Method and device for testing disk drive head while directing gas across the head

This invention relates to methods and devices for testing heads for use in sealed hard drive assemblies.

Hard drive assemblies (HDAs), otherwise known as disk drives, are commonly used for mass storage of computer programs and data. Magnetic recording media (“disks”) are coated with a magnetic material. Data is stored (“written”) on a disk by magnetizing spots on the coating with changes in polarity corresponding to binary bits.

Referring to FIG. 1, the data is written and read by spinning the disk 10 while a magnetic head 12 , mounted on a load beam 16 , “flies” over the upper surface 18 of the disk. The head (a hydrodynamic air bearing slider) flies as a result of a gliding action caused by compression of a layer of air that is dragged along by the spinning disk surface. The air layer is compressed between the upper surface 18 of the disk and the adjacent lower, air-bearing surface 20 of the head.

The head flies very close to the surface of the disk, without touching the disk surface. Referring again to FIG. 1, the distance H between the lower, air-bearing surface 20 of the head 12 and the upper surface 18 of disk 10 is referred to as the “flying height”.

Recently, proposals have been made to design sealed hard drive assemblies (HDAs) that enclose a pure helium atmosphere. It is necessary to test heads that are to be used in sealed HDAs using standard single head dynamic electrical testing (DET). Because the environment in which a head is used affects the way that it will perform, e.g., by changing the flying height of the head, testing should be done with the head in a helium atmosphere.

Heads can be tested in a helium atmosphere by putting a hermetic chamber around the DET tester and filling it with helium. However, almost all DET testers use air bearing spindles that exhaust air, and thus the tester tends to contaminate the helium atmosphere in the chamber. Running the spindle with helium instead of air requires a heavy consumption of helium. The exhaust from the spindle could be ducted outside of the chamber, but this would be mechanically difficult to retrofit onto most common spinstands.

The chamber approach also requires that parts to be tested be transferred into and out of the chamber. Most production DET loads the heads onto the tester manually, so some form of access into the chamber must be provided. Opening the chamber is undesirable due to the loss of helium (typically on the order of several cubic feet), increasing the production cost of the heads. Moreover, purging the air and refilling the chamber with helium is time consuming. Test time in mass production is very expensive, costing on the order of tens of thousands of dollars per second (i.e., one second of test time is equivalent to several tester-months per program), and thus lost time also significantly increases the cost of the heads.

The invention provides methods and devices that allow heads to be tested in a helium environment in a cost-effective way with little or no impact on test time and with minimal consumption of helium. In some implementations, the helium environment adds only a penny or less to the cost of a sealed drive.

In one aspect, the invention features a method of testing a head to be used in a sealed disk drive, including directing a flow of a gas across the head while subjecting the head to electrical testing.

Some implementations may include one or more of the following features. The gas includes helium. The method further includes causing the gas to flow between the head and a disk that is being used in the electrical testing. The method further includes causing the gas to flow out of a manifold. The method includes causing the gas to flow at a flow rate of from about 40 to 60 ft 3 /hr. The method further includes causing the gas to flow across the head for a predetermined time substantially equal to the time required for dynamic electrical testing, e.g., less than 30 seconds, typically less than 15 seconds. The manifold includes an exit through which the gas flows, and the method further includes positioning the exit from about 0.005 to 0.010 inch above the surface of a disk that is being used in the electrical testing. The head and equipment used for electrical testing are exposed to the ambient atmosphere. The electrical testing comprises dynamic electrical testing. The head is surrounded by a shroud.

In another aspect, the invention features a device for testing a head to be used in a sealed disk drive to read/write data of a storage disk. The device includes a manifold having at least one opening for providing a flow of gas from a source of gas, the at least one opening being positioned to direct the flow of gas to a surface of a storage disk positioned adjacent to the head.

Other features and advantages of the invention will be apparent from the description and drawings, and from the claims.

FIG. 1 is a diagrammatic side view of a disk and magnetic head.

FIG. 1A is a diagrammatic perspective view of a helium injection manifold on a Guzik HGA holder.

FIG. 2 is a schematic view indicating the path of helium flow under a slider.

FIG. 3 is a graph including saturation curves in air and with helium injection.

FIG. 4 is a Spectrum Analyzer trace of residual low frequency (LF) after overwrite (OVW).

FIG. 5 is a histogram of the LF amplitude from the traces in FIG. 4, normalized for amplitude.

FIG. 6 is a diagrammatic view showing the helium injection manifold of FIG. 1 used with an optional shroud.

FIGS. 7-7C are perspective, top, and side views of a helium injection manifold according to an alternate embodiment of the invention.

FIG. 1A shows a manifold 30 for providing a helium layer between the air bearing surface 20 of a head (or “slider”) 12 and the surface 18 of disk 10 (FIG. 1; the direction of disk movement is indicated in FIG. 1A by the arrow labeled “Disk Velocity”.) The manifold 30 is mounted on a Guzik Head Gimbal Assembly (HGA) holder 33 . The helium layer 34 (FIG. 2) is localized to the slider-disk boundary layer. The helium is delivered through square tubing 16 , e.g., brass tubing. Helium is fed from the lower left (the area labeled “Helium In”).

Helium exits the manifold 30 through apertures 32 . The area labeled “Helium Out”, when mounted on a dynamic electric tester, is generally about 0.005 to 0.010 inch above the disk surface. The apertures 32 direct the helium flow at the disk surface, forming a “curtain” that excludes the air coming in from the direction of “Disk Velocity” (the air that is generated by the air bearing surface of the slider). The motion of the disk then “drags” the helium under the slider, as illustrated in FIG. 2 . The apertures preferably have a diameter of from about 0.0465″ (#56 drill) to 0.0625″ ({fraction (1/16)}″). The size of the apertures, the spacing between the apertures and the number of apertures will determine the relationship between the pressure and flow rate that has to be supplied to the manifold, and the efficacy of the manifold to both supply a sufficient flow of helium to support the slider and also to block the incoming air from mixing with the helium under the slider.

Preferably, the flow rate of helium from the manifold is from about 40 to 60 ft 3 /hr. If the flow rate is too low, air may be admitted into the helium bearing under the slider, increasing the fly-height. If the flow rate is too high, the pressure of the helium under the slider may increase, increasing the fly-height. Too high a flow rate could also produce more turbulence around the slider resulting in increased Non-repeatable Run-out (NRRO) which is an inability of the slider to remain perfectly above the track under test.