Abstract:
A method of producing a non-planar conforming circuit on a non-planar surface includes creating a first set of conforming layers. The first set of conforming layers is created by applying an oxide dielectric layer to the surface, applying a conductive material layer to the oxide dielectric layer, applying a resist layer to the conductive material layer, patterning the resist layer according to a desired circuit layout, etching the surface to remove exposed conductive material, and stripping the resist layer. The process may be repeated to form multiple layers of conforming circuits with electrical connections between layers formed by blind microvias. The resulting set of conforming layers can be sealed.

Description:
FIELD 
       [0001]    The present application relates to creating circuits on non-planar surfaces. 
       BACKGROUND INFORMATION 
       [0002]    Wiring boards or printed circuit boards often use rigid planar substrates. Some techniques can be used to create ribbon cables, flexible cables typically used for connecting one printed circuit board to another. 
         [0003]    Embodiments allow a circuit to be constructed on any suitable surface, such as a non-planar substrate. An example of such a surface may be a computer case or housing. Incorporating a circuit in such a way can reduce circuit space and weight. 
       SUMMARY 
       [0004]    In one embodiment a method of producing a non-planar conforming circuit on a non-planar anodized surface includes creating a first set of conforming layers. The first set of conforming layers is created by applying an oxide dielectric layer to the surface, applying a conductive material layer to the oxide dielectric layer, applying a resist layer to the conductive material layer, patterning the resist layer according to a desired circuit layout, etching the surface to remove exposed conductive material, and stripping the resist layer. Next the resulting set of conforming layers can be sealed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a flow diagram of the overall process of fabricating a contour conforming non-planar circuit in accordance with one embodiment. 
           [0006]      FIG. 2  is a flow diagram that details the creation of a circuit layer in accordance with one embodiment. 
           [0007]      FIG. 3  is an illustration that depicts a top down view of a portion of a non-planar 3D circuit in accordance with one embodiment. 
           [0008]      FIG. 4  is an illustration that depicts a longitudinal cross-sectional view of a portion of a non-planar 3D circuit in accordance with one embodiment. 
           [0009]      FIG. 5  is an illustration that depicts a cross-sectional view of a portion of a non-planar 3D circuit in accordance with one embodiment. 
           [0010]      FIG. 6  is an illustration that depicts a cross-sectional view of a portion of a non-planar circuit in accordance with some embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    In one embodiment, an anodized non-planar structure can have a circuit fabricated directly on its surface. A mask can be applied to the surface to isolate the circuit area. A first circuit layer can be applied to the exposed area of the surface. The first circuit layer can be created by applying an oxide dielectric layer for planarizing and electrical isolation from the surface substrate. Onto this dielectric layer, conductive material can be deposited. A resist layer can then be added to the dielectric layer. The resist layer can be patterned using, for example, a laser lithographic technique to expose a negative of the desired circuit, leaving behind resist material matching the circuit pattern. Etching solution can be used appropriate to the conductive material to remove the exposed conductive material. The remaining resist layer can next be removed to expose the resulting circuit. If only one layer is desired, then the circuit can be sealed, using for example a parylene layer. 
         [0012]    If additional circuit layers are desired, the next layer can be started by applying an additional oxide dielectric layer for electrical isolation. After applying the next dielectric layer for the next circuit layer, vias or holes can be drilled or etched in the oxide dielectric layer for connecting electrical traces on the two layers as the next conductive layer is applied or for the purpose of bringing an electrical access point from the first layer up to a higher layer. Several circuit layers can be built up in such a manner. The final circuit layer can be sealed for protection and electrical isolation from the remaining environment. 
         [0013]    Each material layer of the circuit layer—the dielectric layer, the conductive material layer, and the resist layer—conforms to the contours of the non-planar surface so that each layer is also non-planar in the same way. For example, if the surface is curved, each layer also curves to match the radial bend of the surface and each subsequent layer. 
         [0014]    Other approaches to build a conforming non-planar circuit could result in a much thicker circuit with a much wider pitch between circuit layers. Other approaches may use a dielectric layer that results in a rough topology which requires applying a much thicker conductive layer. A thinner circuit can be desirable because it allows more layers with less heat resistance and less internal thermal expansion. The method described in the present application achieves a thin circuit thickness and requires little processing. 
         [0015]      FIG. 1  is a flow diagram of the overall process of fabricating a conforming non-planar 3D circuit in accordance with some embodiments. At  110 , the non-planar surface is prepared. The surface can be machined and anodized. For example, an aluminum surface can be anodized to form an anodization layer of about 2.0 mils. The surface can be masked to limit the creation of the new circuit to a targeted area of the surface. At  120 . the first circuit layer is applied. This will be described in further detail below in conjunction with the discussion of  FIG. 2 . At  130 . it is determined whether any additional circuit layers are going to be applied. If so, the flow loops back to  120  where another circuit layer is applied. If not, at  140 , the circuit is sealed. The circuit can be sealed using a parylene conformal coaling layer, such as Parylene-C applied at about 0.25 mils thick. Other coating layers can be used, including Parylene-HT or an epoxy coating. To perform the coating and sealing, a tape mask can be applied suitable for parylene application. Liquid mask pads can be applied over portions of the circuit traces to make conductive pads. The coaling can then be applied and tape masking removed. Liquid mask pads can be cut around and removed to expose part of the circuit traces for connecting points. 
         [0016]      FIG. 2  is a flow diagram that details the creation of a circuit layer in accordance with some embodiments. At  210 , a circuit layer is started by applying a dielectric layer. An oxide dielectric layer can be used. Prior to deposition, the surface can be cleaned using an ozone cleaning method. Then, for example, a layer of aluminum oxide (Al2O3) can be deposited over the surface using a physical vapor deposition (“PVD”) technique. Other application techniques can be used. PVD allows a thin layer of the dielectric to be formed. PVD also results in a smooth substantially uniform thickness over the non-planar surface. This allows the conductive layer to be applied thinly. The oxide dielectric layer can be applied to about 0.3 mils thick or less. The oxide dielectric layer can be applied to the anodized surface or over a previous circuit layer. When applied over a previous circuit layer, the application will generally conform to the previous circuit layer, leaving a topography surface that mimics the previous circuit layer, but that appears substantially smooth due to the thinness of the circuit traces (e.g., 0.045 mils) versus the thinness of the dielectric layer (e.g. 0.3 mils). The resulting surface does not need to be smoothed prior to the application of another circuit layer because the subsequent layer will conform to the new surface. A fill material is not needed to fill these voids to make one circuit layer smooth before adding another circuit layer on top. 
         [0017]    At  220 , if a connection to a lower layer is desired, the oxide dielectric layer can optionally be masked and etched or drilled. Techniques for etching can include wet etching or plasma etching. Piercing the oxide layer by drilling or etching can allow a conductive layer applied in a second circuit layer, for example, to make contact with a conductor located in a first circuit layer forming a blind via electrical connection between layers. 
         [0018]    At  230 , a conductive layer is applied to the oxide dielectric layer. The conductive layer can be made up from several different conductors having different conductive and thermal properties. For example, in some embodiments a seed layer of titanium can be sputtered onto the dielectric, followed by a sputtered copper layer, followed by optional gold plating. One of skill in the art will understand that different conductive materials or deposition techniques can be substituted as desired. In some embodiments, the titanium layer can be sputtered at about 0.005 mils (200 Å) thick or less, the copper layer can be sputtered at about 0.02 mils (0.5 μm) thick or less, and the gold plating can be applied to about 0.02 mils (0.5 μm) thick or less. Therefore, under some embodiments, the conductive layer can be about 0.045 mils or less thick in total (or about 0.35 mils or less thick including the dielectric layer). Thin circuit layers can significantly reduce thermal resistance to the frame of the non-planar surface for improved heat sinking. The masking for applying the dielectric and conductive layers can be removed. 
         [0019]    At  240 , a resist mask layer is applied. The resist layer can be sprayed or electroplated onto the conductive layer and cured. The resist layer can be made from any material suitable for protecting conductive members from etching solutions. At  250 , the circuit is patterned into the resist mask layer. in some embodiments, the circuit is patterned using laser lithography technology. The resist layer can pattern circuit traces down to 2 mils or less width and up to a width that covers the entire layer to be patterned (as with a ground isolation layer). Thus, trace widths can vary within the topography of the layer according to the circuit layer pattern. A pattern can be created and loaded into a laser lithography machine. The laser lithography machine ablates away the resist layer exposing a negative of the circuit layout. In some embodiments, portions of the circuit is patterned using circuit traces at about 2 mils or less wide and spaces between traces at about 3 mils or less wide, for an overall pitch of about 5 mils or less from trace to trace. The resist layer can be touched up as necessary prior to etching. 
         [0020]    At  260 , the circuit is exposed to etching solution. The circuit can be masked to prevent etching solution from affecting other surfaces. Etching solution for each conductive material can be applied successively to etch away conductive material to expose the oxide dielectric. In some embodiments, first a gold etching solution would be used, followed by a copper etching solution, followed by a titanium etching solution. One of skill in the art will recognize that other etching solutions can be used based on the conductive material in the conductive layer. Following etching, these conductive materials have been removed from the unprotected exposed areas of the circuit, such as those areas not covered by the resist mask. 
         [0021]    At  270 , the remaining resist layer is removed, exposing the completed circuit traces. A bright dip cleanup process can be used to remove any residues. At  280 , circuit lines can be inspected and repaired as needed. 
         [0022]    If additional circuit layers are desired, as in step  130  of  FIG. 1 , the flow would continue back to flow element  210  to apply another layer of oxide dielectric as a base to the next layer. If additional circuit layers are not needed, then the circuit would be sealed as described above with respect to flow element  140  of  FIG. 1 . 
         [0023]      FIG. 3  is an illustration that depicts a top down view of a portion of a non-planar circuit n accordance with some embodiments. Three traces  310  are shown on a non-planar surface  340 . The traces follow the contour of surface  340  by elevating over a rising slope  320  and running down a falling slope  330 . One of skill in the ad will understand that the illustration of  FIG. 3  is an example and that additional traces can be added as desired. In addition, more complex non-planar geometries can be used including rounded portions, edges, and curves. 
         [0024]      FIG. 4  is an illustration that depicts a longitudinal cross-sectional view of a portion of a non-planar circuit in accordance with some embodiments. The view of  FIG. 4  depicts the contour change of  FIG. 3  at the perspective of the surface level, looking at a circuit section through one trace as it traverses from one end of  FIG. 3  to the other end of  FIG. 3 . A surface  410  ( 340  of  FIG. 3 ) is non-planar because it has a rising slope and a falling slope. A dielectric oxide layer  420  is formed on non-planar surface  410  ( 340 ) and conforms to the contours of surface  410  ( 340 ). A conductive trace  430  (one of conductors  310  of  FIG. 3 ) is formed on dielectric oxide layer  420  and conforms thereto. A sealing layer  440  is formed on conductive layer  430  and conforms thereto. The distance between traces at void  510  is one part of the the overall circuit pitch, which is the distance between traces plus the width of the trace. 
         [0025]    One of skill in the art will appreciate that  FIG. 4  (and  FIGS. 5 and 6 , below) is not in proportion. For example, dielectric layer  420  and sealing layer  440  are typically much thicker (e.g., 0.3 mils and 0.25 mils, respectively) than the circuit traces (e.g., 0.045 mils). In  FIGS. 5 and 6 , circuit trace  430  thickness (e.g., about 0.045 mils) is much thinner than the width of narrow traces (e.g., about 2 mils). 
         [0026]      FIG. 5  is an illustration that depicts a cross-sectional view of a portion of a non-planar circuit in accordance with some embodiments. The view of  FIG. 5  illustrates the conductive traces for a single layer circuit at the perspective of the surface level, looking at a circuit section from the end at the small cross-section of the three traces  310  of  FIG. 3 . Non-planar surface  410  is depicted at the base. Dielectric oxide layer  420  is formed on non-planar surface  410  and conforms to the contours of surface  410 . Conductive traces  430  (conductors  310  of  FIG. 3 ) are formed on dielectric oxide layer  420  and conform thereto. A sealing layer  440  is formed on conductive layer  430  and conforms thereto. 
         [0027]      FIG. 6  is an illustration that depicts a cross-sectional view of a portion of a non-planar circuit in accordance with some embodiments. The view of  FIG. 6  illustrates the same view as  FIG. 5  except it depicts two layers of circuit traces. Non-planar surface  410  is depicted at the base. Dielectric oxide layers  421  and  422  are formed on non-planar surface  410  by two successive dielectric depositions (the second deposition after formation of the circuit layer) and conform to the contours of surface  410 . Conductive traces  430  (conductors  310  of  FIG. 3 ) are formed on dielectric oxide layer  420  and conform thereto. After the traces  430  have been formed, because an additional circuit layer is made, an additional dielectric oxide layer  422  is applied which conforms to the contour of the circuit traces  430 . The dielectric oxide layer is continued to be applied until an appropriate thickness has been reached over the height of the conductive traces, such as 0.3 mils, as described above. Additional traces  610  are applied to the dielectric layer and the circuit is sealed with sealant  440 . Conductive via  620  can be formed by etching the dielectric layer  420  prior to applying the second conductive layer, thereby forming conducive via  620  when he second conductive layer is sputtered onto the dielectric. 
         [0028]    One of skill in the art will appreciate that in  FIG. 6 , the second dielectric deposition  422  (e.g., about 0.3 mils) is much thicker than circuit traces  430  and  610 . As such, the bumps demonstrating the conformity of the second dielectric layer  422  to the first layer of circuit traces  430  and the conformity of the second layer of circuit traces  610  are exaggerated. 
         [0029]    Several embodiments are specifically illustrated and/or described herein. However, it will be appreciated that modifications and variations of the disclosed embodiments are covered by the above teachings and within the purview of the appended claims without departing from the spirit and intended scope of the invention.