Patent Application
20070103812
1. Field of the Invention
This invention relates to information storage. More particularly, the invention is directed to thin film magnetic heads for reading and/or writing data on magnetically encodable media, such as tape.
2. Description of the Prior Art
By way of background, transducing heads for magnetic information storage systems (e.g., tape drives) have been constructed using thin film techniques. A characteristic of such construction is that the thin film layers which comprise the active transducing elements (read elements, write elements or a combination of both) are embedded in a relatively soft “glassy” material (such as alumina) which has been deposited onto a hard substrate material. The soft material is typically alumina (Al2O3) and the hard material is typically an aluminum oxide-titanium carbide (Al2O3—TiC or AlTiC) ceramic. In applications where the head physically contacts the media, such as tape drives, a hard material block known as a “closure” is often bonded onto the outermost (“overcoat”) layer of the soft material that embeds the active elements. This sandwiches the active elements and surrounding soft material between two hard materials (the head substrate and the closure), thereby protecting against tape wear and providing a flat transducing surface. Like the head substrate, the closure commonly comprises an AlTiC ceramic, although magnetic ferrite materials may also be used.
Conventional assembly techniques call for the use of thermosetting adhesives to bond the closure to the head's soft overcoat layer. Although such adhesives generally fulfill their purpose, there are several concerns with this technique. First, adhesive bond integrity can degrade with age and when attacked by humidity. For example, commonly used thermoset adhesives may have a glass transition temperature of 90° C. (dry) but only 70° C. (wet). If the head operating temperature approaches the glass transition temperature, sliding movement of the closure relative to the soft material in which the read/write elements are embedded (creep) can result in a condition known as gap slip, in which the transducing elements move away from the media. Second, humidity adsorption by the adhesive or differential thermal expansion of the adhesive and the solid bond pieces can also cause gap slip. For high density magnetic tape storage systems, gap slip on the order of 10 nm can cause severe signal loss due to the phenomenon of Wallace spacing losses. Another issue associated with adhesive bonding of the closure is that humidity can also attack the bond interface between the adhesive and the solid materials being bonded, weakening the strength of the bonds. With extended exposure, the bonds can become so weak that the parts separate. A further disadvantage of thermosetting adhesives is that the low glass transition temperature may require that costly ultrasonic bonding techniques and compatible components be used to bond wire leads to bonding pads on the head. Potentially less costly techniques such as hot compression bonding with or without using Anisotropic Conductive Film (ACF) may be precluded insofar as the applied heat and compression could soften the adhesive and allow the components to move.
Accordingly, it is desired to have an improved design for a thin film transducing head for reading and/or writing data on magnetically encodable media.
The foregoing problems are solved and an advance in the art is obtained by a novel transducing head and related fabrication method, and a system for information storage. The transducing head includes a substrate comprising a relatively hard material, a transducer carrier on the substrate comprising a deposited material that embeds one or more transducer elements and which is soft relative to the substrate, a closure on the transducer carrier comprising a relatively hard material, and a metal-to-metal interconnection securing the closure to the transducer carrier. The closure may comprise relatively hard material only, or it may comprise a first layer of relatively soft material on a second layer of relatively hard material, with the first closure layer supporting the metal-to-metal interconnection.
According to exemplary alternative embodiments of the invention, the metal-to-metal interconnection may comprise a first metal layer on the transducer carrier and a second metal layer on the closure, with the first and second metal layers being fused together. If desired, a metal solder bond material may be placed between the first and second metal layers to assist in fusing these layers together, or the solder bond material can be used to provide the metal layers. The solder material can be selected from the group consisting of solder paste, sheet solder and solder depositions. Plural solder layers may be used. One example would be a multi-layer solder comprising a pair of outer solder bond material layers sandwiching reactive laminate layers which melt when sufficient current is passed through them. The heat generated will then melt the reactive layers, enabling the bonding. A tinning material may be used with the solder bond material to improve adhesion.
In cases where the substrate and the closure materials are electrically conductive (such as AlTiC), a conductive connector may be formed to extend through the transducer carrier, which electrically connects the substrate to the closure through the interconnection metal(s). If the closure comprises a layer of soft, electrically insulating material (such as alumina), another conductive connector can be formed to extend through the closure first layer and electrically connect the closure second layer to the interconnection.
The foregoing and other features and advantages of the invention will be apparent from the following more particular description of exemplary embodiments of the invention, as illustrated in the accompanying Drawings, in which:
The invention will now be described by way of exemplary embodiments shown by the drawing figures (which are not necessarily to scale), in which like reference numerals indicate like elements in all of the several views. Although the illustrated embodiments are specific to magnetic tape storage, it should be understood that the invention may also be applied to other magnetic storage systems, such as direct access storage device (DASD) systems, including but not necessarily limited to disk drives.
Turning now to
The substrate 4 and at least a portion of the closure 8 are formed from a relatively hard material, such as AlTiC or the like. The transducer carrier 6 is formed from a relatively soft glassy material, such as alumina or the like. As used herein, the terms “relatively hard” and “relatively soft” are not intended to represent quantitative values, but are instead used qualitatively to refer to the comparative hardness of the substrate 4 and the closure 8, on one hand, relative to the transducer carrier 6, on the other hand. The actual hardness of the substrate 4, the transducer carrier 6 and the closure 8 may therefore vary according to the materials used.
The substrate 4 is formed with a tape bearing surface 14 that is adapted to engage a streaming tape medium T, as shown
The transducer carrier 6 is deposited on an interfacial support surface 20 of the substrate 4 in a sequence of layers. As shown in
It will be appreciated that many other transducer arrangements would also be possible, including a merged head arrangement or a “piggy-back” head arrangement in which a pair of read and write transducers are formed at each data track position, but on different layers within the transducer carrier 6. As is known in the art, the merged head arrangement shares adjacent reader shield and writer pole materials while the piggy-back arrangement has a spacer between the adjacent reader shield and writer pole materials. The merged head construction is thus analogous to the head design used in DASD drives. Other construction alternatives would include an array of adjacent read transducers, and/or an array of adjacent write transducers.
Once the transducers 10 have been formed on the transducer carrier sublayer 22, an additional layer of material can be deposited over the transducers to complete the transducer carrier 6. The bonding pads 12 will also be completed as part of this processing, such that the pads are exposed on an interfacial surface 24 of the transducer carrier 6, as shown in
As shown in
As described by way of background above, the conventional closure bonding technique is based on the use of a thermosetting adhesive interposed between the relatively hard material of the closure and the relatively soft material of the transducer carrier 6. The resultant bond is susceptible to heat and humidity degradation and to swelling due to moisture absorption. A solution proposed herein is to replace the thermosetting adhesive bond with a metal-metal interconnection. Because metals do not adsorb appreciable amounts of water, they will not expand with exposure to humidity. The metal-to-metal interconnection is thus more resilient to attack by humidity. Furthermore, the interface between a metal-to-metal interconnection and the bonded materials is less susceptible to attack by humidity because of the inability for any significant amount of moisture to diffuse into the metal.
Turning now to
The metal layers 42 and 44 can be formed using conventional processes such as sputtering, vacuum deposition, plating, etc. If plating is used, seed layers 42A and 44A should be respectively formed on transducer carrier 6 and the closure 8 prior to applying the metal layers 42 and 44. A suitable seed layer material will be compatible with the metal layer material and will have good wettability relative to the transducer carrier 6 and the closure 8. If the metal layers 42 and 44 are gold, a thin (e.g., 100 Å) layer of a nickel-iron alloy could be used for the seed layers 42A and 44A. If these materials provide unacceptable magnetic effects, alternative seed layer materials, such as chromium or a copper-chromium alloy or tantalum, could be used. A seed layer between the gold material and the alumina or the AlTiC material may also provide better adhesion of the metal layers 42 and 44 to the transducer carrier 10 and the closure 8, respectively.
Turning now to
Unlike the metal layers 42 and 44, the metal layers 52 and 54 are fused together by interposing a metal solder bond material 56 between the layers and heating the solder layer to its melting point. The heating can be performed using any suitable technique, such as by placing the head structure in an oven or on a heating element, or by Joule heating with electrical current. Alternative heating techniques would include ultrasonic heating, pressure heating and reactive heating (see below). To assist the fusing process, a suitable compressive force (as described above) may be applied to the head 2 to place the solder layer 56 under pressure. A suitable material that may be used for the solder layer 56 will be a metal whose melting temperature is not so high as to affect the existing components of the head 2 during the fusing operation, and which has sufficient wettability relative to the metal layers 52 and 54 to provide adequate bond strength. For metal layers 52 and 54 made from gold or an alloy thereof, a solder layer 56 comprising materials such as bismuth, indium, lead, tin, silver, gold, cadmium, copper, antimony, zinc or alloys thereof, may be used. Such materials are present in commercially available solders. An exemplary solder melting point range would be from approximately 109° C. for bismuth-indium solder (e.g., Bi67/In33) to approximately 281° C. for gold-tin solder (e.g., Au80/Sn20). A larger temperature range could potentially also be used. In cases were additional wetting and adhesion between the solder layer 56 and the metal layers 52 and 54 is desired, the use of an interfacial tinning material may be considered. Such material can be deposited (as by sputtering) onto the metal layers 52 and 54 (or either of them) prior to applying the solder layer 56. The tinning material selection will depend on the materials that comprise the solder layer 56 and the metal layers 52 and 54. Exemplary tinning materials include, but are not necessarily limited to, silver, copper, palladium, and platinum, as well as alloys such as silver-platinum, silver-palladium, nickel-palladium, nickel-gold, nickel-gold-copper, and platinum-palladium-gold.
The solder layer 56 can be applied in wire, paste or glue form to the interface between the metal layers 52 and 56. Alternatively, the solder could be formed on the metal layers 52 and 56 (or either of them) as a solder deposition using a suitable deposition process, such as chemical vapor deposition, or via plating. An additional method would be to use commercially available sheet solders placed between the metal layers 52 and 54 to be bonded. One disadvantage of applying solder with conventional methods such as paste, wire or sheets is the difficulty of meeting thin bond lines (several microns). Another disadvantage of paste, wire or sheet solder is the extreme difficulty in avoiding solder material from spreading over these small devices and getting onto unwanted areas such as the tape bearing surface 26 or the bonding pads 12. A disadvantage of a solder deposition is that it involves the overhead of masking and stripping of unwanted materials.
A further alternative would be to create the solder layer 56 using a multilayer sheet solder material having a reactive laminate therein for melting the solder. For example, commercial multilayer reactive laminates are available with alternating layers of nickel and aluminum. The reactive laminate can be disposed between sheets of solder bonding material, such as indium. When an electrical current of suitable magnitude is passed through these materials, the reactive laminate melts the bonding material and a solder bond is formed when the melted materials resolidify.
A potential disadvantage of using prefabricated reactive laminates and bonding material sheets is that their manipulation and application at the extremely small size scale of transducing heads may be somewhat difficult. An alternative approach would be to use deposition processes to directly apply the same materials to create a custom reactive laminate solder layer 56.
Turning now to
An additional feature of the construction shown in
The conductive connector 66 can be formed by etching a via through the transducer carrier 6, then depositing or plating conductive material into the via. A photo process can be used to define the etch area. If the transducer carrier 6 comprises a material such as sputtered alumina, the etching can be performed either with a hydroxide (NaOH or KOH) or an mild acid (H3PO4, e.g.). Both types of etchants have been used in wafer processes. If a plating process is used to form the conductive connector 66, a seed layer should be applied in the via prior to plating.
Turning now to
An additional feature of the construction shown in
Turning now to
An additional feature of the construction shown in
Although the preceding discussion of exemplary closure attachment techniques focuses on a single head 2, this is not intended to signify that the closure attachment process should be performed on a head-by-head basis. Although an assembly method that secures individual closures 8 to individual heads 2 is not to be precluded, persons skilled in the art will appreciate that the closure attachment operation will typically be performed at the wafer, quad or row bar level.
Turning to
The microprocessor controller 106 provides overhead control functionality for the operations of all other components of the tape drive 100. As is conventional, the functions performed by the microprocessor controller 106 are programmable via microcode routines (not shown) according to desired tape drive operational characteristics. During data write operations (with all dataflow being reversed for data read operations), the microprocessor controller 106 activates the channel adapter 104 to perform the required host interface protocol for receiving an information data block. The channel adapter 104 communicates the data block to the data buffer 108 that stores the data for subsequent read/write processing. The data buffer 108 in turn communicates the data block received from the channel adapter 104 to the read/write dataflow circuitry 110, which formats the device data into physically formatted data that may be recorded on a magnetic tape medium. The read/write dataflow circuitry 110 is responsible for executing all read/write data transfer operations under the control of the microprocessor controller 106. Formatted physical data from the read/write data flow circuitry 110 is communicated to the tape interface system 114. The latter includes one or more transducing heads in the read/write head unit 118, and drive motor components (not shown) for performing forward and reverse movement of a tape medium 120 mounted on a supply reel 122 and a take-up reel 124. The drive components of the tape interface system 114 are controlled by the motion control system 112 and the motor driver circuit 116 to execute such tape movements as forward and reverse recording and playback, rewind and other tape motion functions. In addition, in multi-track tape drive systems, the motion control system 112 transversely positions the read/write heads relative to the direction of longitudinal tape movement in order to record data in a plurality of tracks.
In most cases, as shown in
Accordingly, a transducing head and related fabrication method, together with a system that may be used for magnetic information storage, have been disclosed. While various embodiments of the invention have been shown and described, it should be apparent that many variations and alternative embodiments could be implemented in accordance with the teachings herein. For example, as earlier stated, the invention is not limited to tape drive applications and could be used in DASD devices, such as in cases where it is desirable to bond a closure to a disk drive transducing head (e.g., as part of a slider structure or for other reasons). Other magnetic storage applications for the invention may also arise. It is understood, therefore, that the invention is not to be in any way limited except in accordance with the spirit of the appended claims and their equivalents.
