Abstract:
The present invention provides a method of making a molded interconnect device. The method includes the steps of: injection molding a plastic body having thereon at least one patterned circuit trench structure; and filling a conductive material into the patterned circuit trench structure thereby forming a circuit trace on the plastic body.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to a method of fabricating circuit traces on a plastic substrate. More particularly, the present invention relates to a method of making a molded interconnect device. 
         [0003]    2. Description of the Prior Art 
         [0004]    As known in the art, molded interconnect devices (MIDs) have been used in many applications such as automotive and telecommunication industries. MIDs essentially integrate mechanical and electrical functions into one piece and make an important contribution to design in terms of manufacturability and assembly. Unlike printed circuit boards, which are typically limited to two-dimensional planes, MIDs can implement three-dimensional circuitry. Among other things, a circuit pattern with multiple planes allows better spacing of circuitry, as well as the connected switches and buttons. 
         [0005]    Many approaches have been developed for making an MID up to the present. The methods for fabricating an MID and their respective shortcomings can be summarized as follows. 
         [0006]    (1) Laser direct structuring (LDS) technique. This method involves the use of a plastic material impregnated with metal catalyst. The plastic material is activated by laser method. After this, the plastic material is metallized using chemical copper process. U.S. publication No. 2007/0247822 discloses such method. The shortcomings of this method include high production cost due to expensive metal catalyst impregnated plastics and laser tools, and environmental pollution issues due to wet chemical process. 
         [0007]    (2) Microscopic integrated processing technology (MIPTEC). This prior art method uses chemical vapor deposition (CVD) or sputtering to coat plastic material with conductive material, then uses laser to pattern the conductive material and remove the conductive material from the non-metallized area, followed by chemical copper metallization. The shortcomings of this method include high production cost due to expensive CVD or sputtering tool as well as environmental pollution issues due to wet chemical process. 
         [0008]    (3) Hot embossing method. This prior art method is a technique of imprinting microstructures on a substrate (polymer) using a master mold. One of the drawbacks is that the cost of developing molds is high. Besides, there are difficulties of three-dimensional processing. 
         [0009]    (4) Two-shot molding method. This method involves two different plastic materials formed by respective injection mold steps. The two different plastic materials include activable and non-activable plastics. The activable plastic is then metallized by wet chemical processes. The drawbacks include bottleneck of mold development, low design flexibility and high cost of development. 
         [0010]    In light of the above, there is a need in this industry to provide an improved method of fabricating MIDs, which is cost-effective (no laser tool, CVD tool or sputtering tool is required), flexible and has no environmental pollution issues, thereby overcoming the prior art problems and shortcomings. 
       SUMMARY OF THE INVENTION 
       [0011]    It is one objective of the present invention to provide an improved method of making a molded interconnect device, which is clean and cost-effective, in order to solve the above-mentioned prior art problems. 
         [0012]    To achieve the goal, the present invention provides a method of making a molded interconnect device. The method includes the steps of: injection molding a plastic body having thereon at least one patterned circuit trench structure; and filling a conductive material into the patterned circuit trench structure thereby forming a circuit trace on the plastic body. 
         [0013]    In one aspect, the present invention discloses a method of making a molded interconnect device including the steps of providing a body having thereon a first patterned circuit trench structure disposed on a first surface and a second patterned circuit trench structure disposed on a second surface that is not coplanar with the first surface; and filling a conductive material into the first and second patterned circuit trench structures thereby forming a first and second circuit traces on the first and second surfaces of the body. 
         [0014]    These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a schematic diagram showing the process of making a molded interconnect device in accordance with one preferred embodiment of this invention. 
           [0016]      FIG. 2  illustrates a method for selectively filling the patterned circuit trenches of the injection molded plastic body with conductive material according to this invention. 
           [0017]      FIG. 3  is a schematic diagram showing the process of making a molded interconnect device in accordance with another preferred embodiment of this invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    As previously mentioned, either LDS method or MIPTEC method has a drawback in that the production cost is too high because of the expensive metal impregnated plastic and expensive production tools, and that the employed wet chemical processes have environmental issues. To solve these problems, the present invention discloses a novel and eco-friendly method of making a molded interconnect device, which is cost-effective and is applicable to various injection molded plastic structures to form metallized circuit traces on any surface of the injection molded plastic structure. 
         [0019]      FIG. 1  is a schematic diagram showing the process of making a molded interconnect device in accordance with one preferred embodiment of this invention. As shown in  FIG. 1 , an injection molded plastic body  1  is provided having thereon a plurality of patterned circuit trenches  11 ,  12  and  13 . The injection molded plastic body  1  may be formed from polycarbonate, acrylonitrile-butadiene-styrene (ABS), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), liquid crystal polymers (LCP), PA 6, Nylon, polyimide, polypropylene, POM, PPS, COC, or any combination thereof. It is understood that the injection molded plastic body  1  may be formed from other plastic materials that have good bonding ability to metals. 
         [0020]    According to the preferred embodiment of this invention, the patterned circuit trenches  11  and  12  are situated on the first surface  1   a  of the injection molded plastic body  1  and the patterned circuit trench  13  is situated on the second surface  1   b  of the injection molded plastic body  1 . The first surface  1  a and the second surface  1   b  are not coplanar and are two different surfaces of the injection molded plastic body  1 . Further, the patterned circuit trenches  11 ,  12  and  13  may have various trench depths depending upon the design requirements. 
         [0021]    Thereafter, the patterned circuit trenches  11 ,  12  and  13  on the injection molded plastic body are filled with conductive material  20  such as copper paste, silver paste, tin paste or any suitable conductive materials, thereby directly forming circuit traces  11   a    12   a  and  13   a  on the first surface  1   a  and the second surface  1   b  respectively. 
         [0022]      FIG. 2  illustrates a method for selectively filling the patterned circuit trenches of the injection molded plastic body  1  with conductive material according to this invention. First, the surfaces of the injection molded plastic body  1  having thereon the patterned circuit trenches  11 ,  12  and  13  is covered with a thin film  30 . The thin film  30  has openings  31 ,  32  and  33  corresponding to the patterned circuit trenches  11 ,  12  and  13 . Subsequently, conductive material  20  such as copper paste, silver paste, tin paste or any suitable conductive material is filled into the patterned circuit trenches  11 ,  12  and  13 . Finally, the thin film  30  is stripped off. As shown in  FIG. 2 , the formed circuit traces  11   a,    12   a  and  13   a  may slightly protrude from respective surfaces of the injection molded plastic body  1 . 
         [0023]    Further, depending on the characteristics of the conductive materials employed, a post bake or sintering process may be performed after filling the trenches with the conductive material  20  in order to remove the solvent or dispersing agent inside the conductive material  20  and let metal particles to contact each other. According to the preferred embodiment of this invention, the aforesaid post bake or sintering process is carried out at a temperature preferably under 260° C., but not limited thereto. The practical temperature depends on the curing temperature of paste and melting point or anti-deforming capability of the injection molded plastic body  1 . Of course, it is understood that the present invention is not limited to plastic body. Other materials such as ceramic or combination of ceramic and plastic may be used as the body. The ceramic body may be formed by molding methods. 
         [0024]      FIG. 3  is a schematic diagram showing the process of making a molded interconnect device in accordance with another preferred embodiment of this invention. As shown in  FIG. 3 , a body  100  such as injection molded plastic body or ceramic body is provided having thereon a plurality of patterned circuit trenches  101 ,  102 ,  103  and  104 . The body  100  may be formed from polycarbonate, acrylonitrile-butadiene-styrene (ABS), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), liquid crystal polymers (LCP), PA 6, Nylon, polyimide, polypropylene, POM, PPS, COC, or any combination thereof. The body  100  may be formed from other plastic materials that have good bonding ability to metals. In a case that the body  100  is a ceramic body, the ceramic body may be zirconium oxide, aluminum oxide or chromium carbide doped aluminum oxide alloys. 
         [0025]    According to the preferred embodiment of this invention, the patterned circuit trenches  101 ,  102 ,  103  and  104  are situated on different surfaces of the body  100 , wherein the patterned circuit trench  101  is situated on the first surface  100   a,  the patterned circuit trench  102  is situated on the second surface  100   b,  the patterned circuit trench  103  is situated on the third surface  100   c,  and the patterned circuit trench  104  is situated on the fourth surface  100   d.  As shown in  FIG. 3 , the second surface  100   b  and the third surface  100   c  are opposite surfaces. 
         [0026]    Furthermore, the patterned circuit trenches  101 ,  102 ,  103  and  104  may have different trench depths, shapes and sectional profiles depending on the design requirements. Besides, a through hole  105  is provided in the body  100  to communicate the patterned circuit trench  102  with the patterned circuit trench  103 . 
         [0027]    Thereafter, the patterned circuit trenches  101 ,  102 ,  103  and  104  on the body  100  are filled with conductive material  120  such as copper paste, silver paste, tin paste or any suitable conductive materials, thereby directly forming circuit traces  101   a    102 a,  103   a  and  104   a  on the body  100 . Depending on the characteristics of the conductive materials employed, a post bake or sintering process may be performed after filling the trenches with the conductive material  120  in order to remove the solvent or dispersing agent inside the conductive material  20  and let metal particles to contact each other. According to the preferred embodiment of this invention, the aforesaid post bake process is carried out at a temperature preferably under 260° C., but not limited thereto. The practical temperature depends on the curing temperature of paste and melting point or anti-deforming capability of the body  100 . 
         [0028]    Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.