Slider-suspension assembly and method for attaching a slider to a suspension in a data recording disk file

In a data disk file a slider is mechanically attached to the suspension by means of reflowed solder balls. A pattern of solder contact pads is formed on the back side of the slider and a similar pattern of solder-wettable regions is formed on the suspension. Solder balls are formed on either the solder contact pads or the solder-wettable regions, the slider is located on the suspension so that the solder balls are in registration between the solder contact pads and solder-wettable regions, and the solder is heated to reflow, thereby forming solder joints as a mechanical connection between the slider and suspension. When a thin film transducer is formed on the slider trailing edge and the suspension is a laminated type with patterned conductors, solder balls are also formed on the transducer lead terminations on the trailing edge and on a row of solder-wettable regions on the suspension near the location where the trailing edge of the slider is to be located. In this embodiment, when the slider with thin film transducer, with solder balls on the lead terminations, is located over the suspension then all of the solder balls are heated. The solder balls for providing mechanical connection collapse during reflow, thereby causing the solder balls on the transducer lead terminations to come in contact with and flow together with the solder balls formed on the row of solder-wettable regions on the suspension. Thus the mechanical attachment of the slider is made simultaneously with the electrical connection of the transducer lead to the disk file read/write electronics.

TECHNICAL FIELD 
This invention relates to slider-suspension assemblies for data recording 
disk files and to a method for making such assemblies. In particular the 
invention relates to an improved slider-suspension assembly and to a 
method for mechanically and electrically attaching the slider to the 
suspension. 
BACKGROUND OF THE INVENTION 
Disk files are information storage devices which utilize at least one 
rotatable disk with concentric data tracks containing the information, a 
transducer (or "head") for reading data from or writing data to the 
various tracks, and a head positioning actuator connected to the head for 
moving it to the desired track and maintaining it over the track 
centerline during read or write operations. The transducer is attached to 
a slider having an air bearing surface which is supported adjacent the 
data surface of the disk by a cushion of air generated by the rotating 
disk. The slider is attached on its back side (the side opposite the air 
bearing surface) to the suspension, and the suspension is attached to a 
support arm of the head positioning actuator. 
The suspension provides dimensional stability between the slider and 
actuator arm, controlled flexibility in pitch and roll motion of the 
slider relative to its direction of motion on the rotating disk, and 
resistance to yaw motion. The suspension typically provides a load or 
force against the slider which is compensated by the force of the air 
bearing between the slider's air bearing surface and the disk surface. 
Thus, the slider is maintained in extremely close proximity to, but out of 
contact with, the data surface of the disk. The suspension typically 
comprises a load beam, which is mounted at one end to the actuator arm, 
and a flexure element which is attached to the other end of the load beam 
and supports the slider. The load beam provides the resilient spring 
action which biases the slider toward the surface of the disk, while the 
flexure provides flexibility for the slider as the slider rides on the 
cushion of air between the air bearing surface and the rotating disk. Such 
a suspension is described in U.S. Pat. No. 4,167,765, which is assigned to 
the same assignee as this application. An example of a conventional slider 
is described in U.S. Pat. No. 3,823,416, which is assigned to the same 
assignee as this application. 
In the conventional slider-suspension assemblies, the slider is 
mechanically attached to the flexure of the suspension by epoxy bonding. 
The electrical connection between the transducer and the disk file 
read/write electronics is made by twisted wires which run the length of 
the suspension load beam and extend over the flexure and slider. The ends 
of the wires are soldered or ultrasonically bonded to the transducer leads 
on the slider. The fabrication of such a slider-suspension requires manual 
assembly and is thus time consuming and costly. 
Another type of suspension is a composite or laminated structure comprising 
a base layer with patterned electrical leads formed thereon and an 
insulating cover layer, as described in IBM Technical Disclosure Bulletin, 
Vol. 22, No. 4 (Sept. 1979), pp. 1602-1603 and Japanese Kokai Nos. 
53-74414 (Jul. 1, 1978) and 53-30310 Mar. 22, 1978). In the laminated 
suspension described in Japanese Kokai 53-74414, the slider is epoxy 
bonded to the laminated suspension and the transducer leads are soldered 
to the electrical leads formed on the suspension. 
A disadvantage with conventional epoxy bonding of the slider to the 
suspension is that it is difficult to form the assembly such that the 
slider will have a predetermined pitch or roll relative to its direction 
of motion on the disk. Since the epoxy bonding can only result in a 
generally parallel relationship between the back side of the slider and 
the flexure of the suspension, the flexure must be formed or bent prior to 
bonding in order to give the slider a predetermined pitch or roll. Also, 
if it is desired to bond the slider to the suspension at a skew angle in 
order to optimize the angle between the slider's leading edge and the data 
track, some type of fixture is required to align the slider at the time 
the epoxy bond is formed. 
An additional disadvantage with epoxy bonding is that because the epoxy is 
nonconductive, there is no consistent grounding path between the slider 
and the suspension. Thus in the event of static charge build-up on the 
slider the closest path for discharge is from the pole tips of the 
transducer to the disk surface. Static discharge through this path will 
destroy a thin film transducer. 
Static charge build-up on the disk can also destroy a thin film transducer 
if the static discharge occurs from the disk to the pole tips of the 
transducer. This is because in conventional slider-suspension assemblies 
which have only one active thin film transducer on the slider, there is no 
grounding path from the pole tips of the inactive transducer. 
SUMMARY OF THE INVENTION 
The invention is an improved slider-suspension assembly in which the slider 
is mechanically attached to the suspension by a plurality of reflowed 
solder ball connections. When the suspension is the laminated type with 
patterned electrical leads, the electrical attachment of the transducer 
leads to the leads on the suspension is also provided by reflowed solder 
ball connections. 
In the preferred embodiment a pattern of solder contact pads is provided on 
the back side of the slider and a like pattern of solder-wettable regions 
is provided on the generally planar portion of the suspension to which the 
slider is to be attached. Solder balls are then formed on either the 
slider solder contact pads or the solder-wettable regions by, for example, 
evaporation and subsequent reflow of the solder. The slider is then placed 
in contact with the suspension so that the solder contact pads are in 
approximate alignment with respective solder-wettable regions on the 
suspension and the solder balls are in registration between the two 
aligned patterns. The solder balls are then heated to reflow, thereby 
forming a mechanical connection with precise alignment between the slider 
and the suspension. The above-described solder reflow technique is similar 
to the controlled collapse chip connection (C4) process for securing 
semiconductor devices (chips) to printed circuit boards. 
When the suspension is the laminated type and the transducer is the thin 
film type with leads formed on the slider trailing edge and terminating 
generally at the corner between the trailing edge and the slider back 
side, then solder connections between the transducer leads and electrical 
leads on the suspension are formed simultaneously with the above-described 
mechanical attachment. Solder balls are formed on the lead terminations of 
the thin film transducers and on a row of solder-wettable regions near the 
location where the trailing edge of the slider is to be located when the 
slider is attached to the suspension. The solder-wettable regions in the 
row are terminations for the electrical leads formed on the laminated 
suspension. When the slider is located on the suspension with the solder 
balls in registration between the two like patterns on the slider back 
side and the suspension, the solder balls on the transducer leads are then 
in alignment with but not in contact with the row of solder balls formed 
on the suspension. When the solder is heated, the solder balls between the 
back side of the slider and the suspension reflow and collapse, thereby 
causing the solder balls on the transducer leads to contact those formed 
in the row on the suspension. This results in the formation of generally 
right-angled solder joints between the transducer leads and the row of 
associated solder-wettable regions on the suspension. 
The solder-wettable regions for providing mechanical attachment on the 
suspension are electrically grounded back to the actuator arm so that 
static charge on the slider will discharge to ground rather than to the 
disk through the transducer pole tips. In addition, the right-angled 
solder joints on the inactive thin film transducer end at solder-wettable 
regions which are electrically connected to certain of the solder-wettable 
regions for mechanical attachment. Thus, the pole tips of the inactive 
transducer are grounded through the slider back to the actuator arm so 
that static charge on the disk can be discharged through the pole tips of 
the inactive transducer. 
The slider-suspension assembly is usable as a mechanical connection for 
both laminated type suspensions having patterned conductors and the more 
conventional suspensions, such as the stainless steel suspension described 
in the '765 patent. In the case of the conventional suspension, the 
solder-wettable regions are formed on the suspension by depositing 
solder-wettable material, such as copper, directly on the stainless steel. 
In the case of the laminated suspension, the regions are formed by 
providing openings through the insulating cover layer to expose portions 
of the conductive pattern. 
Because orientation of the slider onto the suspension is determined by the 
pattern of solder contact pads, the slider can be reliably located on the 
suspension in a skewed position by merely orienting the solder contact 
pads at the time they are formed on the slider back side. Similarly, by 
altering the size of selected solder contact pads on the slider or the 
solder-wettable regions on the suspension, selected solder balls securing 
the slider to the suspension will form shorter solder joints during 
reflow. This permits the slider to be attached to the suspension with a 
predetermined pitch or roll orientation when the slider flies above the 
surface of the rotating disk.

DESCRIPTION 
A. Prior Art 
A conventional slider-suspension assembly is illustrated in FIG. 1. The 
suspension comprises a load beam 10 and a flexure 12 located at the end of 
load beam 10. The suspension is attached to the disk file actuator arm 
(not shown) by means of a mounting plate 14. The slider 16 is a 
conventional slider formed of ceramic material, such as a mixture of 
alumina (Al.sub.2 O.sub.3) and titanium carbide (TiC). The slider 16 has 
an air bearing surface 18, which includes two rails 20, 22, a back side 24 
opposite and generally parallel to air bearing surface 18, a leading edge 
25 and a trailing edge 26, both of which form end faces oriented generally 
perpendicular to air bearing surface 18 and back side 24. Slider 16 is 
secured to flexure 12 by an epoxy bond between back side 24 and flexure 
12. 
Located on the trailing edge 26 of slider 16 are two thin film read/write 
transducers 28, 30. Typically, multiple thin film transducers are formed 
on a single slider, even though only one transducer is active as a 
read/write element, in order to improve the yield of the slider during the 
thin film fabrication process. The transducers 28, 30 have pole tips 29, 
31, respectively, which extend toward the edge of respective rails 20, 22. 
Transducer 28 has electrical leads 33, 35 and transducer 30 electrical 
leads 37, 39 for connection to the read/write electronics of the disk 
file. 
The epoxy connection between flexure 12 and the back side 24 of slider 16 
does not provide electrical grounding. Thus any static charge on slider 16 
can only be dissipated through the pole tips 29 of active transducer 28 to 
the disk surface, which results in destruction of the thin film 
transducer. 
In the conventional embodiment shown in FIG. 1, the electrical attachment 
to the read/write electronics is made by twisted wires 34 which extend 
from the read/write electronics, through a tube 36 on load beam 10 and out 
the end of tube 36. The ends of wires 34 are soldered or ultrasonically 
bonded to the leads 33, 35 of active transducer 28. The electrical 
connection of the transducer 28 by means of the twisted wires 34 is made 
by manual fabrication. 
B. Preferred Embodiments 
Referring now to FIG. 2, the slider-suspension assembly of the present 
invention is illustrated as slider 16 which is both mechanically and 
electrically connected to a composite or laminated suspension 40. The 
suspension 40 comprises a nonconductive base layer 42, a patterned 
conductive layer 44, and an insulating cover layer 48. The base layer 42 
may be a polyimide sheet and the patterned conductive layer 44 a 
vapor-deposited copper film. The insulating cover layer 48 may be a layer 
of polyimide formed over the patterned conductive layer 44 and bonded to 
the base layer 42. The patterned conductive layer 44 is thus formed 
between base layer 42 and cover layer 48 and is visible in FIG. 2 because 
of the translucency of cover layer 48. The electrical leads 46 form part 
of the conductive layer 44 and extend beneath the slider 16 where they end 
at terminations 47. 
The conductive pattern of layer 44 is better illustrated in FIG. 3 and 
includes electrical leads 46 with terminations 47, and large area portions 
52, 54 which form a supporting base for the mechanical attachment of the 
slider in the manner to be described below. 
The slider 16 (FIG. 2) has an air bearing surface 18, including rails 20, 
22, and a trailing edge 26. Conventional thin film transducers 11, 13 are 
formed on the trailing edge with respective pole tips 15, 17 extending to 
the edges of rails 20, 22 respectively. Each of transducers 11, 13 has a 
pair of electrical leads 19, 21 and 27, 29, respectively, extending across 
the trailing edge 26 toward the corner formed by back side 24 and trailing 
edge 26. As shown in FIG. 2, slider 16 is mechanically bonded to the large 
area portions 52, 54 of conductive pattern 44 by means of reflowed solder 
balls 60 between the slider back side 24 and the conductive layer 44. 
Transducer 11 is the active transducer and electrical connection of it to 
the terminations 47 formed as part of the conductive pattern 44 is made 
through generally right-angled solder joints 86. The leads 27, 29 of 
inactive transducer 13 are connected to extensions 49 of portion 52 of the 
conductive pattern 44. 
The circles shown on FIG. 3 are circular openings 60, 61 and 63 in the 
insulating cover layer 48 which expose the underlying copper of the 
patterned conductive layer 44. Circular openings 60 define a pattern of 
solder-wettable regions on suspension 40 for mechanical attachment of 
slider 16. Circular openings 61, 63 define a row of solder-wettable 
regions along the line where the transducer lead terminations will be 
located when the slider is attached to the suspension. The solder-wettable 
regions 63 are used for electrical connection of leads 46 to transducers 
11. 
The manner in which the solder connection of slider 16 is made to 
suspension 40 can be better understood by reference to FIGS. 4, 5, and 6. 
FIG. 4 illustrates a portion of slider 16 with solder contact pads 70 
formed on the back side 24 and solder-wettable regions 60, 63 formed on 
suspension 40. The solder-wettable regions 63, one of which is shown in 
FIG. 4, are formed on the terminations 47 of leads 46 (Fig. 3). The 
pattern of solder contact pads 70 formed on the back side 24 of slider 16, 
only two of which are shown in FIG. 4, is a mirror image of the pattern of 
solder-wettable regions 60 on portions 52, 54 (FIG. 3). Also shown in FIG. 
4 is the slider trailing edge 26 with transducer 11 formed thereon, and 
transducer pole tips 15, lead 21 and lead termination 41. 
As shown in FIG. 4, each of the contact pads 70 comprises an adhesion film 
74 formed directly onto the slider back side 24 and a solder-wettable film 
76 formed on the adhesion film 74. The solder contact pads are formed on 
the slider back side by a suitable mask having openings which is placed 
over back side 24. The masked slider is then placed in an evaporation dome 
and a crucible containing the adhesion material, such as titanium, is 
evaporated and formed as film 74 on the slider back side 24. Thereafter 
the solder-wettable film, such as nickel, is evaporated onto the adhesion 
film. It is preferable that for a short period of time the evaporation of 
both the titanium and the nickel occur so that an interfacial alloy of 
titanium and nickel is formed between the adhesion film 74 and the 
solder-wettable film 76. If the solder balls are not to be formed for some 
time, then a corrosion-resistant film 78 of, for example, gold is formed 
over the nickel film. The gold film provides a corrosion barrier for the 
solder contact pads 70. The solder contact pads 70 formed in this manner 
provide material which is conductive to the wetting or adhesion of solder 
and thus permit solder balls to be securely adhered to the back side 24 of 
slider 16. Chromium may be used in place of titanium as the adhesion film, 
and copper may be used in place of nickel as the solder-wettable film. 
Referring again to FIG. 3, the solder-wettable regions on suspension 40 are 
formed by removing selected portions of the polyimide insulating layer 48, 
which thereby exposes the circular openings 60, 61 on large area portions 
52, 54 and the circular openings 63 on lead terminations 47. These 
openings in the polyimide layer are preferably formed by the use of a 
conventional mask having the pattern of circles. The polyimide is then 
etched away to expose the underlying copper material, as best shown in 
FIG. 4. 
Referring now to FIG. 5, solder balls 80 are formed on the solder-wettable 
regions 60 and solder balls 82 are formed on solder-wettable regions 61, 
63. The solder balls are preferably formed by first tightly securing a 
mask with circular openings over the suspension, the openings being 
aligned with the etched-away portions of layer 48. A solder paste is then 
spread over the mask and forced through the openings. The mask is removed 
and the solder heated to reflow as solder balls 80, 82. The solder balls 
are then adhered to the regions 60, 61 and 63 of the patterned conductive 
layer 44. The solder balls 80, 82 may also be formed on the suspension by 
evaporating solder through openings in a mask placed over insulating layer 
48, removing the mask and thereafter heating the evaporated solder to 
cause the solder to reflow as solder balls 80, 82. 
FIG. 5 also illustrates solder balls 84 formed on transducer lead 
terminations 41. The solder balls 84 are formed on all of the thin film 
transducers at the wafer level during fabrication of the thin film 
transducers by evaporating solder through a mask placed over the wafer 
before the wafer is cut into the individual sliders. FIG. 5 thus 
illustrates an intermediate step in the method for simultaneously 
mechanically and electrically attaching the slider to the suspension. 
During this step the slider 16 is located on solder balls 80 with the 
solder balls 80 being in registration between solder contact pads 70 and 
solder-wettable regions 60. Solder balls 84 on the slider trailing edge 26 
are aligned with but out of contact with the corresponding row of solder 
balls 82 on the suspension. With the slider supported in this position 
heat is then applied to all of the solder balls. This causes solder balls 
80 to collapse, thereby permitting solder balls 82, 84 to come into 
contact and flow together to form generally right-angled solder joints 86 
for providing the required electrical connection between transducer 11 and 
leads 46. The right-angle joints 86 formed on inactive transducer 13 
provide electrical connection to conductive portion 52 and thus to slider 
16. 
The completed slider-suspension assembly is illustrated in FIG. 6, which 
shows the collapsed solder balls 80 and the joined solder balls 82, 84 
forming the right angled solder joints 86. When the solder has cooled and 
solidified the slider is both mechanically attached to the suspension and 
the transducer leads 19, 21 are electrically connected to the electrical 
leads 46 formed on the suspension. Because the slider 16 is mechanically 
attached to the conductive layer 44 by the electrically conductive solder 
balls 80, an electrical path is provided for static discharge from the 
slider 16, thereby preventing destruction of transducer 11 caused by 
discharge through the pole tip 15 to the disk surface. As shown in FIG. 3, 
the area 54 of conductive layer 44 includes a ground lead portion 55 which 
extends back for grounding connection to the actuator arm (not shown). The 
right-angled solder joints 86 on inactive transducer 13 (FIG. 2) provide 
electrical connection from pole tips 17 to extensions 49 on conductive 
portion 52 and the reflowed solder balls 80 on portion 52. Conductive 
portion 52 in turn is electrically connected to slider 16 by reflowed 
solder balls 80, and slider 16 is grounded by path 55 to the actuator arm 
(not shown). Thus any static charge on the disk will be discharged to 
ground through the pole tips 17 of inactive transducer 13, thereby 
avoiding the destruction of active transducer 11. 
In the embodiment as just described the solder balls 80 are first formed 
onto the solder-wettable regions 60, 61 and 63 of the suspension 40. The 
solder balls 80 could instead be first formed onto the solder contact pads 
70 on the slider 16. In addition, rather than spreading solder paste 
through a mask or evaporating solder through a mask onto either the slider 
back side 24 or the suspension 40, it is also possible to spread 
commercially available performed solder balls over a mask to locate the 
solder balls through openings in the mask and then heat the performed 
solder balls. The solder balls would then be formed and adhered to either 
the slider back side or the suspension and the mask would then be removed. 
It is within the scope of the present invention to provide mechanical 
attachment of the slider 16 directly to a conventional stainless steel 
flexure, such as that described in the '765 patent, provided 
solder-wettable regions are first formed on the stainless steel flexure. 
This may be accomplished by any known method of forming, on the stainless 
steel, metal films which are adherent to solder, and thereafter evporating 
or otherwise forming solder onto the metal films formed on the stainless 
steel flexure. For example, the pattern of solder-wettable regions 60 
could be formed on a stainless steel flexure by electroplating copper. If 
the slider is mechanically attached to the stainless steel suspension in 
this manner, then the electrical connection of the transducer can be made 
through the use of conventional twisted wires as previously described. 
Referring now to FIG. 7, there is illustrated the identical invention with 
the exception that the composite suspension 40 now includes an underlying 
support layer 43, which may be a stainless steel flexure, onto which the 
base layer 42 is adhered. Portions of nonconductive base layer 42 are 
etched away in the areas 83 where solder balls 80 are to be aligned. Thus, 
when the copper layer 44 is formed it is placed in direct contact with 
stainless steel in the areas 83. This allows solder balls 80 to form both 
a mechanical connection and an electrical grounding path to the stainless 
steel support layer 43. 
In all of the embodiments shown and described the solder may be any type 
with a melting point compatible with the other materials used in the 
slider-suspension assembly. For example, eutectic tin-bismuth (SnBi) or 
eutectic tin-lead (SnPb) solder is acceptable. 
Referring again to FIGS. 2 and 3, it should be apparent that if the pattern 
of solder contact pads 70 formed on back side 24 of slider 16 is skewed 
relative to the slider, which is represented by dashed lines in FIG. 3, 
then the slider can be mounted to the suspension in a skewed manner. This 
may be desirable when the slider-suspension assembly is used on smaller 
diameter disk files or on disk files with rotary actuators, where it may 
be desirable to optimize the yaw angle of the slider relative to the data 
tracks. 
It is only necessary that the slider contact pads be approximately aligned 
with their corresponding solder-wettable regions prior to reflow. During 
reflow the solder balls will be wetted to both the contact pads and the 
corresponding solder-wettable regions and will cause the slider to be 
precisely aligned on the suspension. The solder balls used to mechanically 
attach the slider result in the slider back side and suspension being 
generally parallel because any variations in size among solder balls is 
averaged out by the relatively large number of solder balls used. If, 
however, certain of the circular slider solder contact pads and/or 
suspension solder-wettable regions are formed so as to have a larger 
diameter than others in the patterns, but the mask used to form the solder 
on those selected pads or regions has openings all of the same diameter, 
then a larger portion of each of the solder balls that is formed on those 
selected pads or regions during reflow will be wetted to those pads or 
regions. This will result in a shorter solder joint at those selected pads 
or regions. This will permit the slider to be mechanically attached to the 
suspension so as to be slightly nonparallel to the planar suspension, 
because those solder balls formed on larger diameter pads and/or regions 
will form shorter joints when reflowed. For example, with reference to 
FIG. 7, if the solder contact pads and associated suspension 
solder-wettable regions near the leading edge (not shown in FIG. 7) of the 
slider have a larger diameter than those shown near the trailing edge 26 
in FIG. 7, then the slider would be slightly tilted with respect to the 
suspension so that the slider will fly with a slight negative pitch 
attitude. Thus, with the present invention the slider may be mounted to 
the suspension with a slight pitch or roll, thereby eliminating the need 
to preform the flexure. 
While the preferred embodiments of the present invention have been 
illustrated in detail, it should be apparent that modifications and 
adaptations to those embodiments may occur to one skilled in the art 
without departing from the scope of the present invention as set forth in 
the following claims.