Method and apparatus for embedding a chip in a substrate to form a composite air bearing surface

A method and apparatus for embedding a chip in a substrate to form a composite air bearing surface. An example of the method includes securing the substrate in a fixed position, aligning the chip in a first direction with a chip receiving slot in the substrate, depositing adhesive in the chip receiving slot, and aligning the chip in a second direction with the chip receiving slot. The chip is pushed into the adhesive in the chip receiving slot until the air bearing surface of the chip is substantially at a desired protrusion in a third direction in relation to the air bearing surface of the substrate. The adhesive is cured with the air bearing surface of the chip substantially at the desired protrusion in the third direction, and with the chip substantially aligned in the first and second directions with chip receiving slot.

BACKGROUND

1. Technical Field

The present invention relates to heads used to write and retrieve information on magnetic storage tape media. More particularly, the invention concerns a method for embedding a chip that has active elements, in a substrate, to form a composite air bearing surface that may be used, for example, in a tape head.

2. Description of Related Art

Magnetic tape is widely used for storing data in computing systems. Tape heads are used for writing information to the tape and reading information from the tape. A tape head typically includes two modules that each have a plurality of reading and writing elements, that may be called active elements. In each module, the reading and writing elements are formed in a substrate that has a smooth air bearing surface (ABS) which makes contact with and supports the flexible tape as it travels. This type of tape head may be called a contact recording tape head. To minimize the occurrence of decreased signals from spacing losses, damage to the tape, and other problems, the air bearing surface of each module must be very smooth, so that the tape can pass over each module in close proximity to the reading and writing elements. Because of its degree of smoothness, an air bearing surface may be referred to as being optically polished.

Because the reading and writing elements in each module span only a small portion of the tape width, during operation the tape head is moved laterally so that the substrate in each module moves laterally across the tape to line up the reading and writing elements with the tracks on the tape that are being read from or written to. Consequently, the substrates are wider than the width of the tape, and are considerably wider than the portion of the tape spanned by the reading and writing elements, to maintain support of the tape surface and to avoid potentially tearing the tape with sharp edges while lining up the reading and writing elements with tracks that are not in the center of the tape.

Traditionally, the reading and writing elements and the substrate of a module are formed in a semiconductor wafer. Forming the substrate in the wafer requires a much larger area of the wafer than is required for the reading and writing elements. Due to the high cost of wafer space, forming the substrate in the wafer substantially increases the cost of making a module. Consequently, existing methods for making tape heads are not completely cost effective.

SUMMARY

One aspect of the invention is a method for embedding a chip in a substrate, to form a composite air bearing surface. An example of the method includes securing the substrate in a fixed position, and aligning the chip in a first direction with a chip receiving slot in the substrate. The method also includes depositing adhesive in the chip receiving slot in the substrate, and aligning the chip in a second direction with the chip receiving slot in the substrate. The chip is then pushed into the adhesive in the chip receiving slot. The method further includes detecting when an air bearing surface of the chip is substantially at a desired protrusion in a third direction in relation to an air bearing surface of the substrate. Responsive to detecting that the air bearing surface of the chip is substantially at the desired protrusion in the third direction in relation to the air bearing surface of the substrate, the operation of pushing the chip into the adhesive is ceased. The adhesive is at least partially cured to bond the chip to the substrate with the air bearing surface of the chip substantially at the desired protrusion in the third direction, and with the chip substantially aligned in the first and second directions with chip receiving slot in the substrate.

Another aspect of the invention is a tape head read/write module that has a composite air bearing surface. The module includes a substrate that has an air bearing surface, a front, a back, and a chip receiving slot. The chip receiving slot has a front at the front of the substrate, a back at the back of the substrate, a first side, a second side, and a bonding surface. The air bearing surface of the substrate has a first portion adjoining the first side of the chip receiving slot, and a second portion adjoining the second side of the chip receiving slot. The module also includes a chip that has an air bearing surface, a bottom surface, a front, a back, and active elements. The active elements are located proximate to the front of the chip. The chip is inserted in the chip receiving slot in the substrate, with the air bearing surface of the chip substantially aligned with the air bearing surface of the substrate, and with the back of the chip substantially aligned with the back of the substrate.

Other aspects of the invention are described in the sections below, and include, for example, an apparatus for aligning and bonding a chip with a substrate to form a composite air bearing surface.

The invention provides a number of advantages. The invention permits making a composite air bearing surface by embedding a chip that has reading and writing elements, in a substrate, which makes it unnecessary to form the substrate in the expensive semiconductor wafer with the chip. Because the substrate is much larger than the chip and is not made in the wafer, a larger number of chips can be made in the wafer, which advantageously reduces the cost of each chip. Additionally, a larger number of chips can be produced in each row on the wafer, and consequently, the lapping cost per chip is lowered because a larger number of chips can be simultaneously lapped. Further, the composite air bearing surface does not require lapping after the chip is embedded in the substrate, which can be an expensive operation. The invention also provides a number of other advantages and benefits, which should be apparent from the following description.

DETAILED DESCRIPTION

The nature, objectives, and advantages of the invention will become more apparent to those skilled in the art after considering the following detailed description in connection with the accompanying drawings.

I. Hardware Components and Interconnections

A. Tape Head Module

One aspect of the invention concerns a read/write module that has a composite air bearing surface that may be used, for example, in a tape head. As an example, the read/write module may be embodied by the module100shown inFIGS. 1–4.FIG. 1is a perspective view of the module100,FIG. 2is a top view of the module100,FIG. 3is a front view of the module100, andFIG. 4is a sectional view of the module100taken along the line4—4inFIG. 3. The module100includes a composite air bearing surface102, a substrate104, a chip106, and a closure108. As an example, the substrate104and chip106may both be made of N58 AlTiC. The substrate104has a substrate air bearing surface110that has a first portion112and a second portion114. The substrate104also has a bottom116, a front118, a back120, a first side122, a second side124, and a chip receiving slot126. The chip106has a chip air bearing surface128, a bottom surface130(shown most clearly inFIGS. 3 and 4), a front132of the chip106, a front133of the chip air bearing surface128, a back134, a first side136, and a second side138. The substrate air bearing surface110and the chip air bearing surface128together form the composite air bearing surface102. The chip106also has a first front corner139a(shown most clearly inFIG. 2), a second front corner139b, a first back corner139c, and a second back corner139d. The chip106also has active elements140(shown most clearly inFIGS. 2 and 4) that are located proximate to the front132of the chip106. Accordingly, the chip106may be referred to as an active element chip. The active elements140in the chip106may include, for example, eight readers, eight writers, and two servos. However, the active elements140could include larger or smaller numbers of readers, writers, and/or servos. The readers may be, for example, magneto resistive (MR) elements. The readers may also be called sensors. The closure108has a closure air bearing surface141, a front142, and a back144, and the back144of the closure108is attached to the front132of the chip106. Electrical leads (not shown) for the active elements140may be coupled to pads145on the front132of the chip106beneath the closure108. In order to provide connections to the active elements140, the number of pads145provided on the chip106may be greater than the number of pads145shown inFIG. 3.

The length of the substrate104from the first side122of the substrate104to the second side124of the substrate104may be, for example, about 22.5 mm. The height of the substrate from the bottom116of the substrate104to the air bearing surface110of the substrate104may be, for example, about 2.5 mm. The distance from the front118to the back120of the substrate104(the width of the substrate104) may be, for example, about 2.0 mm. The substrate104may also include a first front protrusion146that has a face148, and a second front protrusion150that has a face152. The distance from the face148of the first front protrusion146and the face152of the second front protrusion150to the back120of the substrate104may be, for example, about 2.75 mm. The air bearing surface110of the substrate104has a back edge154. The distance from the front118of the substrate104to the back edge154of the air bearing surface110on the substrate104may be, for example, about 0.63 mm, and in another example could be, for example about 0.80 mm. However, other distances could be utilized.

The tape used with the module100may, as an example, be about 1.27 cm (0.5 inch) wide. However, different tape widths could be used, and, if necessary, the width of the substrate104could be adjusted to accommodate different tape widths.

The length of the chip106from the first side136of the chip106to the second side138of the chip106may be, for example, about 6.8 mm. The thickness of the chip106from the bottom surface130of the chip106to the air bearing surface128of the chip106may be, for example, about 550±15 μm. The distance from the front132to the back134of the chip106(the width of the chip106) may be, for example, about 2.0 mm. Thus, the bonding area on the bottom surface130of the chip106may be about 6.8 mm by about 2.0 mm. The air bearing surface128of the chip106has a back edge156. The distance from the front132of the chip106to the back edge156of the air bearing surface128on the chip106may be, for example, about 0.63 mm, and in another example could be, for example 0.80 mm. However, other distances could be utilized. The distance from the front142to the back144of the closure108may be, for example, about 0.225 mm.

In the module100shown in the illustrated example, the chip106has a tail surface157that may be substantially parallel to the air bearing surface128of the chip106and the air bearing surface110of the substrate104. Similarly, the substrate104has a tail surface158that has a first portion159adjoining a rear portion of the first side166of the chip receiving slot126, and a second portion160adjoining a rear portion of the second side168of the chip receiving slot126. The tail surface158of the substrate104is substantially coplanar with the tail surface157of the chip106. The tail surfaces157,158do not have to be parallel to the air bearing surfaces128,110. The tail surface157of the chip106is located between the air bearing surface128of the chip106and the back134of the chip106, and is located in a plane positioned between the air bearing surface128of the chip106and the bottom surface130of the chip106. Similarly, the tail surface158of the substrate is located between the air bearing surface110of the substrate104and the back120of the substrate104. The tail surface157of the chip106and tail surface158of the substrate104may be formed by a taperless grind operation, discussed below, in which a substantially rectangular rear portion of the composite air bearing surface102is removed. The chip tail surface157and the substrate tail surface158may be, for example, about 0.18 mm from the plane defined by the air bearing surface128of the chip106. The distance from the back134of the chip106to a front edge161of the tail surface157of the chip106, and from the back120of the substrate104to a front edge162of the tail surface158of the substrate104, may be, for example, about 1.75 mm.

As shown most clearly inFIGS. 3–4, the chip receiving slot126in the substrate104has a front163at the front118of the substrate104, a back164at the back120of the substrate104, a first side166, a second side168, and a bonding surface170. The chip receiving slot126also has a first side trough172proximate to the first side166of the chip receiving slot126, and a second side trough174proximate to the second side168of the chip receiving slot126. The first side trough172has a bottom176, and the second side trough174has a bottom178. The depth of the chip receiving slot126is chosen so that the air bearing surface128of the chip106will be substantially aligned with the air bearing surface110of the substrate104over the temperature and humidity ranges to which the module100is likely to be exposed, despite expansion or contraction of the adhesive and tolerance variations in the thickness of the chip106. In the illustrated example, when the chip106is placed in the chip receiving slot126, the back134of the chip106is aligned with the back164of the chip receiving slot126. However, the chip106does not have to extend to the back164of the chip receiving slot126. The length of the chip receiving slot126from the first side166of the chip receiving slot to the second side168of the chip receiving slot126may be, for example about 7.0 mm, and, for example, is centered along the 22.5 mm length of the substrate104. The width of the chip receiving slot126from the front163of the chip receiving slot126to the back164of the chip receiving slot126may be, for example, about 2.0 mm. The distance from the air bearing surface110of the substrate104to the bonding surface170of the chip receiving slot126may be, for example, about 580±15 μm. The distance from the air bearing surface110of the substrate104to the bottom176of the first side trough172and to the bottom178of the second side trough174may be, for example about 0.65 mm.

The first portion112of the substrate104air bearing surface110adjoins the first side166of the chip receiving slot126, and the second portion114of the substrate104air bearing surface110adjoins the second side168of the chip receiving slot126. The chip106is inserted in the chip receiving slot126in the substrate104with the air bearing surface128of the chip106substantially aligned with the air bearing surface110of the substrate104, and with the back134of the chip106substantially aligned with the back120of the substrate104.

An adhesive layer180(shown most clearly inFIGS. 3 and 4) is attached to the bonding surface170of the chip receiving slot126and to the bottom surface130of the chip106. As an example, the adhesive layer180may be U.V. cured. Additionally, the adhesive layer180fills at least a portion of the fist side trough172and/or the second side trough174.

B. Apparatus for Aligning and Bonding a Chip with a Substrate

Another aspect of the invention concerns an apparatus for aligning and bonding a chip106with a substrate104to form a composite air bearing surface102. The apparatus may be called a bonding apparatus, a bonding machine, or a fixture. As an example, the apparatus may be embodied by the apparatus500shown inFIG. 5.FIG. 5is a perspective view of the apparatus500,FIGS. 6 and 6Aare cutaway perspective views of portions of the apparatus500, andFIG. 7is a bottom perspective view of a pick-up chuck502of the apparatus500. The apparatus500includes a housing504that has a substrate seat506(shown most clearly inFIG. 6A). InFIG. 6the substrate104is shown in the substrate seat506, and inFIG. 6Athe substrate seat506is shown without the substrate104. The substrate seat506has back surfaces508a,508b,508c,508d(which can be called datums or stops), a bottom510, a front edge511, and a side512(all shown most clearly inFIG. 6A). In alternative embodiments, the substrate seat506could have one, two, three, or five or more back surfaces. The apparatus500may also include a substrate front clamp514(shown most clearly inFIG. 6) slidably mounted on the housing504for selectively holding the substrate104in the substrate seat506, and a substrate side clamp516(shown most clearly inFIGS. 6 and 6A) slidably mounted on the housing for selectively holding the substrate104in the substrate seat506. The apparatus500also includes an alignment arm518(shown inFIGS. 5 and 6) slidably attached to the housing504. The pick-up chuck502(shown most clearly inFIGS. 5 and 7) is slidably attached to the alignment arm518. The pick-up chuck502has bottom surface520(shown inFIG. 7). A first alignment foot522, and a second alignment foot524(shown inFIG. 7), are attached to the pick-up chuck502, and protrude from the bottom surface520of the pick-up chuck502. The first alignment foot522has a bottom surface526, and the second alignment foot524has a bottom surface528. In alternative embodiments, more than two alignment feet could be used. For example, four alignment feet could be used.

A first fiber optic U.V. light guide530(shown most clearly inFIG. 5) is attached to the housing504. A first end532of the first fiber optic U.V. light guide530is located proximate to the front edge511of the substrate seat506about 2 mm above the bottom510of the substrate seat506. A second end534of the first fiber optic U.V. light guide530is configured for coupling to a U.V. light source (not shown). Similarly, a second fiber optic U.V. light guide536may also be attached to the housing504. A first end538of the second fiber optic U.V. light guide536is located proximate to the front edge511of the substrate seat506about 2 mm above the bottom510of the substrate seat506, and a second end540of the second fiber optic U.V. light guide536is configured for coupling to the U.V. light source. A third fiber optic U.V. light guide542may also be attached to the housing504. A first end544of the third fiber optic U.V. light guide542is located proximate to the back surfaces508b,508cof the substrate seat506, and a second end546of the third fiber optic U.V. light guide542is configured for coupling to the U.V. light source. The U.V. light guides may also be called wands.

The bottom surface520(shown inFIG. 7) of the pick-up chuck502may have a hole548for coupling to a vacuum source (not shown) for holding the air bearing surface128of the chip106against the bottom surface520of the pick-up chuck502. Additionally, a chip seat550(shown most clearly inFIG. 6) that has a slot552for receiving the chip106, may be formed in the housing504, for aligning the chip106in a y direction (which may also be referred to as a first direction) and for holding the chip106before it is picked up by the pick-up chuck502. The chip seat550may have a hole554for coupling to the vacuum source, for holding the chip106on the chip seat550.

The apparatus500may also include an adhesive dispenser556and a base557, which are shown inFIG. 8. The base557may be attached to the housing504. The adhesive dispenser556has a hole558(which may also be called an opening), for dispensing adhesive. The adhesive dispenser556is attached to a first dispenser holder arm559, and a second dispenser holder arm560, which are attached to a dispenser stand561. The adhesive dispenser556may be selectively coupled to an air pressure source (not shown) for pushing the adhesive out of the hole558of the adhesive dispenser556. As an example, an air tube (not shown) may be coupled to the adhesive dispenser for supplying air pressure from an air pressure source for pushing the adhesive out of the hole558. The adhesive dispenser may556be attached to actuators (not shown) for moving the hole558in the adhesive dispenser556over the chip receiving slot126in the substrate104to deposit adhesive in the chip receiving slot126. As an example, three electrical actuators may be attached to the dispenser stand561for moving the adhesive dispenser556in x, y, and z directions. The x direction may be referred to as a second direction, the y direction may be referred to as a first direction, and the z direction may be referred to as a third direction.

Movement of the alignment arm518may be accomplished, for example, by coupling an air pressure source to a cylinder (not shown) attached to, or formed in, the alignment arm518. As an example, a tube may be used to couple air from an air compressor to the cylinder. Air pressure may be applied to one side of the cylinder to move the cylinder and the alignment arm518in a first direction, and may be applied to an opposite side of the cylinder to move the cylinder and the alignment arm518in an opposite direction. The substrate front clamp514and the substrate side clamp516may, for example, be moved in a similar fashion with air pressure. Bearings (not shown) may be utilized to facilitate smooth movement of the alignment arm518. Vertical movement of the pick-up chuck502may be accomplished, for example, with an air bladder562coupled to the pick-up chuck502with a pivot arm564. The air bladder562may be coupled to an air pressure source (not shown) for inflating and deflating the air bladder562. For example, the pick-up chuck502may be moved downward by putting air into the air bladder562, and may be moved upward by removing air from the air bladder562. Air lines, valves, switches, manifolds, and pressure regulators (not shown), may be utilized to couple the air pressure source (or air pressure sources) to the alignment arm518, the bladder562, the substrate front clamp514, the substrate side clamp517, the hole548in the bottom surface520of the pick-up chuck502, the hole554in the chip seat550, and to the adhesive dispenser556. The air pressure source may, for example, provide positive air pressure and/or negative air pressure (to create a vacuum source). A processor, for example a portable computer, may be coupled to the air pressure source, valves, and actuators for controlling operation of the apparatus500. Alternatively, electric actuators could be used to move the alignment arm518, the pick-up chuck502, the substrate front clamp514, and the substrate side clamp516.

Alignment of the plane of the air bearing surface128of the chip106with the plane of the air bearing surface110of the substrate104is accomplished mechanically with the apparatus500, by having a portion of the apparatus500touch the air bearing surface110of the substrate104at specified locations to stop vertical motion of the chip106, as is discussed below. To maintain optimal performance, the fixture500could be periodically realigned, and a mechanized (or manual) fixture cleaning process could be used to clean the fixture500between uses.

In addition to the various hardware embodiments described above, another aspect of the invention concerns a method for embedding a chip in a substrate, to form a composite air bearing surface, which may be used in a tape head. Embedding the chip in the substrate may also be referred to as merging the chip with the substrate.

Overall Sequence of Operation

For ease of explanation, but without any intended limitation, the method aspect of the invention is described with reference to the read/write module100and the apparatus500described above. An example of the method aspect of the present invention is illustrated inFIGS. 9A and 9B, which show a sequence900for a method for embedding a chip106in a substrate104to form a composite air bearing surface102.

The sequence900, may begin with the operation902of attaching a closure108to the chip106, adjacent the active elements140in the chip106. The closure108is attached to the front132of the chip. However, the closure108, which is included for example to reduce tape wear on the active elements140, is not required. The sequence900may also include the operation904of lapping the chip106to form the air bearing surface128on the chip106, prior to performing the aligning operation914discussed below. The sequence900may further include lapping the bottom surface130of the chip106, in operation906, to produce sufficient surface roughness on the bottom surface130to increase adhesive reliability and bond strength (discussed below). Operation908may also be performed, which comprises grinding the chip receiving slot126in the substrate104, prior to the operation916of depositing adhesive in the chip receiving slot126, which is discussed below. The sequence900may also include the operation910of lapping the substrate104to form the air bearing surface110on the substrate104, also prior to the operation916of depositing adhesive in the chip receiving slot126, discussed below. As an example, the air bearing surface110of the substrate104may be lapped after the chip receiving slot126is ground in the substrate104, to avoid distortion of the air bearing surface110that could result if the chip receiving slot126is ground in the substrate104after the air bearing surface110of the substrate104is lapped. In one example the air bearing surface110of the substrate104is polished to the same Ra as the air bearing surface128of the chip106, which may be, for example about 50 Å Ra.

In operation912, the substrate104is secured in a fixed position. As an25example, the substrate104may be secured in the substrate seat506by pressing the substrate front clamp514and/or the substrate side clamp516against the substrate, thereby causing the substrate104to be pushed against the back surfaces508a,508b,508c,508dand the side512of the substrate seat506. In some embodiments there may be a hole (not shown) in the bottom510of the substrate seat506, and air may be evacuated from the hole to hold the bottom116of the substrate104against the bottom510of the substrate seat506. A vacuum source could be coupled to the hole to evacuate air from the hole.

The sequence900also includes operation914, which comprises aligning the chip106in a y direction (also called the first direction) with the chip receiving slot126in the substrate104. The operation914of aligning the chip106in the y direction may be performed before or after the operation916of depositing adhesive (discussed below). The chip106is aligned in the y direction with the chip receiving slot126when the distance from the first side136of the chip106to the first side166of the chip receiving slot126, and the distance from the second side138of the chip106to the second side168of the chip receiving slot, are about the same. Because the distance from the first side136to the second side138of the chip106is slightly less than the distance from the first side166to the second side168of the chip receiving slot126, the chip106will fit into the chip receiving slot126when the chip106is later pushed into adhesive in the chip receiving slot126(in operation922discussed below). As an example, the chip106may be aligned in the y direction by placing the chip106in the slot552in the chip seat550. The slot552is sized and positioned so that when the chip106is placed in the slot552, the first side136of the chip106is about 0.1 mm towards the center of the chip receiving slot126in the y direction from the first side166of the chip receiving slot126, and the second side138of the chip106is about 0.1 mm towards the center of the chip receiving slot126in the y direction from the second side168of the chip receiving slot126. The chip106may be held in position in the slot552by coupling the hole554in the chip seat550to a vacuum source to evacuate air from the hole554in the chip seat550.

In operation916, adhesive is deposited in the chip receiving slot126in the substrate104. Operation916may be accomplished by applying pressure to adhesive in the adhesive dispenser556to cause adhesive to flow from the hole558in the adhesive dispenser556, and by moving the hole558in the adhesive dispenser556over the chip receiving slot126while adhesive flows from the hole556. In one example the adhesive is deposited at least 5 microns thick on the bonding surface170of the chip receiving slot126. However, smaller or larger adhesive thicknesses could be used. In some embodiments the adhesive may be a U.V. curable cyanoacrylate. However, the adhesive does not have to be U.V. curable. Also, the adhesive does not have to be a cyanoacrylate. In one example the adhesive may be part number 4303 manufactured by Loctite Corporation. Loctite 4303 does not require pressing together the parts that are to be bonded. Other adhesives available from Loctite Corporation, for example model numbers 4302 or 4205, or adhesives available from other sources, could also possibly be used. In an alternative embodiment, a U.V. curable adhesive could be placed only near the four corners of the bonding surface170of the chip receiving slot126to hold the chip106in place, and then later a stronger adhesive could be added between the bottom surface130of the chip106and the bonding surface170of the chip receiving slot126to increase the bond strength and reliability.

The humidity characteristics of the adhesive affect the functionality and reliability of the module100. Adhesives generally shrink when cured, and swell when subjected to humidity. The amount of adhesive expansion due to humidity is greater if there is more adhesive thickness. The adsorption of moisture with exposure to elevated temperatures and humidities is low for Loctite 4303, and is between 0.25% and 0.78% by weight. Loctite 4303 was measured to exhibit low humidity expansion of 0.035 mm/mm at 35° C., 95% R.H. (relative humidity). The adsorbed water causes expansion of the adhesive, which increases the protrusion of the air bearing surface128of the chip106, by 3.5±0.4% of the adhesive thickness. For a 60 μm thick adhesive, the expansion would be 2.1±0.2 μm. Adhesive expansion can also degrade the cohesive strength of the adhesive. Additionally, moisture may diffuse along the interface between the adhesive and the substrate104and/or the chip106, potentially degrading the adhesive bond strength. The humidity properties of the adhesive are of interest because the module100is subjected to water if the taperless grind operation936, discussed below, is performed. Furthermore, tape heads used in the data storage industry are also exposed to variations in ambient environmental conditions, which include humidity and temperature variations.

The strength of the bond between the substrate104and the chip106is another important characteristic that affects the functionality and reliability of the module100. The break force of the bond between the substrate104and the chip106ideally should be sufficiently large to prevent (or minimize) movement or degradation of the bond during processing of the module100and when the module100is exposed to environmental conditions over the life of the module100, for example humidity and temperature variations. It is desirable to have a tight distribution of the break force for modules100produced in accordance with the invention. The break force may be measured, for example, by holding the substrate104fixed while applying a pseudo-shear force to the chip106until the bond breaks.

The bottom surface130of the chip106and the bonding surface170of the chip insertion slot126may be made sufficiently rough to improve the bond strength and humidity properties of the bond. Generally, the bottom surface130of the chip106is lapped to make as rough of a surface as can be produced without causing excessive wear on the chip106or excessive bowing of the chip air bearing surface128. The bond strength may be improved by lapping the bottom surface130of the chip106, for example, with a 6 μm diamond paste to produce a surface roughness between about 70 Å Ra and about 205 Å Ra, with an average of about 130 Å Ra. As another example, the bond strength may also be improved by lapping the bonding surface170of the chip insertion slot126to yield a surface roughness of N5–N6, which is 0.8 μm Ra to 1.6 μm Ra.

The sequence900may also include the operation918of evacuating air from the hole548in the bottom surface520of the pick-up chuck502, to pick up the chip106and hold the air bearing surface128of the chip106against the bottom surface520of the pick-up chuck502. The chip106may be picked up by the pick-up chuck502to facilitate moving the chip106by moving the alignment arm518. The alignment arm518may be moved in an x direction (also called the second direction) to align the chip106in the x direction with the chip receiving slot126in the substrate104, in operation920(discussed below). The chip106may be held against the pick-up chuck until the U.V. curing (discussed below) is completed. To evacuate air from the hole548, a vacuum source (not shown) may be coupled to the hole548with a tube (not shown). The vacuum source may be the same vacuum source, or a different vacuum source than the vacuum source used for evacuating air from the hole554in the chip seat550. To facilitate picking up the chip106with the pick-up chuck502, the vacuum source may be decoupled from the hole554in the chip seat550prior to when the chip106is picked up by the pick-up chuck502. The chip106remains aligned in the y direction when it is picked up by the pick-up chuck502on the alignment arm518.

In operation920the chip106is aligned in the x direction with the chip receiving slot126in the substrate104. The chip106may be aligned in the x direction with the chip receiving slot126in the substrate104by substantially aligning the back134of chip106with the back120of the substrate104, or, by substantially aligning the front133of the air bearing surface128of the chip106with the front163of the chip receiving slot126. For example, the chip106may be aligned with the substrate104in the x direction by picking up the chip106with the pick-up chuck502, and then moving the pick-up chuck502and the chip106over the substrate104until the back134of the chip106touches the back surfaces508b,508cof the substrate seat506. Because the substrate104has been secured to the substrate seat506in operation912, the back120of the substrate104also is touching the back surfaces508b,508c(and back surfaces508a,508d) of the substrate seat506.

The sequence900also includes the operation922of pushing the chip106into the adhesive in the chip receiving slot126of the substrate104. The pushing operation922may be accomplished by lowering the pick-up chuck502, while holding the chip106on the bottom surface520of the pick-up chuck502, with the air bearing surface128of the chip106substantially parallel with the air bearing surface110of the substrate104. As an example, in the pushing operation922the chip106is pushed into the adhesive only in the negative z direction. The pushing operation922may also include pushing a portion of the adhesive into a plurality of troughs172,174in the chip receiving slot126in the substrate104. The adhesive may be pushed into the plurality of troughs172,174by the bottom surface130of the chip106as the chip106is pushed into the adhesive. The plurality of troughs172,174are provided so that excessive adhesive will flow into the troughs172,174rather than on to the composite air bearing surface102.

The sequence900further includes the operation924of detecting when the air bearing surface128of the chip106is substantially at a desired protrusion in the z direction in relation to the air bearing surface110of the substrate104. The z direction may also be referred to as the third direction. The z direction is perpendicular to the air bearing surface110of the substrate104, and the desired protrusion of the air bearing surface128of the chip106can be a negative, positive, or zero value with reference to the air bearing surface110of the substrate104. The detecting operation924may be accomplished by detecting when the bottom surface526of the first alignment foot522and the bottom surface528of the second alignment foot524contact the air bearing surface110of the substrate104. The air bearing surface110of the substrate104is used as a datum for determining when the air bearing surface128of the chip106is at the desired protrusion in the z direction. The distance that the first alignment foot522and the second alignment foot524extend from the bottom surface520of the pick-up chuck502is chosen so that the bottom surface526of the first alignment foot522and the bottom surface528of the second alignment foot524will contact the air bearing surface110of the substrate104when the air bearing surface128of the chip106is substantially at the desired protrusion in the z direction.

In operation926, responsive to detecting that the air bearing surface128of the chip106is substantially at the desired protrusion in the z direction in relation to the air bearing surface110of the substrate104, pushing the chip106into the adhesive is ceased. When the bottom surface526of the first alignment foot522and the bottom surface528of the second alignment foot524contact the air bearing surface110of the substrate104, the first alignment foot522and the second alignment foot524prevent the pick-up chuck502from lowering any further, thereby preventing the chip106from being pushed any further into the adhesive.

The protrusion of the air bearing surface128of the chip106in relation to the air bearing surface110of the substrate104is an important parameter concerning the performance and reliability of the module100. The initial protrusion is affected by the dimensional tolerances of the parts and the alignment of the chip106in the chip receiving slot126in the substrate104. Long term changes in the protrusion are caused primarily by temperature and humidity effects. In order to be able to read and write to tape in accordance with desired performance characteristics of the module100, the air bearing surface128of the chip106must be aligned with the air bearing surface110of the substrate104within a protrusion tolerance dictated by the desired performance characteristics of the module100. For example, there is generally no increase in read and write data error rates when the air bearing surface128of the chip106is aligned between about −4 μm and about +11 μm from the air bearing surface110of the substrate104. A negative number (such as −4 μm) indicates that the air bearing surface128of the chip106is lower than the air bearing surface110of the substrate104, and a positive number (such as +11 μm) indicates that the air bearing surface128of the chip106is higher than the air bearing surface110of the substrate104). Too low of a protrusion (wherein the air bearing surface128of the chip106is below the air bearing surface110of the substrate104) may result in a reduction and/or loss of servo, reader, and writer signals in the module due to Wallace spacing losses. Too high of a protrusion (wherein the air bearing surface128of the chip106is above the air bearing surface110of the substrate104) may cause excessive tape wear or damage or loss of servo signals. Generally, the air bearing surfaces128,110are substantially aligned when the air bearing surface128of the chip106is aligned in the z direction to within about −4 μm and about +11 μm from the air bearing surface110of the substrate104.

As an example, the air bearing surface128of the chip106is at the desired protrusion in the z direction when the air bearing surface128of the chip106is about 2 microns above the air bearing surface110of the substrate104. In this example, the air bearing surface128of the chip106is positioned 2 microns above the air bearing surface110of the substrate104to allow for possible lowering of the air bearing surface128of the chip106as the adhesive continues to cure after being initially cured with U.V. light. However, the desired protrusion of the air bearing surface128of the chip106in the z direction could be greater or lesser than 2 microns above the air bearing surface110of the substrate104, or below the air bearing surface110of the substrate104, or when the air bearing surfaces128,110are coplanar. Lapping of the combined air bearing surface102, which may be costly, is not required because the invention permits precisely positioning the chip106in the substrate104to produce the desired protrusion.

The protrusion of the air bearing surface128of the chip106in relation to the air bearing surface110of the substrate may be designated P2at the first front corner139a(shown inFIG. 2) of the chip106, may be designated P3at the second front corner139bof the chip106, may be designed P1at the first back corner139cof the chip106, and may be designated P4at the second back corner139dof the chip106. The protrusions P2and P3at the front corners139a–b, are more important than the protrusions P1and P4at the back corners139c–d, because the back corners139c–dmay later be removed from the composite air bearing surface102by a taperless grind operation (discussed below). If desired, a laser interferometer (which, for example, may be obtained from Zygo Corporation) may be used to measure protrusion tolerances. However, it is not necessary to measure tolerances when the air bearing surface110of the substrate104is used as a datum (reference surface) for detecting when the air bearing surface128of the chip106is at the desired protrusion in the z direction, because the desired protrusion exists when the first alignment foot522and the second alignment foot524contact the air bearing surface110of the substrate104. Using the datum may be quicker than individually measuring the protrusions P1, P2, P3, and P4, and adjusting the position of the chip106.

The sequence900may also include operation928, which comprises holding the chip106, with the air bearing surface128of the chip106substantially at the desired protrusion in the z direction in relation to the air bearing surface110of the substrate104, and with the chip106substantially aligned in the x and y directions with the chip receiving slot126in the substrate104. Due to the orientation of the bottom surface520of the pick-up chuck502, during the holding operation928the air bearing surface128of the chip106is substantially parallel with the air bearing surface110of the substrate104. In operation930the adhesive is cured to bond the bottom surface130of the chip106to the bonding surface170of the chip receiving slot126in the substrate104, with the air bearing surface128of the chip106substantially at the desired protrusion in the z direction in relation to the air bearing surface110of the substrate104, and with the chip106substantially aligned in the x and y directions with the chip receiving slot126in the substrate104. The chip106is held firmly during the curing operation930to prevent the adhesive from pulling the chip106downward when the adhesive shrinks as it is cured, and to keep the air bearing surface128of the chip106parallel with the air bearing surface110of the substrate104.

The curing operation930may comprise shining at least one U.V. light source on the adhesive for a prescribed period of time, for example 15 seconds. As an example, the U.V. light source may use a 200 watt U.V. lamp (not shown) that has adjustable intensity. The light energy output at the end of a U.V. light guide, for example, the first end532of the first fiber optic U.V. light guide530, may be for example, about one-fifth of the light energy from the U.V. lamp. The optimal U.V. light intensity is a function of the type of adhesive used, and is adjusted to not be so high as to burn the outer surface of the adhesive, but to be high enough to penetrate into the adhesive. The exposure time may be adjusted to be longer or shorter than 15 seconds. Applying U.V. light of the desired intensity for the prescribed time period quickly achieves bonding and fixes the location of the chip106, but for many adhesives (such as Loctite 4303 adhesive), will not fully cure the adhesive. Bond strength generally increases with time for at least 30 days. After the U.V. curing, the adhesive thickness between the bonding surface170of the chip receiving slot126and the bottom surface130of the chip106may vary, for example, from about 5 μm to about 60 μm, with a nominal thickness of about 30 μm, due to manufacturing tolerances of the substrate104and the chip106.

As an example, the curing operation930may include shining at least a first U.V. light source on the adhesive proximate to the front132of the chip106for the prescribed period of time, and shining at least a second U.V. light source on the adhesive proximate to the back134of the chip106for the prescribed period of time. In one example, U.V. light from the first end532of the first fiber optic U.V. light guide530and U.V. light from the first end538of the second fiber optic U.V. light guide536are shined on the adhesive proximate to the front132of the chip106for the prescribed period of time, and U.V. light from the first end544of the third fiber optic U.V. light guide542is shined on the adhesive proximate to the back134of the chip106for the prescribed period of time.

In an alternative embodiment, the curing operation930also includes heating the adhesive, at a temperature and for a time period suitable for the adhesive, to further cure the adhesive. As an example, the module100may be placed in an oven to further cure the adhesive. The temperature used for heating the adhesive and the duration of the heating may be chosen to achieve a desired bond strength while avoiding degradation of any other adhesive bonds (for example, the bond between the chip106and the closure108). As an example, the temperature used for heating the adhesive may be from about 50° C. to about 80° C., and the duration of the heating may be from about 1 hour to about 48 hours. The heating temperature may be determined based on characteristics of the adhesive. Although heating the adhesive may be performed as part of the curing operation930, in other alternative embodiments heating of the adhesive may be performed in an additional curing operation, that for example, could be performed after the grinding operation936(discussed below). Adhesive and process characteristics may be considered to determine whether it is desirable to perform heat curing, and to determine whether to perform heat curing as part of the curing operation930and/or as part of an additional later curing operation. In another alternative embodiment, the curing operation930further includes air and/or anerobic curing of the adhesive. Depending on the extent of the curing performed in the curing operation930, the adhesive may be partially cured, or substantially totally cured, after the curing operation930.

After the curing operation930, the sequence900may also include the operation932of ceasing evacuating air from the hole548in the bottom surface520of the pick-up chuck502, to release the chip106from the pick-up chuck502. Also after the curing operation930, the sequence900may additionally include the operation934of ceasing clamping the substrate104in the substrate seat506, for example by ceasing pressing the substrate front clamp514and the substrate side clamp516against the substrate104.

After the curing operation930, (and after releasing the module100from the substrate seat506and the pick-up chuck502), the sequence900may also include the operation936of grinding the substrate104and the chip106to remove a rear portion of the composite air bearing surface102that includes the portion of the composite air bearing surface102that is above the back120of the substrate104. The portion of the composite air bearing surface102that is removed may be, for example, substantially rectangular. This operation936may be referred to as a taperless grind operation. (However, the surface produced by the grind does not have to be taperless.) More specifically, the taperless grind operation936comprises grinding off a portion of the air bearing surfaces110,128of the substrate104and the chip106, to produce the tail surface157of the chip106, and the tail surface158of the substrate104. The tail surface157of the chip106and the tail surface158of the substrate104are substantially coplanar. The portion that is ground off may be, for example, about 22.5 mm long from the first side122of the substrate104to the second side124of the substrate104, by about 1.75 mm wide (from the back120of the substrate104to the front edge162of the tail surface of the substrate104, and from the back134of the chip106to the front edge161of the tail surface of the chip106), by about 180 μm deep (from the air bearing surface110of the substrate104to the tail surface158of the substrate104).

After the chip106and substrate104have been bonded and are partially cured via U.V. exposure, they may sit at ambient conditions, (for example, ˜20° C. and <30% R.H.), for a period of time, for example 24 hours, prior to the taperless grind operation936. During the taperless grind operation936, the module100is exposed to water in a liquid coolant. The water in the coolant can affect the bond strength and can also cause adhesive swelling that results from adsorption of the liquid by the adhesive. After the taperless grind operation936, the bond strength may drop, for example, by about 40%, and the standard deviation of the bond strength may increase, for example, by about 38%. Additionally, after the taperless grind operation936, the protrusion of the air bearing surface128of the chip106may increase, for example, on average about 0.9 μm. Also, it is possible for some bonds to fail due to motion during the taperless grind operation936. In some embodiments, to reduce the number of bonds that fail during the taperless grind operation936, additional U.V. curing, or heat curing, may be performed prior to performing the taperless grind operation936.

III. Other Embodiments

While the foregoing disclosure shows a number of illustrative embodiments of the invention, it will be apparent to those skilled in the art that various changes and modifications can be made herein without departing from the scope of the invention as defined by the appended claims. Furthermore, although elements of the invention may be described or claimed in the singular, the plural is contemplated unless limitation to the singular is explicitly stated.