SPACER LOADING SYSTEM FOR FIELD EMISSIVE DEVICES

Inventors:

William Son

Craig Bae

Jung Jae Kim

Yew Sang Chin

Hafezan Siavosh

Seng Kie Pan Woon Fuang Chan

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 60/724,446, filed October 7, 2005, which is incorporated by reference in its entirety.

BACKGROUND

[0002] This invention relates generally to the manufacture of field emissive flat panel displays and other vacuum electronics devices that include spacers for keeping opposing plates or other structures apart in a lower pressure or vacuum pressure compartment. In particular, embodiments of the invention relate to systems and methods for loading or installing spacers in such devices.

[0003] In vacuum electronics, the physical integrity of a device is a key factor in its functionality and ability to perform in accordance with its design and intended purpose. The device's physical integrity, and in particular the physical integrity of the vacuum enclosure, is also important for meeting and maintaining applicable use and safety standards. To maintain the physical integrity of these devices, many variations of support structures have been used. The support structures are often applied to maintain a desired gap between opposing sides of the device, as the lower pressure inside the device tends to cause the plates to come together. [0004] In field emissive displays (FEDs), a very low pressure level within the device is important for proper trajectories of electrons emitted within the device. The low pressure inside a FED also helps to maintain a particle-free environment to avoid collisions between electrons and particles. Spacers are often used to maintain a separation between a front plate (e.g., an anode) and a back plate (e.g., a cathode) in a FED, where a vacuum pressure is maintained between the two plates. Many types of spacers and other structures have been used to hold apart the plates in a FED. Because of the electrical performance requirements of a typical FED, spacers often must adhere to specific electrical considerations as well as the physical requirements. Some of the types of spacers that are known to those in the art include ceramic walls, cross type, cylinder type, as well as others.

[0005] In a typical FED, the spacers must be placed between the electrical structures in one of the plates — such as the gate and emitter electrodes on a cathode structure of a back plate. As these electrical structures tend to be small (e.g., corresponding to sub-pixels in a display), the placement of the spacers must be very precise to avoid interference of the spacer with the operation of its electrical components. A spacer may interfere with the operation of the FED, for example, by actually blocking an electron beam, or it may interfere by accumulating an electrical charge and having an electrical field effect on a beam. [0006] Placement of spacers has thus been a challenging aspect to the assembly of FEDs. Often, the spacers are made of various dielectric materials due to the electrical requirements of the FED for avoiding adverse effects on the operation of the device. Tools that have been made for placing spacers are typically very expensive to develop and are usually very time consuming in their use or application (also referred to as "tack time" in the assembly process of the devices). Typical manufacturing processes also involve multiple special steps and tools or equipment in the pursuit of placing and attaching spacers to the product or device being manufactured. Accordingly, it is desirable to reduce the time for placing spacers in a FED or other vacuum electronic device as well as eliminating special additional steps or techniques.

[0007] hi addition to speeding up the spacer loading process and eliminating the need for additional special steps or equipment, other difficulties arise in the spacer loading process. As such, controlling many aspects of spacer loading and installation can be both challenging and imprecise. Among such aspects may include controlling an amount of adhesive applied to the spacers and methods of applying and loading the spacers. These steps are often performed manually. And even when these steps are automated they are performed singularly, thereby reducing the efficiency of the process. Other difficulties involve controlling the accuracy of the spacer placement on the plate in both orientation and alignment. Accordingly, it is desirable to develop systems and methods for placing spacers on flat panel displays and other field emissive or vacuum electronics devices that avoid or address one or more of the challenges that face existing systems and methods.

SUMMARY OF THE INVENTION

[0008] Accordingly, a spacer loading system is used to load spacers to a substrate (such as a plate of an electron emitting flat panel display), optionally using various methods for adhering the spacers to the substrate. Not limited to the manufacture of field emissive displays or flat panel displays only, the spacer loading system may be used to place spacers for any of a number of devices whose manufacture involves the precise and accurate

placement of a number of spacer structures onto a surface. To achieve accurate and efficient spacer placement, embodiments of the spacer loading system may have a number of features to place spacers with a high degree of accuracy and precision, reduce production or process time in placing the spacers and thus manufacturing the overall device, and to achieve other benefits above existing systems for loading spacers in field emissive or vacuum electronics devices.

[0009] In one embodiment, a spacer placement system comprises a spacer transfer module, a spacer feeding module, an adhesive application module, and a plate positioning module. The spacer transfer module moves a gang holder to the spacer feeding module, where the gang holder accepts a group of spacers. The spacers are then moved to an adhesive application module, where an amount of adhesive is applied to the spacers, and ultimately to a plate positioning module, where the spacers are placed onto the substrate and the adhesive cured.

[0010] hi one embodiment, the spacer placement system implements a gang bonding method in which a gang holder is adapted to carry multiple spacers, such as one or more rows of spacers to be loaded onto a plate. By carrying and loading a group of spacers at one time, the tolerances in the placement of those spacers with respect to each other can be reduced, hi addition, the simultaneous treatment of the spacers in the process speeds up the manufacture of the device.

[0011] hi another embodiment, an automated system is used to feed a number of spacers into an escapement unit. A vibrating bowl feeds spacers into each nest in the escapement unit. The feeding may use vacuum assistance, gravity, or a combination of both. Once each spacer has been successfully loaded into a nest of the escapement unit, a vacuum sensor detects this condition, and the bowl moves into position to feed a spacer to the next nest in the escapement unit. This can be repeated to load a spacer into each nest in the spacer feeding module's escapement unit, hi another embodiment, a feeding plate includes a number of channels for feeding spacers to an escapement unit at the same time. [0012] hi another embodiment, an adhesive application module includes a roller in a reservoir of adhesive. As the roller turns it takes up an amount of the adhesive, which can be controlled using a blade. The roller may be smooth or include grooves of various dimensions and orientations, designed to take up a desired amount of adhesive. [0013] hi another embodiment, the spacer transfer module includes a mechanism for curing the adhesive once the spacers are in place on a plate. Where a UV glue is used as the adhesive, UV light is applied to the spacers after they are put into the desired location on a

plate but while the spacers are being kept in place by the spacer transfer module (e.g., while still being held by a gang holder). In this way, the close tolerances are maintained until the adhesive is cured and the spacers are secured, thereby avoiding errors in alignment that may otherwise occur while the adhesive is curing. The UV light may be provided by a UV light source mounted to the spacer transfer module.

[0014] Embodiments of the spacer loading system can thus place multiple spacers onto a substrate with efficiency, accuracy, and precision. In one embodiment, the spacer loading system beneficially performs any plurality of the steps of the process of loading spacers as described herein in a single unit, thereby simplifying the process and reducing its time.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 is a side view of a spacer loading system, in accordance with an embodiment of the invention.

[0016] FIG. 2 is a plan view of a spacer feeding module of a spacer loading system, in accordance with an embodiment of the invention.

[0017] FIGS. 3 A through 3C are cross sectional side views of a spacer feeding module illustrating the loading of a spacer from a vibratory bowl to an escapement unit, in accordance with an embodiment of the invention.

[0018] FIG. 4 is a cross sectional side view of an adhesive dipping module, of a spacer loading system, in accordance with an embodiment of the invention.

[0019] FIGS. 5 A and B are a perspective view and a bottom view, respectively, of a gang holder of a spacer transfer module loaded with spacers, in accordance with an embodiment of the invention.

[0020] FIGS. 6A and B each illustrate a spacer feeding module that uses a linear feeding plate, in accordance with embodiments of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS System

[0021] Embodiments of a spacer loading system are capable of placing multiple spacers onto a substrate with efficiency, accuracy, and precision. Ih one embodiment of a spacer loading system, illustrated in FIG. 1, the system comprises a spacer feeding module, an adhesive application module, a plate positioning module, and a spacer transfer module. Using this system, embodiments of a method for placing the spacers onto a substrate include a number of stages. These multiple stages of the method may include feeding a plurality of spacers onto a transfer structure for simultaneous loading, applying an adhesive to the spacers, positioning the spacers on a substrate, and curing the adhesive to secure the spacers.

This method can then be repeated any number of times to place additional sets of spacers onto the substrate. In the manufacture of flat panel FEDs, for example, the spacers may be placed in one or more rows at a time, and the method repeated until all of the rows of spacers have been secured to the substrate.

[0022] The spacers may comprise any of a number of structures suitable for maintaining the structural integrity of flat panel displays or other vacuum electronics devices. Some typical spacer types include posts, which can be used to keep opposing plates apart. In one embodiment, the spacers are about 1.5 mm in length and about 100 μm in width and/or are suitable for placement on a cathode structure of a flat panel FED.

[0023] The substrate onto which the spacers are placed typically comprises a component of the device being manufactured. For flat panel FEDs, for example, the substrate may be the back plate or the front plate of the display. Because of the small size of the electrical components on the back and front plates of a flat panel display, it can be appreciated that placing the small spacers onto one of these plates requires accuracy and precision for proper operation of the display. Where a large number of spacers are to be placed onto the substrate, automating the process can result in large benefits to the manufacturing process. Therefore, the embodiment of the spacer loading system shown in FIG. 1 beneficially performs all of the steps needed to place a plurality of spacers onto a substrate.

Spacer Feeding Module

[0024] The spacer feeding module is an automated system for feeding a number of spacers to the spacer transfer module. In one embodiment, the spacer feeder module comprises a vibratory bowl 105, a linear actuator 110, an escapement unit 115, and a vacuum unit 120. The vibratory bowl 105 serves as a reservoir for the spacers to be loaded. The vibratory bowl 105 is configured to vibrate by employing a mechanism that imparts a vibration stimulus to the bowl 105. Alternatively, any other suitable means of imparting a vibration or similar movement to the vibratory bowl 105 may be used. The vibratory bowl 105 is mounted on the linear actuator 110 to allow the bowl 105 to move in a linear manner to address each feeding location of the escapement unit 115. As described below, the vibration of the bowl 105 causes spacers in the bowl 105 to feed into the escapement unit 115, from which the spacers can be picked up by the spacer transfer module. [0025] FIG. 2 illustrates a top view of the vibratory bowl 105 and the escapement unit 115, in accordance with one embodiment of the spacer feeding module. The vibratory bowl 105 includes a channel 107, which in one embodiment is a topical channel or groove that helps to direct the spacers. When the bowl 105 vibrates, the spacers contained in the bowl

105 randomly move within the bowl 105. While moving randomly within the bowl 105, some of the spacers tend to become caught in the channel 107 so that they move within the channel only and tend to move in the channel 107 towards the edge of the bowl 105. Where the channel 107 meets the edge of the bowl 105, a feeding point 108 is created for feeding the spacers to the escapement unit 115.

[0026] In one embodiment, the escapement unit 115 comprises a cylindrical shaft having a number of nests 117 for receiving spacers 155 from the bowl 105. The nests 117 correspond to the shape and size of the spacers 155. For cylindrical spacers 155, for example, the nests 117 may be formed by drilling holes in the escapement unit 115. The pitch, or spacing, between the nests 117 in the escapement unit 115 can be determined according to the desired pitch between spacers 155 when loaded onto the substrate, thus maintaining the pitch between the spacers 155 from this point in the spacer feeding module to the final product (e.g., a FED device being manufactured). In one embodiment, the escapement unit 115 is changeable to allow for a different types, sizes, and/or pitch of the spacers 155. [0027] In operation, in one embodiment, the vibratory bowl 105 feeds spacers 155 into the escapement unit 115 one at a time. Starting from one end of the escapement unit 115, the feeding point 108 of the vibratory bowl 105 is aligned with a nest 117 at one end. A spacer 155 is loaded into the nest 117, and the bowl 105 moves laterally, byway of the linear actuator 110, relative to the escapement unit 115 so that its feeding point 108 is aligned with a next nest 117. This movement is depicted by the arrow in FIG. 2. This is repeated until each of the nests 117 contains a spacer 155.

[0028] FIGS. 3 A through 3C illustrate a side view of the operation of feeding a spacer 155 into a nest 117 in accordance with one embodiment of the invention. In FIG. 3 A, the feeding point 108 of the bowl 105 has been aligned with an empty nest 117 of the escapement unit 115. As illustrated in FIG. 3B, the vibratory bowl 105 is then tilted towards the escapement unit 115, and the escapement unit 115 is rotated towards the bowl 105 so that the channel 107 and the nest 117 are aligned. As shown, the bowl 105 and the escapement unit 115 each rotate 45 degrees, but other angles and orientations are possible for other designs. In one embodiment, the escapement unit 115 is rotated so that the nest 117 is at least at an angle of about 30 degrees from a level position to achieve a sufficient gravitational force for successful reception of the spacer 155 into the nest 117. Alternatively, rather than both elements rotating, one can rotate to obtain proper alignment, or a movement other than or in addition to rotation may be incorporated into the system. Unblocked, the spacer 155 falls into the nest 117, as shown in FIG. 3B.

[0029] In one embodiment, a smaller hole 118 is drilled through the escapement unit 115 where the nest 117 is so that air can pass therethrough. The vacuum unit 120 (shown in FIG. 1) is coupled to the escapement unit 115 at the hole 118 to provide suction therethrough. In this way, vacuum suction assists in feeding the spacer 155 into the nest 117. The hole 118 is smaller than the nest 117 or otherwise has some structural blocking feature so as to prevent the spacer 155 from falling through the escapement unit 115. The spacer feeding module can thus use a combination of vibratory forces, gravity, and vacuum assistance to feed the spacer 155 into each nest 117.

[0030] Once a spacer 155 has been successfully loaded into the nest 117, the bowl 105 and the escapement unit 115 rotate back to their original positions, as shown in FIG. 3C. The bowl 105 then moves so that its feeding point 108 is aligned with a next nest 117, as shown in FIG. 2. The process shown in FIGS. 3 A through 3C is then repeated to fill the nest 117 with a spacer 155. Once full, the escapement unit 115 is rotated upright so that the spacers 155 are in vertical alignment or another orientation for being picked up by the spacer transfer module (described below).

[0031] In addition to assisting in the loading of spacers into the escapement unit, the vacuum unit 120 can be used to sense the presence of a spacer 155 in a nest 117. In one embodiment, a separate vacuum means is coupled to each hole 118 of the escapement unit 115, for example by way of a flexible tube. Using a vacuum sensor associated with each hole 118, the vacuum unit 120 can detect whether the corresponding nest 117 contains a spacer 155. If the nest 117 is filled, the sensed pressure is expected to be lower than if the nest 117 is not filled, since when filled a spacer 155 blocks the hole 118 and allows the vacuum unit 120 to generate a lower pressure in the hole 118.

[0032] In one embodiment, if one or more of the nests 117 remains unfilled after the bowl 105 has reached the end of the nests 117 (e.g., as determined using vacuum sensing), the entire escapement unit 115 is emptied, and the feeding process begins again. Emptying the escapement unit 115 may be accomplished by rotating the nests 117 to point downward so that the spacers 155 fall out due to gravity. Alternatively, the spacers 155 could be forced out using positive pressure from blowing into the nests, for example, by reversing the vacuum unit 120 to provide a positive pressure to the nests 117 to purge the escapement unit 115 of spacers 155. Alternatively, if the system knows which nests 117 are not filled (e.g., using vacuum sensing), the bowl may be aligned with those unfilled nests 117 until all of the nests 117 are filled. Once proper vacuum sensing is achieved for all of the nests 117, indicating that all the nests 117 have been successfully loaded, the process continues. In yet another

embodiment, the bowl 105 remains at each nest 117 until the nest 117 is filled, as indicated for example by vacuum sensing.

[0033] IQ practical operation of the spacer feeding system, spacers may fall onto the ground rather than into a nest 117. In one embodiment, these spacers may be captured in a reservoir (not shown) and then recycled (e.g., put back into the bowl 105) using a process that may be automatic or manual.

[0034] In another embodiment of the spacer feeding module, a linear feeding plate is used instead of a vibrating bowl. One embodiment of a linear feeding plate is illustrated in FIG. 6 A. The linear feeding plate comprises a plate 205 that has multiple tracks 210 machined or otherwise formed into it as shown. The tracks 210 correspond to the nests 117 in the escapement unit 115 so that spacers 155 can be fed from the linear feeding plate to the escapement unit 115. The tracks 210 maybe slightly tapered from one end of the plate 205 to the other so that the tracks 210 become narrower towards the edge from which the spacers 155 are fed onto the escapement unit 115. A vibration may be imparted to the linear feeding plate while spacers 155 are placed on the top surface of the plate 205. In this way, the spacers 155 on the plate 205 are generally directed into the tracks 210 and towards the nests 117 in the escapement unit 115. One benefit of this embodiment is that the nests 117 are fed simultaneously instead of one by one, which can further reduce the process time. [0035] In a variation on this embodiment, shown in FIG. 6B, the linear feeding module further includes diagonal channels 215 that are cut into the top surface of the plate 205. The diagonal channels 215 maybe oriented away from the center of the plate 205 and towards the feeding edge of the plate 205, as shown in FIG. 6B. In this way, the diagonal channels 215 help to spread the spacers 155 across the top surface of the plate 205 so they enter each of the linear feeding tracks 210, including those toward the outside edge of the plate 205. The diagonal channels 215 are preferably not as deep as the linear feeding tracks 210 so they do not affect the movement of spacers 155 that are already in those tracks 210. [0036] In another embodiment, a variation of the tapered tracks 210 may include a "stepped" pattern so that where the tracks 210 are wider at one end, one or more of the tracks 210 step inward as they narrow to the feeding end near the escapement unit 115. One possible advantage of such a design is to inhibit the possibility of spacers 155 becoming lodged within a track 210, side by side or vertically, and thus prevented from progressing further towards the escapement unit 115.

Adhesive Application Module

[0037] One embodiment of the adhesive application module 125 is illustrated in cross sectional side view in FIG. 4. The adhesive application module 125 includes a roller 127, a reservoir of adhesive material 165, a wiper element 128, and a door 129. In one embodiment, the adhesive material 165 is a UV glue, which cures upon application of UV light. Accordingly, the adhesive application module 125 is preferably opaque when using a UV adhesive material 125 to prevent premature curing of the material 165 within the module 125. The entire module is enclosed with opaque covers. The door 129 allows for selectively blocking the adhesive 165 from light and/or preventing evaporation of the glue, while also allowing access to the roller 127.

[0038] The roller 127 is partially submerged into a reservoir of adhesive material 165. The roller 127 may be designed with grooves or channels or may have a smooth surface to control the amount of adhesive 165 taken up by the roller 127. The roller 127 is mounted on a shaft that is linked to a motor. In operation, the roller 127 rotates through the adhesive 165, taking up a layer of the adhesive 165 on its surface as the roller 127 rotates. The amount of the adhesive 165 that is taken up on the surface of the roller 127 depends, at least in part, on the viscosity of the adhesive 165 used and the speed of rotation. In one embodiment, a wiper element 128 situated next to the roller 127 wipes off excess adhesive 165 to maintain a consistent layer or amount of the adhesive 165 on the surface of the roller 127. The wiper element 128 may be adjustable so that this amount can be controlled. [0039] When a group of spacers 155 loaded on the spacer transfer module are ready to have adhesive 165 applied thereto, the door 129 of the adhesive application module 125 opens to allow access to the roller 127. As shown in FIG. 4, the spacer transfer module then lowers the spacers 155 towards the roller 127 close enough so that some amount of adhesive material 165 taken up by the roller 127 is transferred to the spacers 155. The amount of material 165 transferred to the spacers 155 can be controlled by controlling positioning of the spacers and the amount of adhesive material 165 taken up by the roller 127 (as described above).

[0040] In the manual application of adhesive to spacers, the amount of adhesive applied to and the coverage of the adhesive on each spacer can be challenging to control. With embodiments of the adhesive application module 125, the use of the roller 127, the wiper element 128, and the transfer module to automate the movement of the spacers help to control and make consistent the adhesive 165 that is applied to each spacer 155.

Plate Positioning Module

[0041] In one embodiment, the plate positioning module includes a high precision X-Y-θ stage 130 (which may comprises a group of individual coupled X, Y, θ and stages) and a vision system 140 mounted on the spacer loading system. Preferably, the plate positioning module is mounted to a granite table, which may rest on the spacer loading system or be integral with it. The granite table is used to reduce the effect of vibration, which could otherwise be problematic for high precision spacer placement.

[0042] The plate 135 (or other substrate) that is to have the spacers loaded thereon is mounted on a platform of the stage 130. The plate 135 may be mounted to the stage 130 by vacuum, and it need not directly contact the stage 130. In this way, adjustment of the stage 130 in the X, Y, or θ directions causes a corresponding movement of the plate 130. As used herein, the X and Y directions are axes parallel to a surface of the system and orthogonal to the orientation of the spacers 155, and the θ direction is an angular rotation in the plane of the X and Y axes. In other embodiments, the stage 130 may allow for movement in other directions, such as the Z direction parallel to the loading of the spacers 155. [0043] In one embodiment, the vision system 140 comprises a pair of cameras. In one embodiment, the cameras can have a field of view of about 500 x 500 μm and a depth of field of about 30 μm. The cameras preferably have mobility and adjustment capabilities to acquire proper focus, which can be achieved by manual movement of the cameras or by mounting them on an X-Y stage. In one embodiment, the cameras are equipped with lenses that enable the cameras to have a depth of focus that allow them to view a substrate at one depth and the gang holder 150 at another depth (i.e., when not lowered to deposit the spacers 155). Alternatively, the vision system 140 may comprises two or more pairs of cameras for this purpose.

[0044] The entire vision system 140 may be mounted on a motorized Z stage, which allows for adjustment for variations in thickness of various plates 135. Such a motorized Z stage can be used to move the vision system 140 with respect to the surface of the plate 135 to maintain a correct focal distance. The cameras may target specific parts of the plate 135, such as markings or other predetermined relative features. The cameras may also target reference points at the two ends of the gang holder 150 of the spacer transfer module (described below). [0045] In operation, the X-Y-θ stage 130 moves the plate 135 to a first loading position, and the spacer transfer module brings a group of spacers 155 into a position close to where the spacers 155 are to be mounted on the plate 135. The cameras can then be aimed to specific relative positions on the plate as well as to specific locations on the spacer transfer

module. The vision system 140 records these positions, as they are viewed by the cameras. The X-Y-θ stage 130 may then be used to adjust the position of the plate 135 so that the plate 135 is directly below the spacers 155 at locations where the spacers 155 are to be placed on the plate 135. The amount and type of adjustment is determined based on the difference in position between the plate 135 and the spacers 155 loaded in the spacer transfer module, as recorded by the vision system 140.

[0046] When the plate 135 is properly positioned, the spacer transfer module lowers the spacers 155 onto the plate 135 to load them (as described below). Once the spacers 155 are mounted, the X-Y-θ stage 130 returns to its initial position before the correction and adjusts to allow for a next group (e.g., row) of spacers 155 to be loaded onto the plate 135.

Spacer Transfer Module and Spacer Curing

[0047] The spacer transfer module is used to move the spacers around the spacer loading system. As illustrated in FIG. 1, an embodiment of the spacer transfer module includes a transfer unit 145, which may hang from a beam or upper section of the spacer loading system. The transfer unit 145 allows the spacer transfer module to move from one part of the spacer loading system to another. In one embodiment, the transfer unit 145 provides for movement at least laterally from one end of the system to the other (i.e., in the x-direction) as well as vertically (i.e., in the z-direction) to each process module in the system. [0048] Affixed to the transfer unit 145 is a gang holder 150. The gang holder 150,is designed to hold the spacers 155 in a row or other configuration suited for placement on the plate 135. The spacer transfer module may further include a vacuum unit 160 for keeping the spacers in place in the gang holder 150 using, at least in part, a lowered pressure (e.g., a vacuum) generated between the gang holder 150 and the spacers 155. FIGS. 5A and 5B illustrate a perspective view and a bottom view, respectively, of the gang holder 150 loaded with a group of spacers 155. In the embodiment illustrated, the lower portion of the gang holder 150 has a ridged surface that secures the spacers 155 in place and in a fixed pitch relative to each other. As seen in FIG. 5B, the gang holder 150 may have one or more holes 152 drilled therethrough, allowing for the vacuum unit 160 to generate a suction to assist in keeping the spacers 155 in place and secured to the gang holder 150. [0049] As can be appreciated, the gang holder 150 maintains an accurate orientation of the spacers 155 with respect to each other, at least along a critical axis. The gang holder 150 fixes the spacers 155 in alignment to ensure that they are held and placed properly. This alignment preferably includes spacing displacement as well as rotational alignment (e.g., that the spacers 155 in a correct orientation with respect to the plate 135 onto which they are to be

installed). For example, in the case of FEDs and similar devices, the gang holder 150 may hold the spacers 155 perpendicularly and in one or more rows with respect to the column or emitter electrode direction of the device. In a flat panel FED, space is typically very limited in the column direction of the cathode structure due to the close proximity of sub-pixels to sub-pixel features in that direction. Accordingly, where the spacers are being loaded onto a cathode structure of a FED, the spacers may be loaded in rows in a perpendicular orientation with respect to the gate electrodes. By loading the spacers between the gate electrodes in an orthogonal orientation perpendicular to the direction of the gate electrodes (and thus parallel to the emitter electrodes), more positioning tolerance is allowed. Depending on the design of the field emissive device being manufactured, other orientations may be used. [0050] With this spacer transfer module, a gang loading method may be applied in which a group of spacers 155 can be placed on a plate 135 or other substrate at the same time. A row of spacers, multiple rows of spacers, or any other fixed configuration of spacers can be handled and installed in a single step. This tends to increase the speed of the manufacturing cycle as well as improve the quality and precision of the resulting device. Variations to the number of spacers in a given row depend upon the size of the device being manufactured; therefore, the spacer transfer module may be configured to accept different removable gang holders having varying sizes and configurations to hold the aligned spacers. [0051] In one embodiment, the spacer transfer module further includes a UV light source 165. The UV light source 165 may comprise fiber optics and any of a wide variety of optical elements to deliver the UV light from the UV light source 165 to the adhesive at each spacer's loading position. Such additional optics may include lenses, mirrors, fiber optics, and other mechanisms for creating a sufficient amount of UV exposure to cure the adhesive. Beneficially, this may result in the application of UV light from multiple perspectives so that the adhesive is not cured from just one side. An additional benefit of using fiber optic wires is for control of thermal effects to the cathode on the plate due to the applied UV light. Beneficially, curing the adhesive using light sourced from the spacer transfer module eliminates an additional step of having to expose the adhesive to UV light, as the adhesive can be exposed at the time the spacers 155 are loaded. Moreover, the adhesive can be cured in place, while the spacers 155 are secured firmly in place by the gang holder 150, leading to more consistent and precise placement of the spacers 155.

[0052] Although particular embodiments of a transfer structure have been described, it can be appreciated that other types of transfer structures can be used with other elements of the spacer loading system for receiving, holding, and moving a plurality of spacers at a time.

Operation

[0053] In operation, in one embodiment of a method for loading spacers 155 onto a plate 135, the transfer unit 145 moves the gang holder 150 to the spacer feeding module. This is done by moving the gang holder 150 to the appropriate position as well as lowering it to the appropriate height. Once the escapement unit 115 has been filled and the spacer feeding module is ready to feed a group of spacers 155 to the gang holder 150, the spacer transfer module collects the spacers. This may be facilitated by turning on the vacuum unit 160 of the spacer transfer module. To allow the spacers 155 to transfer to the gang holder 150, the spacer feeding unit may turn off its vacuum unit 120.

[0054] In one embodiment, the vacuum unit 160 of the gang holder 150 senses the vacuum pressure through the holes 152 for each spacer 155 that has been picked up. hi this way, the gang holder 150 can determine whether spacers 155 have been picked up for each position. Transfer of all of the spacers 155 from the escapement unit 115 of the spacer feeding module to the gang holder 150 may be unsuccessful for various reasons, such as if one or more of the spacers 155 are defective. For example, if a defective spacer 155 (e.g., a short one) is in a nest 117 of the escapement unit 115, that spacer 155 may not be picked up by the gang holder 150, as the vacuum unit 160 will not be able to apply sufficient suction to it. If this occurs, the gang holder 150 maybe programmed to drop all of the spacers 155 by turning off the vacuum unit 160. In one embodiment, the spacers 155 are dropped into a recycling system so they can be reused.

[0055] In one embodiment, after the gang holder 150 is loaded with spacers 155, the transfer unit aligns the bottoms of the spacers 155 by placing them, temporarily, upon a plate or other flat surface, which may be located near the escapement unit 115. This step may be used to ensure that there is an equal distance from the bottom of each spacer 155 to the bottom of the gang holder 150. In this way, the gang holder 150 can maintain equal and consistent height of the spacers 155 with respect to each other on the gang holder 150, useful for the subsequent steps in the manufacture process described herein. This may also be a convenient way to calibrate the location of the spacers 155 on the gang holder 150. [0056] In one embodiment, following the alignment of the bottoms of the spacers 155 on the gang holder 150, the transfer unit 145 moves to a sensing location affixed to the plate positioning module. This location may be outfitted with a laser sensor, a camera system, or some other detection system to confirm the existence of a spacer 155 in each desired location on the gang holder 150. For example, the transfer unit 150 may pass the bottom of each spacer 155 held by the gang holder 150 by a laser sensor that verifies the correct number of

spacers is found by the sensor. If a failure occurs (i.e., if the sensor recognizes that one or more spacers 155 are missing from the gang holder 150), the transfer unit 145 may be programmed to move the spacers 155 to a dumping position to be reclaimed or recycled. The transfer unit 145 then moves back to the spacer feeding module to reattempt a loading of spacers 155 onto the gang holder 150, as described above.

[0057] Once the gang holder 150 is correctly loaded with spacers 155, the transfer unit 145 moves it to the adhesive application module 125, where an adhesive is applied onto the tips of the spacers 155. hi one embodiment, this adhesive is a UV light adhesive, which can be cured through the application of UV light. Dipping of the spacers 155 is accomplished by way of vertical (z-axis) travel of the gang holder 150 to place the spacers against or near the surface of the roller 127 of the adhesive application module 125. This movement is preferably done with a high degree of precision and accuracy and in a manner so as to control the amount of adhesive acquired by the spacers to assure a high degree of uniformity, hi one embodiment, the roller 127 stops momentary while it is in contact with the spacers 155, but the roller 127 rolls again before a subsequent application with spacers 155 so that it again takes up a uniform layer of adhesive.

[0058] When sufficient adhesive is applied to the spacers 155 on the gang holder 150, the spacers 155 can be loaded onto the plate 135. Before this happens, the stage 130 of the plate positioning module moves the plate 135 to a location appropriate for placement of the spacers 155. As described above, this is accomplished by way of the vision system 140, which determines the position of the plate 135. To determine the location of the plate 135, the vision system 140 may use electrodes, reference markings, alignment keys, or various features on the plate 135. The transfer unit 145 then moves the gang holder 150 to the placement location, and the vision system 140 determines the position of the gang holder 150. Based on the relative position of the plate 135 and the gang holder 150, the stage 130 is again used to adjust the plate 135. At this point, the spacers 155 are directly above their desired locations on the plate 135. The gang holder 150 then lowers the spacers 155 onto the plate 135. [0059] hi one embodiment, in which a UV light adhesive is applied to the spacers 155, the UV light source 165 is turned on to cure the UV adhesive. Preferably, the adhesive is cured while the gang holder 150 is still maintaining the position of the spacers 155 on the plate 135. Once the UV adhesive is cured, the transfer unit 145 moves the gang holder 150 up and away from the plate 135, and the process may be repeated again with another group of spacers 155 loaded on to the gang holder 150.

[0060] Alternatively, the steps above involving application and curing of an adhesive may be slapped, and the spacers can be secured by some other means, including mechanical, depending on the ultimate design of the device being manufactured. Summary

[0061] In at least some of the embodiments of the spacer loading system, the processing steps of spacer loading, positioning, and adhering are all performed in one location and by a single system or tool. This increases the speed in which the overall process is performed, and it leads to increased accuracy and precision of the resulting placement. These benefits are seen in the resulting manufactured device, which is expected to be cheaper to make and have superior performance.

[0062] In one embodiment, the spacer loading system is designed to be performed in at least a class 1OK clean room environment. The lack of human involvement or participation required by embodiments of the system allow for less particulate contamination. Typically, multiple stand-alone units or systems are necessary to perform the functions that are embodied by this single tool, and the additional transferring of plates/devices adds further exposure to contaminants and opportunities for failures on the basis of mishandling. These problems are addressed by embodiments of the system.

[0063] The foregoing description of the embodiments of the invention has been presented for the purpose of illustration; it is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above teachings. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.