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IDEMA Asia-Pacific October 2010

Suspension Design Considerations: Suspension Design Considerations: DSA vs SSADSA vs SSA

Peter HahnK.C. Ee

Amaninder Dhillon

IDEMA Asia-Pacific October 2010 2

About MPTAbout MPT

Wangnoi Rojana

Business: Suspensions for HDD

Founded: 1984

Facilities:

Thailand WangnoiRojana

ChinaChang-an, Dong-guan

U.S.A.Murrieta, California

Corporate Info:Headquarters – Wangnoi, Thailandwww.magnecomp.com

Chang-an, China


ContentsContents

• Overview• DSA Types• Requirements: DSA vs SSA• Stroke and FRF of DSA vs SSA• Cleanliness• Other DSA Considerations• Summary


Why DSA?Why DSA?

• Enterprise drives improved throughput performance with DSA• With multiple-platter designs of 3.5” and 2.5”, 400k+ tpi is not

easily manageable in meeting TMR budget and various performance targets

• BPI improvement is much more difficult now• Industry largely exhausted more economical improvement

solutions for TPI improvement– servo technology– butterfly mode control, spindle stability, windage control, dampers etc– DSA’s turn now

• In the long run, DSA also supports high TPI required for SMR, BPM and EAMR/HAMR

• DSA is rapidly becoming the standard for new drive products


DSA Adoption TrendDSA Adoption Trend

0

10

20

30

40

50

60

70

80

90

100

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

2014

perc

ent

Enterprise perforamnce demand and slow bpi growth

today

M ore chanllenging mechanical plat forms

Less chanllenging plat forms - such as some single plat ters

Early adopters

Takeoff phase

Rapid Transition Phase

General Adoption Phase

• The on-and-off predictions and experimental implementations turned into a stable migration trend now


DSA TypesDSA Types

• Most common DSA style for new products today is Dual PZT on MP• MP based DSA pushes servo BW from SSA’s mid/high 1000 to mid 2000 or higher• Gimbal based rotational type or other improved type of DSA will become a necessity when MP based DSA

servo BW is not sufficient

• The rest of this discussion focuses on Dual PZT on MP

Need slider-rotational typeDesign optimization is challenging

Very little arm mode coupling

All

Two PZT’s in Gimbal(Gimbal Based DSA)

Desktop/EnterpriseAllApplication

Lift-off shock is not suitable for notebooks

Arm mode couplingLimitations

Less arm mode couplingHigher lift-off shockAdvantages

PZT on Loadbeam (LB Based DSA)

PZT’s on Mountplate (MP Based DSA)

Platform

Single PZT on MP

Dual PZT on MPSingle PZT on LB PZT’s in Gimbal Area

(shown photo above: CAT)


Dual PZT on MPDual PZT on MP DSA Example DSA Example -- viewsviews

Stroke shown in one direction only

• Example shown– 11 mm length: swage

boss to gimbal dimple– 5.7 mm Loadbeam

length– 30 um LB thickness– 100um PZT thickness


Performance Requirement List Performance Requirement List –– SSA vs DSASSA vs DSA

SSA DSADyanmics FRF FRF

Op shock Op shockNon-op shock Non-op shockGram stability Gram stabilityStatic attitude stability Static attitude stability Circuit corrosion Circuit corrosion

PZT electrical groundingPZT depoling marginDSA stroke

LPC LPCSST particles SST particles

PZT particles

Environmental Stability (temp/humidity/voltage)

Shock

Stability

Contamination

• In addition to the apparent construction difference, the addition of PZT motor function presents more performance items to consider


Typical Design ParametersTypical Design Parameters

Notes:1. Allows common DSA Motor design for multiple form factors2. Allows space for PZT in Mountplate3. Generally, DSA has lower frequency

5.8 max desirable2up to 7mmDimple to MP edge

25 to 3025 to 100umLoadbeam Thickness

n/a

300-350

800 -1300

20 to 24

20 to 25

7 to 8.5

5 to 6

12-14

150-170

SSA

150 mostly1umMountplate Thickness

800 -1300N/mLifter Stiffness

300-350G’s/gramfStatic Lift-off Shock

10 to 25nm/VDSA Stroke

20 to 24N/mHinge Stiffness (Kv)

18 to 22 3kHzSway Resonance

7 to 8.5 3kHz1st Torsion Resonance

5 to 6 3kHz1st Bending Resonance

12-14degFree-state Angle

DSAUnitUnitDescriptionDescription


PZT Location

DSA fundamentalDSA fundamental

idealsusppzt

suspmodified kk

kδδ ×

+−= )1(

idealideal yxstroke δ×=

1

1ltVdideal ××= 31δ

idealsusppzt

susp

kkk

yxstroke δ×

+−×= )1(

1

1

1x

1y

When Ksusp is low (suspension SST body is stiff)

+ additional stroke from Bridge rotation

T-bar Bridge

Bridge rotation

Stroke Efficiency

This is relatively small

Improves Stroke Efficiency Lowers Sway Frequency

Approximating stroke based on static analysis

DSA converts PZT’s X movement into Y movement by rotating Loadbeam

Geometric Stroke Multiplication Factor

piezo displacement coefficient

voltage

PZT thickness

PZT length

idealδ Head Location

Contraction

Expansion


PZT width

Stroke and SwayStroke and Sway

The Support Structure and PZT size/location greatly affects stiffness, stroke and sway

10.0

12.0

14.0

16.0

18.0

20.0

22.0

24.0

26.0

28.0

30.0

0.80.911.11.21.31.4

PZT location : Y1 (mm)

Stro

ke (n

m/V

)

20000

20500

21000

21500

22000

22500

23000

Sw

ay F

req.

(Hz)

stroke

sway freq.

PZT Location: Y1


SSA 5.7mm LB 30um

-20

-10

0

10

20

30

40

50

0 10000 20000 30000 40000 50000

Frequency (HZ)

Gai

n (d

b)

LB Length Effect LB Length Effect –– LB Shorter for PZT Motor LB Shorter for PZT Motor

lift-off (G/gm) 376B1 (KHz) 7.1T1 (KHz) 9.4

Sway (KHz) 23.4

SSA 6.9mm Loadbeam 30um

-20

-10

0

10

20

30

40

50

0 10000 20000 30000 40000 50000

Frequency (HZ)

Gai

n (d

b)

lift-off (G/gm) 330B1 (KHz) 6.6T1 (KHz) 7.6

Sway (KHz) 26.8

• More interactions between LB and MP

• T2 and T3 become more challenging to control

• Once PZTs are added, structure is somewhat strengthened

FRF

More

Complex

PZTs added here

Shorter

LBLonger

MP


PZT StressPZT Stress

0.0

5.0

10.0

15.0

20.0

25.0

30.0

0 0.2 0.4 0.6 0.8 1 1.2

MP bridge width (mm)

PZT

max

. str

ess

(MPa

) pzt width = 1pzt width = 0.5

FSA = 12.30, loaded angle = 2.90

gramload = 2.5 gramf

Max PZT stress at loaded suspension condition

Bridge width

• The tensile strength of PZT is about 80 MPa. about 100% safety margin with this example

• Needs to verify for the worst case of gramload, applied voltage and op shock.

10.0

12.0

14.0

16.0

18.0

20.0

22.0

24.0

80 90 100 110 120 130 140 150 160

PZT thickness (um)

Stre

ss (M

Pa) o

r St

roke

(nm

/V)

Stress at 1000 G lift-off (MPa)

stroke (nm/V)

Thicker PZT lowers the stress on PZT, but lowers the stroke

10

22

10


DSA DSA -- Major Mode ShapesMajor Mode Shapes

2Torsion @ ~ 16.3 KHz

1 Bending @ ~ 6.7 KHz 1Torsion @ ~ 9.2 KHz

3Torsion @ ~ 29.1 KHz

-20

-10

0

10

20

30

40

0 10000 20000 30000 40000 50000

Frequency (HZ)

Gai

n (d

b)

Sway @ ~ 23.0 KHz

5.7mm LB, 30um thick


Cleanliness ConsiderationCleanliness Consideration

PZT is constructed much like concrete

Mix of various materials is cured

Slab is cut to pieces (wafer to dies)

Good in compression mode and not optimal in tension mode

On the cut surfaces, loose grains or particles may be developed, unless treated properly


PZT Encapsulation ApproachesPZT Encapsulation Approaches

Make gaps and fill them with epoxy

Final dicing – side walls encapsulated

Add encap material on PZT side walls

Construction

Remarks

Description

Patent No

•Allows more DSA design flexibility•Simpler suspension manufacturing process.

Epoxy is filled in the gap before dicing PZTs

6,703,767 (MPT)

Epoxy on Cut Edge. PZT Level

Vapor Coating of Dysanfilm

2002/14815

Anti-release Material on Cut Face

Thin polymer coating of all PZT surfaces

6,930,861

Thin Polymer Coating, PZT Level

Provides effective sealing of side walls

Epoxy applied to the cut edges after attaching PZTs to suspension body

n/a

Epoxy Filling. Suspension Level

MPT supports the first two types of encapsulation in DSA designs


Other ConsiderationsOther Considerations

1. Not all piezoelectric materials are suitable for HDD– Ultra high d31 PZT’s (>350 pm/V), Single crystal PZT’s and polymer

based piezo (PVDF) have very low Curie temperature

2. Short term temperature exposure for process handling, with typical HDD-grade PZT’s:– 160oC for DSA– (~220oC for SSA suspensions)

3. PZT grounding by conductive epoxy on SST– Connection resistance can be reduced by applying electric current

through the epoxy interface depending on bond joint features– Other solutions are available including added gold plated strip or

gold plated mountplate

4. Stroke Sensitivity to driving voltage condition must be verifiedunder long term THB testing


SummarySummary

• HDD industry is transitioning to DSA rapidly • MP based DSA is most common and Dual PZT on

Mountplate is widely used currently • Addition of PZT motors makes the DSA suspensions

behave differently from the SSA type• DSA design requires careful balancing of Performance

and Reliability in FRF, Stroke, Cleanliness and Stability


Magnecomp Precision TechnologyMagnecomp Precision Technology

• Prepared to support transition to DSA• Ramping up DSA products to high volume • Can assist in DSA designs and improving reliability for

DSA implementation

• Contact Information– Peter Hahn: [email protected]

Thank you

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