Patent Publication Number: US-2016240449-A1

Title: Method for Electrophoretically Depositing a Film on an Electronic Assembly

Description:
TECHNICAL FIELD 
     This application is a divisional of U.S. patent application Ser. No. 13/620,202, filed on Sep. 14, 2012, which application is hereby incorporated herein by reference. 
     BACKGROUND 
     The necessity to provide smaller, thinner, lighter, cheaper electronic systems with reduced power consumption, more diverse functionality and improved reliability has driven a stream of technological innovations in all technical fields involved. This is certainly also true for the areas of assembly and packaging which provide protective enclosure against mechanical and thermal outside influences, as well as chemical or irradiation-induced attacks. 
     SUMMARY OF THE INVENTION 
     In accordance with an embodiment a packaged component comprises a component carrier comprising a component carrier contact and a component disposed on the component carrier, the component comprising a component contact. The packaged component further comprises a conductive connection element connecting the component carrier contact with the component contact, an insulating film disposed directly at least on one of a top surface of the component or the conductive connection element, and an encapsulant encapsulating the component carrier, the component and the enclosed conductive connection elements. 
     In accordance with an embodiment a method for manufacturing a system comprises electrophoretic depositing an insulating film on a component carrier, attaching a component to the component carrier by placing an adhesive layer of the component to the insulating film of the carrier and encapsulating the component and the component carrier. 
     In accordance with an embodiment a method for manufacturing a system comprises placing a component on a component carrier, connecting a component contact of the component to a component carrier contact of the component carrier and electrophoretic depositing an encapsulation material thereby encapsulating the component and the component carrier. 
     In accordance with an embodiment a method for manufacturing a system comprises placing a component on a component carrier and connecting a conductive connection element to a component contact of the component and to a component carrier contact of the component carrier. The method further comprises electrophoretic depositing an insulating film at least on one of a top surface of the component and the conductive connection element, and encapsulating the component. 
     In accordance with an embodiment a method for manufacturing a system comprises placing a component on a leadframe, connecting a metal clip to a component contact of the component and to a lead of the leadframe, isolating metal surfaces on the component, the metal clip and the leadframe by electrophoretic depositing a polymer on the metal surfaces and encapsulating the component, the metal clip and the leadframe. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  illustrates an electrophoretic deposition (EPD) process tool; 
         FIG. 2  illustrates in cross-sectional view of an embodiment of a packaged component; 
         FIG. 3  illustrates an embodiment of a method for manufacturing a packaged component; 
         FIG. 4  illustrates an embodiment of a method for manufacturing a packaged component; 
         FIG. 5  illustrates an embodiment of a step in the method for manufacturing a packaged component according to  FIG. 4 ; 
         FIG. 6  illustrates in cross-sectional view of an embodiment of a system; and 
         FIG. 7  illustrates an embodiment of a method for manufacturing the system. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     The making and using of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention. 
     The present invention will be described with respect to preferred embodiments in a specific context, namely electrophoretic deposition (EPD) of a polymer on a system (e.g., component/component carrier) or portions thereof. Embodiments of the invention may also be applied, however, to other electrochemical deposition processes such as the electrochemical deposition of material layers. For example, embodiments of the invention may also be applied to electroplating processes. 
       FIG. 1  shows an example of an electrophoretic deposition (EPD) process tool  100  which is used to deposit an insulating layer on a workpiece. The EPD process tool  100  comprises a reactor chamber  110  (e.g., a bath) which is filled with a liquid medium  120 . A first electrode (e.g., cathode)  140  is positioned in the center of the reactor chamber  110  where the EPD occurs. Two second electrodes (e.g., anodes)  130  are located in equal distances from the first electrode  140  in peripheral regions of the reactor chamber  110 . A direct current (DC) power supply  150  is in conductive contact to the first electrode  140  and the second electrodes  130 . The DC power provides the electric field to initiate and maintain the movement of positively charged particles  125  moving towards the first electrode  140 . The charged particles  125  are polymer molecules comprising amino groups which may have been protonated due to the presence of a low concentration of weak acid in the EPD process tool  100 . In order to avoid sedimentation and to ensure uniform polymer deposition the liquid medium  120  is continuously stirred and a constant temperature is maintained by a temperature stabilizing system (not shown). 
     A workpiece is disposed on the first electrode  140  or clamped between clamps forming the first electrode  140 . Under the influence of the electric field the polymer molecules  125  deposit on the first electrode  140  and form a perfectly uniform polymer layer. The charged polymer molecules  125  subsequently discharge to form a coherent uncharged polymer layer or polymer coating (insulating layer/coating). The polymer coating exhibits high thickness uniformity even when deposited on complex structures with difficult-to-reach surface portions. The polymer may be selectively coated to specific areas of the workpiece or over the entire workpiece. 
     The initially high deposition rate of charged polymer molecules  125  may eventually slow down due to the increased insulation of the deposited insulating polymer coating. Thus, the EPD processes may be self-limiting to a certain extent. 
       FIG. 2  illustrates a cross-sectional view of an embodiment of packaged component  200  comprising an encapsulation based on electrophoretic deposition (EPD). The packaged component  200  comprises a component  250  and a component carrier  210 . 
     The component  250  comprises a first main surface or top surface  255  and a second main surface or bottom surface  256 . The top surface  255  may be the front side of the component  250  and the bottom surface  256  may be the back side of the component  250 . In one embodiment, the first main surface  255  is the surface where the active areas are predominately disposed and the second main surface  256  is the surface which is active area free or which is predominately active area free. 
     The component  250  comprises a substrate. The substrate may be a semiconductor substrate such as silicon or germanium, or a compound substrate such as SiGe, GaAs, InP, GaN or SiC, or alternatively, other materials. The substrate may be doped or undoped and may comprise one or more wells. The substrate may comprise a thickness of about ≦20 μm or about ≦50 μm. The semiconductor substrate may be a single crystal silicon or a silicon-on insulator (SOI). One or more interconnect metallization layers may be arranged on the substrate. A passivation layer is disposed on the interconnect metallization layers to electrically isolate and structure component contact pads of the component  250 . 
     The component  250  may be a chip or die. The component  250  may comprise a discrete device such as a single semiconductor device or an integrated circuit (IC). For example, the component  250  may comprise a semiconductor device such as a MOSFET or a power semiconductor device such as a bipolar transistor, an insulated gate bipolar transistor (IGBT), a power MOSFET, a thyristor or a diode. Alternatively, the component  250  may be a resistor, a protective device, a capacitor, a sensor or a detector, for example. The component may be a system on chip (SoC). In one embodiment the component  250  comprises a discrete device such as a transistor, wherein the top surface  255  comprises a source and the bottom surface  256  comprises a drain. Alternatively, the top surface  255  comprises a drain and the bottom surface  256  comprises a source. Yet in a further embodiment, the top surface  255  comprises a source, drain and electrode. 
     The component carrier  210  may be a workpiece, a substrate, a leadframe, or a printed circuit board (PCB). In one embodiment the component carrier  210  is a leadframe comprising a metal such as copper (Cu) or a copper alloy, nickel (Ni) or nickel alloy, silver (Ag) or silver alloys, or a combination thereof. 
     The component  250  is attached to the component carrier  210  at the component placement area. For example, the bottom surface  256  of the component is attached to the top surface of the component carrier  210 . In one embodiment the component  250  is bonded to the component carrier  210  via a solder layer, a eutectic bonding layer or an epoxy bonding layer. Alternatively, the component  250  is bonded or glued to the component carrier by an adhesive tape or a conductive tape. In one embodiment the connection between the component  250  and the component carrier  250  is an electrical contact. Alternatively, the connection is an insulating barrier layer. 
     The packaged component  200  further comprises conductive connection elements  261 ,  262  such as conductive clips or wire bonds. For example, component contacts or component contact pads  251 ,  252  disposed on a top surface  255  of the component  250  are bonded to component carrier contacts or component carrier contact pads  211 ,  212  on the component carrier  210 . Conductive clips  261 , 262  may connect the component contact pads  251 ,  252  with the component carrier contact pads  211 ,  212 . The conductive clips  261 ,  262  may be attached to the sidewalls of the component  250 . Alternatively, the conductive clips  261 ,  262  may be spaced from the sidewalls of the component  250  with a small distance. The conductive clips may comprise a metal such as aluminum (Al), copper (Cu), silver (Ag) or gold (Au). Alternatively, the conductive clips may be wires. 
     The packaged device  200  further comprises an encapsulation  205 . The encapsulation  205  is formed by an electrophoretic deposition (EPD). The encapsulation encapsulates the component  250 , the conductive connection elements  261 ,  262  and the component carrier  210 . Portions  213 ,  214  of the component carrier  210  may not be encapsulated. 
     The encapsulation material  205  of the packaged device  200  may comprise a polymer. For example, the polymer may comprise acrylic resins, polyurethane resins, epoxies, epoxies with an anime type hardener or polar high performance thermoplastics. Alternatively, the encapsulation material  205  of the packaged device  200  may comprise a monomer. Suitable monomers may comprise at least one functional group such as an amine-structure, an acid-structure, a carbonyl-structure, a sulfonate-structure, an isocyanate-structure or a hydroxyl-structure. 
     In one embodiment the component  250  may be a thin component  250  or an ultra-thin component  250 . For example, the component  250  may comprise a thickness of less than about 20 μm or a thickness between about 20 μm and about 50 μm. The corresponding encapsulation  205  may comprise a thickness of below about 20 μm or alternatively a layer thickness of about 20 μm to about 50 μm. For components  250  with a larger thickness, the encapsulation comprises a thickness of up to about 500 μm. 
       FIG. 3  shows an embodiment of a method to manufacture a packaged component  300 . In a first step  302 , a component is placed on and attached to a component carrier. The component and the component carrier may be the same as described with respect to  FIG. 2 . 
     The component is attached to the component carrier at the component placement area. For example, the bottom surface of the component is attached to the component carrier. In one embodiment a metal layer disposed on the bottom surface of the component is bonded to the top surface of the component carrier using soldering, eutectic bonding or epoxy bonding. Alternatively, the bottom surface of the component is bonded or glued to the top surface of the component carrier using an adhesive tape, a solder paste or a solder tape. 
     In step  304 , the component carrier contact pads are connected to the component contact pads. Conductive connection elements connect the component carrier contact pads with the component contact pads. For example, conductive clips are used to connect the component contact pads to the component carrier contact pads. The conductive clips may be attached to the sidewalls of the component. In one embodiment the conductive clips are galvanically deposited on the sidewalls. Alternatively, the conductive clips may be clip bonded to the pads. Alternatively, the conductive clips do not attach the sidewalls of the component but provide a small space between the component and the clip along the sidewalls. In one embodiment the conductive connection elements are wire bonds which are wire bonded, ball bonded, or otherwise bonded to the pads. 
     In step  306 , the component, the conductive connection elements and the component carrier are encapsulated using cationic electrophoretic deposition (EPD). For example, a polymer coating encapsulates the component, the component carrier and the conductive connection elements. The polymer coating may comprise an acrylic resin, a polyurethane resin, an epoxy, an epoxy with an anime type hardener or polar high performance thermoplastics. For example, a monomer coating encapsulates the component, the component carrier and the conductive connection elements. Suitable monomers may comprise at least one functional group such as an amine-structure, an acid-structure, a carbonyl-structure, a sulfonate-structure, an isocyanate-structure or a hydroxyl-structure. 
       FIG. 4  shows an embodiment of a method to manufacture a packaged component  400 . In a first step  402 , a component carrier is coated with an electrophoretic deposited film. The component carrier may be placed into an EPD bath as described with respect to  FIG. 1 . An insulating film may be formed on the component carrier. The insulating film may be a thin film or an ultra-thin film. The insulating film may be about 5 μm to about 10 μm thick. Alternatively, the insulating film may be about 10 μm to about 20 μm thick. In one embodiment the insulating film may be less than 50 μm thick. 
     The component carrier may be a conductive substrate, a leadframe or a printed circuit board with conductive traces on its surface or surfaces. In one embodiment the component carrier is a leadframe comprising a metal such as copper (Cu) or a copper alloy, nickel (Ni) or nickel alloy, silver (Ag) or silver alloys, or a combination thereof. The insulating film may be a polymer film. For example, the polymer film may comprise an acrylic resin, a polyurethane resin, an epoxy, an epoxy with an anime type hardener or polar high performance thermoplastics. Alternatively, the insulating film may be a monomer film. Suitable monomers may comprise at least one functional group like an amine-structure, an acid-structure, a carbonyl-structure, a sulfonate-structure, an isocyanate-structure or a hydroxyl-structure. 
     In step  404  a component is attached to the coated component carrier.  FIG. 5  shows this step for a leadframe  510 . The component  550  is attached to the EPD coated leadframe  510 / 505 . The component may be the same as described with respect to  FIG. 2 . The component  550  comprise an insulation layer  560  on it bottom surface. 
     The EPD film  505  disposed on the leadframe  510  provides an insulating/protective film. Moreover, the EPD film  505  together with the insulation layer  560  provides an excellent mechanical connection. The insulation layer  560  may be adhesive layer. For example, the adhesive layer  560  may comprise epoxy resins, polyimide resins or cyano ester compounds. The adhesive bonding between the component  550  and the leadframe  510  may be obtained via thermo-compression bonding. Bonding parameters may be: Temperature 100-250° C.; bonding force 1-50 N; bonding time 100-1000 ms. 
     In one embodiment, the adhesive layer  560  and the EPD film  505  may form an interleaved interface. Such an interface forms a strong bond between the component  250  and the component carrier  210 . In one embodiment a “polymer-to-polymer” interface may provide a strong interface when the adhesive layer  560  and the EPD film  505  comprise complementary materials. Numerous strong chemical bonds are formed during the attachment process. For example, the EPD based material and the adhesive material may comprise the same time of base resin. Moreover, complementary materials may be isocyanate groups vs. amino or hydroxyl ligands, epoxy vs. amino or carboxylate groups, or ester groups vs. amino ligands. 
     In step  406  portions of the EPD coating are removed. In one embodiment, the component carrier, e.g., a leadframe, is not coated at the end of the leads  513 ,  514 . The leads  513 ,  514  are configured to be electrically connected to a conductive terminal and therefore are EPD coating free. The coating  505  is removed from these portions by masking the component carrier  510  and removing the coating  505  portion at the end of the leads  513 ,  514 . Alternatively, the coating  505  is not deposited at the end of leads  513 ,  514 . For example, the component carrier  510  is masked before it is EPD coated. The masking material may be a material which is easily removable, e.g., with a water solution. Moreover, the EPD coating is not deposited at or is removed from areas where the conductive connection elements are connected to the leads. 
     In step  408 , the component carrier contact pads are connected to the component contact pads. Conductive connection elements are connected to the component carrier contact pads and to the component contact pads. For example, conductive clips are connected to the component contact pads with one end and to the component carrier contact pads with the other end. The conductive clips may be attached to the sidewalls of the component. The conductive clips may be clip bonded. Alternatively, the conductive clips do not attach the sidewalls of the component but provide a small space between the component and the clip along the sidewalls. The wire bonds are wire bonded, ball bonded, or otherwise bonded to the pads. The conductive connection elements may be connected to an ESD coating free component carrier contact pad. Alternatively, the conductive connection elements may be connected through the ESD coating of the component carrier contact pads. 
     In step  410 , the component, the conductive connection elements and the component carrier are encapsulated with an encapsulation material. For example, the component, the component carrier and the conductive connection elements are encapsulated with a molding compound. The molding compound may comprise a thermoset material or a thermoplastic material. The molding compound may comprise a coarse grained material. In one embodiment the molding compound may be applied to encapsulate the component and at least portions of the component carrier. Alternatively, the encapsulation material may be a laminate material such as a prepreg material. 
       FIG. 6  illustrates a cross-sectional view of an embodiment of system  600  comprising an EPD coating film. The system  600  comprises a component  650  and a component carrier  610 . 
     The component  650  comprises a first main surface or top surface  655  and a second main surface or bottom surface  656 . The top surface  655  may be the front side of the component  650  and the bottom surface may be the back side of the component  650 . In one embodiment, the first main surface  655  is the surface where the active areas are predominately disposed and the second main surface  656  is the surface which is active area free or which is predominately active area free. 
     The component  650  comprises a substrate. The substrate may be a semiconductor substrate such as silicon or germanium, or a compound substrate such as SiGe, GaAs, InP, GaN or SiC, or alternatively, other materials. The substrate may be doped or undoped and may comprise one or more wells. The semiconductor substrate may be a single crystal silicon or a silicon-on insulator (SOI). One or more interconnect metallization layers may be arranged on the substrate. A passivation layer is disposed on the interconnect metallization layers to electrically isolate and structure component contact pads of the component  650 . 
     The component  650  may be a chip or die. The component  650  may comprise a discrete device such as a single semiconductor device or an integrated circuit (IC). For example, the component  650  may comprise a semiconductor device such as a MOSFET or a power semiconductor device such as a bipolar transistor, an insulated gate bipolar transistor (IGBT), a power MOSFET, a thyristor or a diode. Alternatively, the component  650  may be a resistor, a protective device, a capacitor, a sensor or a detector, for example. The component may be a system on chip (SoC). In one embodiment the component  650  comprises a discrete device such as a transistor, wherein the top surface  655  comprises a source and the bottom surface  656  comprises a drain. Alternatively, the top surface  655  comprises a drain and the bottom surface  656  comprises a source. Yet in a further embodiment, the top surface  655  comprises a source, drain and electrode. 
     The component carrier  610  may be a workpiece, a substrate, a leadframe, or a printed circuit board (PCB). In one embodiment the component carrier is a leadframe comprising a metal such as copper (Cu) or a copper alloy, nickel (Ni) or nickel alloy, silver (Ag) or silver alloys, or a combination thereof. 
     The bottom surface  656  of the component is attached to the component carrier  610 . In one embodiment the metal layer is bonded to the top surface of the component carrier using a soldering, eutectic bonding or an epoxy bonding. Alternatively, the second main surface  656  of the component is bonded or glued to the top surface of the carrier using an adhesive tape, a solder paste or a solder. In one embodiment the connection between the component and the component carrier is an electrical connection. Alternatively, the connection is an insulating barrier. 
     The system  600  further comprises connection elements  661 ,  662  such as conductive clips or wire bonds. For example, component contacts or component contact pads  651 ,  652  disposed on the top surface  655  of the component  650  are bonded to component carrier contacts or component carrier contact pads  611 ,  612  of the component carrier  610 . The component contacts  651 ,  652  of the component are wire bonded, ball bonded, clip bonded or otherwise bonded to the contacts of the component carrier. The wires or conductive clips  661 ,  662  comprise a metal such as aluminum (Al), copper (Cu), silver (Ag) or gold (Au). 
     The system  600  further comprises an EPD coating  605 . The EPD coating  605  is disposed on all conductive or all metallic surfaces of the system  600 . For example, the EPD coating  605  may cover the connection elements  661 ,  662 , the top surface  655 , the component carrier surfaces (e.g., lead frame) such as the component carrier contacts (e.g., leads). In one embodiment the EPD coating  605  may cover only selected portions of the metallic surfaces. 
     System  600  may comprise a polymer coating  605  on component contact pads  651 ,  652 , the component carrier contact pads  611 ,  612 , and the conductive connection elements  661 ,  662  between the component contact pads and the component carrier contact pads. Other electrically conductive surfaces of the component  650  may also covered with the polymer film  605 . In one embodiment surface portions of the leads  613 / 614  are not covered with the polymer film  605 . 
     The EPD film  605  may be an electrically insulating film and may comprise a layer thickness of below about 20 μm. Alternatively, the EPD film  605  may comprise a layer thickness of about 20 μm to about 50 μm. The insulating film  605  may provide protection of conductive portions of the packaged device  200 . The insulating film  205  may protect against corrosion for example. 
       FIG. 7  shows an embodiment of a method to manufacture a packaged component  700 . In a first step  702 , a component is placed on and attached to a component carrier. The component and the component carrier may be the same as described with respect to  FIG. 6 . 
     The bottom surface of the component is attached to the component carrier. In one embodiment a metal layer disposed on the bottom surface of the component is bonded to the top surface of the component carrier using soldering, eutectic bonding or epoxy bonding. Alternatively, the bottom surface of the component is bonded or glued to the top surface of the component carrier using an adhesive tape, a solder paste or a solder tape. 
     In step  704 , component carrier contact pads are connected to the component contact pads. Conductive connection elements connect the component carrier contact pads with the component contact pads. For example, the conductive connection elements are conductive clips or bond wires. The conductive connection elements may be wire bonded, ball bonded, clip bonded or otherwise bonded. 
     In step  706 , the conductive surfaces of the component, the component carrier and the conductive connection elements are coated with an insulating material using cationic electrophoretic deposition (EPD). For example, the system may be disposed in an electrophoretic deposition (EPD) tool as described with respect to  FIG. 1 . The system may be coated with a thin film or an ultra-thin film. The thin film or ultra-thin film may comprise material similar to previous embodiments. The insulating film may be about 5 μm to about 10 μm thick. Alternatively, the insulating film may be less than 20 μm thick. 
     In one embodiment the EPD film may coat the leadframe, the conductive connection elements and the top surface of the component. For example, the leadframe is coated at the component attach area except where the component is attached to the leadframe. The leadframe is further coated with the EPD film on the leads except where the leads are connected to the conductive connection elements and except where the leads are configured to be bonded to a further carrier or substrate. The component is EPD coated over the entire top surface except where the conductive connection elements are connected to the component contacts. In one embodiment the component is only EPD coated at the small component contact pad but not over the entire to surface of the component. 
     In one embodiment only the top surface of the component is EPD coated. Alternatively, only the conductive connection elements are coated. Moreover, any metallic surfaces of the system (component, component carrier and conductive connection elements) can be chosen to be EPD coated. For example the top surface of the component and the conductive connection elements are EPD coated while the component carrier is not (e.g., because the component is a non-conductive substrate or the component carrier is masked). 
     In step  708 , the component, the component carrier and the conductive connection elements are encapsulated. For example, the component, the component carrier and the conductive connection elements are encapsulated with a molding compound. The molding compound may comprise a thermoset material or a thermoplastic material. The molding compound may comprise a coarse grained material. In one embodiment the molding compound may be applied to encapsulate the component and at least portions of the component carrier. Alternatively, the encapsulation material may be a laminate material such as a prepreg material. 
     An advantage of the EPD technique is fast polymer or monomer coating of semiconductor packages, systems or devices. In particular, the semiconductor packages, systems or devices can be processed in parallel and in large numbers. In comparison to other coating techniques heat does not need to be applied. Accordingly, thermo-mechanical stress during coating is reduced to a minimum. For example, warpages for leadframes during alternative coating processing could be prevented by the EPD technique. Another advantage is the ability of an equally coating of topographical surfaces including surfaces of small vias. 
     In some embodiment, curing temperatures or after deposition temperatures for EPD generated films may be at a substantially lower temperature than curing or after deposition temperatures of conventional encapsulation materials. For example, EPD film temperatures may be between 50° C. and 100° C. while conventional encapsulations material temperatures may be over 150° C. Lower deposition temperature may result in lower thermal stress between the disposed material and the workpiece. Furthermore, thermal stress may be significantly alleviated by the incorporation of polycyclic compounds in the base resins of the EPD polymers. Such resin modifications may lower the CTEs of EPD-generated film materials by a factor of two or more. 
     In some embodiments, the shift towards a lower CTE may be achieved by incorporating polycyclic aromatic moieties (naphthalene, anthracene, phenanthrene, perylene, pyrene, etc.) in the base resin. A polyimide type resin comprising a polycyclic compound exhibits a CTE of 20.0 ppm/K which is very close to the CTE values of wire bond materials, for example. 
     In some embodiments, the EPD process provides more material choices for encapsulants than traditional molding processes. For example, the base resin chemistry for an EPD process provides a wide variety of polymer options to choose from. Contrary to molding processes the polymer materials are not limited to materials having a deposition temperature of above 150° C. Moreover, the EPD materials may have a lower viscosity at the operation temperature than traditional materials because the EPD materials are deposited employing a liquid medium. Due to the relaxation of the selection criteria base resin choices for EPD coating may include not only commonly used polymer types like epoxy or polyacrylate resins but also high performance thermoplastic materials like polycarbonates, polyamides, polyamides-imides, polysulfones, or fluorinated conjugated polymers. 
     In some embodiments, the use of high performance polymers promises advantages regarding heat resistance, dimensional stability, chemical resistance and creep resistance. Since EPD-applicable resins must be able to carry charges in the suspension medium, the base resin materials may be modified to incorporate functionalities/ligands which are either inherently ionic or become ionic after suspension of the polymer particles in the EPD bath. 
     The nature of the charge-providing ligands is different for cationic and anionic EPD applications. For example, polymers for cationic EPD may comprise quarternary ammonium groups or amino groups which convert into ammonium ligands after being protonated in the presence of a low concentration of acid (e.g. formic, acetic, proprionic, butyric, nitric or hydrochloric acid) in the suspension liquid. 
     Alternatively positive charging of polymer entities may also derive from phosphonium or sulfonium ligands. In the case of anionic EPD the polymers may comprise carboxylate or sulfonate groups, or acidic OH functionalities (e.g. phenolic groups). Epoxy, polyacrylate or polybutadiene compounds may be employed as base resins in film materials which can be used for either cationic or anionic EPD. Maleic resins, on the other hand, are typically only used for anionic EPD, while polyurethanes are preferentially employed in film materials designed for cationic EPD applications. 
     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. 
     Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.