Assembly of DSA suspensions using microactuators with partially cured adhesives

Abstract

A method of assembly a dual stage actuated suspension includes either applying an adhesive to a microactuator motor and then B-staging the adhesive, or applying an adhesive that has already been B-staged such as in film adhesive form to the microactuator then assembling the microactuator into a suspension and then finishing the adhesive cure. The adhesive can be applied to bulk piezoelectric material, with the adhesive being B-staged either before or after it is applied to the bulk piezoelectric material, and the piezoelectric material then singulated into a number of individual piezoelectric microactuators. The method allows greater control over how much adhesive is used, and greater control over spread of that adhesive and control over potential contamination, than traditional liquid epoxy dispense methods.

Claims

1. A method of assembling a dual stage actuated disk drive suspension, the method comprising: applying a first strip comprising a first and conductive adhesive to a first surface of a piezoelectric material; applying a second strip comprising a second and non-conductive adhesive to the first surface of the piezoelectric material; partially curing the conductive adhesive and the non-conductive adhesive; dicing the piezoelectric material into a plurality of individual piezoelectric components, each piezoelectric component having conductive and non-conductive adhesive on a common surface thereof and respectively at generally opposite ends thereof; assembly a first one of the piezoelectric components into a suspension; and additionally curing in a single curing step the conductive and non-conductive adhesives to fully cure them, the fully cured non-conductive adhesive providing a mechanical connection between the first piezoelectric component and the suspension, and the fully cured conductive adhesive providing an electrical connection between the first piezoelectric component and the suspension for use in actuating the first piezoelectric component.

2. The method of claim 1 wherein at least one of the conductive and non-conductive adhesives is applied via a printing step, and the partial curing step is performed after the adhesive printing step.

3. The method of claim 1 wherein at least one of the conductive and non-conductive adhesives is applied to the piezoelectric material as a previously partially cured film.

4. The method of claim 1 wherein the partial curing step comprises B-staging such that the conductive and non-conductive adhesives are no longer tacky.

5. The method of claim 1 wherein the partial curing step comprises ultraviolet B-staging.

6. The method of claim 1 wherein the partial curing step comprises heat B-staging.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a perspective view of a prior art disk drive assembly having a DSA suspension.

(2) FIG. 2 is a top plan view of the prior art suspension 105 in FIG. 1.

(3) FIG. 3 is a perspective view of a prior DSA suspension to which the present invention is applicable.

(4) FIG. 4 is a sectional view taken along section line C-C in FIG. 3.

(5) FIG. 5 is a sectional view taken along section line D-D in FIG. 3.

(6) FIG. 6 is a process flow diagram of the process used to attach the PZT to the suspension in FIG. 3.

(7) FIG. 7 is a process flow diagram of the simplified process used to attach a PZT to a suspension according to the invention.

(8) FIG. 8 is a perspective view of a DSA suspension minus the flexure gimbal assembly, according to an embodiment of the present invention that employs integrated adhesive patterns printed onto the PZT.

(9) FIG. 9 is an exploded view of the suspension of FIG. 8.

(10) FIG. 10 is a perspective view of one of the PZTs of the suspension of FIG. 8, showing the integrated adhesive film underneath.

(11) FIG. 11 is a perspective view of a portion of a DSA suspension according to an additional embodiment of the invention, in which integrated adhesive film is used on the top surface of the PZT.

(12) FIG. 12 is a perspective view of the PZT in FIG. 11.

(13) FIG. 13 is a side cut-away view of a PZT having a wrap-around electrode according to an additional embodiment of the invention.

(14) FIG. 14 is a process flow diagram for the prior epoxy dispensing and bonding steps for the PZT of FIG. 3

(15) FIG. 15 is a process flow diagram for the prior epoxy dispensing and bonding steps and for the PZT of the present invention shown in FIG. 13.

(16) FIGS. 16A-16G illustrate the manufacturing steps for making the PZT with wrap-around electrode shown in FIG. 13.

(17) FIGS. 17A and 17B are isometric views of a PZT wafer at selected steps during the manufacturing process according to the present invention.

(18) FIGS. 18A-18G show an alternative manufacturing process that could be used to produce the PZT of FIG. 13.

(19) FIG. 19 is a perspective view of a PZT with adhesive being applied thereto according to the invention.

(20) FIG. 20 is a top perspective view of the PZT of FIG. 19 illustrating the adhesives thereon being B-staged.

(21) FIG. 21 is a side cutaway view of the PZT of FIG. 20 after it has been applied to a suspension.

(22) FIG. 22 is a side cutaway view of the PZT having a wrap-around electrode after it has been applied to a suspension.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(23) A first aspect of the invention is the use of adhesive film to attach the PZT to the suspension. FIG. 7 illustrates the method. Conductive epoxy is dispensed at the interconnect (710). The PZT having the integrated adhesive film or other B-staged adhesive is then attached to the suspension (712), and the adhesive is then cured (714). Conductive epoxy is then dispensed at (716) and cured (718). The step of epoxy dispensing on the load beam is eliminated by using a PZT with integrated adhesive film. PZT with integrated adhesive film can be manufactured with either laminated adhesive film on it at the PZT wafer level or by printing or by a wafer backside coating process as used in the semiconductor industry. Because the adhesive film is attached to the PZT at the wafer level before dicing into individual PZT dies, process simplification and cost savings can be achieved. Also, tight control of the adhesive thickness can be achieved. As shown in FIG. 7 the use of a PZT with integrated adhesive also simplifies the process when compared to FIG. 6. The step of non-conductive epoxy dispensing at the load beam is eliminated using the method of the invention.

(24) A suspension design that facilitates the use of integrated adhesive film is shown in FIGS. 8-10. FIG. 8 is a perspective view of a DSA suspension, less the flexure gimbal assembly for clarity of illustration, according to an embodiment of the present invention that employs integrated adhesive film or patterns printed onto the PZT. PZTs 830 are affixed to the suspension component to which it is mounted, in this case to baseplate 812. Actuation of the PZTs moves load beam 820 such that the head slider which is located at the distal end of the load beam moves radially.

(25) FIG. 9 is an exploded view of the suspension of FIG. 8.

(26) FIG. 10 is a perspective view of one of the PZTs 830 of suspension 810 of FIG. 8, showing the integrated adhesive film or printed adhesive 834, 836 underneath. In this embodiment, the integrated adhesive films 834, 836 located at both ends of PZT 830 are formed by applying adhesive film or printing adhesive patterns on the PZT wafers before dicing and singulation into individual PZT pieces. The exposed PZT surface between the adhesives will allow for electrical connection with liquid epoxy to the suspensions's electrical circuit.

(27) FIG. 11 is perspective view of a portion of a DSA suspension according to an additional embodiment of the invention, in which integrated adhesive film is used on the top surface of PZTs 1130 in order to bond the PZTs to recessed portions of baseplate 1112.

(28) FIG. 12 is a perspective view of the PZT in FIG. 11. In this design, the integrated adhesive film or printed adhesive 1134 is located at the top surface of the PZT. The integrated adhesive film covers the entire top surface, or substantially the entire top surface, and thus no patterning of the adhesive is required. Also, conductive adhesive film can be used in this design, such that the grounding through the base plate can be achieved once the PZT is attached to the base plate. This will further eliminate the required step of grounding the PZT to the baseplate with conductive liquid epoxy as shown in FIG. 6.

(29) The adhesive film used can be either conductive or non-conductive, depending on whether an electrically conductive connection to the suspension or the interconnect circuit is desired, or a non-conductive connection to the suspension. Film adhesives are generally preformed or B-staged, and are available in rolls, sheets, or die-cut shapes.

(30) B-Staged Epoxy

(31) In a slightly different embodiment, instead of applying adhesive film to the PZT and/or to the suspension, adhesive is applied to the PZT and is B-staged before final assembly.

(32) The term B-staged or B-staging as used herein means, after a flowable adhesive has been dispensed, partially hardening the adhesive so that its flow rate is substantially reduced to the point that it no longer flows freely as a liquid, but is not so hard such that it is no longer available for effectively adhering to another surface. B-staging involves temporarily exposing the adhesive to an environment which causes accelerated hardening of the adhesive, then removing the adhesive from that environment such that the hardening rate slows down considerably so that the adhesive does not substantially harden during assembly. The removal of the PZT from that increased hardening environment can include simply removing the hardening accelerant from the environment. B-staging can cure or otherwise harden the adhesive to a degree such that the adhesive is no longer tacky. One method of B-staging is to partially cure a cross-linking polymer such as epoxy, such as by applying heat and/or UV, such that the epoxy achieves less than 10% cross-linking, then removing the curing source. For epoxies that are B-staged using heat, the epoxy may be immediately quenched down to a lower temperature at which cross-linking is negligible, i.e., at which the epoxy effectively ceases to harden, in order to stop the cross-linking process. For epoxies that are B-staged using UV, removing the PZT from the increased hardening environment can mean simply turning off the UV curing lamps.

(33) With some adhesives, the adhesive may be mixed into a solvent to form a slurry, the solvent being one that evaporates at a lower temperature than which cross-linking begins to occur significantly. The adhesive may be a printable paste that is applied to the PZT. After dispensing, the adhesive is exposed to a specified thermal regime designed to evolve a majority of the solvent from the material without significantly advancing resin cross-linking. The result is an epoxy or other adhesive that no longer flows, but that is still available for adhering to another surface with the full or nearly full adherent strength of the epoxy.

(34) B-staging an adhesive permits the adhesive and substrate construction to be staged, or held for a period of time prior to the bonding and curing, without forfeiting performance. A secondary thermal cure cycle yields fully crosslinked, void-free bonds. As used herein, the term fully crosslinked means at least 90% crosslinked.

(35) The adhesive may take the form of a solid, thermosetting paste. The adhesive may be a printable paste that is printed by any known printing techniques that are suitable for use with adhesive, including screen printing, stencil printing, ink jet printing, spraying, stamping, and others. An advantage of using such printing techniques is that the adhesive can be dispensed in very fine and precise patterns onto the PZT, which helps to achieve control and repeatability of the adhesive's total mass and distribution within the finished suspension. One commercially available silver-filled conductive epoxy that is suitable for fluid jetting, screen printing, and stamping is EPO-TEK H20E by Epoxy Technology, Inc. of Billerica, Mass.

(36) A UV B-stage adhesive can be used. Such an adhesive is dispensed, then irradiated with UV energy in order to B-stage it. B-staging immediately after printing freezes the adhesives in position, which helps to precisely control any spread of the liquid epoxy. Unlike thermal staging, irradiating with UV energy eliminates the danger of advancing the thermoset reaction of the adhesive. UV B-staging can occur in seconds, while the thermal alternative can take an order of magnitude longer for the process.

(37) Liquid epoxy or other adhesive may be first dispensed onto the PZT and/or onto the suspension, and then the epoxy is B-staged to the point that its flow is reduced to a negligible amount. The parts can then be assembled in the final, clean room assembly area for the disk drives, and the adhesive then fully cured either by heat or by UV. Such techniques have been used, or have been proposed to be used, in the integrated circuit (IC) packaging field under the broad term of wafer backside coating (WBC). Wafer backside coating techniques using both conductive and non-conductive adhesives can be adapted from die attach processes used in IC packaging to PZT attach processes for suspensions. Inkjet printing of polymers, both conductive and non-conductive, has also been proposed. Such inkjet printing techniques can be adapted for use in printing adhesives onto the PZTs for bonding those PZTs to suspensions.

(38) It is anticipated that one method of production will be to begin with a wafer of PZT material, either applying already B-staged adhesive to it such as in adhesive film form or applying adhesive to it then B-staging the adhesive, then dicing the wafer into individual PZT microactuator motors. Pick-and-place machinery will be used to pick up the individual PZT die with the B-staged adhesive on it, assemble the PZT die to the suspension, and dwell there for the appropriate time and under the appropriate temperature and pressure conditions in order to fully cure the adhesive, and thus fully adhere the PZT to the suspension.

(39) Wrap-Around Electrode

(40) In another aspect, the invention is of a method of producing a piezoelectric microactuator or other electronic device having a wrap-around electrode, such that both the drive voltage and ground electrodes are located and accessible on the same side of the device.

(41) FIG. 13 is a side cut-away view of a PZT according to an additional aspect of the invention. PZT 1330 has a bottom electrode 1334 and a wrap-around electrode 1336 that enables simplified electrical connections to the PZT. In this embodiment, the top electrode 1336 is wrapped around the PZT onto one end of the bottom PZT surface. The driving voltage is thus applied to the bottom surface of the PZT on a first end thereof, and the electrical ground is connected to the bottom surface on the opposite end. Thus, both electrodes 1334, 1336 can be electrically connected by conductive epoxy 1340, 1342, respectively, on the same surface or side of the PZT. This reduces the number of epoxy bonding steps to two steps and eliminates the difficult to control epoxy height tolerance on the top PZT surface. Also, only a single curing step is needed.

(42) FIG. 14 is a flow diagram of a manufacturing process using prior epoxy dispensing and bonding steps for attaching the PZT to its suspension as shown in FIG. 3. Conductive epoxy is first dispensed for grounding (1410). Non-conductive epoxy is then dispensed for insulation (1412). The PZT is then attached to the suspension, at step 1414. The epoxies are then cured (1416). A second epoxy dispensing step is then performed (1418). Finally, that last-dispensed epoxy is cured (1420). The process required two separate curing steps.

(43) FIG. 15 is a flow diagram of a manufacturing process according to the present invention for bonding the PZT to its suspension as shown in FIG. 13. Conductive epoxy is dispensed for grounding (1510). Conductive epoxy is then dispensed for the signal or driving voltage for the PZT (1512). The PZT is then attached to the suspension (1514). Finally, the assembly is cured (1516). The figures illustrate the simplification that is obtained by using a PZT with a wrap-around electrode according to the invention.

(44) FIGS. 19-21 illustrate the preparation and placement of a PZT having B-staged adhesive according to the invention. FIG. 19 is a perspective view of a PZT 1930 with adhesive 1920, 1924 being applied to what will be the bottom surface of PZT 1930. In general, the adhesive can be applied by any one of a number of known techniques including screen printing, stencil printing, ink jet printing, spraying, application as a film, and others. In general, any patterns desired of a combination of conductive adhesive and/or non-conductive adhesive may be applied to PZT 1930. In the illustrative embodiment shown, the adhesive is sprayed by ink jet heads 1910, 1911, to produce one strip of conductive epoxy 1924, and one strip of non-conductive epoxy 1920. The two strips can be of different thicknesses, with one strip being thicker than the other.

(45) FIG. 20 is a top perspective view of PZT 1930 with the adhesives being B-staged. In the figure, the epoxy strips 1920, 1924 are being UV B-staged. In general, adhesives 1920, 1924 can be B-staged using any known technique including thermal B-staging and UV B-staging. Furthermore, the two strips of adhesive 1920, 1924 can be B-staged to different extents, leaving one strip more cured or hardened than the other. For UV curing, masks or screens can be used in order to irradiate one strip more than the other.

(46) FIG. 21 is a side cutaway view of PZT 1930 after it has been applied to a suspension. FIG. 21 is analogous to FIG. 3 and illustrates how the present invention can simplify the prior process. After PZT 1930 has been positioned, pressure is applied to at least the left side of the PZT as seen in the figure in order to squeeze non-conductive epoxy 1920 so that it flows into the gap between the PZT and polyimide layer 314, and covers the previously exposed stainless steel 312 adjacent the PZT. The pressure could be applied by mechanically pressing on the PZT. Alternatively, depending on how much hardening occurred during the B-staging process, the weight of the PZT itself may provide sufficient force and pressure to squeeze non-conductive epoxy 1920 into that gap. After the PZT is positioned, and pressed down if necessary, conductive epoxy 322 is applied so as to bridge the gap between the metallized top surface of the PZT, which defines the drive electrode, and copper contact pad 316 which supplies the drive voltage to the PZT. All of the epoxy in the assembly is then cured at the same time in a single curing step. This process eliminates the need for a second curing step as was required for the assembly and process of FIGS. 3-6.

(47) FIG. 21 represents only one of a number of possible different types of electrical connections and electrical connection methods for providing the PZT driving voltage and ground to the PZT. Many other connection types and methods are possible, such as disclosed in U.S. Pat. No. 8,189,301 to Schreiber, and U.S. Pat. No. 7,751,153 to Kulangara. The present invention is applicable in suspensions that employ various types of electrical connections to the PZTs.

(48) As an alternative to the bonding structure shown in FIG. 21, PZT 1930 could be extended farther to the left in the figure, such that the PZT is bonded directly to copper contact pad 316.

(49) FIGS. 16A-16G illustrate the manufacturing steps for making the PZT with wrap-around electrode shown in FIG. 13. First, a PZT block or wafer 1630 is placed onto a transfer tape 1602, with PZT bottom surface 1631 facing downward (FIG. 16A). Next, an appropriate mask is placed over the top surface of the PZT wafer, and a metallization layer 1604 such as aluminum metallization is sputtered onto the top surface (FIG. 16B). The mask leaves strips 1606 of PZT surface not metallized. Kerf 1608 is then cut into the PZT wafer to separate a first portion, which will be referred to as a PZT precursor 1632, from the rest of the wafer (FIG. 16C). A second mask 1612 is placed over PZT precursor 1632, and additional metallization 1605 is sputtered into the kerfs onto the sides of PZT precursors 1632 within kerfs 1608 in order to make those sides electrically conductive and electrically continuous with the metallizations on the top surface of the PZT adjacent the kerfs (FIG. 16D).

(50) Next, the PZT precursor 1632 is flipped over and preferably placed onto a second transfer tape in order to expose what had been the bottom surface 1631 of the PZT precursor (FIG. 16E). That bottom surface 1631 will continue to be referred to as the bottom surface even though it is now facing upward. A metallization layer 1614 is then sputtered onto the entire bottom surface 1631 of the PZT precursor (FIG. 16F). Finally, a new cut 1616 is made into the PZT, separating the first PZT generally in half and defining what will be referred to as first PZT 1634 and second PZT 1636 (FIG. 16G).

(51) The result of this process is two PZTs 1634, 1636 each of which has the same structure. A narrow stripe of metallization 1650 on the first PZT's top surface 1633 and near its end, defines a first electrode. The first electrode 1650 electrically wraps around via the metallized side surface 1605 of the PZT to the bottom surface 1631 of the PZT and to the metallization 1604 that generally covers bottom surface 1631. A second electrode 1652 on the top surface 1633 of the first PZT covers most, but not all, of the PZT top surface 1633. In this way, a first PZT has been constructed whose first electrode 1650 is located on the same surface of the first PZT as the second electrode 1652. Generally speaking, the first electrode can be the electrode at which the PZT drive voltage is applied with the second electrode being the electrode at which the PZT is grounded, or vice versa. The second PZT is substantially identical to the first PZT.

(52) FIGS. 17A and 17B are isometric views of a PZT wafer at selected steps during the manufacturing process according to the present invention. FIG. 17A is an isometric view of the PZT strips 1634, 1636 at the end of the process in FIG. 16. Now, the PZT is ready for poling; the final dicing operation can be performed afterward to create the individual PZTs as shown in FIG. 17B. The result is a first row of PZTs 1638 and a second row of PZTs 1640, both having wrap-around electrodes.

(53) FIGS. 18A-18G illustrate alternative manufacturing steps for making the PZT having a wrap-around electrode. The PZT wafer 1830 is placed onto a transfer tape 1802 with its bottom surface 1831 facing downward (FIG. 18A). Kerfs 1808 are then cut into PZT 1830 to separate a first portion, which will be referred to as a PZT precursor 1832, from the rest of the wafer (FIG. 18B). The kerfs 1808 on either side of PZT precursor 1832 are then filled with a conductive and hardenable material 1820, such as conductive epoxy paste containing copper, silver, or other conductive material or particles (FIG. 18C). Silver epoxy is one such commonly used material, and will be used as an example. Silver epoxy 1820 is then allowed to harden. Next, an appropriate mask is placed over the top surface of PZT precursor 1832, and a metallization layer 1804 such as aluminum metallization is sputtered onto the top surface (FIG. 18D). The mask prevents metallization along two narrow strips 1806, 1807 on the top surface of the PZT precursor near the ends thereof. The result is that the PZT precursor 1832 has two relatively narrow stripes of metallization 1842, 1844 on the top surface of the PZT precursor near either end thereof, and a large metallization area 1846 generally centered on the PZT precursor. At this point in the process, each stripe of metallization 1842, 1844 near an end of the PZT precursor is electrically connected to the silver epoxy 1820 on the end of the PZT precursor to which that stripe is adjacent, and each of the two stripes of metallization 1842, 1844 and the large metallized region 1846 in the center are all electrically isolated or electrically discontinuous from each other.

(54) Next, the PZT precursor is flipped over and preferably placed onto a second transfer tape in order to expose what had been the bottom surface 1831 of the PZT precursor (FIG. 18E). That bottom surface 1831 will continue to be referred to as the bottom surface even though it is now facing upward. A metallization layer 1814 is then sputtered onto the entire bottom surface of the PZT precursor (FIG. 18F). Finally, a new cut 1818 is made into the PZT precursor, cutting the PZT precursor generally in half, and another cut 1816 is made through the silver epoxy, thereby separating the PZT precursor in half and defining what will be referred to as first and second PZTs (FIG. 18G). The cut 1816 is within kerf 1808 and is narrower than kerf 1808 so as to leave the side of the PZT precursor covered with conductive silver epoxy 1820, and thus serves as an electrical bridge or wrap-around from the PZT's top surface to its bottom surface.

(55) The result of this process is two PZTs each of which has the same structure. A narrow stripe of metallization 1844 on the first PZT's top surface 1833 and near its end, defines a first electrode. The first electrode 1844 electrically wraps around via the silver epoxy 1820 to bottom surface 1831 of the PZT and to the metallization that generally covers bottom surface 1831. A second electrode 1852 on the top surface 1833 of the first PZT covers most, but not all, of the PZT top surface 1833. In this way, a first PZT has been constructed whose first electrode 1844 is located on the same surface of the first PZT as the opposite electrode 1852. The second PZT is substantially identical to the first PZT.

(56) FIG. 22 is a side cutaway view of the PZT having a wrap-around electrode such as the PZTs of either FIG. 16G or FIG. 18G, after it has been applied to a suspension. PZT 1830 has a first and wrap-around electrode 1844 which serves as the drive or positive electrode, and a second electrode 1852 which serves as the ground electrode. Drive electrode 1844 is bonded to copper contact pad 316 on polyimide layer 314 over stainless steel substrate 312, via conductive epoxy 1924. Ground electrode 1852 is grounded to stainless steel substrate 328 via gold bond pad 326 and conductive epoxy 1928. Strips of conductive epoxy 1924 and 1928 can be B-staged epoxies as discussed above, with the epoxies fully cured after the parts have been assembled as shown in the figure. This embodiment completely eliminates the need to dispense any epoxy within the suspension assembly room, and eliminates any liquid or paste epoxy from that room, and thereby helps to keep that environment free from contamination.

(57) It will be understood that the terms generally, approximately, about, and substantially, as used within the specification and the claims herein allow for a certain amount of variation from any exact dimensions, measurements, and arrangements, and that those terms should be understood within the context of the description and operation of the invention as disclosed herein.

(58) It will further be understood that terms such as top, bottom, above, and below as used within the specification and the claims herein are terms of convenience that denote the spatial relationships of parts relative to each other rather than to any specific spatial or gravitational orientation. Thus, the terms are intended to encompass an assembly of component parts regardless of whether the assembly is oriented in the particular orientation shown in the drawings and described in the specification, upside down from that orientation, or any other rotational variation.

(59) All features disclosed in the specification, including the claims, abstract, and drawings, and all the steps in any method or process disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. Each feature disclosed in the specification, including the claims, abstract, and drawings, can be replaced by alternative features serving the same, equivalent, or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

(60) It will be appreciated that the term present invention as used herein should not be construed to mean that only a single invention having a single essential element or group of elements is presented. Similarly, it will also be appreciated that the term present invention encompasses a number of separate innovations which can each be considered separate inventions. Although the present invention has thus been described in detail with regard to the preferred embodiments and drawings thereof, it should be apparent to those skilled in the art that various adaptations and modifications of the present invention may be accomplished without departing from the spirit and the scope of the invention. For example, instead of selectively applying and partially curing adhesive on the PZT, adhesively could be selectively applied and partially cured on other suspension components such as the flexure. Accordingly, it is to be understood that the detailed description and the accompanying drawings as set forth hereinabove are not intended to limit the breadth of the present invention.