Electricity: measuring and testing – Magnetic – Magnetic information storage element testing
Reexamination Certificate
2001-02-09
2002-10-29
Strecker, Gerard R. (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetic information storage element testing
C324S537000
Reexamination Certificate
active
06472866
ABSTRACT:
FIELD OF THE INVENTION
This application relates generally to testing systems for magnetic media read/write head elements and more particularly to testing read/write head elements prior to final assembly of the storage device.
BACKGROUND OF THE INVENTION
The need for more efficient data storage devices has become critical with the staggering pace of advances in computer technology. The most common data storage device used today is the disc drive. Most disc drives are composed of one or more magnetic media discs attached to a spindle. A spindle motor rotates the spindle and discs at a constant high speed. An actuator assembly adjacent to the disc(s) has actuator arms extending over the discs, each with one or more flexures extending from each actuator arm. A read/write head is mounted at the distal end of each of the flexures. The read/write head includes an air bearing slider enabling the head to fly in close proximity above the corresponding surface of the associated disc. Information is stored on and retrieved from the magnetic media discs via the read/write head.
A flex assembly provides the requisite electrical connection paths for the actuator assembly while allowing pivotal movement of the actuator assembly during operation. The flex assembly includes circuitry to which head wires are connected; the head wires being routed along the actuator arms and the flexures to the heads. The flex assembly typically includes circuitry for controlling the write currents applied to the heads during a write operation and a preamplifier for amplifying read signals generated by the heads during a read operation. The flex assembly terminates at a flex bracket for communication through the base deck to a disc drive printed circuit board mounted to the bottom side of the disc drive. The actuator assembly and the flex assembly are usually combined before the disc drive is assembled. The product of this combination is called the head stack assembly (“HSA”).
Disc drive manufacturers are attempting to increase the amount of information stored on existing disc drives to meet the increased demand for information storage. Manufacturers have, for example, increased the areal density of their disc drives to fit more information on a constant sized disc. Areal density is a measurement of the number of bits of information that can be stored on one square inch of disc space. Increased areal density, however, requires a sophisticated read/write head to access information stored on the disc media. Some current disc drives use a dual element transducer head to overcome some of the problems encountered with increased areal density. One element is dedicated to read data and a second element is dedicated to write data, in a dual element transducer head. Some disc drives utilize magnetoresistive (MR) type element transducer for reading data. The resistance of a MR element transducer changes as it is subjected to a varying magnetic field. This change in resistance is used as means to read data on a magnetic disc. An inductive element is typically used for writing information on a magnetic disc.
As mentioned above, a HSA usually consists of heads, flexures, actuator arms, head wires, and a flex assembly with a printed circuit board and a preamplifier. Many processing steps are required to manufacture such a HSA. Each step completed increases the likelihood that the delicate read/write heads will be damaged. Electrostatic discharge (“ESD”) or physical contact between the head and some other mechanical part, for example, may damage the sensitive magnetoresistive element in the head. As a result of this damage risk, a manufacturer must verify that the read/write heads operate properly before placing the HSA into a disc drive. Current verification methods, however, are time consuming, expensive, and subject the heads to an additional risk of damage.
There are two common methods of testing MR read/write heads. The first is dynamic testing, where a dynamic electrical tester (“DET”) is used to test the HSA. A DET simulates actual disc drive operation by placing the HSA within a magnetic media cylinder and then spinning the magnetic media cylinder at high speed. The magnetic media cylinder is basically a stack of one or more discs that imitates the disc or discs in a disc drive. A data signal, sent by the DET through the HSA's write head element, is stored on the magnetic media cylinder. Next, the DET uses the HSA's read head element to retrieve the data written by the write head element. A determination of whether the head elements are functioning properly can be made by comparing the two signals. Although very accurate, dynamic electrical testing is time consuming, expensive, and potentially destructive (the heads risk being destroyed if they come in contact with the media, being spun at high speeds).
The second common method of testing a HSA is called static testing. In static testing, the HSA is placed within a changing magnetic field; the variation of the magnetic field induces small signals within the head elements. These signals are then sent through the preamplifier. A signal analyzer connected at the output of the preamplifier reads the signals. Static testing, although faster, cheaper, and less destructive, has undesirable inherent limitations. The first limitation occurs when a high frequency magnetic field is applied to the HSA. When such a field is applied, stray currents are induced within the electrical conductors that connect the head elements to the preamplifier. These currents overpower and mask the useful diagnostic signals from the head element, rendering high frequency electrical field-testing inadequate. One potential solution is to apply a low frequency magnetic field. The second limitation of static testing is encountered, however, when a low frequency magnetic field is applied to prevent a current from being induced within the electrical conductors. The preamplifiers used in the HSA's are not designed with a low frequency channel; therefore, low frequency signals will not pass through the preamplifier. An attempt to test the signal at the output of the preamplifier thus yields unsatisfactory results. It is in respect to these considerations and others that the present invention has been made.
SUMMARY OF THE INVENTION
In accordance with the present invention, the above and other problems are solved by a testing system that does not require dynamic testing and permits the use of a low frequency magnetic field to test the magnetoresistive (“MR”) head elements. In the present invention, the completed head stack assembly (“HSA”) is placed in the test apparatus. Test probes are aligned and placed in electrical contact with the electrical leads coming from each head element, between the head and the preamplifier. The HSA is then placed in a changing magnetic field. The changing magnetic field induces electrical signals within the MR head elements. Unlike prior testing methods, however, the location of the test probes permits the application of a magnetic field of a sufficiently low frequency so as not to induce stray currents in the head element electrical leads. The condition and characteristics of the each head element can be determined by analyzing these electrical signals.
In accordance with other aspects, the present invention relates to a method of testing MR read/write head elements in an assembled HSA by placing test probes in electrical contact with the electrical leads of the read/write head elements, between the MR head elements and the preamplifier, generating a changing magnetic field around a portion of the MR elements, inducing a test signal within the MR elements, and analyzing the test signal induced in the MR elements and determining whether the MR elements are functioning properly.
These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.
REFERENCES:
patent: 3699430 (1972-10-01), Kruklitis
patent: 3710235 (1973-01-01),
Merchant & Gould P.C.
Seagate Technologies LLC
Strecker Gerard R.
Wahl John R.
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