Patent Application
20150198496
Pressure sensing devices have become ubiquitous the past few years as they have found their way into many types of products. Utilized in automotive, industrial, consumer, and medical products, the demand for pressure sensing devices has skyrocketed and shows no signs of abating.
Pressure sensing devices may include pressure sensors as well other components. Pressure sensors may typically include a diaphragm or membrane. When a pressure sensor in a pressure sensing device experiences a pressure, the membrane responds by changing shape. This change in shape causes one or more characteristics of electronic components on the membrane to change. These changing characteristics can be measured, and from this these measurements, the pressure can be determined.
Often, the electronic components are resistors that are configured as a Wheatstone bridge located on the membrane. As the membrane distorts due to pressure, the resistance of the resistors changes. This change results in an output of the Wheatstone bridge. This change can be measured through wires or leads attached to the resistors.
These pressure sensors are manufactured as die on wafers. The individual die may be tested during a process referred to as wafer-sort testing, where nonfunctional die may be marked with ink or otherwise identified. The functional or non-inked die may be assembled into packages and tested again at a final test, with the passing devices being shipped to customers.
It may be desirable to have the wafer-sort testing be thorough, that is, to identify as many nonfunctional die as possible. Each nonfunctional die that is not identified at wafer-sort testing may be packaged and tested unnecessarily a second time at final test. To avoid packaging and retesting nonfunctional devices, it may be desirable to test pressure sensor die at wafer-sort testing under an applied pressure. For increased reliability and consistency, it may be desirable that the applied pressure be well-controlled.
Thus, what is needed are circuits, methods, and apparatus that may apply a well-controlled pressure to a pressure sensor die or other integrated circuit die during wafer-sort testing.
Accordingly, embodiments of the present invention may provide circuits, methods, and apparatus that may apply a well-controlled pressure to a pressure sensor die or other integrated circuit die during wafer-sort testing. In an illustrative embodiment of the present invention, a flow of fluid may be directed towards a device-under-test by nozzle. A resulting backpressure in the nozzle may be measured and used to adjust one or more parameters until the resulting backpressure reaches a target value. The resulting backpressure may be equal to, or used as a proxy for, the pressure applied to the device-under-test. When the target backpressure is reached, the device-under-test may be tested.
In an illustrative embodiment of the present invention, a fluid may be received and provided by a flow controller. The flow controller may provide the fluid at a first flow rate to a first branch of a Y-shaped nozzle. The fluid may be directed at a device-under-test by a second branch of the Y-shaped nozzle. A resulting backpressure may be measured by a pressure sensor at a third branch of the Y-shaped nozzle. A height of an opening of the second branch of the Y-shaped nozzle relative to a device-under-test may be varied, for example, with a height or Z-controller, thus varying the resulting backpressure. When a targeted backpressure is reached, the pressure sensor may send a signal to the Z-controller, which may then substantially maintain the height of the nozzle over the device-under-test. Once the specific backpressure is reached, the pressure sensor die or other integrated circuit may be tested. These devices may be wafer-sort tested at zero pressure, one or more different pressures, or a combination of zero and one or more different pressures.
Embodiments of the present invention may provide various feedback techniques for controlling the pressure at a device-under-test. In various embodiments of the present invention, a resulting backpressure may be measured using a pressure sensor or other appropriate device. In one embodiment of the present invention, a nozzle may be lowered (or raised) until a specific or target backpressure is reached. From there, the nozzle may be held in place to substantially maintain the flow rate of the fluid. For example, a mechanism, such as the above Z-controller, may continue to monitor the backpressure signal from the pressure sensor and lower the nozzle (or raise the wafer) when the measured backpressure drops below the specific backpressure and raise the nozzle (or lower the wafer) when the backpressure exceeds the specific backpressure. Once the specific backpressure is reached, the pressure sensor die or other integrated circuit may be tested.
In other embodiments of the present invention, a range of backpressure may be targeted instead of a specific value. For example, the nozzle may be lowered (or wafer raised) until a range of targeted backpressure is reached. From there, the nozzle may substantially maintain its position. For example, a mechanism may monitor the backpressure signal and lower the nozzle (or raise the wafer) when the measured backpressure drops below the targeted range of backpressure, raise the nozzle (or lower the wafer) when the measured backpressure exceeds the range of targeted backpressure, and maintain the position of the nozzle when the measured backpressure is in the range of targeted backpressure. Once the targeted range backpressure is reached, the pressure sensor die or other integrated circuit may be tested.
In other embodiments of the present invention, the nozzle may be lowered until a target backpressure is reached. Once the target is reached, the position of the nozzle may simply be maintained and the device may be tested.
In other illustrative embodiments of the present invention, other parameters may be varied with, or instead of, relative nozzle height to provide a well-controlled pressure. For example, in a specific embodiment of the present invention, a flow rate of a fluid may be varied until a desired backpressure is measured.
Again, a pressure sensor may provide a signal indicating the measured backpressure to the flow controller. The flow controller may increase (or decrease) the flow rate of the fluid until a specific backpressure is reached. From there, the flow controller may substantially maintain the flow rate of the fluid. For example, the flow controller may continue to monitor the backpressure signal and increase the flow rate when the measured backpressure drops below the specific backpressure and decrease the flow rate when the backpressure exceeds the specific backpressure. Once the specific backpressure is reached, the pressure sensor die or other integrated circuit may be tested.
In other embodiments of the present invention, a range of backpressure may be targeted instead of a specific value. For example, the flow controller may increase the flow rate of the fluid until a range of targeted backpressure is reached. From there, the flow controller may substantially maintain the flow rate of the fluid. For example, the flow controller may continue to monitor the backpressure signal and increase the flow rate when the measured backpressure drops below the targeted range of backpressure, decrease the flow rate when the measured backpressure exceeds the range of targeted backpressure, and maintain the flow rate when the measured backpressure is in the range of targeted backpressure. Once the targeted range backpressure is reached, the pressure sensor die or other integrated circuit may be tested.
In other embodiments of the present invention, the flow controller may increase the flow rate until a target backpressure is reached. Once the target is reached, the flow controller may simply maintain the present flow rate and the device may be tested.
In still other embodiments of the present invention, a width of the opening of the nozzle may be varied. For example, the nozzle may be narrowed (or widened) until a specific backpressure is reached. From there, the nozzle width may be maintained to substantially maintain the flow rate of the fluid. A mechanism may continue to monitor the backpressure signal and narrow the opening of the nozzle when the measured backpressure drops below the specific backpressure and widen the opening of the nozzle when the backpressure exceeds the specific backpressure. Once the specific backpressure is reached, the pressure sensor die or other integrated circuit may be tested.
Again, in other embodiments of the present invention, a range of backpressure may be targeted instead of a specific value. For example, the nozzle may be widened or narrowed until a range of targeted backpressure is reached. From there, the nozzle may substantially maintain its width. For example, a mechanism may monitor the backpressure signal and widen the nozzle when the measured backpressure drops below the targeted range of backpressure, narrow the nozzle when the measured backpressure exceeds the range of targeted backpressure, and maintain the width of the nozzle when the measured backpressure is in the range of targeted backpressure. Once the targeted range backpressure is reached, the pressure sensor die or other integrated circuit may be tested.
In other embodiments of the present invention, the nozzle may be widened or narrowed until a target backpressure is reached. Once the target is reached, the width of the nozzle may simply be maintained and the device may be tested.
Again, in the above embodiments of the present invention, a known pressure is applied to a device-under-test while the device is being tested. This allows for electrical wafer-testing of pressure sensor devices at actual pressure. Test results, such as resistance measurements at a pressure, can be used by themselves, or with test results at zero or other pressures to determine whether a device is functional, and in some circumstances could be used to determine a grade or binning of a device.
In other embodiments of the present invention, instead of testing a device at a fixed pressure, the pressure may be varied during a test. The pressure may be varied by changing a height of a nozzle, a fluid flow rate, or a width of a nozzle opening. In still other embodiments of the present invention, instead of only performing electrical tests on a device-under-test, mechanical-oriented tests may also be performed. That is, mechanical tests, such as tests to determine a mechanical or physical deflection of the membrane, may also be performed.
In these and other embodiments of the present invention, the height, flow rate, or nozzle width may be initially calibrated before being used to apply pressure to a pressure sensor membrane. For example, a nozzle may be positioned above a die, wafer, or other structure that is less susceptible to deflection than a membrane. The nozzle may be positioned above a test structure, a portion of a frame, or other similar inflexible region. Fluid may be directed toward the test structure or frame. The nozzle height, flow rate, or nozzle width may be varied as described above until a target backpressure is reached.
The nozzle may then be moved over the membrane on the device-under-test and the same nozzle height, flow rate, and nozzle width may be used while fluid is directed at the membrane. A change in pressure may be measured. In various embodiments of the present invention, this change in pressure may be measured and used to determine a deflection of the membrane or other appropriate parameter.
In other embodiments of the present invention, the change in pressure may be measured and the nozzle may be lowered, fluid rate increased, or nozzle opening narrowed until the target backpressure is reached again. This change in height, fluid rate, or nozzle opening may be used to determine a deflection of the membrane or other appropriate parameter. It should be noted that these mechanical-oriented tests may be performed on a device-under-test in the absence of any wafer-probe or other electrical testing.
Also, other types of mechanical tests, such as burst tests may be performed using embodiments of the present invention. For example, a fluid pressure may be increased until a membrane reaches a point of mechanical failure. A measured pressure at the point of failure could be used to evaluate membrane thickness, wafer integrity, or other parameters.
In various embodiments of the present invention, different fluids may be provided by the flow controller. For example, air or an inert gas may be provided by the flow controller. In various embodiments of the present invention, nitrogen, argon, or other gas or fluid may be provided by the flow controller. In various embodiments of the present invention, the fluid may be heated or cooled to change a temperature of a device-under test, or portion thereof, during testing. It should also be noted that the passage of fluid across a membrane may have a cooling effect on a device-under test.
Various embodiments of the present invention may test wafers using the above techniques in different ways. For example, each die may be individually tested. That is, a flow rate, nozzle height, or nozzle width may be varied for each die. In other embodiments of the present invention, the results of testing one die may be used in testing one or more other die. For example, once a flow rate corresponding to a specific backpressure is known, this flow rate may be set by the flow controller and used in testing one or more following wafers. In this case, the flow controller may simply set the flow rate while testing the later die and not adjust the flow rate based on the measured backpressure. In other embodiments, the flow controller may use a flow rate corresponding to a specific backpressure measured on a first die and use that as a starting flow rate on later die, while using the measured backpressure to adjust the flow rate. These and other techniques may include the other types of feedback and parameter adjustments described herein.
Various embodiments of the present invention may incorporate one or more of these and the other features described herein. A better understanding of the nature and advantages of the present invention may be gained by reference to the following detailed description and the accompanying drawings.
Wafer 110 may be placed on a surface of holder 120. During testing, holder 120 may be moved by chuck 130. Chuck 130 may also provide a suction or vacuum force to keep wafer 110 in place on holder 120. Probe card 150 may support one or more probes 140. Probes 140 may make contact with pads (not shown) on individual die on wafer 110. Probes 140 may provide input voltages or currents and measure output voltages or currents at these pads. Probe card 150 may be supported by a frame 152 residing on a support structure 154.
Again, it is desirable to identify as many improperly functioning die on wafer 110 as possible during this wafer-sort testing. An improperly functioning die missed at this stage results in that improperly functioning die being packaged and tested again at final test. Identifying such an improperly functioning die at wafer-sort reduces total packaging costs and improves final test yield.
Pressure sensors may be tested at a zero pressure state. Such testing may be sufficient to identify a good number of improperly functioning die at wafer-sort. To improve wafer-sort testing, and therefore to reduce packaging costs and improve final test yields, embodiments of the present invention may provide methods, circuits, and apparatus for additionally testing pressure sensors while they are under pressure. That is, embodiments of the present invention may enable the testing of die on a wafer at one or more different pressures. These tests may include electrical tests, such as resistance measurements, and mechanical tests, such as membrane deflection measurements.
Accordingly, the apparatus in this figure may include nozzle 160 to provide a flow 170 of fluid to a surface of a die on wafer 110. This fluid may be directed to a membrane on a pressure sensor or other structure. Flow 170 may provide a pressure at the membrane of the pressure sensor. In other embodiments of the present invention, nozzle 160 may provide a vacuum, which may provide a negative pressure at the membrane of the pressure sensor die being tested.
The resulting pressure, negative or positive, may deform the membrane, which may result in a pressure reading from the pressure sensor die on wafer 110. The pressure sensor reading from the device-under-test may be read using one or more probes 140. The results of these measurements may be used to identify a properly functioning or an improperly functioning die on wafer 110.
By providing a flow 170, nozzle 160 does not need to come into contact with wafer 110, thereby protecting both wafer 110 and nozzle 160.
In a specific embodiment of the present invention, a pressure sensor die being tested may include a Wheatstone bridge, multiple active devices, or other structures. An input voltage may be applied to the Wheatstone bridge or other structure using one or more probes 140. A resulting output voltage from the Wheatstone bridge or other structure may be read using one or more probes 140. These voltages may be measured with zero or one or more positive or negative pressures applied to the membrane of the device-under-test. For example, a die may be tested at zero pressure and one or more positive pressures.
It should be noted that, while embodiments of the present invention are particularly well suited for testing pressure sensors, other devices, such as flow rate sensors, touch screens, touch switches, and other types of devices may be tested, using embodiments of the present invention.
For example, a flow rate sensor may include a die with two resistors, one on each side of a wire. Current may be passed through the wire, generating heat. This heat may change the value of the neighboring resistors. As air or another fluid passes across the surface of the flow rate sensor, a value of one resistor may change relative to the other. The difference in values of the resistors may provide an indication of the rate of flow of the fluid. The air or other fluid may be applied, using techniques according to embodiments of the present invention.
To improve the repeatability and usefulness of this pressure testing, embodiments of the present invention may provide methods, circuits, and apparatus for providing a well-controlled pressure. By providing a well-controlled pressure, testing accuracy and repeatability may be improved. Embodiments of the present invention may provide a well-controlled pressure by providing a fluid flow 170 at an output of nozzle 160, measuring a resulting backpressure, and then using the measured backpressure to adjust fluid flow 170. Fluid flow 170 may be varied by changing a height of nozzle 160 relative to wafer 110, by varying a flow rate through nozzle 160, by varying a width of an opening or other portion of nozzle 160, or by varying other appropriate parameters. Examples of this are shown in the following figures.
Sensor 240 may be connected to a third branch 234 of nozzle 160. Sensor 240 may sense a backpressure in nozzle 160. The backpressure of nozzle 160 may be the same or related to a pressure being experienced by the device-under-test. Sensor 240 may use this backpressure measurement to control a height of nozzle 160 relative to wafer 110. Specifically, Z-controller 250 may control the height by moving nozzle 160. In other embodiments of the present invention, Z-controller 250 may adjust this height by moving the position of chuck 130.
Specifically, sensor 240 may provide a measured backpressure signal 255 to a height control unit or Z-controller 250. Z-controller 250 may provide a height signal 255 to adjust the vertical position of nozzle 160. Alternately, Z-controller 250 may provide a height signal 257 to control a height or Z-position of wafer 110 by moving chuck 130 up or down. In various embodiments of the present invention, care should be taken that changing the height of wafer 110 does not cause probes 140 to form unreliable connections with pads on the device-under-test or that probes 140 do not damage the device-under-test or adjoining structures. In this example, as the relative height of nozzle 160 relative to wafer 110 increases, the measured backpressure, and hence the applied pressure at the device-under-test, may decrease, while a decrease in height may increase the backpressure and applied pressure.
Again, these techniques may be used to measure electrical properties of a device-under-test at a pressure. Similar techniques may also be used to measure physical or mechanical properties of the device-under-test. For example, the amount of deflection of a membrane may be estimated or determined.
In a specific embodiment of the present invention, the height of a nozzle may be initially calibrated. For example, a nozzle may be positioned above a die, wafer, or other structure that is less susceptible to deflection than a membrane, such as a test structure, a portion of a frame, or other similar inflexible region. Fluid may be directed toward the test structure or frame. The height of the nozzle may be varied as described above until a target backpressure is reached.
The nozzle may then be moved over the membrane on the device-under-test and the same nozzle height may be used while fluid is directed at the membrane. A change in pressure may be measured. In various embodiments of the present invention, this change in pressure may be measured and used to determine a deflection of the membrane or other appropriate parameter.
In other embodiments of the present invention, the change in pressure may be measured and the nozzle may be lowered until the target backpressure is reached again. This change in height may be used to determine a deflection of the membrane or other appropriate parameter.
Also, other types of mechanical tests, such as burst tests may be performed using embodiments of the present invention. For example, a fluid pressure may be increased until a membrane reaches a point of mechanical failure. A measured pressure at the point of failure could be used to evaluate membrane thickness, wafer integrity, or other parameters.
In various embodiments of the present invention, fluid 220 may be air, argon, nitrogen, or other inert or non-inert gas. In various embodiments of the present invention, the fluid may be heated or cooled to change a temperature of a membrane during testing. It should also be noted that the passage of fluid across a membrane may have a cooling effect on a device-under test.
Again, similar techniques may be used to measure physical or mechanical properties of the device-under-test. In a specific embodiment of the present invention, the fluid flow rate may be initially calibrated. For example, a nozzle may be positioned above a die, wafer, or other structure that is less susceptible to deflection than a membrane, such as a test structure, a portion of a frame, or other similar inflexible region. Fluid may be directed toward the test structure or frame. The flow rate of fluid in the nozzle may be varied as described above until a target backpressure is reached.
The nozzle may then be moved over the membrane on the device-under-test and the same nozzle height may be used while fluid is directed at the membrane. A change in pressure may be measured. In various embodiments of the present invention, this change in pressure may be measured and used to determine a deflection of the membrane or other appropriate parameter.
In other embodiments of the present invention, the change in pressure may be measured and the flow rate may be increased until the target backpressure is reached again. This change in flow rate may be used to determine a deflection of the membrane or other appropriate parameter.
Flow controller 210 may provide fluid 220 to a first branch 232 of nozzle 160. Nozzle 160 may provide this fluid through opening 238 of a second branch 236 to the device-under-test. A resulting backpressure may be read by sensor 240, which may be attached to nozzle 160 through third branch 234. Sensor 240 may provide a measured backpressure signal 255 to width control circuits 450. Width control circuit 450 may provide a width signal 455 to nozzle 160. Nozzle 160 may open or constrict as a result of this signal. For example, an opening 238 may open or constrict under control of signal 455. Specifically, if the measured backpressure 255 is below a desired level, the width signal may instruct opening 238 to constrict, thereby increasing the measured backpressure at sensor 240. If the measured backpressure 255 is above a desired level, the width signal may instruct opening 238 to widen, thereby decreasing the measured backpressure at sensor 240. As before, the backpressure measured by sensor 240 may be the same as, or a proxy for, the pressure applied to the device-under-test.
Again, similar techniques may be used to measure physical or mechanical properties of the device-under-test. In a specific embodiment of the present invention, the nozzle opening width may undergo an initial calibration. For example, a nozzle may be positioned above a die, wafer, or other structure that is less susceptible to deflection than a membrane, such as a test structure, a portion of a frame, or other similar inflexible region. Fluid may be directed toward the test structure or frame. The opening in the nozzle may be varied as described above until a target backpressure is reached.
The nozzle may then be moved over the membrane on the device-under-test and the same nozzle height may be used while fluid is directed at the membrane. A change in pressure may be measured. In various embodiments of the present invention, this change in pressure may be measured and used to determine a deflection of the membrane or other appropriate parameter.
In other embodiments of the present invention, the change in pressure may be measured and the nozzle opening may be narrowed until the target backpressure is reached again. This change in nozzle opening may be used to determine a deflection of the membrane or other appropriate parameter.
In various embodiments of the present invention, a backpressure measured by sensor 240 may be used to adjust the pressure received by the die in various ways. For example, a feedback loop may adjust a parameter to increase the pressure when the measured backpressure is too low. When the measured backpressure is too high, the loop may adjust a parameter to decrease the pressure. In other embodiments of the present invention, a targeted range of pressures may be used. If a measured backpressure is below the targeted range, a parameter may be varied to increase the pressure, while, if a measured backpressure is above the targeted range, a parameter may be varied to decrease the measured backpressure. When a measured pressure is in the targeted range, no adjustment is made. In still other embodiments of the present invention, a pressure may be increasingly or decreasingly ramped until a desired backpressure is reached. At that time, no further changes to the parameter are made. These and other types of feedback configurations may be employed by embodiments of the present invention. Examples are shown in the following figures.
Accordingly, in act 510, a pressure is increased, while a resulting backpressure is measured in act 520. In act 530, a targeted backpressure is reached. At this time, the device may be tested. If a backpressure falls low, as in act 540, the pressure may be increased in act 545. Similarly, when the backpressure becomes excessive in act 550, the backpressure pressure may be decreased in act 555.
The pressure may be increased in the above example by decreasing a height of nozzle 160 relative to wafer 110 (by either lowering nozzle 160 or raising wafer 110, or both), by increasing a flow rate of fluid 210 in nozzle 160, or by constricting opening 238 on nozzle 160. The pressure may be decreased in the above examples by increasing a height of nozzle 160 relative to wafer 110 (by either raising nozzle 160 or lowering wafer 110, or both), by decreasing a flow rate of fluid 210 in nozzle 160, or by widening opening 238 of nozzle 160.
Again, the pressure may be increased in the above example by decreasing a height of nozzle 160 relative to wafer 110 (by either lowering nozzle 160 or raising wafer 110, or both), by increasing a flow rate of fluid 210 in nozzle 160, or by constricting opening 238 on nozzle 160. The pressure may be decreased in the above examples by increasing a height of nozzle 160 relative to wafer 110 (by either raising nozzle 160 or lowering wafer 110, or both), by decreasing a flow rate of fluid 210 in nozzle 160, or by widening opening 238 of nozzle 160.
Again, the pressure may be increased in the above example by decreasing a height of nozzle 160 relative to wafer 110 (by either lowering nozzle 160 or raising wafer 110, or both), by increasing a flow rate of fluid 210 in nozzle 160, or by constricting opening 238 on nozzle 160. The pressure may be decreased in the above examples by increasing a height of nozzle 160 relative to wafer 110 (by either raising nozzle 160 or lowering wafer 110, or both), by decreasing a flow rate of fluid 210 in nozzle 160, or by widening opening 238 of nozzle 160.
In various embodiments of the present invention, each of the die on wafer 110 may be tested according to one of the methods outlined above. In other embodiments the present invention, one or more parameters, such as a height setting, flow rate, or nozzle width, may be stored and used in testing one or more subsequent die. An advantage of this may be to reduce overall test time. A disadvantage may be that one or more of these parameters may not be accurate for an adjacent die and may lead to either incorrectly identifying functional die as non-functional or nonfunctional die as functional. An example is shown in the following figure.
In other embodiments of the present invention, pressure testing may be performed on a limited number of die on the wafer. For example, only one die in N may be tested, where N is 2, 5, 10, or other number. This may help to reduce wafer-sort test times.
In various embodiments of the present invention, more than one of the above methods may be employed in testing a wafer. For example, a position of nozzle 160 may be controlled until an initial pressure is achieved. From there, the flow rate may be varied and testing may be done at different pressures.
In various embodiments of the present invention, various types of tests may be performed. For example, it may be desirable to perform a destructive test where pressure is increased until a mechanical failure of a membrane or other portion of a device-under-test occurs. In various embodiments of the present invention, these destructive tests are done on devices that have been previously identified as non-functional.
The above description of embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form described, and many modifications and variations are possible in light of the teaching above. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Thus, it will be appreciated that the invention is intended to cover all modifications and equivalents within the scope of the following claims.
