PATENT DOCUMENT

Publication Number: US-8568184-B2
Application Number: US-60892809-A
Country: US
Kind Code: B2

Title: Display modules

Abstract:
An electronic device may have a display. The display may have active components such as display pixels formed on a display substrate layer. The display substrate layer may be formed from a glass substrate layer. Thin-film transistors and other components for the display pixels may be formed on the glass substrate. An encapsulation glass layer may be bonded to the glass substrate using a ring-shaped bond structure. The ring-shaped bond structure may extend around the periphery of the encapsulation glass layer and the substrate glass layer. The bond structure may be formed from a glass frit, a solid glass ring, integral raised glass portions of the glass layers, meltable metal alloys, or other bond materials. Chemical and physical processing operations may be used to temper the glass layers, to perform annealing operations, to preheat the glass layers, and to promote adhesion.

Claims:
What is claimed is: 
     
       1. A method for forming a display module, comprising:
 forming an integral ring-shaped raised ridge around a peripheral portion in a first layer of glass on which electrical components are formed; 
 bonding a second layer of glass to the integral raised ridge in the first layer of glass to encapsulate the electrical components, comprising:
 applying localized heat from a first heat source to the integral raised ridge in the first layer of glass; and 
 applying global heat from a second heat source to all of the first layer of glass. 
 
 
     
     
       2. A method for forming a display module, comprising:
 forming an integral ring-shaped raised ridge using soda lime around a peripheral portion in a first layer of glass on which electrical components are formed; and 
 bonding a second layer of glass to the integral raised ridge in the first layer of glass to encapsulate the electrical components. 
 
     
     
       3. The method defined in  claim 1 , further comprising forming an integral ring-shaped raised ridge around a peripheral portion in the second layer of glass that mates with the integral ring-shaped raised ridge in the first layer of glass. 
     
     
       4. The method defined in  claim 1  further comprising tempering the first layer of glass. 
     
     
       5. The method defined in  claim 1  further comprising annealing the first and second layers of glass. 
     
     
       6. The method defined in  claim 2 , further comprising:
 processing a glass frit formed of frit particles having edges to smooth the edges; and 
 depositing the glass frit around the periphery of the first layer of glass, and wherein bonding the second layer of glass to the integral raised ridge in the first layer of glass comprises:
 applying light to the glass frit; and 
 before applying the light to the glass frit, heating an area of the second layer of glass that does not contact the glass frit using a heating element that contacts the area of the second layer of glass. 
 
 
     
     
       7. The method in  claim 2 , further comprising bonding a solid ring-shaped gasket between the first and second layers of glass. 
     
     
       8. The method defined in  claim 2 , further comprising filtering the glass frit by frit diameter before depositing the glass frit. 
     
     
       9. The method of  claim 2  further comprising tempering the first layer of glass by coating the first layer of glass with a potassium-based paste and applying heat to the first layer of glass. 
     
     
       10. The method in  claim 2 , wherein heating the area of the second layer of glass that does not contact the frit further comprises heating the area of the second layer of glass with a heated chuck. 
     
     
       11. The method in  claim 2 , further comprising cooling the second layer of glass.

Description:
This application claims the benefit of provisional patent application No. 61/225,870, filed Jul. 15, 2009, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     This relates to electronic devices and, more particularly, to displays for electronic devices. 
     Electronic devices such as cellular telephones, handheld computers, and portable music players often include displays. A display generally contains an array of individually controllable pixels. Transistors such as thin-film transistor may be used in controlling the pixels. For example, in pixels that contain light-emitting diodes, the transistors may be used in controlling the light-emitting diodes and, in pixels that are based on liquid crystals, the transistors may be used in controlling the state of the liquid crystal material. Using arrangements such as these, pixels can be used to present visual information for a user. 
     Thin-film transistors and other materials for forming display pixels are typically formed on glass substrates. A glass substrate on which an array of thin-film transistors has been formed is sometimes referred to as a thin-film transistor (TFT) glass substrate or TFT glass. 
     An unsealed TFT glass substrate is vulnerable to damage from exposure to moisture and other environmental factors. As a result, a layer of encapsulation glass is used to encapsulate the components on the TFT glass. 
     With conventional arrangements, a peripheral seal between the TFT glass and encapsulation glass is formed using a glass frit (i.e., small particles that can be melted to form glass). The glass frit is placed around the perimeter of the TFT glass to surround the electrical structures on the TFT glass. The encapsulation glass is placed on top of the glass frit. Once the glass frit is sandwiched between the TFT glass and the encapsulation glass, a laser is used to melt the glass frit. The resulting encapsulated TFT glass forms a display module. 
     The melted frit forms a hermetic seal between the TFT glass and the encapsulation glass. The seal is suitable for preventing environmental intrusion into the sealed interior portion of the display module. However, conventional materials and processes for forming sealed display modules of this type may be unable to satisfactorily withstand damage when subjected to unintended impacts. It would therefore be desirable to be able to provide improved ways for forming display modules. 
     SUMMARY 
     Display modules and methods for forming display modules are provided. The display modules may include a thin-film transistor (TFT) glass substrate layer that includes thin-film transistors and other display components. These components may be sensitive to environmental exposure. A layer of encapsulation glass may be used to encapsulate the sensitive components. The TFT glass and encapsulation glass may be bonded using bond structures and bonding techniques that help minimize the likelihood of damage when an electronic device containing the display module is inadvertently dropped. 
     Bond structures may be used in forming a seal between the TFT glass and the encapsulation glass. Bond structures may be formed in a ring-shaped bond region that surrounds the periphery of the glass layers. Bond structures may be formed in a substantially rectangular ring shape. 
     Small glass pieces, known as frit, may be used to form bond structures. The frit may be polished or filtered to ensure that smooth polished frit of a certain size is used in the bond structures. Epoxy and other adhesives may also be used in the bond structures. Light-adsorbing materials may also be included in bond structures to facilitate laser melting during bond formation. 
     Display module damage such as damage from crack formation may arise from excessive stress in the glass layers when heat is applied to the periphery of the glass layers during bond formation. In order to reduce stress, a second heat source may be applied to the glass layers so that the glass layers are placed in an expanded state during bond formation. Tempering by heat or chemical treatment may also be used. 
     A solid gasket of bond material such as a ring-shaped gasket may be also used to form bond structures. The gasket may be formed from a ring of solid glass in addition to or instead of using loose frit material The gasket may have a substantially rectangular ring shape. 
     A raised ring-shaped surface may also be formed around the periphery of a glass layer using a material such as soda lime. The raised ring-shaped surface may be used in addition to or instead of using loose frit material. 
     Metal alloys may also be used to form bond structures. Adhesion promotion layers may be formed on the glass surfaces prior to the deposition of metal alloys. 
     Any of the bond structures may be annealed using a laser or other localized heat source. 
     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of an illustrative portable electronic device with a display in accordance with an embodiment of the present invention. 
         FIG. 2  is a perspective view of an illustrative display module in accordance with an embodiment of the present invention. 
         FIG. 3  is cross-sectional side view of an illustrative display module in accordance with an embodiment of the present invention. 
         FIG. 4  is a flow chart showing illustrative equipment for forming display modules in accordance with an embodiment of the present invention. 
         FIG. 5  is a diagram showing how frit particles may be polished in accordance with an embodiment of the present invention. 
         FIG. 6  is a diagram showing how a heat source may be used to heat a glass layer during bond formation in accordance with an embodiment of the present invention. 
         FIG. 7  is a diagram showing illustrative tempering of a glass layer in accordance with an embodiment of the present invention. 
         FIGS. 8A and 8B  are diagrams showing how a solid gasket of bond material may be used to form bond materials in accordance with an embodiment of the present invention. 
         FIGS. 9A-9G  are diagrams showing an illustrative approach for bonding glass layers using a raised surface arrangement in accordance with an embodiment of the present invention. 
         FIGS. 10A-10E  are diagrams showing how a metal alloy that may be used to bond glass layers in accordance with an embodiment of the present invention. 
         FIG. 11  is a diagram showing how a localized application of heat may be used for annealing in accordance with an embodiment of the present invention. 
         FIG. 12  is a diagram showing how bond structures may be formed from multiple adjacent materials or structures in accordance with an embodiment of the present invention. 
         FIG. 13  is a flow chart showing illustrative steps in forming a display module from glass layers in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices such as computers, handheld devices, computer monitors, televisions, cellular telephones, media players, and other equipment may have displays. An example is presented in  FIG. 1 . In the example of  FIG. 1 , device  10  is a portable device such as a portable media player, tablet computer, handheld electronic device, or cellular telephone. This is merely illustrative. Device  10  may, in general, be any suitable electronic device. The arrangement of  FIG. 1  is an example. 
     As shown in  FIG. 1 , portable electronic device  10  may have housing  12 . Housing  12 , which is sometimes referred to as a case, may be formed from one or more individual structures. For example, housing  12  may have a main structural support member that is formed from a solid block of machined aluminum or other suitable metal. One or more additional structures may be connected to the housing  12 . These structures may include, for example, internal frame members, external coverings such as sheets of metal, etc. Housing  12  and its associated components may, in general, be formed from any suitable materials such as plastic, ceramics, metal, glass, etc. Input-output ports such as an audio jack and data ports, user input interface components such as buttons and other input-output devices may be provided in housing  12 . 
     A display such as display  14  may be mounted within housing  12 . Display  14  may be, for example, a liquid crystal display (LCD), organic light emitting diode (OLED) display, or a plasma display (as examples). Touch sensor electrodes may be included in display  14  to provide display  14  with touch sensing capabilities (e.g., touch screen). Display  14  may contain a number of layers of material. These layers may include, for example, layers of optically transparent glass. Layers of plastic and optical adhesive may also be incorporated into display  14 . A liquid crystal display may have layers of polarizer, light diffusing elements, light guides for backlight structures, and a liquid crystal layer. An organic light-emitting diode (OLED) display may have organic materials that are used in producing light. 
     An array of circuit components such as a thin-film transistor (TFT) array may be used to drive the image pixels in a display. This array of circuitry is generally formed on a substrate material such as glass. The substrate glass layer on which the thin-film transistors and/or other circuitry for the display are formed is therefore sometimes referred to as the TFT glass substrate or TFT glass. 
     The thin-film transistors and other circuitry on the TFT glass may be protected from environmental exposure by sealing the display with a layer of glass (sometimes referred to herein as encapsulation glass). Conductive traces such as indium-tin oxide (ITO) traces may be used to form capacitive electrodes for a touch sensor portion of display  14 . The conductive traces may be formed on one or more sides of a glass layer in the display. 
     A display structure such as a TFT glass layer to which a layer of encapsulation glass has been attached forms a portion of display  14  and is therefore sometimes referred to herein as a display structure or display module. 
     As shown in  FIG. 1 , display  14  may be mounted in case  12  using a structure such as bezel  16 . Bezel  16  may be formed from a portion of case  12  or a separate structure. Display mounting arrangements without visible bezels may also be used. 
     The TFT glass layer and encapsulation layer may be bonded together at their edges. There is generally a width associated with this bond region. To enhance the aesthetics of device  10 , it may be desirable to ensure that the bond region width is not too large. This may help hide the bond region from view when display  14  is mounted in device  10  (e.g., behind bezel  16 ). 
     Although thin bond regions are desirable when bonding an encapsulation glass onto the surface of a TFT glass layer, bond regions that are too thin may make a display susceptible to damage. It is therefore desirable to provide display  14  with a durable and shock resistant bond. 
     An exploded perspective view of an illustrative display module is shown in  FIG. 2 . As shown in  FIG. 2 , display module  18  may include layer  22  (i.e., a TFT glass substrate layer) and layer  20  (i.e., an encapsulation glass layer). Bond structures  24  may be used in forming a seal between encapsulation glass  20  and TFT glass  22 . Bond structures  24  may be formed in a ring-shaped bond region that surrounds the periphery of layers  22  and  20  and thereby surrounds electrical components  26  such as thin-film transistors and other display pixel circuitry  26 . Bond structures  24  may have a substantially rectangular ring shape. Display module  18  may form all or part of display  14  of  FIG. 1 . 
     A cross-sectional side view of display module  18  is shown in  FIG. 3 . As shown in  FIG. 3 , bond structures  24  may be used to form a hermetic seal around the periphery of electrical components  26 . This prevents environmental intrusion into the interior of display module  18 . 
     Bond structures  24  may be formed by placing a separate material or materials between glass layer  20  and  22 . For example, bond structures  24  may include small pieces of glass. These glass pieces, which are sometimes referred to as glass frit or frit, may be exposed to heat so that they melt and form a glass seal for display module  18 . Typical materials for forming frit include oxides. The identities of the constituent oxides in the frit and the relative amount of each oxide may be chosen so that the frit has a desired coefficient of thermal expansion. For example, the makeup of the frit may be chosen so that the coefficient of thermal expansion of bond structures  24  matches the coefficients of thermal expansion of layers  20  and  22 . 
     If desired, bond structures  24  may include epoxy and other adhesives, metal alloys with relatively low melting points such as tin-based solder or lead-based solder, brass-based alloys for forming brazed joints (sometimes referred to as braze or braze alloys), bulk glass, raised portions of layers  20  and  22 , adhesion promotion layers, treated surfaces and other treated structures, etc. Layers  20  and  22  may be formed from borosilicate glass, aluminosilicate glass, or other suitable glasses. 
     Illustrative equipment for forming display module  18  of  FIGS. 2 and 3  is shown in  FIG. 4 . As shown in  FIG. 4 , semiconductor and glass fabrication tools  28  may be used to form glass layers such as glass layers  20  and  22 . Tools  28  may also be used to form electrical components such as thin-film transistors on TFT layer  22 . 
     Tools  30  may be used in attaching encapsulation glass  20  to TFT glass  22 . Tools  30  may include tools for depositing layers of material on glass layers such as physical layer deposition tools. Tools  30  may also include photolithography tools or other tools for patterning deposited materials. 
     Physical layer deposition tools in tools  30  may include sputtering tools, evaporation tools, and tools for depositing materials by spray-on techniques, spin-on techniques, and screen printing (as examples). These tools may be used to apply metals, metal alloys, dielectrics, polymers, glasses, semiconductors (e.g., conductive semiconductors such as ITO), other suitable materials, or combinations of these materials. Materials such as frit may be dispensed from a nozzle or may be applied to a glass layer using screen printing. To facilitate application by screen printing techniques, binders and liquid may be incorporated into the frit to ensure that the frit has the consistency of paste. 
     Tools  30  may include tools for applying other bond structure materials such as solder, braze, and other meltable metal alloys, tools for applying adhesive to the glass layers, tools for modifying the surface properties of the glass layers (e.g., by chemical treatment using a liquid or application of a chemical paste, by abrasion, ion bombardment, etc.), etc. 
     Bonds may be formed using self-curing materials such as epoxy that cures at room temperature. To ensure a high-quality bond that satisfactorily prevents environmental intrusion, epoxy bonds may be supplemented or replaced with bonds formed from glass and/or metal. These bonds may be formed by applying heat and/or pressure. For example, frit or other glass-based bond material may be melted by application of high pressure. Generally, heat or a combination of heat and pressure is used. Following bond formation, additional treatments may be applied. For example, after a glass frit has been melted to seal encapsulation glass  20  to TFT glass  22 , an annealing operation may be performed on the melted frit layer. 
     Pressure may be applied by using mechanically positioned metal tooling (e.g., forms or other templates in which glass layers may be pressed together, particularly around their edges). Localized heat may be applied using a lamp (e.g., an infrared lamp), a laser (e.g., an infrared laser), a flame source, induction heating, a heated metal chuck or other metal structure (e.g., a heated press), or other suitable heat source. These localized heat sources may be mounted on an x-y translation stage (or display module  18  may be mounted on a stage) to allow the rate of translation and the position of the heat source relative to the structures of display module  18  to be controlled. By controlling the rate of translation and the power of the laser or other localized heat source, the rate of heating, the overall heating amount, and the rate of cooling after heating may be controlled. In addition to or as an alternative to local heating arrangements, heat may be applied globally to the glass layers and bonding structures. Heat may be applied globally using a furnace, a lamp, a heated chuck, etc. 
     Illustrative techniques that may be used in improving the quality of the bond formed by bond structures  24  and which may therefore help reduce the likelihood that display module  18  will become cracked or otherwise damaged when subjected to an inadvertent mechanical or thermal shock are described in connection with  FIG. 5-13 . Tools such as tools  30  of  FIG. 4  may be used in forming bonds of the type described in connection with  FIGS. 5-13 . 
     One potential source of weakness in bond structures  24  when bond structures  24  are formed from melted frit is the nature of the frit particles. Conventional frit may, for example, have numerous sharp edges and a wide range of particle sizes, as shown in the upper left corner of  FIG. 5 . The irregular shapes and sizes of conventional frit may give rise to potential stress points when bond structures  24  are formed. For example, conventional frit may include a non-negligible number of large particles. These large particles may bear against a particular portion of a glass layer and may therefore produce localized stress. This localized stress in the glass may serve as an initiation point for subsequent crack formation. 
     One way that the likelihood of localized stress formation may be reduced involves the use of smooth frit particles. As shown in  FIG. 5 , unprocessed frit  32  may be converted into processed frit  32  and  42 . Unprocessed frit  32  may have jagged edges and a wide range of particle sizes. Frit  32  may be ground into smaller and more rounded particles such as particles  32  and  42  (e.g., using a grinding machine or other suitable polishing tool). A filtering tool may be used to sort the processed frit by size. For example, the filtering tool may be used to perform a binning operation in which frit is segregated into different groups (bins) based on frit diameter. A frit of a desired size may then be selected to use in forming bond structures  24 . Using this type of approach, the filtering tool may be used to produce processed frit with a relatively narrow range of frit diameters or processed frit with a relatively wide range of frit diameters. 
     As shown in the upper right portion of  FIG. 5 , processed frit  32  may, for example, be formed from smooth (rounded) frit particles having a relatively narrow particle size distribution (shown by narrow particle diameter distribution curve  36  in particle diameter distribution graph  34 ). As shown in the example of the lower right portion of  FIG. 5 , processed frit  42  may have rounded particles of a variety of diameters including large diameter particles such as large particle  44  and small diameter particles such as small particle  46 . The relatively wide range of frit particle diameters in processed frit  42  is evidenced by the relatively wide particle size distribution curve  40  of particle diameter distribution graph  38 . 
     Because processed frit particles such as particles  32  and  42  are rounder and therefore smoother than unprocessed frit particles  32 , processed frit  32  and  42  may be less likely than unprocessed frit to produce localized stress in a frit bond. The uniform size of frit  32  may also help to reduce stress by removing larger particles that could press against a glass layer. Processed frit with a relatively wide range of particle sizes may be advantageous in reducing stresses that might arise from voids between particles. This is because the smaller particles in frit  42  may fill interstitial gaps between the larger particles in frit  42 . If desired, other materials (e.g., melting metal alloys, non-oxide dielectric fillers, etc.) may be used to help fill voids and reduce stress formation. 
     Frit such a processed frit  32  and  42  and the other materials used to form bonding structures  24  may include light-absorbing materials. These light-absorbing materials may facilitate laser melting during bond formation. 
     Display module damage such as damage from crack formation may arise from excessive stress (i.e., tensile stress) in the glass layers  20  and  22  in the vicinity of bond structures  24 . This may be addressed by heating one or more of the glass layers during bond formation. For example, a heat source such as heater  30 A of  FIG. 6  may be used to heat encapsulation glass  20  before light  48  is applied to the frit of bond structures  24  from laser  30 B. This type of arrangement may be used to heat encapsulation glass  20  to a temperature that is significantly above room temperature (e.g., above 50° C., 100° C., 200° C., 400° C., or higher), but that is sufficiently low to avoid damage to components in display module  18  such as thin-film transistors and other circuitry  26  on TFT glass  22 . By preheating encapsulation glass  20  (and/or TFT glass  22 ) in this way, the heated glass is placed in an expanded state during bond formation. Following bond formation, the heated glass layer (e.g., encapsulation layer  20 ) is cooled. Because the encapsulation glass contracts as its cools, the encapsulation glass and the glass formed by melting the frit contract at substantially the same time. Because both the encapsulation glass and frit shrink together, situations in which the frit contracts more than the encapsulation glass and thereby generates undesired tensile stress in encapsulation glass can be avoided. 
     In some cases, instead of heating the entire surface, the glass layer may be selectively heated at a portion of the surface as, for example, around the perimeter in the region of the seal. Additionally or alternatively, the side edge of the glass layer may be heated. 
     It should be appreciated that the temperature may be controlled through the process. For example, the temperature may be adjusted at different times during the process to help control thermal issues. 
     If desired, all or part of the glass layers in display module  18  may be tempered. During tempering, the surface of the glass layer is placed in compressive stress. This may help prevent crack formation during subsequent impact events. 
     Tempering may be performed by localized heating (e.g., using a laser) or by chemical treatment. With one illustrative chemical treatment arrangement, a glass layer is coated with a potassium-based paste and is subjected to elevated temperatures. During this chemical tempering process, relatively small sodium ions in the glass are replaced with relatively large potassium ions from the potassium material. This places the surface of the glass that contains the potassium into a compressive stress condition and thereby chemically tempers the glass. 
     This type of approach is shown in  FIG. 7 . Initially, glass layer  50  is untreated, as shown in the upper portion of  FIG. 7 . Glass layer  50  in  FIG. 7  represents glass encapsulation glass  20  and/or TFT glass  22 . As shown in the middle portion of  FIG. 7 , untreated glass  50  may be coated with tempering material  52  (e.g., a potassium paste). Material  52  may, for example, be placed in a ring shape around the periphery of glass  50 . After heat treatment at an elevated temperature, the potassium or other chemical tempering material may diffuse into the surface of glass  50 , to form tempered region  54 . Because tempered region  54  is under compressive stress, tempered region  54  is less likely to suffer damage when glass  50  is subjected to unexpected shocks. Localized chemical tempering in the vicinity of bond structures  24  may be used in conjunction with other bond formation processes (e.g., frit processing, encapsulation layer pre-heating, etc.) before and/or during these other bond formation processes. For example, potassium-based material may be incorporated into a frit paste so that tempering occurs during the frit melting process. Although only one side is shown, it should be appreciated that both pieces of glass can be selectively or totally tempered depending on the needs of the assembly. 
     As shown in  FIGS. 8A and 8B , a solid gasket of bond material such as ring-shaped gasket  24  may be used to form bond structures  24 . Gasket  24  may be formed from a hoop (ring) of solid glass (in addition to or instead of using loose frit material). Gasket  24  may have a substantially rectangular ring shape. The glass in the ring structure may, for example, be formed from the same type of material as glass  20  and/or glass  22 . As shown in  FIG. 8A , glass ring  24  may be configured to form a seal around the periphery of glass layers  20  and  22 . Following application of pressure and/or heat using tools  30 , the glass of ring  24  fuses with the glass of layers  20  and  22  and forms a bond (shown as bond  24  in the cross-sectional view of  FIG. 8B ). The glass ring may be tempered using chemicals and/or heat. 
     If desired, glass layers such as layers  20  and/or  22  may be provided with raised ring-shaped surfaces. The raised ring-shaped surface may be used to help form bonding structure  24 . An illustrative approach for bonding glass layers  20  and  22  using a raised glass surface arrangement is shown in  FIGS. 9A-9G . 
     An untreated glass layer  50  (i.e., TFT glass  22  and/or encapsulation glass  20 ) is shown in  FIG. 9A . As shown in  FIG. 9B , glass layer  50  may be coated around its periphery with a layer of glass forming material  56  such as soda lime. Following heat treatment, the material  56  forms raised glass portion  58  on layer  50 , as shown in  FIG. 9C . 
       FIG. 9D  shows how layer  50  and its raised portion  58  may be placed on top of a mating layer  50 ′. If layer  50  is a TFT layer, layer  50 ′ may be an encapsulation layer. If layer  50  is an encapsulation layer, layer  50 ′ may be a TFT layer. 
     By application of heat and/or pressure, raised portion  58  forms a diffusion bond with layer  50 ′ (i.e., layers  50  and  50 ′ fuse together to form bond structure  24  of  FIG. 9E ). 
     In the arrangement shown in  FIGS. 9F and 9G , both upper layer  50  and mating lower layer  50 ′ have raised portions formed from glass forming materials. During the bond formation process illustrated in  FIG. 9F , regions  58  and  58 ′ are subjected to pressure and/or heat. This forms a diffusion bond between layers  50  and  50 ′ (shown as bonding structure  24  in  FIG. 9G ). 
     In another embodiment (not shown), a frit material and/or a solid glass ring may be disposed between one or both raised areas to help facilitate formation of a proper seal. 
     As shown in  FIGS. 10A-10E , TFT glass  22  and encapsulation glass  20  may be bonded using a melted metal alloy such as metal alloy  64 . Metal alloy  64  may be a lead-based solder, a tin-based solder or other non-lead-based solder, a brass-based melting metal alloy, or other suitable meltable metal alloy. 
     As shown in  FIG. 10A , layers  20  and  22  are initially not bonded. To ensure satisfactory adhesion between metal alloy  64  and the glass of layers  20  and  22 , an adhesion promotion surface may be created. 
     In the example of  FIG. 10B , an adhesion promoting surface has been created by depositing adhesion promotion layers  60  on the surfaces of glass layers  20  and  22  in the vicinity of the bond region. Adhesion promotion layers  60  may be formed from a material that bonds well to glass and that provide a high-adhesion platform for subsequent deposition of metal alloy  64 . As an example, adhesion promotion layers  60  may be formed from indium-tin oxide (ITO) traces or adhesion promoting metal traces. Metal alloy  64  may then be placed between layers  60  and melted to form bond structures  24  ( FIG. 10C ). 
     In the example of  FIG. 10D , adhesion promotion surfaces  62  have been created by treating surface regions  62  of glass layers  20  and  22  with chemicals and/or physical treatments such as ion bombardment, etc. This allows metal alloy  64  to adhere properly between layers  60  following melting to form bond structures  24  ( FIG. 10E ). 
     Any of the bond structures that are formed may be annealed using a laser or other localized heat source or using a more global heat source. During annealing operations, stress that might lead to cracks may be released from the glass layers and bond structures. Global annealing operations may be performed using a furnace, an induction heater, a heated chuck or other fixture, a lamp or laser, etc. Local annealing operations may be performed using a laser, a lamp, induction heating equipment, a heated fixture (e.g., a fixture that applies heat to the perimeter of the display module by clamping the display module between respective heated metal parts), etc. 
     Localized application of pressure and/or heat during the formation of bond structures  24  may help prevent damage to sensitive components such as thin-film transistors. As shown in  FIG. 11 , heat for annealing and/or bond formation may be applied locally (i.e., in the vicinity of bond structure  24 ) using laser  30 B. Laser  30 B may be translated in direction  66 . Light beam  48  may be an infrared laser light beam and may be focused onto bond structures  24  as shown in  FIG. 11 . Glass layers  20  and  22  may be transparent to infrared light, which allows most of the power from laser  30 B to be absorbed in the frit or other material that is used in forming bond structures  24  (e.g., a solid glass gasket). The material of bond structures  24  may include light-absorbing components to facilitate infrared laser light absorption. 
       FIG. 12  shows how bond structures  24  may be formed from multiple adjacent materials or structures. For example, bond structures  24  may be formed by a frit or metal alloy bond material  24 A. Adjacent structure  24 B may be composed of a different material (e.g., a different metal, a different dielectric, an adhesive, a polymer, etc.). 
     Illustrative steps involved in forming display module  18  from glass layers  20  and  22  are shown in  FIG. 13 . 
     At step  67 , components for display module  18  may be fabricated. These components may include TFT glass  22  and encapsulation glass  20 . Thin-film transistors and other circuitry  26  may be formed on TFT glass  22 . Organic layers may be formed in circuitry  26  for use in OLED display modules  18 . If frit is to be used in forming bond structures  24 , the frit may be processed as described in connection with  FIG. 5 . 
     At step  68 , the components that were formed during the operations of step  67  may be pre-processed. Examples of preprocessing operations that may be performed include adhesion promotion operations such as operations to form ITO traces or adhesion promotion surfaces, operations to preheat encapsulation glass  20  (and/or glass  22 ), and operations to selectively increase the thickness of glass layer  20  and/or  22  in the vicinity of the bond region as described in connection with  FIGS. 9A-9G . 
     After performing desired pre-processing operations in step  68 , encapsulation glass  20  may be bonded to TFT substrate glass  22 . Bond formation operations may involve localized heating (e.g., by directing laser light or other light onto the bond region or otherwise using a localized heat source to heat up the bond). Bond formation operations may also involve the application of pressure. For example, the periphery of glass layers  20  and  22  may be pressed together using a metal press. Combinations of heat and pressure may also be used. 
     The material that is used in forming bond structures  24  may be glass frit, a ring-shaped glass gasket, raised glass regions that form an integral portion of glass layers  20  and  22 , a meltable metal alloy, other suitable bond materials, or any suitable combination of these bond structure materials. The heating rate and the cooling rate of the bond may be controlled. For example, the cooling rate may be slowed sufficiently to allow for simultaneous bond formation and annealing. 
     Annealing and other post-processing operations may also be performed during one or more separate operations. These optional operations are illustrated as post-processing operations  72 . Annealing may be used to relieve built-up stress (e.g., built-up tensile stress in glass layers  20  and  22 ) that might otherwise make module  18  susceptible to damage. 
     The foregoing is merely illustrative of the principles of this invention and various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention.

Metadata:
Filing Date: 20091029
Publication Date: 20131029
Grant Date: 20131029
Priority Date: 20090715
Inventors: PREST CHRISTOPHER D.
ZADESKY STEPHEN P.
PAKULA DAVID A.
Assignee: APPLE INC
CPC Classifications: [{"code": "H10K71/851", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K50/8423", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K50/84", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10K50/8426", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/8722", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10K59/126", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10K59/8721", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/8721", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/8722", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 42352518