Seagate Technology Characterizes Hard Drive Defects More Rapidly with NI-Based Solution

Author(s):
Jason Pressesky - Seagate Technology

Industry:
Electronics

Products:
Measurement Studio, PXI/CompactPCI,

The Challenge:
Developing a faster acquisition system to identify defective sites on disk surfaces.

The Solution:
Using NI Measurement Studio and PXI to synchronize two NI 5112 high-speed digitizers and an NI 6602 counter timer module, we created a solution that digitizes interferometer waveforms and logs disk defect locations.

Developing a Faster Way to Test Hard Drives
At Seagate Technology, one of the world’s largest manufacturers of disk drives, the thin film magnetic media in the hard disk drives typically undergo a series of final tests before incorporating them into the hard-drive assembly. The purpose of these tests is to count and characterize the number of defects and detect any roughness on the disk surface that might exceed the head-disk separation, approximately 20 nm. The traditional testing method uses specially calibrated recording heads or transducers. This method requires frequent maintenance, which generates unproductive material costs, excessive labor costs, and equipment downtime. We chose an alternative method, interferometry, a non-contact, optical-inspection technique. We selected this method because it provides the height information needed to scan a surface for defects under our stringent standards.

Requirements for this system included:

• Ease of integration with existing test equipment platforms\
• A simple command interface between the optical-inspection systems
• Ability to run with the minimum amount of intervention on behalf of the host system
  

The system uses an interferometric measuring system from Polytec Optronics. This device generates an output signal that is representative of the disk surface topography as it passes beneath the inspection laser beam.
During testing, a precision air-bearing spindle rotates the disk at 12,000 to 15,000 rpm, while the optical probe scans the entire surface of the disk in the radial direction.

The NI 5112 high-speed digitizer captures interferometer waveforms in response to a trigger signal. The interferometer generates a trigger signal if the displacement signal moves out of the allowed displacement window. We used the integrated PXI backplane to transmit the NI 5112 trigger signal to the NI 6602 counter. The NI 6602 counter registers the spin stand radial and linear encoder counts in order to latch the exact radial and angular coordinates of the defect. The complete test time is about 50 s, much faster than conventional test and inspection techniques for comparable surface coverage.

Integrating NI Hardware for Optimal Performance
PXI gives us the flexibility we need to synchronize the NI 5112 digitizers and the NI 6602 counter, all in the same chassis. We used two NI 5112 scope modules to digitize the waveform from the interferometer - one for the beam inspecting the top of the hard-drive platter and another for the beam inspecting the bottom. We chose this module for three reasons. First, it is National Instruments fastest digitizer, acquiring data at a rate of up to 100 MS/s. Second, with its automatic restart feature we can run our entire test and receive a complete list of defects at the end, rather than stopping the test after each defect. Finally, the NI 5112 module features extended memory - 16 MB of memory per channel. With this extended memory, we can shave seconds off each test by logging the data directly onto the module instead of waiting for information to write to the hard drive. To preserve memory, the NI 5112 only saves data containing, or immediately surrounding, a defect. We set the memory buffer to record 50 percent pretrigger and 50 percent post-trigger to ensure a clean recording of each defect.

To log the exact location of these defects on the hard drive, we used four channels on the NI 6602 counter. On both the top and bottom of the hard-drive media, we used a channel to measure the distance from the center and another to measure the rotational distance, or the angle of the defect. When the interferometer’s sensor detects a defect, an analog trigger fires, telling the NI 6602 counter to log the exact location of the defect.

Creating Applications in Weeks Instead of Months with Measurement Studio
We chose Measurement Studio to create this application because it complements Microsoft Visual Basic, a programming language with which we are already comfortable. We can also perform tasks that would otherwise take too much time and manpower to accomplish.

The ActiveX controls for Visual Basic simplify the PXI hardware configuration and synchronization, so we can accomplish more in less time. With the complete set of tools for hardware interfacing, signal analysis, and visualization, we created our application in weeks instead of months.

For more information, contact:

Jason Pressesky

Senior Engineering Manager

Seagate Technology

47010 Kato Rd.

Fremont, CA, 94538

Tel: (510) 353-4926

E-mail: jason_l_pressesky@notes.seagate.com.

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