Abstract:
The invention relates to a method for vacuum deposition of circuitry onto a thermoplastic material. In one of its aspects, the invention relates to a vacuum deposition of circuitry for automotive applications. In another of its aspects, the invention relates to a vehicular lamp housing incorporating a circuit placed thereon by vacuum deposition. In another of its aspects, the invention relates to a vehicular lamp housing with vacuum deposition of circuitry powering light-emitting diodes. In another of its aspects, the invention relates to a vehicular lamp housing with a vacuum deposition of circuitry powering removable incandescent lamps.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to a method for vacuum deposition of circuitry onto a thermoplastic material. In one of its aspects, the invention relates to vacuum deposition of circuitry for automotive applications. In another of its aspects, the invention relates to a vehicular lamp housing incorporating a circuit placed thereon by vacuum deposition. In another of its aspects, the invention relates to a vehicular lamp housing with vacuum deposition of circuitry powering light-emitting diodes. In another of its aspects, the invention relates to a vehicular lamp housing with a vacuum deposition of circuitry powering removable incandescent lamps.  
           [0003]    2. Description of the Related Art  
           [0004]    It is known to create circuit boards using vacuum deposition on a microscopic scale. In this method, microscopic vacuum deposition is accomplished by use of a focused electron beam to create circuitry tracks on the circuit board. Each track is developed on the circuit board to a thickness of only a few angstroms to provide a circuit capable of carrying the very small currents required by the circuit board.  
           [0005]    A larger-scale vacuum deposition process is known in creating reflectorized surfaces such as for the interior of a lamp housing to provide a reflective backdrop for an incandescent lamp for projecting light through a lens covering the lamp housing for observation by other motorists. Such large-scale vacuum deposition is accomplished in a vacuum deposition chamber. Lamp housings to be deposited with the reflective coating are physically masked and passed in front of a chromium target subjected to a high voltage, which causes chromium particles to leave the target and embed in the plastic material of the lamp housing. This process creates a coating of chromium on the plastic housing 200 to 400 angstroms thick on unmasked portions of the lamp housing. The reflectorized lamp housing is then provided with a covering translucent lens and electrical circuits and bulbs as is known in the prior art. Such prior art lamp housings come in many forms.  
           [0006]    Referring to one example of a prior art lamp housing assembly shown in FIG. 1, a housing  10  has an inner surface  12 , usually coated with a reflective material, and a number of apertures  14  for insertion of lamps  16  from a rear portion of housing  10 . The front portion of housing  10  is covered by a translucent lens  18 , lens  18  commonly having regions of different colors based on the function of the lamp  16  projecting light through that portion of the lens  18 . The individual lamps  16  are provided power through a wire harness  17  connected to each of the lamps  16 .  
           [0007]    [0007]FIGS. 2 and 3 show further prior art embodiments wherein bulbs  16  are each carried by a removable socket  22 , and insertion of the socket  22  into the apertures of the housing electrically connects the bulbs  16 , in the case of FIG. 2, to a flexible printed circuit  24 , or in the case of FIG. 3, to a stamped metal harness  26 , the printed circuit  24  or stamped metal harness  26  themselves being electrically connected to the automobile&#39;s electrical system to complete a current-carrying circuit. Each of the prior art embodiments of FIGS. 2 and 3 further requires additional interface pieces  28 ,  30 ,  32  for attaching and mating the bulbs to the housing  10 .  
           [0008]    Referring now to FIG. 4, a further embodiment of a prior art lamp housing  40  is adapted to receive a number of light-emitting diodes (LED)  42  held in a snap LED holder  44  constructed with offsets  46  for matching the contour of the housing  40 . The front of the housing  40  is covered by a lens  48 .  
           [0009]    Yet another prior art embodiment is shown in FIG. 5 wherein a housing  50  carries a printed circuit board  52  with a number of LEDs  54  mounted thereon, a reflector  56  covering the printed circuit board  52  with LEDs  54  projecting therethrough, and a lens  58  mounted to the front of the housing  50  to seal the housing  50 , holding the printed circuit board  52  and reflector  56  therein.  
           [0010]    Each of these prior art lamp housings has inherent disadvantages. The wire harness type lamp housing (FIG. 1) has a high piece price, mechanical size constraints, and is labor intensive to build and install. The flex circuit (FIG. 2) can be costly, and sealing the flex circuit to the housing, as well as the mechanical integrity of the electrical connector to the housing are limiting factors. Servicing, capital equipment costs and installation costs of the assembly are further disadvantages. The metal circuit stamping housing (FIG. 3) has the disadvantages of high tooling costs, handling costs, sealing and installation costs. The flat LED metal frame (FIG. 4) has a high piece price, planar design limitations, limited suppliers, and is limited to LED designs. The LED printed circuit board assembly (FIG. 5) has a high piece price, is limited to a planar design, has high installation costs, and, again, is only for use with LEDs.  
           [0011]    It would be advantageous to provide a lamp housing to overcome the disadvantages of the prior art, in that it would be adaptable to use with LEDs as well as conventional incandescent or other available lamp technologies, is adapted for providing different colors of light, specifically white light, and is efficient in both space requirements and installation costs.  
         SUMMARY OF THE INVENTION  
         [0012]    The invention relates to a method for vacuum deposition of circuitry onto a thermoplastic material. In one of its aspects, the invention relates to vacuum deposition of circuitry for automotive applications. In another of its aspects, the invention relates to a vehicular lamp housing incorporating a circuit placed thereon by vacuum deposition. In another of its aspects, the invention relates to a vehicular lamp housing with vacuum deposition of circuitry powering light-emitting diodes. In another of its aspects, the invention relates to a vehicular lamp housing with a vacuum deposition of circuitry powering removable incandescent lamps.  
           [0013]    In one specific application of the method of vacuum depositing circuitry according to the invention, the invention can be applied to an automotive lamp housing wherein the lamps are electrically connected to the vehicle electrical system by an electrical circuit embedded on the surface of the lamp housing by direct metallization of the circuitry onto the lamp housing, such as by vacuum deposition. In one of its aspects, the invention contemplates metallization of the circuitry to the interior of the housing for direct connection of a plurality of light-emitting diodes for buttressing light from the lamp housing. In another of its aspects, the housing includes openings for removably receiving incandescent or other conventional lamps electrically connected to the electrical circuit embedded in the housing. In another of its aspects, the electrical circuit embedded in the housing is electrically connected to the automotive electrical system at a single location. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    In the drawings:  
         [0015]    [0015]FIG. 1 is a prior art lamp assembly comprising a housing, a lens, and various light sources provided with a wire harness interconnecting the various light sources to an electrical system of a vehicle;  
         [0016]    [0016]FIG. 2 is a prior art lamp assembly comprising a housing, a lens, and various light sources provided with a flex circuit interconnecting the various light sources to an electrical system of a vehicle;  
         [0017]    [0017]FIG. 3 is a prior art lamp assembly comprising a housing, a lens, and various light sources provided with a metal circuit stamping interconnecting the various light sources to an electrical system of a vehicle;  
         [0018]    [0018]FIG. 4 is a prior art lamp assembly comprising a housing, a lens, and various light sources provided with snap LEDs metal-framed assemblies interconnecting the various light sources to an electrical system of a vehicle;  
         [0019]    [0019]FIG. 5 is a prior art lamp assembly comprising a housing, a lens, and various light sources provided with LED printed circuit board assemblies interconnecting the various light sources to an electrical system of a vehicle;  
         [0020]    [0020]FIG. 6 is an exploded perspective view of a direct metallization of circuitry onto a plastic automotive lamp housing according to the invention;  
         [0021]    [0021]FIG. 6A is an enlarged view of an LED being placed against the circuitry of FIG. 6;  
         [0022]    [0022]FIG. 7 is a further embodiment of direct metallization of circuitry onto a plastic automotive lamp housing according to the invention;  
         [0023]    [0023]FIG. 8 is a rear perspective view of a lamp housing having a complicated topography prior to application of a circuit directly thereto;  
         [0024]    [0024]FIG. 9 depicts application of a mask to the lamp housing of FIG. 8 according to the invention;  
         [0025]    [0025]FIG. 10 depicts metallization of the lamp housing of FIGS.  8 - 9  with mask applied;  
         [0026]    [0026]FIG. 11 depicts the lamp housing of FIGS.  8 - 10  with the circuitry applied and mask removed;  
         [0027]    [0027]FIG. 12 is a front perspective view of the lamp housing of FIG. 6, having a complicated topography prior to application of a circuit directly thereto;  
         [0028]    [0028]FIG. 13 depicts application of a mask to the lamp housing of FIG. 12 according to the invention;  
         [0029]    [0029]FIG. 14 depicts metallization of the lamp housing of FIGS.  12 - 13  with mask applied; and  
         [0030]    [0030]FIG. 15 depicts the lamp housing of FIGS.  12 - 14  with the circuitry applied and mask removed. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0031]    The inventive process described herein starts with a plastic substrate. One such example is an injection-molded plastic housing, the plastic housing provided with convenient track areas to deposit the circuitry, wherein the housing is further modified to eliminate sharp comers to allow for complete, continuous, uniform deposition of the circuit trace over the topography of the housing . The housing is placed in a mask. The mask covers most of the housing, leaving only the exposed areas that will be embedded or coated with a copper or other metallic deposit during the vacuum deposition process. The masked part is then placed in a vacuum deposition chamber. The chamber is activated, a vacuum is drawn in the chamber, and the deposition process begins. A “target” in the chamber is subjected to an electrical charge, forcing a release of metallic particles into the vacuum. The metallic particles bombard the exposed areas of the plastic substrate and are embedded into the plastic surface. The metallic particles build a layer of metallic material on the plastic part until the desired trace thickness is reached. It was found that the metallic material, such as copper, deposited on the plastic part reaches the desirable conductivity when the thickness of the trace reaches 1 to 4 microns (or 1,000 to 4,000 angstroms). This increased thickness of the vacuum deposition increases the conductivity of the deposited circuit tracks so that the deposited circuit track can handle the current requirement for the intended application. The part can then be removed from the vacuum chamber and further processed for its end use.  
         [0032]    An example of an embodiment of the invention is shown in FIG. 6 in a lamp assembly  100  with direct metallization of lamp circuitry (a “spray circuit”  120 ) onto a lamp housing  110 . The assembly  100  further comprises a plurality of light-emitting diodes (LEDs)  130  and a lens  140 .  
         [0033]    The lamp housing  110  has an outer, or back, surface  112  and an inner surface  114 . The housing  110  is divided into a number of compartments  116 , wherein the inner surface  114  of each compartment  116  is generally concave in nature.  
         [0034]    Spray circuit  120  is applied to inner surface  114  of housing  110  by one of various known methods of vacuum deposition, as such as sputter, cathodic arc, and E-beam technologies. Other variations or modifications of these methodologies, as are known in the art, will function for the purpose of depositing the spray circuit  120  on the housing  110 , but the method chosen must accomplish the result while optimizing the overall manufacturing process, particularly with regard to cycle times involved in the chain of manufacture, such as the molding time necessary for the housing  110 . The spray circuit  120  is applied to the inner surface  114  of housing  110 , placing the spray circuit  120  within the compartments  116  of the housing  110 . LEDs  130  are then placed into the circuit  120  within the compartments  116  of the housing  110  using a conventional pick-and-place robot system. The LEDs  130  are placed directly to the surface contour of the inner surface  114  of the housing  110  (see FIG. 6A). The LEDs  130  are then soldered in place using known methods such as convection reflow, infrared reflow, silver epoxy, or standard wave solder for planar through-hole designs. In a preferred process, the LEDs  130  are held in place prior to soldering by using an adhesive dispensing capability of the pick-and-place robot system. The spray circuit  120  is electrically connected to the vehicle&#39;s electrical system through the back surface  112  of housing  110  by a single conventional wire connector (not shown).  
         [0035]    After placement of the LEDs  130  into the spray circuit  120  on the inner surface  114  of housing  110 , lens  140  is then sealed to lamp housing  110 , enclosing compartments  116  and preventing the infiltration of dirt or moisture into the compartments  116  of housing  110 .  
         [0036]    The assembly  100  thus presents a unitary, sealed assembly for installation in a vehicle using simple mechanical connectors for physical attachment to the vehicle, and a single space- and labor-efficient electrical connector to the vehicle&#39;s electrical system.  
         [0037]    A further embodiment of a lamp assembly  200  according to the invention is disclosed in FIG. 7. Assembly  200  comprises a housing  210 , a spray circuit  220 , a spray seal  225 , and a plurality of bulbs  230  and sockets  235 .  
         [0038]    Housing  210  comprises a back surface  212  and an inner surface (not shown) having a reflective coating thereon, divided into compartments, and sealed by a lens (not shown). Housing  210  further comprises a number of keyed openings  214  opening into the compartments of the housing  210 . The housing is prepared for deposition of the spray circuit  220  onto the back surface  212  of the housing  210  in the same manner as described in the first embodiment of the invention, namely, a mask is applied to the back surface  212  of the housing  210  and the housing is placed in a vacuum deposition chamber wherein metallic particles are embedded in the exposed back surface  212  of the housing  210  where the mask does not cover the housing  210 .  
         [0039]    Spray circuit  220  is configured to provide a pair of terminals  222 ,  224  at each keyed opening  214  of the housing  210 , whereby each of the terminals  222 ,  224  will connect with bulb  230  to complete a circuit for providing electrical energy to the bulb  230 . After deposition of the spray circuit  220  on the back surface  212  of housing  210 , a spray seal  225 , using conventional printed circuit board coating methods, is applied to the back surface  212  for electrically insulating and protecting the spray circuit  220 . It is also anticipated to apply a protective coating to the circuit as a further step of the vacuum metallization process, while the lamp housing  210  is still in the vacuum metallization chamber. The terminals  222 ,  224  will necessarily be exposed to enable electrical connection of the bulbs  230  therewith. Spray circuit  220  further includes a single terminus  226  for electrically connecting the spray circuit to the vehicle electrical system through the use of a single conventional electrical connector and wiring (not shown).  
         [0040]    The lamp assembly  200  now presents a unitary assembly for installation in a vehicle and connection to the vehicle electrical system through a single connector and wire via the terminus  226 . Prior to or after installation of the lamp assembly  200  in a vehicle, lamps  230  and sockets  235  can be adjoined to housing  210 . Sockets  235  are configured to removably carry lamps  230 , holding lamps  230  physically and providing an electrical connection between lamps  230  and spray circuit  220 , as is commonly known in the art. Sockets  235  are further configured to engage keyed openings  214  of housing  210 , whereby upon insertion of socket  235  in opening  214  and rotation of socket  235 , socket  235  is mechanically engaged within opening  214  for retaining bulb  230  within housing  210 . Simultaneously, upon rotating socket  235  in keyed opening  214 , an electrical connection is made between socket  235  and terminals  222 ,  224 , as is well known in the art. Bulb  230  is also therefore electrically connected to terminal  222 ,  224  completing the electrical circuit including bulb  230 .  
         [0041]    Assembly  200  therefore provides the advantage of being a single unit that can be installed in a vehicle using common mechanical fasteners and can be electrically connected to a vehicle electrical system by a single common electrical connector and wiring, making for simplified, labor-saving installation. Replacement of bulbs  230  as they bum out is accomplished by removing the damaged lamp  230  from housing  210  by rotating socket  235  within keyed opening  214 , removing socket  235  and lamp  230  from housing  210 , removing and replacing lamp  230 , then reinstalling in housing  210 .  
         [0042]    FIGS.  8 - 11  depict steps of the method incorporated in the invention, the further embodiment of a lamp assembly  300 , including a lamp housing  310  forming by injection-molding processes known in the art.  
         [0043]    As shown in FIG. 8, the lamp housing  310  includes a back surface  312 , a number of keyed openings  314  passing through the housing  310 , and a terminus  326  for the spray circuit to be applied for electrical connection to the vehicle&#39;s electrical system.  
         [0044]    Referring to FIG. 9, a mask  340  is secured to the back surface  312  of the lamp housing  310 . Mask  340  includes a precise pattern of openings  342  coordinated with the back surface  312  of the lamp housing and, more particularly, the keyed openings  314  and the terminus  326  of the lamp housing  310 . When the mask  340  is applied to the back surface  312  of the lamp housing  310 , the mask  340  covers the entirety of back surface  312  except for those portions of back surface  312  that are exposed through openings  342 .  
         [0045]    Referring now to FIG. 10, the lamp housing  312  with applied mask  340  is then placed in a vacuum metallization chamber. A vacuum is applied to the chamber and a metallizing or sputtering target  350  is energized causing metallic particles  352  to be expelled from the surface of the target  350 . As the metallic particles  352  strike the masked lamp housing  310 , they are deposited on the exposed portions of the lamp housing  310  through the openings  342  of the mask  340 . This metallization process is carried out until a sufficient layer of the metallic particles  352  is deposited on the lamp housing  310  to form an electrical circuit having the capacity for the expected current load.  
         [0046]    Upon removal from the vacuum metallization chamber, referring to FIG. 11, the mask  340  is removed, exposing the back surface  312  of the lamp housing  310 . The metallic particles  352  of the vacuum metallization process can be seen in FIG. 11 to form circuit traces  320  on the back surface  312  of the lamp housing  310 , the circuit traces  320  connecting each of the keyed openings  314  of the lamp housing  310  with the terminus  326  for electrical connection to the vehicle&#39;s electrical system. Subsequent to the application of the circuit traces  320  on the lamp housing  310 , a spray seal, as discussed in the previous embodiment, is applied to the lamp housing  310  to protect the circuit traces  320 .  
         [0047]    With reference to the process of FIGS.  8 - 11 , FIGS.  12 - 15  presents a like process for the embodiment of FIG. 6, wherein FIG. 12 depicts the lamp housing  110  prior to the application of a spray circuit. In FIG. 13, a mask  440  is applied to housing  110 . Mask  440  includes a number of openings  442 . In FIG. 14, the housing  110  with applied mask  440  is placed in a vacuum deposition chamber wherein a target  450  is charged, and causing metallic particles  452  to be ejected and deposited on the exposed portions of housing  110  through openings  442 . FIG. 15 shows the housing  110  with embedded circuit traces  120  on a front face thereof.  
         [0048]    The direct metallization of circuitry on a plastic substrate, according to the invention, provides the advantage of more economical construction, assembly and installation, and, with respect to one example application in the area of vehicular lamp housings, further provide a more compact installation due to the elimination of need for external assemblies mounted to a housing that would increase the space needed for the housing in the vehicle. These circuits and assemblies are instead molded directly into the housing, conforming to the contour of the housing, minimizing space requirements, and eliminating the need for additional assemblies to the housing. The material for the housing must necessarily be chosen such that its temperature characteristics are compatible with the temperature characteristics of the electrical components mounted to it. Such compatibility will avoid any melting of the plastic housing due to electrical component heat dissipation. The spray circuits  120 ,  220 ,  320  must also necessarily be configured to handle the current requirements of the electrical components.  
         [0049]    Ideally, the cycle time of the vacuum deposition chamber will be compatible with the cycle time of other equipment in the fabrication chain, such as the molding machine, thereby adding no additional cycle time to the assembly cost. It is anticipated that a single operator can unload the molding machine, such as an injection press, and load the vacuum chamber with the masked housing. It is also anticipated that the vacuum chamber will simultaneously place the reflective coating and the spray circuitry on the housing.  
         [0050]    While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation, and the scope of the appended claims should be construed as broadly as the prior art will permit.