Magnetic slider, head gimbal assembly and method for manufacturing the same

Embodiments of the present invention provide a magnetic slider of which terminals have a sufficiently large process margin for the laser condition in the SBB process. According to one embodiment, a magnetic slider comprises: a read element and a write element; plural wiring lines which are connected to the read element and the write element; a protective film which covers the read element, the write element and the plural-wiring lines; plural slider pads formed on the protective film; and plural studs which respectively connect the slider pads and the wiring lines and are covered by the protective film, wherein each of the slider pads comprises a chromium film, a nickel iron film and a gold film, the nickel iron film is formed between the chromium film and the gold film, and the chromium film is formed between the nickel iron film and one of the studs and is in contact with the protective film.

CROSS-REFERENCE TO RELATED APPLICATION

The instant nonprovisional patent application claims priority to Japanese Patent Application No. 2006-240126 filed Sep. 5, 2006 and which is incorporated by reference in its entirety herein for all purposes.

BACKGROUND OF THE INVENTION

Since a magnetic slider is used in a magnetic disk drive, it is necessary to make a HGA (Head Gimbal Assembly) which has the magnetic slider assembled to a suspension. This assembly includes the step of mechanically affixing the magnetic slider to the suspension and the step of electrically connecting the magnetic slider to the suspension. To implement this electrical connection, gold pads on the magnetic slider are joined to lead pads on the suspension mainly by using the SBB (Solder Ball Bonding). The SBB technology sets a globular chip of solder between a gold pad and lead pad and joins them together by melting the solder with a laser. Recently, this method has become the mainstream method for electrically connecting a magnetic slider to a suspension since reliable electrical connection can be obtained and almost no concern is needed about the risk of ESD (Electro-Static Discharge).

Japanese Patent Publication No. 1996-235527 (“Patent Document I”) discloses a terminal or terminal lead pad which is fabricated by plating the rear surface (opposite to the air bearing surface) of a thin film magnetic slider with Ni, NiFe, Au, Cu or other metal and depositing Au or other bonding metal thereon. The terminal or terminal lead pad is connected to a terminal conductor of the suspension spring by thermo compression bonding, ultrasonic compression bonding or the like or by using a conductive adhesive.

Japanese Patent Publication No. 1997-181125 (“Patent Document 2”) discloses a structure used to connect a semiconductor chip to a package. This structure comprises an adhesion/barrier layer adhering to the substrate of the semiconductor chip, a NiFe metal solderable layer and a lead-free solder. As the barrier layer, Cr one is cited. The NiFe metal solderable layer is designed to dissolve into the solder.

Japanese Patent Publication No. 1999-120514 (“Patent Document 3”) discloses a structure for terminals of thin film magnetic heads. A barrier layer containing Cr and an electron supply layer composed of a noble metal, below an Au film, can be formed by continuous sputtering. By welding a bonding wire to the Au film, the terminal is electrically connected to a current source provided externally.

BRIEF SUMMARY OF THE INVENTION

Embodiments in accordance with the present invention provide a magnetic slider of which terminals have a sufficiently large process margin for the laser condition in the SBB process. According to one embodiment, a magnetic slider comprises: a read element and a write element; plural wiring lines which are connected to the read element and the write element; a protective film which covers the read element, the write element and the plural wiring lines; plural slider pads formed on the protective film; and plural studs which respectively connect the slider pads and the wiring lines and are covered by the protective film, wherein each of the slider pads comprises a chromium film, a nickel iron film and a gold film, the nickel iron film is formed between the chromium film and the gold film, and the chromium film is formed between the nickel iron film and one of the studs and is in contact with the protective film.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention relate to a magnetic slider used in a magnetic disk drive and, more particularly, to the gold pads or electrical connects of the magnetic slider which are structured so as to improve the process margin and reliability thereof.

Described below are those found through studies done by the inventors and others. For SBB, since a gold pad is irradiated by a laser, the gold pad is required to be heat-tolerant enough to endure this laser irradiation. In addition, the gold pad is exposed to temperature changes including temperature rises and falls while the magnetic slider is used in a magnetic disk drive. Therefore, the gold pad must be reliable enough to endure high temperature-included temperature cycle test.

The structure disclosed in Patent Document 1 has NiFe inserted below the gold as an adhesion layer. The gold pad is formed on the alumina protective film of the magnetic slider and connected to a Cu stud which goes through the alumina protective film. Thus, the gold pad is in contact with both alumina protective film and Cu stud. To secure the reliability, the gold pad must be sufficiently adhesive to both substances. However, adhesivity between gold (Au) and alumina is very low. This is because a NiFe adhesion layer is conventionally inserted below the gold film.

The NiFe adhesion layer shows good adhesivity to the Cu stud but its adhesivity to alumina is very low. Therefore, decreasing its area of contact with the Cu stud or relatively increasing its area of contact with the alumina may result in an insufficient adhesivity of the gold pad. For SBB, the laser power must be minimized so as not to give excessive thermal stress to the periphery of the gold pad. In this respect, it is preferable to make smaller the area of the Cu stud. Since the thermal conductivity of Cu is higher than that of alumina, if the area of the Cu stud is large, the laser irradiation results in a large amount of heat radiated away through the Cu stud. In this case, if energy is not sufficiently used to melt the solder, it may be necessary to excessively raise the laser energy, resulting in the occurrence of excessive stress around the gold pad and cracks in the alumina protective film. On the other hand, reducing the area of the Cu stud makes it possible to lower the laser power since the thermal radiation is reduced. Lowering the laser power reduces thermal stress around the gold pad and therefore avoid cracks in the alumina protective film. However, since the NiFe adhesion layer does not allow the area of the Cu stud to be reduced as mentioned above, it is not possible to lower the laser power.

Cr is sometimes used instead of NiFe since a Cr adhesion layer shows good adhesivity to alumina when the film is formed thereon and therefore a gold pad formed using the Cr adhesion layer is strongly adhered. However, such gold pads were peeled off and disconnected as a result of a high temperature-included temperature cycle test that was carried out. This phenomenon may be attributable to the high temperature heating which may cause Cr diffusion into the Au to such an extent that Cr disappears from the interface with the alumina.

Embodiments of the present invention are directed to the heat tolerance for laser heating in the SBB process. It is an object of embodiments of the present invention to provide a magnetic slider whose slider pads are reliable gold pads which show a heat-tolerance enough high to endure laser heating in the SBB process and do not peel off during high temperature-included temperature cycle test.

Here, representative embodiments of the present invention are briefly described. This is a magnetic slider comprising: a read element; a write element; plural wiring lines connected to the read element and write element; a protective film which covers the read element, write element and plural wiring lines; plural slider pads provided on the protective film; and plural studs which connect slider pads to wiring lines and are covered by the protective film, wherein each of the slider pads comprises a chromium film, a nickel iron film and a gold film which are formed such that the nickel iron film is disposed between the chromium film and the gold film and the chromium film is disposed between the nickel iron film and the stud and made in contact with the protective film.

Thanks to the superior heat-tolerance, the above-mentioned magnetic slider has a sufficiently large process margin for the laser conditions in the SBB process. That is, the control margin for the laser power and other process conditions in the SBB process is improved. In addition, the high heat tolerance makes it possible to provide a highly reliable magnetic slider which does not deteriorates even after high temperature-included temperature cycle test is done. Further, since the Cu stud area can be reduced thanks to the high adhesivity to alumina, it is possible to lower the laser power and consequently avoid the occurrence of cracks in the alumina protective film.

The following will describe embodiments of the present invention with reference to the drawings.FIG. 2provides a general view of a head gimbal assembly HGA21. A head slider23is fixed onto a suspension22with adhesive and electrically connected to wiring lines24on the suspension22.FIG. 3is an enlarged perspective view of a portion where the magnetic slider23is connected to the wiring lines24. The electrical interconnection is done by SBB process. For wire bonding to a gold pad, a gold ball is pressed to the gold pad while ultrasound is applied thereto. This forms fresh gold surfaces on the respective sides and causes plastic flows which bond them together. The SBB process uses a different bonding phenomenon to bond a gold pad to a suspension pad by melting a solder ball through laser irradiation. In the SBB process, a solder ball26is placed between a slider pad55and a lead pad25and the solder ball26is irradiated with a laser beam27. This laser irradiation melts the solder, resulting in the slider pad55connected electrically with the lead pad25. InFIG. 4, the solder is melted. The solder ball70has a major diameter of, for example, 80 μm, 110 μm or 130 μm. The solder ball26is lead-free.

FIG. 5is a perspective view provided to schematically explain the structure of a portion of the magnetic slider23including the slider pads.FIG. 6shows a section of the magnetic slider23cut perpendicular to the ABS52band the body edge52where major components are included. The outline of the magnetic slider23is formed by a rectangular body52d, which is, for example, a sinter of Al, Ti and C called AlTiC, and by a protective film52fdeposited on one body edge52e. Four slider pads55a,55b,55cand55dare respectively connected to the write and read head sections which are formed in the magnetic slider23. For simplicity, the number of slider pads is assumed to be four in this figure. As shown inFIGS. 3 and 4, two more slider pads may be formed between the four slider pads which are respectively connected to the write and read head sections. These two slider pads are connected to a heater which is formed in the magnetic slider in order to adjust the flying height.

In a magnetic disk drive where the magnetic slider23is installed, the ABS52bfaces a magnetic disk surface and receives a buoyant force from an air flow thereon. By etching the AlTiC, a center pad52cand other various outer pattern features are formed thereon. In and near the center pad52carea, the body edge52eperpendicular to the ABS52bhas the write and read head sections formed by thin film process to constitute the magnetic head58.

The thin film magnetic head58formed in the magnetic slider23is a combination magnetic head in which a read head section to reproduce magnetic information recorded on a magnetic disk3and a write head section to record magnetic information on the magnetic recording medium are integrated. For example, the read head section is fabricated by sequentially stacking an insulation layer121, lower shield layer119, gap layer115, read transducer117, gap layer111and upper shield layer113on the body52dnear to the ABS52b. The upper shield layer113also serves as the lower magnetic shield of the write head section. The upper shield layer113and auxiliary pole of the write head section may be formed from separate ones. Between the gap layers111and115, a read element117comprised of a giant magneto-resistive film (GMR film) and a magnetic domain control film is formed. To read information recorded on the magnetic disk3, the read element117is arranged so as to face the ABS52b. If the read element is a tunneling magneto-resistive device (TMR device) where current flows in the film thickness direction, the gap layer115between the lower shield layer119and the read element117and the gap layer111between the upper shield layer113and the read element117can be eliminated and the upper and lower electrodes which sandwich the read element117can also serve as shields. To the read element117, one pair of lead layers105cand105dis connected. The lead layers105cand105dare formed of a metal such as tantalum (Ta). The lead layers105cand105dare respectively connected to the internal pads103cand103dwhich are formed above the read head section.

The write head section is comprised of a main pole109, shield layer113and coil107. The main pole109and the shield layer113are magnetically connected at the center of the coil107, which comprises a magnetic circuit with a recording gap formed around the ABS52b. Along this magnetic circuit, a magnetic flux produced by the current flowing through the internal coil107is passed. One end of the coil107, located at the center, is connected to the lead layer105a. The other or peripheral end is connected to the lead layer105b.

The lead layers105aand105bare respectively connected to the internal pads103aand103bwhich are formed above the gap layer111. The internal pads are copper layers formed by sputtering or CVD. To the internal pads103a,103b,103cand103d, electrode studs101a,101b,101cand101dare respectively connected. Each electrode stud is a column with a square section perpendicular to the flowing direction of current. Having a length X of 30 μm, it is formed by such a method as copper plating. To the electrode studs101a,101b,101cand101d, the slider pads55a,55b,55cand55dare respectively connected.

The magnetic head58, lead layers105a,105b,105cand105d, internal pads103a,103b,103cand103dand electrode studs101a,101b,101cand101d, which are formed on the body edge52e, are covered by the alumina protective film52f. The slider pads55a,55b,55cand55dare formed on the surface of the protective film52for the trailing edge surface52a. Each electrode stud, internal pad and lead layer set constitutes a separate current path from its slider pad to the magnetic head. Of each current path, the portion which is directly connected to the slider pads is formed separately from the lead layers105a,105b,105cand105d. Thus, since the lead layers cannot be connected directly to the slider pads55a,55b,55cand55d, the electrode studs101a,101b,101cand101dare provided.

Each slider pad is connected to a lead pad by SBB process. During write, a magnetic flux occurs between the upper shield layer113, which serves also as the lower magnetic pole, and the upper magnetic pole109if write current is supplied via the slider pads55aand55b, causing a recording signal magnetic field around the recording gap. By this signal magnetic field, it is possible to record information by magnetizing the magnetic disk. During read, sense current is supplied to the GMR film of the read element117via the slider pads55cand55d. The GMR film changes its resistance depending on the magnetic field from the magnetic disk. It is therefore possible to read information recorded on the magnetic disk by detecting the change of the resistance as a voltage.

FIG. 1is a diagram to show the configuration of the slider pad according to the present embodiment. The upper portion ofFIG. 6including the internal pad103dis enlarged. The slider pad55has a chromium (Cr) film30, a nickel iron (NiFe) film31and a gold (Au) film13. The Cr film30is disposed between the NiFe film31and the stud101to secure adhesion between the stud and the upper layer. The NiFe film31is disposed between the Au film13and the Cr film30. When the slider pad55and the lead pad28are connected by SBB process, the molten solder ball reacts with Au to form an AuSn alloy. The NiFe film31is disposed as a diffusion prevention layer to prevent the gold tin (AuSn) alloy from diffusing into the copper (Cu) stud. Preferably, the Cr film30is 20 to 100 nm in thickness. If the Cr film30is excessively thin, it is difficult to secure adhesion to the alumina. If the Cr film30is made excessively thick, the film may peel off since the stress in the film becomes larger. Preferably, the NiFe film31is 40 to 100 nm in thickness. If the NiFe film31is excessively thin, it is difficult to prevent Cr diffusion into the Au and Sn diffusion into the Cu. As well, making the NiFe film31excessively thick lowers the productivity since the stress in the film is enlarged. Preferably, its Ni content is not lower than 40% since Ni functions to prevent diffusion. Preferably, the Au thickness is 1 to 10 μm. After depositing most of this thickness by sputtering, the film is finished by plating. The Au film has the purpose of securing solder wettability in the SBB process. To produce a sufficiently thick AuSn alloy by reaction with the solder, it is preferable to make the Au film not thinner than 1 μm. In view of cost, the Au film should be thinned. Functionally, it is not necessary to make the film thicker than 10 μm.

To verify the effect of employing the Cr/NiFe/Au slider pad55, we examined characteristics of its Cr50 nm/NiFe50 nm/Au5.1 μm (100 nm sputtered and 5 μm plated) sample in comparison with corresponding ones. As shown inFIG. 7, we placed a solder ball26on each slider pad55and irradiated it with a laser beam27. The slider pads prepared as examples for comparison with the Cr/NiFe/Au sample were: comparative example 1—Cr50 nm/Au5.1 μm (100 nm sputtered and 5 μm plated); comparative example 2—Ta50 nm/Au5.1 μm (100 nm sputtered and 5 μm plated); and comparative example 3—Cr50 nm/Ta50 nm/Au5.1 μm (100 nm sputtered and 5 μm plated). Cr is expected to secure adhesion to the alumina. Ta is expected to suppress mutual inter-metal diffusion by Au, Cu, AuSn alloy, etc. We carried out SBB process for each specimen. As shown inFIG. 8, laser irradiation melts the solder to spread over the gold pad. The molten solder reacts with the Au film to produce the AuSn alloy35. After the SBB process, we evaluated the shear strength of each specimen.FIG. 9shows the result. The laser energy (LASERENG) was set to a typical level of 35 mJ and, as acceleration conditions, to 55 mJ and 110 mJ. Ten samples were tested for each of the prepared specimen groups: present embodiment (SAMP), comparative example 1 (COMP1), comparative example 2 (COMP2) and comparative example 3 (COMP3). Plotted in this figure are their average shear fracture strength (STRENGTH). According to the figure, all specimens had almost the same shear fracture strength of 110 g with no significant difference if soldering was done with the laser energy set to 35 mJ. Setting the laser energy to 55 mJ also resulted in almost the same shear fracture strength around 110 g with no difference among the specimens. However, after soldering was done with the laser energy raised to 110 mJ, the comparative example 1 (conventional structure), comparative example 2 and comparative example 3 showed shear fracture strengths of 60 g, 85 g, and 85 g respectively while the present embodiment showed the highest shear fracture strength of 93 g. That is, the present slider pad embodiment can maintain the largest adhesivity since its deterioration is small even if the laser energy is maximized for acceleration. This slider pad structure can widen the process margin with respect to the laser energy.

After shear fracture strength measurement was performed on specimens soldered with the laser energy set to 110 mJ for maximum acceleration, we observed their fracture planes. As shown inFIG. 11, the fracture planes are classified into three types: those along the boundary between the alumina and the adhesion layer (including the diffusion preventing layer); those along the boundary between the adhesion layer and the AuSn alloy layer; and those in the AuSn alloy region. If a specimen showed more than one type of fracture plane, the fracture plane having the largest area was considered as the specimen's fracture plane.FIG. 10shows the result. In the case of the comparative example 1 (Cr/Au) which showed the smallest adhesivity as described above, 80% fractured along the boundary between the alumina and the adhesion layer (Cr). It is certain that the Cr diffusion into the Au layer was increased during laser heating at 110 mJ, resulting in the deteriorated adhesivity to the alumina. For the comparative example 2 (Ta/Au) and comparative example 3 (Cr/Ta/Au) which showed intermediary adhesivity, the majority (Ta/Au 50%, Cr/Ta/Au 80%) were fractured along the boundary between the Ta layer and the AuSn alloy layer, indicating deterioration of the adhesivity between the Ta layer and the AuSn alloy layer. In the case of the present Cr/NiFe/Au embodiment which showed the largest adhesivity, 70% caused fracture in the AuSn alloy region. This indicates no adhesivity problem occurs between the alumina and the Cr layer, between the Cr layer and the NiFe layer or between NiFe layer and the Au layer even if 110 mJ laser irradiation is done.

Further, we performed a high temperature-included temperature cycle test on specimens after they were given the SBB process with the laser power set to the typical level of 35 mJ. The temperature cycle test repeated 300 temperature cycles. In each temperature cycle, the temperature was set to 125° C. for 30 minutes and then set to −40° C. for 30 minutes. After that, we evaluated the conduction NG rates by measuring the resistance of a head element of each specimen via the gold pads and evaluated the condition of each gold pad to check if the pad was peeled off by observing its external appearance and cross section by SEM. In addition, we carried out an elemental analysis of cross sections of gold pads to examine the mutual diffusion of constituent metals.FIG. 12shows results of these evaluations. While the comparative example 1 of the conventional structure showed a conduction NG rate of 2.2%, no failure occurred in the other specimens. Accordingly, some included in the comparative example 1 were found to be peeled off by SEM-used external appearance observation. In the case of the comparative example 2 and comparative example 3, peel off was found along the boundary between the TA and the AuSn alloy by SEM-used cross-section observation. By the elemental analysis made of cross sections of gold pads, Sn diffusion into the Cu stud was verified in the comparative example 1, comparative example 2 and comparative example 3. In the present pad embodiment, Sn diffusion into the Cu pad was not found. This result indicates that Ta does not sufficiently function as the diffusion preventing layer to suppress Sn diffusion from the AuSn alloy. On the other hand, it is found that NiFe in the present embodiment functions as the diffusion preventing layer to suppress the diffusion of Sn.

The above-mentioned evaluation results indicate the stud pad structure (Cr/NiFe/Au) according to embodiments of the present invention is sufficiently heat-tolerant even if the applied laser energy is raised to accelerate the deterioration. In addition, since it showed the best result in the high temperature-included temperature cycle test, this structure is verified to be superior in reliability for commercialization. This structure can not only secure the adhesivity of the laser-bonded gold pad but also improve the device.