Welding stress isolation structure for head suspension assemblies

In a suspension assembly for a disk drive, a welding isolation structure for creating an isolated weld point and for substantially eliminating undesirable propagation of welding stresses during the welding of elements of the suspension assembly. The welding isolation structure is placed on selected locations on suspension assembly elements. The isolation structure includes a welding area, at least one isolation slot including a through aperture delineating at least a portion of the perimeter of the welding area, and at least one junction tab bridging the isolation slot and connecting the welding area to the remainder of the load beam. The isolation slots are designed to substantially relieve and contain welding stresses. In the suspension assembly, the tabs of each weld point are oriented generally in directions other than towards other weld points, such that additive and uneven propagation of welding stresses is prevented. The tabs can include curves, such as S-shapes, to attenuate propagation of remaining welding stresses. Additional isolation slots can be placed adjacent and generally opposite the junction tabs from the welding area to further relieve remaining welding stresses.

FIELD OF THE INVENTION 
The present invention relates to head suspension assemblies (HSAs) for data 
storage disk drives. In particular, the present invention is a welding 
stress isolation structure for creating an isolated weld point, to 
substantially eliminate undesirable propagation of welding stresses caused 
by expansion and contraction of material heated during welding of elements 
of an HSA. 
BACKGROUND OF THE INVENTION 
HSAs are the components in a disk drive that position a read/write head 
assembly over the spinning surface of a data storage device (e.g. a 
magnetic hard disk). HSAs are some of the smallest and most delicate 
components of a rigid disk drive. An HSA includes a suspension assembly 
and a head assembly. The head assembly is positioned at a distal end of 
the suspension assembly. The suspension assembly is an elongated spring 
structure. Suspension assemblies act in a similar fashion to the needle 
arm in a record player, positioning the head assembly nanometers from the 
surface of a spinning disk in the disk drive. Typical suspension 
assemblies measure less than 20 mm long and are 0.03 to 0.1 mm thick. 
Suspension assemblies generally include elements such as an elongated load 
beam, a gimbal flexure located at a distal end of the load beam, and a 
base plate or other mounting means located at a proximal end of the load 
beam. 
The head assembly is mounted to the gimbal flexure. The gimbal flexure 
provides gimballing support to the head assembly. The head assembly 
includes an air bearing slider and a read/write magnetic transducer formed 
on the slider. The slider is a head assembly element aerodynamically 
shaped to use the air stream generated by the spinning disk to produce a 
lift force which supports the head assembly above the disk. 
During operation of the disk drive; the whole suspension assembly is 
designed to work together to maintain the head assembly at a desired 
orientation with respect to the surface of the disk. The orientation or 
attitude of the head assembly and of the HSA is defined by a pitch axis 
angle measurement and a roll axis angle measurement (pitch angle and roll 
angle) measured in relation to a manufacturing datum plane. The 
manufacturing datum plane is a horizontal plane representing a suspension 
mounting surface of an actuator. The pitch and the roll axes are parallel 
to the horizontal plane and are mutually perpendicular, intersecting at a 
point on the head bonding platform. The roll axis is usually aligned with 
the longitudinal axis of the suspension assembly. Roll errors are 
undesired changes in the roll angle. Pitch errors are defined as undesired 
changes in the pitch angle. 
A design goal for magnetic disk drives is to "fly" the head at the closest 
possible distance and at a desired attitude with respect to the surface of 
the disk, since the size of the magnetic field "spot" written and read by 
the transducer is directly proportional to the square of the distance 
between the transducer and the disk. Small changes in distance and/or 
attitude can cause the head assembly to "crash", that is, to hit the 
surface of the spinning disk. A crash can destroy both the transducer and 
any data recorded on the surface of the disk. 
Elements of a suspension assembly, such as the load beam and the gimbal 
flexure, are often attached together by welds. During welding, intense 
heat is applied to weld points on the surface of the elements to be 
welded. A zone of expanded molten material joining the two elements is 
created. The zone is then allowed to cool down. Since the zone loses heat 
to the outside atmosphere and to the surrounding material, the zone cools 
from the outside in, contracting as it cools. Once the zone has cooled, 
the solidified material holds the suspension assembly elements together. 
The rapid heating and cooling creates welding stresses as the heated 
material expands and contracts due to its positive coefficient of thermal 
expansion, and therefore pushes and pulls the surrounding material. Even a 
single weld point located in a symmetrical position on the suspension 
assembly (where forces can be spread in a symmetrical pattern over 
relatively large surfaces and are therefore diminished), can cause welding 
stresses that can warp or deform suspension assembly elements. 
Yet, in certain circumstances, such as when weld points are close together 
or when the geometry of a suspension assembly element impedes even 
distribution of welding stresses, welding stresses can unevenly propagate 
and can undesirably add upon each other. Since the material surrounding a 
pre-existing weld point is fixed, welding stresses from a new nearby weld 
point will tend to unevenly propagate and concentrate in a direction 
opposite and away from the pre-existing weld point. The intensified uneven 
stresses, added to existing stresses from the pre-existing weld, can lead 
to warping or curling of the suspension assembly element. 
Such uncontrolled stresses and subsequent deformation can affect the pitch 
and roll angles of the HSA. Given the precision required from HSAs, even a 
small variation in the pitch or roll angle of an HSA element can render 
the HSA defective by making it prone to crashes or by affecting the size 
and accuracy of the magnetic field read/write spot. Defective HSAs can 
compromise the reliability of the whole disk drive and destroy both the 
disk and its data. 
SUMMARY OF THE INVENTION 
The present invention is a welding stress isolation structure for creating 
an isolated weld point on a suspension assembly element. The welding 
stress isolation structure is designed to substantially eliminate 
deformation of the suspension assembly element caused by undesirable 
propagation of welding stresses. 
The isolation structure includes a welding area, at least one slot 
delineating the perimeter of the welding area, and a junction tab. The 
welding area is a generally flat metal surface located on a selected 
location on the suspension assembly element. The welding area has a 
perimeter delineated or defined by at least one isolation slot. The 
isolation slot is a through aperture on the suspension assembly element. 
The slots help relieve and redirect the welding stresses. The junction tab 
is a generally rigid piece of material supporting the welding area and 
connecting the welding area to the remainder of the suspension assembly 
element opposite the isolation slot from the welding area. 
In a preferred embodiment, the isolation structure has a generally circular 
welding area delineated by two isolation slots, through holes shaped as 
generally circumferential or semicircular arcs. The slots are separated by 
two junction tabs connecting opposite ends of the welding area to the 
remainder of the suspension assembly element. 
To reduce propagation of welding stresses through the junction tabs, some 
embodiments of the isolation structure include irregularly shaped junction 
tabs, some of the tabs having stress relieving curves. One such embodiment 
includes a generally S-shaped junction tab, that is, a junction tab having 
two connecting opposite radial curves. 
Another embodiment of the welding stress isolation structure includes a 
generally rigid junction tab having a first segment and a second segment. 
The first segment includes a generally straight portion of material 
connected to the welding area and extending generally in a radial 
direction away from the welding area. The second segment is a curved 
portion connected at one end to the first segment and at another end to 
the remainder of the suspension assembly element. The second segment can 
be shaped as a generally planar elliptical curve having a 180 degree 
radial break. 
Another embodiment of an isolation structure reduces propagation of welding 
stresses through the junction tabs by placing additional slots through the 
suspension assembly element adjacent and generally opposite the tab from 
the welding area. The slots are radially spaced from the welding area and 
include through apertures shaped as arc segments. 
A preferred embodiment of a suspension assembly in accordance to the 
present invention includes a gimbal assembly attached to a load beam by 
four weld points. Each weld point is located within and isolated by a 
welding stress isolation structure etched on the load beam. 
Each isolation structure has two junction tabs aligned on opposite ends of 
a welding area, the tabs separating two generally semicircular isolation 
slots. A first and a second isolation structure are placed on a roll axis 
of the suspension assembly and have their respective junction tabs aligned 
with a pitch axis. 
A third and a fourth isolation structure are placed adjacent to each other 
and on opposite sides of the roll axis, in between, but not contiguous to, 
the first and second isolation structures. The junction tabs of the third 
and fourth isolation structures are aligned with the roll axis and 
oriented to prevent propagation of welding stresses in the direction of 
other isolation structures. The location and orientation of the stress 
isolation structures is intended to minimize additive or uneven welding 
stresses in a suspension assembly element. In other embodiments, stress 
isolation structures of different shapes can be located on selected 
locations on the load beam, the gimbal flexure, or both the gimbal flexure 
and the load beam.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention is a welding stress isolation structure for 
substantially reducing the undesired propagation of welding stresses 
caused by expansion and contraction of material in and surrounding a weld 
point during welding of elements of an HSA. The stress isolation structure 
helps to prevent pitch and roll angle deviations (pitch and roll errors) 
caused when welding stresses deform suspension assembly elements. 
Welding stress isolation structures in accordance with the present 
invention can be used to isolate weld points in a variety of suspension 
arm elements. Suspension arm elements are elements of a disk drive 
included in or connected to the HSA, such as a base plate, a combined base 
plate arm, an actuator, a gimbal flexure, a spring region, or a support 
structure. The stress isolation structures can be placed on either or both 
of the suspension arm elements to be welded together. 
FIG. 1 illustrates a suspension assembly 110 having a load beam 120, a 
gimbal flexure 130, and a base plate 140. Load beam 120 is an elongated 
planar metal spring element. Load beam 120 includes a base plate region 
122 at a proximal end; a spring region 124 adjacent the base plate region 
122, a rigid region 126 adjacent the spring region 124, and a gimbal 
attachment region 128 at a distal end. 
Gimbal flexure 130 is attached to the gimbal attachment region 128 by four 
weld points 132A-132D. The term weld point is used to refer to the welded 
spot joining elements of an HSA. In the embodiment shown, base plate 140 
is attached to the base plate region 122 by eight weld points 142A-142C 
and 142. 
Gimbal flexure 130 is a spring structure to which a head assembly (not 
shown) is attached. The gimbal flexure 130 provides gimballing support to 
the head assembly and holds the head at a predetermined orientation with 
respect to the surface of a spinning disk. Base plate 140 is a metal 
support structure congruent to the base plate region 122. 
FIG. 2 is a detailed isometric top view of a distal end of the suspension 
assembly 110 shown in FIG. 1. Suspension assembly 110 has four welding 
stress isolation structures 150A-150D in accordance with the present 
invention, each one surrounding a respective weld point 132A-132D. 
Load beam 120 is attached to gimbal flexure 130 by weld points 132A-132D. 
Each weld point 132A-132D is located in the middle of a respective welding 
stress isolation structure 150A-150D. Since stress isolation structures 
150A-150D are all similar to each other, the description of the elements 
of stress isolation structure 150A equally applies to stress isolation 
structures 150B-150D. 
Stress isolation structure 150A includes a welding area 152, generally a 
flat portion of the load beam 120. The welding area 152 is generally 
shaped as a circle having a diameter of 1 mm. The welding area has a 
perimeter delineated by two isolation slots 154. Isolation slots are holes 
or apertures through the suspension assembly element placed in close 
proximity to the weld point to reduce the propagation of stresses from the 
weld point to the remainder of the suspension assembly element. In the 
embodiment shown in FIG. 2, slots 154 are generally shaped as semicircular 
arc segments having a radial width of 0.25 mm and defining the perimeter 
or circumference of the welding area 152. Since different suspension 
assembly designs and welding patterns have different support requirements, 
the slots of different embodiments can have different shapes and 
dimensions. 
Two junction tabs 156A separate the ends of the two slots 154 from each 
other, support the welding area 152, and connect the welding area 152 to 
the remaining portions of the load beam 120 across the isolation slot 
(opposite the isolation slot from the welding area). A first end of each 
junction tab 156A is connected to the welding area 152. A second end is 
connected to the rest of the load beam 120. The two junction tabs 156 
function as rigid bridges positioned at opposite ends of the welding area 
152. In the embodiment shown in FIG. 2, the junction tabs 156A-156D have a 
width of 0.25 mm. 
The size of the welding area, the proximity and shape of the slots, the 
placement, design, and dimensions of the junction tabs all can vary 
depending on the needs (such as time and temperature of welding, required 
mechanical support, materials used, weld strength, positioning of other 
weld points, and expected propagation of weld stresses) of each suspension 
assembly. Other embodiments can include a different number of slots or 
differently shaped slots. 
A preferred method for manufacturing the stress isolation structures 150A 
is to etch the slots 154 while etching other features of the load beam 
120. The stress isolation structure 150A can also be stamped, electrically 
discharged machined, or manufactured by other methods known in the art. 
Similar stress isolation structures can be provided at aligned locations 
on the gimbal flexure 130. 
During welding, intense heat is applied to the weld point 132A (a preferred 
method is for the operator to aim laser light beam pulses having an 
intensity between 80 watts to 140 watts for one to five milliseconds at 
the weld point 132A). Due to the positive thermal coefficient of expansion 
of metal load beam elements, the weld point 132A and the surrounding 
welding area 152 tend to expand when heated. The opening or void provided 
by slots 154 provides the welding area 152 an expansion buffer zone and 
allows the welding area 152 to expand and welding stresses to dissipate 
without affecting surrounding material. The slots 154 relieve and contain 
the expansion forces in a limited area. Conversely, when the welding area 
152 cools (usually in less than two milliseconds) and contracts, pulling 
in surrounding material, the slots 154 contain the transmission of the 
contraction forces. Containment of thermal expansion and contraction 
forces, and therefore of welding stresses, substantially eliminates 
deformation and pitch and roll errors caused by the welding process. 
To prevent or minimize the transmission of welding stresses through 
junction tabs 156A-156D, isolation structures 150A-150D of suspension 
assembly 110 are located and oriented so as to minimize additive or uneven 
welding stresses. Orientation of a stress isolation structure is generally 
defined as the direction of an axis extending from the weld point through 
the second end of the junction tabs of the isolation structure. Welding 
stresses propagate outwardly from the weld spot along a radial vector. 
Since remaining welding stresses (stresses not absorbed by the isolation 
structure) can be propagated by the physical connection between the 
welding area and the remaining portion of the suspension assembly element 
provided by the junction tabs the orientation of an isolation structure is 
also the general direction any remaining welding stresses are expected to 
propagate. 
Isolation structures 150A and 150D of FIG. 2 are located on a roll axis 
100. The roll axis 100 is co-linear with a longitudinal center axis of the 
suspension assembly 110. Both isolation structures 150A and 150D have 
junction tabs 156A and 156D aligned with a pitch axis 200. The pitch axis 
200 is orthogonal to the roll axis 100. The roll axis 100 and the pitch 
axis 200 intersect at a point on the head bonding platform of the gimbal 
flexure 130. 
The likelihood that welding stresses will deform a suspension assembly 
element and affect the pitch or roll angle of the suspension assembly 
element generally depends on the magnitude and direction of the welding 
stresses. Uneven welding stresses propagating along the roll axis 100 are 
more likely to cause pitch errors. Uneven welding stresses traveling 
perpendicularly to the roll axis 100 are more likely to cause roll errors. 
Attenuated, non-additive stresses and stresses that are evenly distributed 
across relatively large areas are less likely to cause either pitch or 
roll errors. 
Placement of the isolation structures 150A and 150D on the roll axis 100 
reduces pitch angle errors by allowing even propagation of remaining 
welding stresses across the entire width of symmetrical halves of the 
suspension assembly 110. Additionally, placement of the junction tabs 156A 
and 156D perpendicular to the roll axis 100, and orientation of the tabs 
156A and 156D in a direction other than in the direction of other welds or 
areas of fixed material, substantially reduces or minimizes undesirable 
propagation and addition of remaining welding stresses along the roll axis 
100, thereby reducing pitch errors. 
Isolation structures 150B and 150C are positioned side-by-side on either 
side of the roll axis 100 and have junction tabs 156B and 156C aligned 
parallel to the roll axis 100. The placement and orientation of the 
isolation structures 150B and 150C allow even propagation of remaining 
welding stresses in a longitudinal direction and distributed along the 
entire length of the suspension assembly 110, thereby reducing the 
possibility of roll errors. 
FIG. 3 is a detailed isometric bottom view of the distal end of the 
suspension assembly 110, including gimbal flexure 130. The gimbal flexure 
130 includes a gimballing spring structure including spring arms 134 and a 
planar head bonding platform 136 for attachment of the head assembly, the 
spring arms 134 supporting the head bonding platform 136. 
Gimbal flexure 130 includes four welding stress isolation structures 
170A-170D, surrounding the weld points 132A-132D respectively. Other 
embodiments of suspension assemblies can have welding stress isolation 
structures only on the gimbal flexure or only on the load beam. Isolation 
structures 170A-170D have similar elements, a similar orientation, and are 
aligned opposite to welding structures 150A-150D. Each isolation structure 
170A-170D has a welding area 172, a flat portion of the surface of the 
gimbal flexure 130. Each welding area 172 is delineated and defined by two 
semicircular isolation slots 174. Two junction tabs 176 separate the 
respective two slots 174. 
FIG. 4 is a detailed isometric view of a proximal end of the suspension 
assembly 110 illustrated in FIG. 1. Eight weld points 142A, 142B, 142C and 
142 on the suspension assembly secure or couple the load beam 120 to a 
base plate 140. Selected weld points 142A-142C are isolated by welding 
stress isolation structures 160A-160C, similar to isolation structures 
150A-150D. 
Each isolation structure 160A-160C includes a welding area 162, generally a 
flat portion of the surface of the load beam 120. Each welding area 162 
has a perimeter delineated and defined by isolation slots 164. Isolation 
slots 164 are through apertures or holes and are generally shaped as 
circumferential arc segments. Isolation structures 160A-160C each include 
two slots 164, each slot shaped generally as a semicircle. Two junction 
tabs 166 respectively, separate the respective two slots 164 from each 
other, support each welding area 162, and connect each welding area 162 to 
the rest of the load beam 120. Junction tabs 166 are each positioned at 
opposite ends of the respective welding area 162. The junction tabs 166 of 
all three isolation structures 160A-160C are aligned along a propagation 
axis 300 parallel to the pitch axis of the suspension assembly 110. The 
alignment of tabs 166 allows welding stresses to uniformly propagate along 
the entire width of the suspension assembly 110 along the propagation axis 
300, substantially eliminating the influence of base plate welding 
stresses in the pitch direction. 
FIG. 5 is an enlarged detail plan view of a second embodiment of an 
isolation structure 250 in accordance with the present invention. Elements 
in this and other embodiments similar to those elements of the first 
isolation structure 150 are labelled with the same two last digits. 
Isolation structure 250 includes a welding area 252, two isolation slots 
254 encircling welding area 252, and two junction tabs 256. The two 
junction tabs 256 are aligned at oppositely aligned ends of the welding 
area 252. 
To reduce propagation of remaining welding stresses through the junction 
tabs, some embodiments of the isolation structure include irregularly 
shaped junction tabs. In isolation structure 250, each tab 256 is 
generally S-shaped or Z-shaped. That is, each junction tab 256 includes 
two connecting sharp radial break curves in opposite directions. Because 
welding stresses tend to propagate in straight lines, the two sharp radial 
curves mitigate the propagation of welding stresses across tab 256. 
FIG. 6 is an enlarged plan view of a third embodiment of an isolation 
structure 350. Isolation structure 350 has one generally circumferential 
slot 354, delineating a circular welding area 352. One tab 356 bridges the 
slot 354 and connects and supports the welding area 352. Circular slot 354 
mitigates expansion and contraction forces in almost all directions. Any 
remaining welding stresses can propagate in only one direction. 
FIG. 7 is an enlarged plan view of a fourth embodiment of an isolation 
structure 450 in accordance with the present invention. Isolation 
structure 450 includes two isolation slots 454 and two junction tabs 456. 
Each junction tab 456 includes a first segment 458 connected to a welding 
area 452 and extending generally in a straight line radially away from the 
welding area 452 and a second segment 460 connected to the first segment 
458 and to the remaining portion of a suspension assembly element. The 
second segment 460 is shaped as a generally planar elliptical curve having 
approximately a 180 degree radial break. Like the sharp radial curves of 
the embodiment of FIG. 5, the curved second segment 460 absorbs and 
mitigates welding stresses. 
FIG. 8 shows an enlarged plan view of a fifth embodiment of an isolation 
structure 550. Isolation structure 550 resembles isolation structure 150A 
of FIG. 2, having a generally planar welding area 552, two circumferential 
slots 554, and two junction tabs 556 located at oppositely aligned ends of 
the welding area 552 and separating the two circumferential slots 554. 
However, isolation structure 550 further includes two additional 
arc-shaped slots 564, each located outside the periphery of slots 554 and 
adjacent and generally opposite the junction tab 556 from the welding area 
552. The slots 564 are radially spaced from the welding area 552 and 
define a portion of a circumference concentric and larger than the 
circumference defined by slots 554. The additional slots 564 provide 
additional isolation to help diffuse any remaining welding stresses 
transmitted through tabs 556. 
A distal end of a suspension assembly 610 having two weld points 632A and 
632B placed respectively within welding stress isolation features 650A and 
650B in accordance with the present invention is illustrated in FIG. 9. 
Suspension assembly 610 includes a load beam 620 attached to a gimbal 
flexure 630 by the two weld points 632A and 632B. 
The stress isolation features 650A and 650B are located along a roll axis 
100 and each has a welding area 652 supported by two tabs 656 aligned 
opposite each other and in parallel with a pitch axis 200. The orientation 
of the tabs 656 directs remaining welding stresses symmetrically along the 
width of the load beam 620 and perpendicularly away from the roll axis 
100. The location and orientation of the two stress isolation features 
650A and 650B is primarily expected to reduce pitch variation. 
Suspension assemblies including isolation structures in accordance with the 
present invention have significant advantages over those suspension 
assemblies bonded or fixed together solely by conventional weld points. 
Isolation structures, such as 150A, can be used to isolate weld points 
bonding a variety of suspension arm elements. For example, the load beam 
can be welded directly to an actuator arm or to an actuator. By relieving 
welding stresses, and by allowing for isolation structure orientation and 
placement to distribute any remaining welding stresses, the present 
invention substantially eliminates pitch and roll errors caused during 
welding of suspension assembly elements. More accurate control of the 
attitude of HSAs translate to more reliable and accurate disk drives. 
Although the present invention has been described with reference to 
preferred embodiments, those skilled in the art will recognize that 
changes may be made in form and detail without departing from the spirit 
and scope of the invention.