Chip-on-CAPS (cable-patterned suspension)
2730IEEE TRANSACTIONS ON MAGNETICS,VOL.36,NO.5,SEPTEMBER2000
Chip-On-CAPS(Cable-Patterned Suspension)
T.Ohwe,A.Gouo,H.Mutoh,H.Miura,F.Tamura,and H.Kira
Abstract—A write frequency has been increasing by improve-ment of a write driver and a write head for higher transfer rate in hard disk drives.A certain method for high write frequency operation is to put a write driver chip on the suspension.We de-signed a chip-on-cable-patterned suspension(C-CAPS)that is an integrated wireless suspension with a write driver chip on.This paper describes the first observation of the effect on the chip-on-suspension in the write frequency and what type of the C-CAPS is suitable,especially relating to the location of a chip,for high per-formance hard disk drives.Next,we clarify characteristics of the C-CAPS,such as write current transition time,interface between the chip and disk,shock resistance,frequency response,thermal deformation due to temperature increase of the chip,and static at-titude change due to bonding the chip.We conclude the C-CAPS contributes to increase a write frequency and the best location of a chip is on the tip of the load beam for high performance hard disk drives.
Index Terms—Hard disk drive,suspension,head,slider,write driver,chip,write current transition time,resonant frequency, shock resistance,static attitude,thermal deformation,CAPS, flying height.
I.I NTRODUCTION
A write current frequency has been increased up to over400
Mbps by improvement of,for example,a write driver chip and a write head in hard disk drives.This40%annual increase in a write current frequency can be achieved not only by improving a write driver chip and write head but also the careful selection of a chip location.One solution for higher writing frequency is chip-on-cable-patterned suspension(C-CAPS)concept that is an integrated wireless suspension for pico-sliders[1]with a write driver chip on.There are two ideas for the location of a chip.One possible location is on a load beam tip,which is very close to a slider,the other possible location is on a base plate which is very far away from a slider(Fig.1).
II.A NALYSIS AND E XPERIMENTS
A.Write Current Transition Time
A write current transition time was measured first to confirm an effect of the C-CAPS by an EO probe technique that utilizes an electro-optical crystal[2].A C-CAPS with a chip on the load beam tip and conventional CAPS were compared.The distance
Manuscript received February20,2000.
T.Ohwe is with Fujitsu Ltd.
A.Gouo is with the Department of HDI,Advanced File Technology Division, Fujitsu Ltd.,Kawasaki211-8588,Japan.
H.Mutoh,H.Miura,and F.Tamura are with the Development,Advanced File Technololgy Division,Fujitsu Ltd.,Kawasaki211-8588,Japan.
H.Kira is with the Micro Assembly,Advanced File Technololgy Division, Fujitsu Ltd.,Kawasaki211-8588,Japan.
Publisher Item Identifier S
0018-9464(00)08048-1.
Fig.1.Chip location variation for chip-on-CAPS.
between the chip center and slider center is about2mm for the
C-CAPS.The distance between the chip center and slider center
is about15mm for the conventional CAPS.The write drivers
having equivalent writing capability were used.Each suspen-
sion was connected to the circuit board where a read ampli-
fier was attached by wires at the bonding pads.We placed a
write driver chip on the circuit board for the conventional CAPS.
Since a write driver chip is operated with a differential mode,a
write current transition time is shown as an average time with
T(rise)and T(fall).T(rise)or T(fall)mean the time for a10to
90%increase or decrease in output.We observed the write cur-
rent transition time for the C-CAPS with a chip on the load beam
tip is about0.99ns and that for the conventional CAPS is about
1.39ns.We confirmed the write current transition time for the
C-CAPS with a chip on the load beam tip is faster than that for
the conventional CAPS by about29%(Fig.2).We next com-
pared the write current transition time after moving a chip from
the tip of a load beam to a base plate.The distance between the
chip center and slider center was about9mm for the C-CAPS
with a chip on the base plate.The write current transition time
for the C-CAPS with a chip on the base plate is about1.07ns.We
confirmed the write current transition time for the C-CAPS with
a chip on the load beam tip is faster than that for the C-CAPS
with a chip on the base plate by about7%.This is resulted from
reduction in capacitance and inductance of signal patterns by
shortening the distance between a write driver chip and a head.
This means the C-CAPS with the chip location at the tip on the
load beam is best for increasing the write current frequency in
hard disk drives.
0018–9464/00$10.00?2000IEEE
OHWE et al.:CHIP-ON-CAPS(CABLE-PATTERNED SUSPENSION)
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Fig.2.Write current transition time for C-CAPS with chip on load beam tip and conventional CAPS.
B.Interface between Chip and Disk
We next investigated interface between a chip and disk.Re-duction of a clearance between a chip and disk is a possible cause of a contact during an excess shock or the z-height change.
A slider is0.3-mm thick and a chip is0.18-mm thick including bonding pads.If a chip is on the base plate,which is very far from a slider,the z-height change of-0.12mm allows a contact between a chip and disk due to thickness difference between a chip and slider.This means height of a chip must be reduced to prevent a contact and to keep the z-height tolerance of at least
0.25mm,which is enough tolerance for practical z-height variation.
C.Shock Resistance
Increase of the suspension equivalent mass due to bonding a chip on the load beam tip may cause reduction in shock resis-tance.We measured the shock resistance using a C-CAPS with a chip on the load beam tip and conventional CAPS.Mass of a write driver chip is0.47mg including bonding pads.The sus-pension equivalent mass of a C-CAPS with a chip on the load beam tip is increased by6.9%comparing to that of the con-ventional CAPS by bonding a chip.This increase in suspension equivalent mass is equal to the shock resistance reduction of 10G considering reduction of the head/disk separation accel-eration.We measured the shock resistance applying25-G step increment with1-ms duration against aluminum disks.A rigid base attaching a disk and a suspension was dropped to observe the shock resistance.A disk surface tester was used to inspect disk surface damages.We confirmed that the shock resistance is the same225G for both suspensions.This shock resistance is enough tolerance for high performance hard disk drives.In the C-CAPS with a chip on the load beam tip,damages observed on the disk surface were not by the chip but by the
slider.Fig.3.Mechanical frequency response of C-CAPS with chip on load beam tip and conventional CAPS.(a)C-CAPS with chip on load beam.(b)Conventional
CAPS.
Fig.4.Flying height during driving chip.
D.Frequency Response
Increase of suspension equivalent mass due to bonding a chip on the load beam tip may reduce the resonant frequency in the access direction.Frequency responses in the access direction were measured by using a LDV for both a C-CAPS with a chip on the load beam tip and conventional CAPS.The first,second, and third resonant peaks at11.6kHz,13.7kHz,and19.0kHz in the conventional CAPS show the second torsion,sway,and third torsion modes respectively.These frequencies at the first and second resonant peaks increase by about0.8kHz and0.9kHz respectively in the C-CAPS with a chip on the load beam tip (Fig.3).The resonant peak at the third torsion mode is not seen in the frequency response of the C-CAPS,this is because the resonant frequency in the third torsion mode has been increased up to over20kHz.This increase in the resonant frequencies for the C-CAPS is because effect of stiffness increase of a load beam in the roll and sway direction due to bonding a chip is greater than effect of suspension equivalent mass increase. E.Thermal Deformation
Temperature rise by driving a chip may cause flying height variation due to the thermal deformation of the suspension in the pitch direction.We measured the flying height of the C-CAPS with a chip on the load beam tip during driving a chip.We mea-sured the temperature of the junction area that connects between the suspension pads and chip pads by monitoring the diode char-acteristics in the chip during driving a chip.We observed this current drive raised the temperature of the junction area by about 80deg.,so that the total temperature including ambient temper-ature will go up to about105deg.Even in such a circumstances, we could have confirmed that no flying height change occurred for60minutes during driving a chip(Fig.4).This means the thermal deformation of the suspension due to the temperature rise by driving a chip is negligible.
2732IEEE TRANSACTIONS ON MAGNETICS,VOL.36,NO.5,SEPTEMBER2000
F.Static Attitude
We used a gold bumping method with ultra sonic vibration and heating for bonding a chip on the load beam tip.If this process is poor,process error may cause the static attitude change of a suspension in the pitch and roll direction.These cause the flying height change that affects R/W performance and reliability of hard disk drives.Especially,the static attitude change in the pitch direction also causes the loading force change.We observed that the static attitude change due to bonding a chip on the load beam tip is less than5%of the tolerance and the change of the loading force is less than3%of the tolerance.We confirmed these changes are negligible for performance and reliability of hard disk drives.
III.C ONCLUSION
We evaluated the effect on utilizing of C-CAPS and where is the best location of a write driver chip for high performance hard disk drives.We could have confirmed that the C-CAPS contributes to increase transferring data and a chip location at the tip of a load beam configuration is especially effective.We clarify that configuration can increases the write current tran-sition time by30%comparing to the conventional CAPS and by7%comparing to the C-CAPS with a chip on the base plate. We also clarify that the C-CAPS does not deteriorate the char-acteristics such as interface between a chip and disk,resonant frequency,shock resistance,thermal deformation,and static at-titude.The chip-on-CAPS with a chip on the tip of a load beam configuration is suitable for high performance hard disk drives.
R EFERENCES
[1]T.Ohwe,T.Watanabe,S.Yoneoka,and Y.Mizoshita,IEEE Trans.
Magn.,vol.32,pp.3648–3650,1996.
[2]H.Sekiguchi,H.Hama,A.Fujii,S.Wakana,and T.Nagai,JSAM,1999.