Electricity: measuring and testing – Magnetic – Magnetic information storage element testing
Reexamination Certificate
2001-11-02
2003-06-17
Strecker, Gerard R. (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetic information storage element testing
C029S090010
Reexamination Certificate
active
06580266
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to manufacturing and testing apparatus for thin film disks and more particularly to apparatus and methods for detecting film delamination defects in thin film disks.
BACKGROUND OF THE INVENTION
A typical prior art head and disk system
10
is illustrated in FIG.
1
. In operation the magnetic transducer
11
is supported by the suspension
13
as it flies above the disk
16
. The magnetic transducer
11
, usually called a “head” or “slider,” is composed of elements that perform the task of writing magnetic transitions (the write head
23
) and reading the magnetic transitions (the read head
12
). The electrical signals to and from the read and write heads
12
,
23
travel along conductive paths (leads)
14
which are attached to or embedded in the suspension
13
. The magnetic transducer
11
is positioned over points at varying radial distances from the center of the disk
16
to read and write circular tracks (not shown). The disk
16
is attached to a spindle
18
that is driven by a spindle motor
24
to rotate the disk
16
. The disk
16
comprises a substrate
26
on which a plurality of thin films
21
are deposited. The thin films
21
include ferromagnetic material in which the write head
23
records the magnetic transitions in which information is encoded. The thin film protective layer (not shown in
FIG. 1
) is typically the last or outermost layer.
The conventional disk
16
typically has a substrate
26
of AIMg or glass. The thin films
21
on the disk
16
typically include a chromium or chromium alloy underlayer that is deposited on the substrate
26
. The magnetic layer in the thin films
21
is based on various alloys of cobalt, nickel and iron. For example, a commonly used alloy is CoPtCr. However, additional elements such as tantalum and boron are often used in the magnetic alloy.
FIG. 2
illustrates one common internal structure of the thin films
21
on disk
16
. The protective overcoat
35
is used to improve wearability and corrosion. The magnetic layer
34
is immediately under the overcoat
35
. The magnetic layer
34
is deposited on an underlayer
33
which is in turn deposited on a seed layer
32
. The seed layer
32
is deposited on the substrate
26
. Since the seed layer
32
is the initial thin film deposited on the substrate
26
, it plays a critical role in the adherence of the thin film structure to the substrate. For nonmetallic substrates various seed layer materials have been suggested including chromium, titanium, tantalum, CrTi, Ni
3
P, MgO, carbon, tungsten, AlN, FeAl, RuAl and NiAl.
One of the prior art steps in processing thin film magnetic disks has been burnishing. The burnishing process flies a special type of slider structure over the disk surface to physically remove high spots from the disk surface. U.S. Pat. No. 5,658,191 to Brezoczky describes a type of burnishing head and the process of using it.
The prior art manufacturing process for thin film disks has included various optical, magnetic and physical tests. An optical inspection system is described in U.S. Pat. No. 6,100,971 to Imaino, et al., which is commonly assigned with the present application. One physical test is called a glide test. A glide test is used to gauge the suitability of the surface of the disk for “flying” the read/write (R/W) head. One prior art glide test is described in U.S. Pat. No. 6,262,572 issued to Franco, et al. A glide test using a thermo-resistive element is used to detect thermal asperities which are caused by irregularities in the surface of the disk. Franco '572 suggests using a glide head that is much wider than an actual R/W head in order to speed up the process of testing a disk.
One of the failure mechanisms for thin film disks is delamination of the thin film structure from the substrate. In typical manufacturing procedures delaminations are often not detected until the disk is installed in and tested in the final disk drive assembly. It is clearly advantageous to detect defects on a disk prior to installation in a drive. An additional problem in delamination defect analysis is being able to locate the defect in a microscope field for failure analysis. The critical defects are not visible with the naked eye, so it can be time consuming to search for the defect using any type of high magnification device.
SUMMARY OF THE INVENTION
The applicants disclose an apparatus and method for detecting and marking delamination defects on thin film disks. The apparatus includes a read/write (R/W) head and a burnishing head mounted on separate arms that access the disk while spinning on the test stand. The R/W head performs an initial magnetic test of selected areas on the disk to establish an initial defect map. The burnish head is then flown over the surface for an extended time to accelerate and open up the latent delamination defects by impacting protruding material. The R/W head then performs a second magnetic test which is compared against the first test to identify the delamination defects which have been developed by the burnishing. The delamination defects are then marked with a magnetic pattern which aids in optically locating the defect, for subsequent failure analysis.
REFERENCES:
patent: 5423111 (1995-06-01), Mori
patent: 5658191 (1997-08-01), Brezoczky
patent: 5764545 (1998-06-01), Cannata et al.
patent: 5825180 (1998-10-01), Guzik
patent: 6100971 (2000-08-01), Imaino
patent: 6262572 (2001-07-01), Franco et al.
Coufal, et al., Monitoring of Adhesion Strength Between Materials by Photo-Acoustic Pulse Generation at or Near the Interface, IBM Technical Disclosure Bulletin, 07-85, pp. 487-490.
Horne, et al., Method and Apparatus for Detecting Defects and Delaminations on a Thin Film Disk, IBM Technical Disclosure Bulletin, 03-94, pp. 521-522.
Baumgartner Bradley Frederick
Duan Shanlin
Liu Yan
Robinson Bob C.
Tang Li
Hitachi Global Storage Technologies - Netherlands B.V.
Knight G. Marlin
Strecker Gerard R.
LandOfFree
Thin film delamination detection for magnetic disks does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Thin film delamination detection for magnetic disks, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Thin film delamination detection for magnetic disks will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3112780