Electricity: measuring and testing – Magnetic – Calibration
Reexamination Certificate
2002-08-14
2004-09-28
Patidar, Jay (Department: 2862)
Electricity: measuring and testing
Magnetic
Calibration
C324S207250, C029S595000
Reexamination Certificate
active
06798193
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to sensing devices and sensing techniques thereof. The present invention also relates to magnetic sensors. The present invention additionally relates to printed circuit board (PCB) and small outline integrated circuit (SOIC) devices and components utilized in magnetic sensor packages. The present invention also relates to techniques for calibrating magnetic sensors.
BACKGROUND OF THE INVENTION
A variety of magnetic sensors are known in the art. Such magnetic sensors are utilized in automotive applications, including, but not limited to, camshaft, crankshaft and rotary position sensors. Such sensors often are configured to include Hall effect or magnetoresistive (MR) transducers, which are typically combined within magnetic or ferromagnetic targets having a pattern of features keyed to mechanical details being monitored by the magnetic sensor. These features represent the magnetic signature of a magnetized target or the presence or absence of ferromagnetic metal in various sizes on a metal target placed near an associated transducer.
Semiconductor Hall elements and magnetoresistors, in particular, are widely used in magnetic sensing applications. Such “Hall” elements are based on the Hall effect, well known in the art, which arises from the Lorentz force acting on the charge carriers in a conductive material. This phenomenon arises as follows: given a rectangular thin plate of conductive material with an electric potential applied along the Y axis and a magnetic field applied perpendicular to the plate (along the Z axis), the Lorentz force is represented by the formulation F=q(v×B), such that the variable q represents the charge of the carrier (usually electrons), the variable v represents the velocity of the charge carrier, and the variable B represents the magnetic field. The force distorts the current flow and crowds it toward one side of the conductive plate. This phenomenon distorts the equipotential lines and generates a Hall voltage.
The Hall voltage is proportional to &mgr;B, wherein the variable &mgr; represents the mobility of the material, and the variable B represents the magnitude of the magnetic field. Pickoff points for the Hall signal (V
o1
-V
o2
) are usually located at the midpoint of the plate along the Y axis. In long plates, a Hall electric field balances the Lorentz force, and the current flow becomes parallel to the Y axis, driving the Hall voltage to zero. Most practical Hall elements are roughly square and the current flow is at an angle with respect to the excitation voltage. This is what gives rise to the geometric magnetoresistance effect, which is further described below.
The fact that the current must travel further in a short Hall plate when a magnetic field is applied causes an increase in resistance. This phenomenon is referred to as the geometric magnetoresistance effect. Magnetoresistor (MR) elements typically have their length less than or equal to their width. A long resistor would thus not exhibit a magnetoresistance effect. Practical sensors generally utilize a large number of elements in series to increase the insertion resistance. The geometric magnetoresistance effect is proportional to &mgr;
2
B
2
for small fields (i.e., where &mgr; represents the mobility) and thus requires a significant magnetic bias to obtain a useful signal. The change in resistance is identical for a positive or negative field of the same magnitude.
Magnetic sensors are generally utilized to sense the position or location of a particular target. When a metal target is circular in shape, for example, the sensing mechanism may be referred to as a “gear tooth sensor” because of the resemblance of the target to a toothed mechanical gear. These gear tooth sensors are often used in the automotive arts in situations in which the target is linked to a crankshaft for use in engine control.
As a result of government regulations and the desire by automobile manufactures for the ability to provide misfire detection in automobile engines, the required accuracy and repeatability of automotive gear tooth sensors have been steadily increasing in recent years. In combination with these increasing requirements, operating conditions of gear tooth sensors now include increased air gap dimensions and axial run-out conditions. Additionally, larger effective magnetic signals are required to improve the signal-to-noise ratio of the device.
The magnitude of the effective magnetic signals in a gear tooth sensor can be increased by increasing the size and strength of the permanent magnet or, alternatively, by decreasing the distance between the permanent magnet and the target. If the size and strength of the magnet are increased, the overall costs of the gear tooth sensor will also be increased. A less expensive method for producing larger magnetic signals involves the design of a package for the gear tooth sensor that can minimize the distance between the permanent magnet and the ferromagnetic target. Such a reduction in the distance between the magnet and the target can also permit smaller permanent magnets to be utilized at a reduced cost.
With regard to the characteristic that permits the magnet to be placed closer to the target, it should be understood that in the past gear tooth sensors have been constructed with small outline integrated circuit (SOIC) component packages. These structures are typically disposed on an electrical substrate, such as a flex circuit or printed circuit board (PCB). The permanent magnet is disposed beneath the SOIC component and is usually separated from it by some type of plastic thickness.
In a typical prior art gear tooth sensor package of this type, the resulting distance between the pole face of the permanent magnet and the target comprises the plastic thickness on which the electrical substrate is mounted. Such a resulting distance also can determine the thickness of the electrical substrate (e.g., printed circuit board, flex circuit) and the SOIC thickness, which includes the stand-off height of the leads, the bottom plastic thickness of the SOIC, the lead frame thickness, the die thickness, the wire bond maximum height, the clearance above the wire bond maximum height, and the top plastic thickness of the SOIC.
Based on the foregoing, it can be appreciated that sensor designers continually seek refinement of the target system to improve engine control. Many sensing applications require a small diameter probe sensor with a short mounting profile from an associated mounting flange to a spinning ferrous target. Some application specifications require a calibrated magnetic circuit to ensure proper performance at all times and under all possible conditions. Devices based on such applications may also require sealing for an automotive under-the-hood environment and to provide an O-ring type seal to the engine. Having an O-ring configuration incorporated into the sensor reduces the working diameter of the internal sensor construction.
The present inventors have determined that a process issue associated with such prior art designs that must be overcome involves the use of integrated-circuit (IC) packages that may be mounted 90 degrees to the plane of the printed circuit board. Such a configuration requires a much more difficult through-hole soldering process that results in a greater amount of reworking, which in turn affects cost and efficiency. The present inventors have thus concluded that a solution to these issues involves the creation of a new design that utilizes an SOIC package that eliminates the need for a secondary through-hole soldering process to attach the IC. According to the present invention, an SOIC solder attachment results in a more robust process and eliminates the solder rework created by the through-hole solder process.
BRIEF SUMMARY OF THE INVENTION
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention and is not intended to be a full description. A full appreciation of
Johnson Curtis B.
Mueller Douglas L.
Ricks Lamar F.
Stolfus Joel D.
Zimmerman Mike W.
Fredrick Kris T.
Honeywell International , Inc.
Lopez Kermit D.
Ortiz Luis M.
Patidar Jay
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