Process for producing a slider having composite welding studs

A slider incorporates welding studs for assembly with a spring arm. Each of the welding studs includes a base that is integral with the slider. The base has a controlled height and is made from a first material. Each of the welding studs further includes a meltable stud member which is placed on the base. The meltable stud member is made from a second material that has a melting point which is lower than that of the first material of the base.

The present invention relates to a slider having composite welding studs 
and to a production process. It is used in magnetic recording, 
particularly recording on a hard disk. 
PRIOR ART 
Magnetic head sliders are generally bonded to the end of an arm serving as 
a spring. The electrical connections between the head and the external 
circuits are provided by twisted conductor wires welded to the slider and 
supported by the arm. 
In order to avoid the use of such wires, it is possible to use connection 
tracks formed on the upper face of the slider (i.e. the face opposite to 
the disk) and on the spring arm. In order to obtain the electrical 
connections, while ensuring the necessary welding and mechanical strength 
of the slider beneath the end of the arm, welding studs are formed between 
the tracks of the slider and those of the arm. 
Thus, U.S. Pat. No. 4,789,914 describes an assembly shown in the attached 
FIG. 1. In the latter it is possible to see a slider 10 with connection 
tracks 12, the end 20 of a spring arm, together with a connection circuit 
22 and, between them, the welding studs 24. 
This means for fixing the slider beneath the arm suffers from the 
disadvantage of not ensuring a controlled spacing between the arm and the 
slider. Thus, under the pressure exerted by the spring arm, certain studs 
are crushed during the welding operation and the slider can come into 
contact with the arm, so that its mobility is impaired. 
The object of the present invention is to obviate this disadvantage. 
DESCRIPTION OF THE INVENTION 
To this end, according to the invention each welding stud is of a composite 
nature in the sense that it comprises two parts, namely a first part or 
base, which is made from a material not meltable at the temperature at 
which welding takes place, said base having a certain controlled height 
ensuring a minimum spacing between the slider and the arm, and a second 
part constituted by a meltable material stud member, which will form the 
actual weld. Thus, even if the meltable stud members are crushed to a 
greater or lesser extent as a function of the planeity defects of the 
parts, the slider and the arm will still be spaced by a minimum distance 
equal to the height of the bases. 
More specifically, the present invention relates to a slider having welding 
studs for an assembly with a spring arm, characterized in that each 
welding stud comprises on the one hand a base integral with the slider, 
said base having a controlled height and being made from a first material 
and on the other hand a meltable stud member located on the base, said 
meltable stud member being made from a second material having a lower 
melting point than the first material. 
The first material is advantageously a conductive material, e.g. copper, 
nickel or nickel alloys. 
The second material can e.g. be tin, lead, indium or alloys thereof (e.g. 
tin--lead). 
In an assembly according to the invention, the studs can be used both for 
the mechanical strength of the means and for electrical connections. 
However, optionally, certain studs may only be used for mechanical 
strength purposes. 
For those of the studs used for electrical connection purposes, the base 
will be formed on a connection track on the slider and the meltable stud 
member will be in contact with a similar connection track located beneath 
the spring arm. 
The formation of the welding studs on the actual slider is particularly 
interesting in collective constructions of sliders. 
The present invention also relates to a process for the production of a 
slider/spring arm assembly, the slider being in accordance with what was 
stated hereinbefore. According to the invention, this process comprises 
the following operations: 
on a slider are formed bases from a first material having a first melting 
point, said bases having a controlled height, 
on each of the said bases is then formed a second meltable stud member from 
a second material having a second melting point below that of the first 
material, 
the spring arm is assembled on the slider in a position forming the working 
position of the assembly, 
the temperature of the studs is raised to above the second melting point of 
the second material, but below the first melting point of the first 
material. 
In a special embodiment, in addition deposition takes place of third, 
supplementary multiple stud members on the end of the spring arm, said 
supplementary stud members being made from the second material and being 
placed at locations corresponding to the meltable studs deposited on the 
bases, said third supplementary stud members being welded to the first 
studs during the final operation.

DETAILED DESCRIPTION OF THE DRAWINGS 
FIGS. 2a to 2h illustrate eight stages of a production process according to 
the invention. 
The starting product is a substrate 30, e.g. a silicon wafer, which will be 
used for forming the slider (FIG. 2a). On said substrate 30 is deposited a 
thin conductive coating 32 having a good adhesion, e.g. a chromium coating 
(FIG. 2b). 
On said conductive coating 32 is then deposited a photosensitive film 34 
having a thickness h equal to the minimum desired spacing between the 
slider and the end of the spring arm (FIG. 2c). This thickness can e.g. be 
75 .mu.m. 
By photolithography of said film 34 openings 36 are formed at appropriate 
locations, with a diameter equal to the diameter of the bases which it is 
wished to produce (FIG. 2d). This diameter can vary between approximately 
100 and 200 .mu.m. 
Conductive studs 38 are formed in said openings by electrolytic growth of a 
first conductive material, e.g. copper, while using the conductive coating 
32 as the electrode (FIG. 2e). 
The studs obtained are planarized e.g. by a polishing method, in order to 
bring the metal level with the film 34, which provides the bases 40 (FIG. 
2f). 
The meltable stud members 42 are formed by the electrolytic growth of a 
second material, such as tin-lead, on the bases 40 (FIG. 2g). The film 34 
is then dissolved and the adhesion coating 32 is etched, so as to leave 
the composite studs 40-42 (FIG. 2h). 
The process described hereinbefore assumes that the studs are produced by 
electrolytic growth. It would also be possible to proceed in another way, 
e.g. by etching and in this case there would be no need for the conductive 
adhesive coating 32. 
In a possible embodiment illustrated in FIG. 3, not only are the studs 
40-42 deposited on a slider 58, but also supplementary meltable stud 
members 44 are placed beneath the spring arm 56. These stud members 44 can 
be of the same material as the meltable studs 42, e.g. tin-lead. These 
supplementary stud members are positioned facing the meltable stud members 
42 located at the top of the bases 40 on the slider. 
The assembly of the slider beneath the end of the spring arm preferably 
takes place in accordance with FIG. 4. 
The slider 58 is held on a reference plane 60, e.g. by suction. The spring 
arm 56 is held on a pedestal 62 integral with the reference plane 60. This 
pedestal 62 represents the base or foot of the spring arm in a final 
assembly. Thus, the arm is placed in the very position which it will 
occupy in operation. 
The relative positioning of the slider with respect to the spring arm takes 
place either manually under the microscope, or automatically using optical 
detection. In this position, the arm exerts a force on the welding studs 
40, 42. 
Using a laser beam, infrared heating means, or any other appropriate means, 
the temperature of the welding studs is raised to above the melting point 
of stud members 42 (and if appropriate the supplementary stud members 44). 
In practice, with the materials conventionally used (tin, tin-lead), the 
temperature is raised to the range 150 to 250.degree. C. The meltable stud 
members melt and are crushed to a greater or lesser extent as a function 
of the position and dimensions of the different parts. 
Thus, even if the spring arm is not perfectly parallel to the plane of the 
slider (which frequently occurs), the minimum spacing between the spring 
and the slider will be equal to the thickness of the copper studs 40, the 
tin thickness including the height differences due to the poor twisting of 
the spring. Thus, when the assembly is installed on the recording disk, 
the spring will have retained its slight bias shape, but the plane of the 
slider will be perfectly parallel to that of the foot of the spring.