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Quasi Static Testing. Ultimate Solution for Cost Effective Quality Verification and ESD Analysis of GMR Heads. Henry Patland Wade Ogle 2192 Bering Drive San Jose, CA 95131 hpatland@isiguys.com www.isiguys.com. Welcome to Complex World of GMR Head.

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Quasi static testing l.jpg

Quasi Static Testing

Ultimate Solution for Cost Effective Quality Verification and ESD Analysis of GMR Heads

Henry Patland

Wade Ogle

2192 Bering Drive

San Jose, CA 95131



Manufacturing gmr heads with good yield reliability and cost l.jpg
Manufacturing GMR heads with good Yield, Reliability and Cost

  • GMR is a new complex technology requiring new manufacturing and test methodology

  • GMR technology provides huge advances in Arial Density

  • GMR is the most ESD sensitive mass produced device in the world

Is There an ultimate test solution for manufacturing GMR heads with good Yield, Reliability and Cost?

Gmr manufacturing process l.jpg


(Semiconductor Process, Test)


(Wafer Slicing, Row Level Lapping, Test)


(Row Dicing, Slider Level Lapping, Test)


(Assy from Sliders, Suspension, FCBA’s, Test)


(Assy from HGA’s, Actuator, VC, FCBA’s, Preamp Chip, Test)


(Assy from HSA’s, Media, Enclosures, Drive PCB, Servo,Test)

GMR Manufacturing Process

How many places in your manufacturing process can GMR elements get damaged?

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Basics of Quasi-Static Testing Cost

The roots of QST are derived from actual drive operation

As GMR passes over a disk it is introduced to a variety of magnetic field.

In simplest terms the resistance of the GMR is dependent on the magnetic field applied to it.

In ideal case the relationship of GMR resistance to applied field is linear, but we don’t live in ideal world.

Close To Ideal Transfer Curve

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QST Testing as a Concept Cost

Quasi Static Testing can characterize the GMR performance,

with the following advantages over DET Testing:

  • Independent of external influence (disk variation)

  • Significantly more flexible, with the ability to subject the GMR to any variety of operating conditions.

  • Can analyze pure GMR performance with higher resolution than DET Testing.

  • Reduced Risk of Handling or Tester damaging heads

  • QST Testing is inexpensive, fast, relatively simple, and requires significantly lower maintenance and operating costs compared to DET Testing.

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QST Transfer Curve Cost

Parametrics extracted from QST Transfer Curve

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Common Anomalies which cause errors in a drive Cost

Baseline anomalies

Single Bit Jumps (Kinks)

Amplitude variation


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Can QST screen out these Anomalies? Cost

  • Amplitude / Asymmetry Variation

  • Baseline Shift / Popping

  • Field Induced Instabilities (Kinks)

  • Reader Induced Instabilities

  • Writer Induced Instabilities

  • ESD Soft/Hard Damage (Amplitude, Pin-Reversal, Asymmetry)

  • DET/Drive Correlation

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Amplitude/Asymmetry Variation Cost

Poor Amplitude

High Asymmetry

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Base Line Shift / Popping Cost

Barkhausen Jump

Large Hysteresis

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Field Induced Instabilities Cost

Field Instability at 40 Oe

Kink / MaxSlope

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Reader Induced Instabilities Cost

Reader Instability

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Writer Induced Instabilities Cost

Writer Induced Instabilities


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ESD Soft / Hard Damage Cost

Amplitude and

Asymmetry Degradation

No Amplitude – Hard Damage

Pin-Layer Reversal

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Drive Anomaly Correlation Cost

Amplitude variation in Drive caused by High Hysteresis shown in Transfer Curve

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Test conditions Cost


Sweep: 275 Oe

Measured at 250 Oe

Bias Current: 5 mA

Guzik 1001 + 1701

Frequency: 5 MHz

Filter: 60 MHz

Bias Current: 5 mA

RPM: 5400

QST to DET Correlation

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Additional Functionality of QST Testers Cost

  • Static Tests of HSA components including Preamp Chip, Voice Coil, FCBA, Writer

  • Elevated Temperature Testing

  • PZT Suspension Testing

  • ESD Failure Threshold Testing

Esd damage to gmr heads is considered one of the worst problems in manufacturing today l.jpg
ESD Damage to GMR heads is considered one of the worst problems in Manufacturing Today

  • Due to sensitivity to ESD, GMR heads can be easily damaged or destroyed by the slightest ESD event caused by Humans or Machines in Manufacturing

  • Unfortunately, this problem is here to stay and will only get worse in near future as the ESD Failure Voltage level is inversely proportional to Arial Density

  • CDM (Charged Device Model) is rapidly becoming the standard for characterizing GMR head ESD Failure Thresholds

Qst can characterize esd damage by applying a controlled esd events to gmr head l.jpg

Sensor Damage problems in Manufacturing Today

Multiple distributed melting points

HBM: 10% Resistance Change

CDM: 100% Resistance Change

QST can characterize ESD damage by applying a controlled ESD events to GMR head



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What can be done about GMR head ESD Sensitivity ? problems in Manufacturing Today

  • Improved design of GMR head which is less sensitive to ESD

  • Eliminate ESD events from Manufacturing

  • Monitor GMR head performance after every significant process to isolate and eliminate ESD events in Manufacturing

As Al Wallash – Maxtor would put it:

“Don’t loose your head over ESD”

Whatever you do, QST Testing can Help!

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By Applying Varying Amplitude ESD Events to GMR Head, QST can easily determine heads Failure points

Resistance Failure


Amp Failure

Pin Reversal



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Direct-CDM Sweep can easily determine heads Failure points

CDM Failure Threshold at 5V

Partial Damage

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QST is the Ultimate Test Solution for GMR head manufacturing can easily determine heads Failure points

  • QST Testing Methodology can be applied from Wafer to HDA level testing

  • QST Testing can screen out bad heads early in manufacturing process

  • QST Testing can identify which processes in Manufacturing are ESDing your heads

  • QST Testing is fast and inexpensive

  • QST Testing can be done with None or Very Little Handling on many test levels

  • QST surpasses DET in analyzing pure GMR performance

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References can easily determine heads Failure points

[1] J.Himle, R.Cross, M.Greenwell, “Drive-Level Instabilities Correlated to Quasi-Static Field Testing”, MMM-Intermag 2001

[2] C. Moore, “A Comparison of Quasi-Static Characteristics and Failure Signatures of GMR Heads subjected to CDM and HBM ESD Events”

[3] Integral Solutions Int’l, “Quasi 97” and “QST-2002” Tester

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Acknowledgements can easily determine heads Failure points

  • Al Wallash – Quantum/Maxtor

  • Mark Nichols – Quantum/Maxtor

  • Jenny Himle - Maxtor