MXPA98006593A - Package for a sensor device of a magnet field - Google Patents

Abstract

The present invention relates to a package for a sensor device of a magnetic field, of the type used in the assembly and packing of integrated circuits, which comprises in combination: a magnet to create a magnetic field, a semiconductor sensor Without encapsulating located within said magnetic field to sensitize the power of said magnetic field, said sensor is adapted to detect a ferromagnetic object passing through said field, a lead metal frame having a coupled cushioned die, upon which said sensor is secured, an assembly for securing said magnet in close proximity to the sensor and magnet mentioned, a sensor and a lead frame assembled to form a semiconductor integrated circuit encapsulated in a plastic package molded in a single operation, said assembly having a or more outgoing to ensure the im

Description

PACKAGE FOR A SENSOR DEVICE OF A MAGNETIC FIELD BACKGROUND OF THE INVENTION The present invention relates to a sensor device of a magnetic field and relates to the assembly and packing of the integrated circuits including a given Hall effect sensor and a magnet to reduce the minimum distance obtainable between the sensor device and the ferromagnetic object that is being captured. Magnetic sensing devices that can detect the presence of a ferromagnetic object in the vicinity of the sensing device have been widely used. Such sensor devices typically use a magnetic field and employ sensing apparatuses that detect changes in the strength of a magnetic field. The strength of a magnetic field is defined as the magnetomotive force developed by a permanent magnet by the distance in the direction of magnetization. As an example, an increase in the strength of a magnetic field, which corresponds to the reluctance drop of a magnetic circuit, will occur while an object made of a highly magnetic permeability material, such as iron, is moved towards the magnet. Magnetic permeability is the ease with which lines of magnetic force, called magnetic flux, can pass through a magnetized substance with a given magnetic force. quantitatively, it is expressed as the ratio between the magnetic flux density (the number or lines of magnetic flux per unit area, which are perpendicular to the flow direction) produced and the strength of the magnetic field, or magnetizing force. Because the output information signal of a sensor device of a magnetic field depends on the strength of the magnetic field, it is effective in detecting the distance between the sensor device and the object within the magnetic circuit. The range within which the object can be detected is limited by the flux density, which is measured in gauss or teslas. Where it is desired to determine the speed or rotational position of a rotating object, such as a disc mounted on an axis, the object is typically provided with surface features projecting towards the sensor device, such as the teeth. The proximity of the tooth to the sensing device will increase the strength of the magnetic field. Accordingly, by monitoring the output of the sensing device, the rotational speed of the disc can be determined by correlating the peaks at the sensor outputs with the known number of teeth at the circumference of the disc. Likewise, when the teeth are irregularly spaced in a predetermined pattern, the rotational position of the body can be determined by correlating the intervals of the peaks with the known number of intervals between the teeth on the disc. One prominent form of such a sensing device is a Hall effect sensor.

A Hall effect sensor depends on a transverse current flow that occurs in the presence of a magnetic field. The Hall effect sensor is driven primarily by a direct current voltage source having electrodes at both ends of the Hall effect sensor, creating a longitudinal current flow through the sensor body. In the presence of a magnetic field, a transverse current is induced in the sensor which can be detected by a second pair of electrodes transverse to the first pair. The second pair of electrodes can then be connected to a voltmeter to determine the potential created through the surface of the sensor. This transverse current flow increases with a corresponding increase in magnetic field strength. The Hall effect sensor is mounted inside and perpendicular to a magnetic circuit that includes a permanent magnet and an exciter. The exciter is an element of high magnetic permeability that has projected surface characteristics, which increase the strength of the magnetic field of the magnet by reducing the distance between the surface of the exciter and the permanent magnet. Typically, the exciter will be in the form of a series of spaced teeth separated by notches, such as teeth in a gear. The exciter moves relative to the stationary Hall effect sensor element, and in doing so, changes the reluctance of the magnetic circuit to cause the magnetic flux passing through the Hall effect element to vary correspondingly to the position of the teeth . With the change in the magnetic flux a corresponding change in the strength of the magnetic field occurs, which increases the transverse current of the Hall effect sensor. With the increase in product sophistication, magnetic field sensing devices have also become common in products that depend on electronics for their operation, such as automotive control systems. Common examples of automotive applications are the detection of the ignition timing of the crankshaft of the machine and / or camshaft, and the detection of the speed of the wheels for anti-skid braking systems and four-wheel steering systems. For detecting the speed of the wheels, the exciter is typically an exciting wheel mounted inboard of the vehicle wheel, the driving wheel is mechanically connected to the wheel so as to rotate with the wheel. The driving wheel is provided with a number of teeth extending axially from the perimeter of the driving wheel to the magnetic field sensor mounted inwardly. As mentioned before, the driving wheel is formed of a highly magnetically permeable material, such as the iron, so that each tooth rotates towards the sensing device, the magnetic field strength increases as a result of the decrease in the reluctance of the magnetic circuit. Subsequently, the reluctance of the magnetic circuit increases and the strength of the magnetic field decreases as the tooth moves away from the sensing device. In the situation when a Hall effect sensor is used, there will be a corresponding peak in the potential of the device through the transverse electrodes as each tooth of the device passes. A common deficiency of magnetic field sensing devices is their dependence on output information on the distance of the exciter and the sensing device, known as air separation. More specifically, by increasing the air separation, the maximum range of output information of the device decreases and thus the resolution of the output information decreases and makes it more difficult to accurately analyze the output information of the device. The output information of the Hall effect device is directly proportional to the strength of the magnetic field, and therefore it is sensitive to the separation of air in magnetic fields of low force. Conventionally, air separation is defined as the distance between the exciter and the outer surface of the package containing the sensing device. An "effective air separation" can be described as the distance between the exciter and the sensing device alone. As can be seen in FIG. 1, prior art magnetic sensors (10) typically include a permanent magnet (14), and a sensor device (16) encapsulated in a package (18). However, this type of packaging is not appropriate for harsh environments, particularly those of a car. As a result, such packaged sensing devices are subsequently included in an additional envelope (overmold) 20) which provides protection against moisture and dirt. Accordingly, while the air separation of the sensor device (22), the distance between the exciter and the packing of the sensor device may not change, the effective air separation of the sensor device (24), the distance between the exciter and the sensor device alone can be significantly increased. In this way, while improving the life of the sensing device, a particularly significant deficiency in this aspect is the decrease in peak force of the magnetic field upon passing a tooth in the vicinity of the sensing device due to the largest effective air separation. . In addition, a variety of steps are required to assemble the numerous components of this assembly. Still another problem is that it is desirable to have the sensor device (16) as close as possible to the magnet (14) because the magnetic field decreases as a function of air separation. Being closer allows the use of a smaller or lower energy magnetic product. Thus, it is desirable to provide a packaging scheme for a magnetic field sensing device, such as the Hall effect device, which will provide reliable protection of the environment while also preventing an excessive increase in effective air separation between the sensing device and The exciter, which reduces the number of assembly steps, and which allows this sensor device to be as close as possible to the magnet. SUMMARY OF THE INVENTION CONSISTS In an assembly of integrated circuit magnetic field sensors include a magnet, a sensor and a metal conductor frame encapsulated in a plastic package. The magnet creates a magnetic field. A semiconductor sensor is located within the magnetic field to detect the strength of the magnetic field. The sensor allows the detection of a ferromagnetic object that passes through the field. The conductor frame has a bearing for embedding the die with which the sensor is fixed and an assembly for securing the magnet in close proximity to the sensor. The assembly for securing the magnet may be a pair of projections or spring-like retaining nails formed by projections of the conductor frame that hold the magnet. The magnet, the sensor and the conductor frame are encapsulated in a plastic package to form a semiconductor integrated circuit in which a thin layer of the packaging covers the sensor. The sensor is adjacent to the ferromagnetic object and is positioned from the ferromagnetic object in order to reduce the distance between the sensor and the ferromagnetic object and still maintain a separation of air between the plastic package and the ferromagnetic object to allow the passage to the ferromagnetic object. In the preferred embodiment, the sensor is a Hall effect device which may have one or more Hall effect elements for detecting the edges of the ferromagnetic object such as the teeth of the gear. A feature of the invention is the fabrication and encapsulation of the magnetic field sensor as an integrated circuit so that only a thin portion of the plastic package covers the sensing element of the elements of the Hall effect cell and the effective air separation between the Given and the exciter is minimized, which allows manufacturers or end users more flexibility in the design, since they can balance the needs for an improved resolution of the sensing device and the need to have a minimum separation to compensate the inequality of the Gears caused by heat expansion, uneven teeth and gear wear. A second inventive feature is the use of the retaining nails in the conductor frame to secure the magnet so that it is separate from the sensor die of the elements of the Hall cell only by the bearing that embeds the die which thus allows a closest proximity to the magnet and given sensor of the elements of the Hall cell. The nails also provide an accurate location to center the magnetic field and provide rigidity during transfer to the encapsulation mold. The nails also keep the magnet against the conductor frame so as not to increase the separation between the magnet and the sensor. further, the nails simplify the assembly process since adhesives or healing care steps are not needed and no additional fasteners are required. Yet another feature is that the nails are docile and accommodate the size and shape of the magnet, which reduces the need for critical part sizes and tolerance. All these characteristics reduce the cost of the product. A third inventiveness is that the structure of the conductor frame, the sensor die of the Hall cell elements and the magnet, allow the integrated circuit Hall effect sensor unit to be manufactured in a standard industrial integrated circuit and encapsulation assembly plastic. This makes the sensor device less expensive because it has fewer manufacturing steps and provides a complete plastic packing around all the elements of the magnet sensor unit thus providing better environmental protection against dust, dirt, corrosives and the fluids of machines.

DESCRIPTION OF THE INVENTION The characteristic details of the present invention are clearly shown in the following description and the accompanying drawings as an illustration of that and serving the same reference signs to indicate the same parts in the figures shown. Figure # 1 shows a diagram of the structure of a magnetic field sensor device of those previously known in the field of art. Figure # 2 shows a diagram or structure of the magnetic field sensor of the present invention. Figure 3 shows a top perspective view of the magnetic field sensor conductor frame of Fig. 2 Figure 4 shows a perspective top view of the conductor frame of Fig. 3 after the next assembly step to add a die, a magnet and link wires to the conductor frame. Fig. 5 shows a perspective top view of an integrated circuit formed by the transfer mold of the conductor frame of Fig. 4. Figure 6 shows a top perspective view of the integrated circuit of the Fig. 5 with the conductor frame trimmed. With reference to said figures and the invention in general, the present invention is particularly suitable for automotive applications, such as magnetic field sensing devices for detecting the speed of the wheels for an electronic anti-skid brake system. For the purpose of the description, the magnetic field sensing device illustrated in FIG. 2 is represented as an integrated circuit Hall effect sensor unit (32) which is used to detect the rotational speed of a toothed drive wheel (34) for an automotive anti-skid system (not shown) in automobiles. The driving wheel (34) is engaged for rotation with one of the wheels of the automobile, the speed of rotation of which is required to feed back to the anti-skid circuit to prevent a complete blockage of the wheel during braking. Referring fully to Fig. 2, the integrated circuit Hall effect sensor unit (32) is secured within the overmold (36) which is mounted adjacent to the drive wheel (34) for the purpose of locating the effect sensor unit. Integrated circuit hall (32) near the drive wheel (34). The overmould (36) can be of any suitable shape and construction, and can be adapted, for example, to be mounted on a machine block (37). The overmold (36) is located radially from the driving wheel (34) to thereby position the integrated circuit Hall effect sensor (32) at a predetermined distance from a series of teeth (38) formed on the perimeter of the driving wheel . This distance is called the air separation (40), which is of primary interest for the purposes of the present invention. In general, the air separation (40) will depend on the particular application and the result of the tolerances of the devices used. Air separations of 0.5 to 2.0 millimeters are not unusual, such as that of the embodiment illustrated in FIG. 2.

Between each tooth (38) there is a notch (42) which clearly delineates the adjacent teeth (38). In general, the teeth (38) are evenly spaced by the notches (42) around the periphery or circumference of the driving wheel (34) and are substantially identical in shape and size. The overmold (36) is fixed in a stationary position adjacent the teeth (38) from the driver wheel (34) so that the teeth (38) and the notches (42) alternately pass through the integrated circuit Hall effect sensor unit as the car wheel is turning. Looking further at Fig. 2, the integrated circuit Hall effect sensor unit (32) has a conductor frame (44), a sensor die of the elements of the cell (46) linked to the upper face of the conductor frame ( 44) and a permanent magnet (48) mounted flush with the lower face of the conductor frame (44). The die (46) can have a single element of the Hall cell centered or multiple elements, for example, two Hall effect sensors, which could be spaced apart at 0.088 inches. These sensors form a detector on the contour to detect when the edges of the teeth pass (38). The entire assembly of the conductor frame (44), the die (46), and the magnet (48) is then packaged in a plastic package (50) by a conventional plastic mold transfer packaging process. This complete assembly forms an integrated circuit Hall effect sensor unit (32), which is generic in nature and can be used in a variety of applications with the overmold (36) providing the means for mounting it in each application as it was previously described. Together, the driving wheel (34) and the permanent magnet (48) define a magnetic circuit. The permanent magnet (48) is oriented with its poles aligned with the driving wheel (34), and the sensor die of the elements of the Hall cell (46) is positioned inside the integrated circuit Hall effect sensor unit (32) , so that the resulting magnetic field is pefendicular to the integrated circuit Hall effect sensor unit (32). With this spatial relationship between the components of the magnetic circuit, the presence of the tooth (38) of the driving wheel (34) adjacent to the sensor of the elements of the Hall cell (46), causes an increase in the magnetic flux of the magnetic circuit , which lowers the reluctance of the circuit and thus affects the output information of the sensor unit of the integrated circuit Hall effect (32) as the driving wheel (34) is rotated. The overmold (36) secures the integrated circuit Hall effect sensor (32) in its exact location so that it is properly spaced from the drive wheel (34). The air separation (40) is the distance between the edge of the plastic package (50) and the exciter (34). The effective air separation (54) is the distance between the sensing die of the elements of the Hall cell (46) and the exciter (34). The plastic package (50) provides complete protection against all environmental hazards such as moisture, corrosives, dust, dirt and oil, as it completely covers the entire sensor die assembly of the Hall cell elements ( 46), the Conductor frame (44) and the permanent magnet (48). The effective air separation (54) is reduced in size because only a layer of plastic of the minimum thickness necessary to provide protection is between the die (46) and the exciter (34). The reduction in the plastic layer between the die (46) and the exciter (34) is important for several reasons. Due to heat expansion, uneven gears, wear and other factors, it is desirable to keep air separation as large as possible to compensate for unequal gears. At the same time, the sensitivity can be increased for the magnetic field sensor as an integer, if the air separation (40) is minimized and the effective air separation (54) is diminished. By having a thinner plastic layer covering the surface of the die (46), it allows automakers to have more flexibility in designing the sensor to balance compensation needs for unequal gears and to improve sensitivity. Fig. 3 is a perspective view of the conductor frame (44) shown in Fig. 2, has a bearing for embedding the die (58) to receive the sensor die of the elements of the Hall cell (46), the retaining nails (60, 62) the mounting magnet (48) and the packing conductors (64, 66, 68). The rails (70), side rails (72) and tie bars (76) complete a segment of the conductor frame (44). A continuous series of identical segments will form a strip of the conductor frame used in a typical integrated circuit assembly process. The conductor frame (44) can, for example, be made from a three-quarter to full-length non-magnetic copper alloy CDA 151 to give it sufficient spring to allow the retaining claws (60, 62) sufficient tension to hold the magnet (48). The conductor frame must be soft enough to bend, but hard enough to maintain its shape for the assembly process. The sensor die of the elements of the Hall cell can be adhered to the bearing to embed the die (58) with a conductive epoxy or a polyamide adhesive. Typically an anti-skid brake system would be a two-conductor package while the ignition system would be a four-conductor package, depending on the type of device used. Fig. 4 shows the conductor frame (44) in the next step of the assembly process with the sensor sensor of the elements of the Hall cell (46) adhered to the bearing to embed the die (58) and the magnet (48) secured by the tension of the retaining nail springs (60, 62). The sensor die of the elements of the Hall cell (46) has a minimum of three link bearings, which are connected by gold link wires (80, 82, 84) to the packaging conductors (64, 66, 68). ) respectively. The frame, of conductors (44), the sensor die of the elements of the Hall cell (46), and the magnet (48), form the assembly of the conductor frame that will be encapsulated in plastic by a mold transfer process. The packaging conductors (64, 66, 68) provide the output information signal for the integrated circuit. Fig. 5 shows a perspective view of the integrated circuit Hall effect sensor unit (32) after the sensor die of the elements of the Hall cell (46), the conductor frame (44), and the magnet Permanent (48) have been encapsulated in plastic packaging (50) by the process of transfer of molds. Fig. 6 shows the integrated circuit Hall effect sensor unit (32) after the rails (70), the tie bars (72) and the obstruction bars (74) have been cut out and the packaging conductors (64). , 66, 68) are extended from the packaging. This is the final step of the assembly and encapsulation process of the integrated circuit. The improved operation of the magnetic field sensor device (30) is as follows. The arrangement of the permanent magnet (48) with the driving wheel (34) initiates a magnetic circuit around, creating a magnetic field with a predetermined magnetic flux whose density depends on the magnetic force of the magnetic circuit. The magnetic flux of the magnetic circuit extends between the poles of the permanent magnet (48), one of which will be the south pole while the other is the north pole. The poles are oriented to be perpendicular to the integrated loop Hall effect sensor unit (32), such that one of the poles is arranged close to it and the other is moved away from it. A large percentage of the magnetic flux is contained within a closed circuit that can be traced from the farthest pole of the integrated circuit Hall effect sensor unit (32), through a large air gap between this pole and the drive wheel (34) and back through the air gap (40) to the pole closest to the integrated circuit Hall effect sensor unit (32). The rotation of the driving wheel (34) produces cylindrical fluctuation in the reluctance of the magnetic circuit, which then causes a corresponding fluctuation in the strength of the magnetic field captured by the integrated circuit Hall effect sensor unit (32). The transverse current of the integrated circuit Hall effect sensor unit (34) increases with the increase in magnetic field strength corresponding to a tooth (38) which is in the vicinity of the integrated circuit Hall effect sensor unit (32). ), and decreases with a decrease in the strength of the magnetic field corresponding to the notch (42) which is in the vicinity of the integrated circuit Hall effect sensor unit (32). The magnetic field sensing device (30) is a contour detector and captures each edge of each tooth (38). Accordingly, by knowing the number of teeth (38) on the driving wheel (34) and the fact that the given Hall effect sensor has two sensors to detect the edges, the Hall effect sensor can be used to determine the speed at which the wheel turns. Therefore, an inventive feature is the fabrication and encapsulation of the magnetic field sensor as if it were an integrated circuit, so that only a thin portion of the plastic package (50) covers the sensing element of the elements of the Hall cell (46) and the effective air separation (54) between the die (46) and the exciter (34) is minimized. This allows the manufacturer greater flexibility in the design, as they can balance the need for improved resolution of the sensing device and the need to have a certain minimum clearance to compensate for the unevenness of the gears caused by the expansion by heat, by teeth unequal and by wear of gears.

A second inventive feature is the use of the retaining nails (60, 62) in the conductor frame (44) to secure the magnet (48) such that it is separate from the sensor die of the elements of the Hall cell (46). ) only by the bearing to embed the die (58). This allows a tight tolerance of the magnet face to the sensor socket of the elements of the Hall cell. The advantage is that by maintaining a fixed distance, the variations in the field are much lower, allowing a much more consistent product. The nails (60, 62) also provide an accurate location for centering the magnetic field and providing stiffness during transfer to the encapsulation mold. In addition, the nails simplify the assembly process as adhesives or healing care steps are not required. Still another feature is that the nails are docile and accommodate the size and shape of the magnet, which reduces the need for critical size parts and tolerances. All these characteristics reduce the cost of the product. A third inventive feature is that the structure of the conductor frame (44), the sensor die of the elements of the Hall cell (46) and the magnet (48) allows the integrated circuit Hall effect sensor unit (32) to be manufactured as a single encapsulated plastic integrated circuit manufactured in a standard process of integrated circuit assembly and plastic encapsulation. This makes the sensor device less expensive because there are fewer manufacturing steps and provides a complete plastic packing around all the elements of the integrated circuit Hall effect sensor unit (32), and thus provide better environmental protection against the dust, the earth, the corrosives and the fluids of the machines. It should be noted that it is within the scope of this invention to use a magnetoresistor as a sensing device of a magnetic field. A magnetoresistor is a device whose resistance varies with the strength of the magnetic field applied to the device. Typically, the magnetoresistor is a thick sheet of electrically conductive material, such as a metal or semiconductor. For many automotive applications, the preferred form of a magnetoresistor is a thin elongated body of a high load mobility semiconductor material, such as indium antimonide (InSb) or indium arsenide (InAs), which has contacts at its ends. The magnetoresistor is mounted inside and perpendicular to a magnetic circuit that includes a permanent magnet and an exciter. The exciter moves relative to the element of the stationary magnetoresistor, and in doing so, changes the reluctance of the magnetic circuit to thereby cause the magnetic flux through the magnetoresistor element to vary in such a manner as to correspond to the position of the teeth of the exciter. With the change in the magnetic flux, the corresponding change in the strength of the magnetic field occurs, which increases the resistance of the magnetoresistor. While the preferred improvements of the invention have been shown and described, numerous variations and alternate additions will occur to those skilled in this skill. According to this, the intention of the invention is that it is only limited in terms of the claims that are claimed.

Claims (13)

CLAIMS: Having described the invention is considered as a novelty and therefore the content of the following clauses is claimed as property of the inventors.

1. A magnetic field sensor assembly comprising: a magnet to create a magnetic field; a semiconductor sensor that is located within said magnetic field to capture the strength of said magnetic field, said sensor adapted to allow the detection of a ferromagnetic object passing through said magnetic field; a conductor frame having a bearing for embedding the die in which said sensor is secured and an assembly for securing said magnet in close proximity to said sensor and said magnet, sensor and conductor frame assembled to form an encapsulated semiconductor integrated circuit in a plastic package.

2. The assembly of the magnetic field sensor as described in clause 1, in which a thin plate of said plastic package covers the sensor, said sensor in dimension according to the ferromagnetic object as to reduce the distance between sensor and said ferromagnetic object and to maintain a sufficient air separation between said plastic package and said ferromagnetic object to allow the passage of said ferromagnetic object.

3. The assembly of the magnetic field sensor as described in clause 1, in which the sensor has one or more magnetic field sensor elements.

4. The assembly of the magnetic field sensor as described in clause 3, in which said multiple magnetic field sensor elements are spaced apart to capture the forces of the magnetic fields in different places.

5. The assembly of the magnetic field sensor as described in clause 1 in which said sensor is a semiconductor die having one or more sensor elements of Hall effect magnetic fields.

6. The assembly of the magnetic field sensor as described in clause 1 in which said assembly for securing said magnet has one or more projections to secure the magnet.

7. The assembly of the magnetic field sensor as described in clause 6 in which said conductor frame is made of a metal having sufficient spring tension for said assembly to secure said magnet to secure said magnet.

8. The assembly of the magnetic field sensor as described in clause 7 in which said magnet is adjusted under pressure within the said projection (s) to be secured.

9. The assembly of the magnetic field sensor as described in clause 1 in which said sensor has one or more magnetic field or magnetic sensor elements and in which said assembly for securing said magnet has one or more projections to ensure said magnet.

10. The assembly of the magnetic field sensor as described in clause 9 in which one or more of the magnetic field sensing elements are Hall effect elements.

11. The assembly of the magnetic field as described in clause 11 in which said multiple magnetic field sensing elements are adapted to detect the edges of said ferromagnetic objects.

12. The assembly of the magnetic field as described in clause 1 that has an overmold that covers a portion of said plastic sensor packaging, said overmold is used to position said sensor.

13. The assembly of the magnetic field comprising: a magnet to create a magnetic field; a semiconductor sensor located within said magnetic field to capture the strength thereof, the adapted sensor allows the detection of a ferromagnetic object passing through said magnetic field; a conductor frame having a bearing for embedding the die in which said sensor is secured and an assembly having one or more projections for securing said magnet in close proximity to said sensor, said conductor frame made of a metal having sufficient spring tension for said assembly having one or more projections to secure said magnet; said magnet, sensor and conductor frame encapsulated in a plastic package to form a semiconductor integrated circuit in which a thin layer of said plastic package covers said sensor, said sensor adapted to be adjacent to said ferromagnetic object, said sensor positioned with respect to said ferromagnetic object in such a way as to reduce the distance between said sensor and said ferromagnetic object and to maintain a separation of air between said plastic package and said ferromagnetic object so as to allow the passage to said ferromagnetic object. . The assembly of the magnetic field as described in clause 13 in which said semiconductor sensor has one or more sensor elements of Hall effect magnetic fields.