, such as testing paddles of the type shown in FIG. 1 (but not shown in FIGS.  2  and  3 ), are brought into contact with the leads from the device to perform electrical testing in a generally known manner. The paddles extend through slots  90 ,  92  and are controlled in part through bellows  94 ,  96 . After the electrical testing is done, magnetic testing is performed, and then pin  82  is retracted to allow the device to continue down track  50  to a sorter as described in connection with FIG.  1 . The magnetic testing could be performed either before or after the electrical testing. 
     To perform the magnetic testing, a magnetic field is provided by a magnetic core assembly  100  that is made of a high permeability material, such as permalloy  80 , which has a D.C. permeability of about 75,000 at B=100 Gauss. Core assembly  100  supports two coils  99 ,  101  (FIG. 2) at a location near the electrical testing area. 
     FIG. 4 is a perspective view showing in more detail core assembly  100  removed from the testing device. Core assembly  100  has a back plate  102  and a front plate  104 , each of which is made from a number of laminated layers of high permeability material. The laminated structure provides high permeability, low eddy-current losses, and low hysteresis. While the number of layers can vary, it has been found that a laminate of 7-8 layers is sufficient. These layers are glued together after first being annealed to increase permeability. 
     Back plate  102  is a single integral member that has two parallel L-shaped legs  105 ,  106  and a cross piece  108 . L-shaped legs  105 ,  106  have long vertical legs parallel to the track and shorter horizontal legs  110 ,  112  extending perpendicular to the track. Cross piece  108  connects the tops of the vertical legs, and at its center has a recessed region  114  that is recessed in a direction perpendicular to plate  102 . At region  114 , an opening receives actuating pin  82 , which contacts the device being tested. Each of the longer vertical legs has an opening  116  near its respective horizontal leg for receiving a pin or screw  117  for rigidly mounting back plate  102  to a support bracket  118  (FIG.  3 ). 
     Front plate  104  is roughly an inverted T-shape with a vertical post  120  and an integral horizontal cross piece  122 , together forming a vertical plane parallel to the track at the testing location. At the ends of cross piece  122  are two horizontal legs  124 ,  126  extending perpendicular to the cross piece (and the track) and positioned to abut horizontal legs  110 ,  112  from back plate  102 . Post  120  has an opening  130  for receiving a screw  132  for connecting front plate  104  to track  50 . 
     Wrapped around the pairs of horizontal legs of the back plate and the front plate, i.e., legs  112  and  126 , and legs  110  and  124 , are two coils  99 ,  101  with many turns. These coils are electrically coupled to a control system that controls the current flowing into the coils, and hence controls the magnetic field, preferably up to 1000 Gauss. The coils are on a bobbin and are provided over the horizontal legs of the back plate before the front plate is mounted to the track. The bobbins are held tightly on the pairs of horizontal legs. 
     Near the top of post  120  is a high permeability stud  140  that extends horizontally into track cover  84  at a position near the device being tested. Stud  140  can be simply rectangular with a single flat face, or it can have two parallel legs extending toward the device, with one leg longer than the other to create air gaps with different widths. 
     As best shown in FIG. 3, stud  140  has a larger diameter or diagonal portion  142  and a reduced cross-sectional portion  144  (shown in dashed lines) that forms a shoulder  146 . Reduced cross-sectional portion  144  extends into a hole in cover  84 , while shoulder  146  contacts the outside of cover  84 . 
     In prior testing devices, a cover for the testing location would typically be made of stainless steel and would include a series of mirrors that were used with fiber optic lines to sense when a device was at a location along the track. According to the present invention, however, the mirror at the actuator pin is omitted while the front surface of the stud, extending into the cover, is polished so that it has a reflective surface. Also, track cover  84  is made of a low permeability material, such as a G-10 machinable plastic. The actuator pin and the stud thus each perform multiple functions, including completing a magnetic circuit. 
     As shown particularly in FIGS. 3 and 4, back plate  102 , front plate  104 , actuator pin  82 , and stud  140  form a magnetic circuit with the device in a gap between pin  82  and stud  140 . The plates, stud, and actuator pin are all made of high permeability materials to form the magnetic circuit. Other materials near this magnetic circuit are made of low permeability or non-permeable materials. In prior testing devices similar to that shown in FIG. 1, there were many components made of stainless steel in the 400 series, which has high permeability. According to the present invention, however, the cover, the components of the support frame, and other components are made of machinable plastic, or of a low permeability stainless steel, such as stainless steel in the 300 series, which has a permeability of about 1.0 at B=20 Gauss. These low permeability components include cover  84 , screw  117 , bracket  118 , and screw  132 . The track itself, both in prior testing systems and in the system of the present invention, is made from aluminum with low permeability. 
     Referring to FIGS. 2 and 5, track  50  has a slit  150  along one side and extending at about midway in the vertical direction relative to a device  152  being tested. Slit  150  extends about half the width of track  50  to create a gap that helps to minimize Lorentz forces. (As is well known, a change in a desired magnetic field, including a step function, creates current loops that induce a magnetic field that is opposite to and works against the desired magnetic field.) 
     A method for using a testing system according to the present invention involves testing both electrical and magnetic characteristics. When a device is brought to the testing location and the actuator pin holds the device in place, electrical tests are performed through the pins. The magnetic test is preferably performed after the electrical test because the magnetic test takes more time and because the results of the electrical test may make magnetic testing unnecessary. To make the magnetic test, one or more magnetic fields are provided around the device, and the upward signal is read from the device to determine whether the device is properly sensing the magnetic field. In one particular example, fields of +400 gauss, and −400 Gauss are applied. The coils allow the magnetic field to be applied rapidly; as a result, the magnetic field testing is very fast, e.g., 100 msec. The magnetic field testing is sufficiently fast to prevent any delay in the system because even with the additional time of the magnetic test, the testing procedures are still faster than mechanical delays in the system. 
     The testing mechanism can also be used for calibration. In a highly sensitive magnetic field sensor, stresses in the device can create changes in the signal produced from the sensor, even at an external magnetic field of 0. To calibrate the testing device, a device is positioned in the testing area, and a signal is received when the magnetic field equals 0 to determine a zero offset, i.e., the signal that is produced from various magnetic fields introduced by other parts of the circuitry of the testing machine. When this offset is determined, a magnetic field is introduced, and the desired electrical signal is received. 
     Having described an embodiment of the present invention, it should be apparent that other modifications can be made without departing from the scope of the appended claims. For example, while the magnetic generating assembly has been described for use with a device that tests 8-pin SOIC type packages, it should be understood that principles of the present invention can be applied to handlers for testing other types of devices.