Abstract:
In an electronic part at least partially covered by a cured synthetic resin, an easy-and-secure partial removal of the synthetic resin from a surface portion of a substrate of the electronic part for obtaining a desired shape of the synthetic resin is brought about by treating the surface portion through sputtering or plasma before curing the synthetic resin on the surface portion.

Description:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT 
     The present invention relates to an electric part at least partially covered by a synthetic resin and a producing method therefor. 
     In a prior art method for producing an electronic part as disclosed by Publication of U.S. Pat. No. 5,153,385, a sputter etched polyimide coat applied over the substrate improves an adhesion between a molding compound to the substrate. 
     OBJECT AND SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an electric part partially covered by a synthetic resin, in which electric part the synthetic resin is easily and securely removed from a part of a substrate of the electronic part to obtain or leave a desired shape of the synthetic resin on the substrate and/or is securely fixed to another part of the substrate, and to provide a producing method for such electronic part. 
     According to the present invention in an electric part comprising, a substrate including an electrode, an electronic element chip arranged on the substrate and connected to the electrode, and a synthetic resin cover covering the electrode and the electronic element chip, 
     the substrate has a first surface portion on which the synthetic resin cover is arranged, and a second surface portion on which the synthetic resin cover is prevented from being arranged, and the second surface portion is metallic and is formed or exposed through at least one of sputtering (including sputter etching) and plasma-treatment (for example, plasma-etching) to be prevented or restrained from including at least one of oxide and hydroxide. 
     Since the second surface portion on which the synthetic resin cover is prevented from being arranged is metallic and is formed or exposed before curing the synthetic resin thereon through at least one of sputtering, sputter etching and plasma-etching to be prevented or restrained from including at least one of oxide and hydroxide, a synthetic resin adhering to the second surface portion is easily and securely removed from the second surface portion so that a shape of the synthetic resin cover is desirably formed. 
     If the second surface portion abuts on the first surface portion or a metallic surface which includes the second surface portion and is prevented or restrained from including the at least one of oxide and hydroxide extends slightly as a part of the first surface portion under the synthetic resin cover, a relatively thin and/or narrow part of the synthetic resin on the second surface portion is easily, securely and correctly removed from a relatively thick and/or wide part of the synthetic resin on the first surface portion so that the shape of the synthetic resin cover is desirably formed on the first surface portion. 
     The substrate can include a gold layer whose thickness is less than 0.1 μm, for example, 0.03 μm, to form thereon the second surface portion. 
     The second surface portion is prevented or restrained from including the at least one of oxide and hydroxide through at least one of sputtering and sputter-or-plasma-etching of the second surface portion for removing the at least one of oxide and hydroxide from the second surface portion. The first surface portion is formed through at least one of sputtering and plasma-etching of a synthetic resin layer for deforming or removing locally the synthetic resin layer or refreshing-or-activating a surface of the synthetic resin layer, so that an adhering strength between the first surface portion and the synthetic resin cover is increased. 
     According to the present invention, in a method for producing an electric part, comprising the steps of: mounting an electronic element chip onto a substrate, curing a part of a synthetic resin on a first surface portion of the substrate to cover the electronic element chip, and another part of the synthetic resin on a second surface portion of the substrate along which the synthetic resin is supplied onto the first surface portion, and removing the another part of the synthetic resin from the second surface portion, 
     the second surface portion is formed on a metallic layer through at least one of sputtering, sputter etching and plasma-etching for removing at least one of oxide and hydroxide from the metallic layer, before curing the synthetic resin on the substrate. 
     Since the second surface portion is formed on the metallic layer through at least one of sputtering, sputter etching and plasma-etching for removing at least one of oxide and hydroxide from the metallic layer before curing the synthetic resin on the substrate, the synthetic resin adhering to the second surface portion is easily and securely removed from the second surface portion so that the shape of the synthetic resin cover is desirably formed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an oblique projection view showing a substrate used for the present invention. 
     FIG. 2 is a cross sectional view of the substrate. 
     FIG. 3 is an oblique projection view showing an electric part of the present invention. 
     FIG. 4 is a cross sectional view of the substrate before mounting an electronic element chip on the substrate. 
     FIG. 5 is a cross sectional view of the substrate after mounting the electronic element chip on the substrate. 
     FIG. 6 is a partially cross sectional view showing the substrate in a plasma-etching device. 
     FIG. 7 is a partially cross sectional view of the substrate after connecting electrically through a wire the electronic element chip to an electrode of the substrate. 
     FIG. 8 is a partially cross sectional view of the substrate before covering the electronic element chip with a synthetic resin. 
     FIG. 9 is a partially cross sectional view of the substrate after curing the synthetic resin. 
     FIG. 10 is a partially cross sectional view of the substrate when the cured synthetic resin is partially removed from the substrate. 
     FIG. 11 is a partially cross sectional view of the substrate before joining interface-electrode-balls to the substrate. 
     FIG. 12 is a partially cross sectional view of the substrate after joining the interface-electrode balls to the substrate. 
     FIG. 13 is a diagram showing a relationship between a plasma-etching time and a strength against shearing separation between the cured synthetic resin and a metallic surface of the substrate, and a relation-ship between the plasma-etching time and a strength against shearing separation between the cured synthetic resin and an etching-resistant surface of the substrate. 
     FIG. 14 is a partially cross sectional view of another electric part of the present invention. 
     FIG. 15 is a partially cross sectional view of another electric part of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     As shown in FIGS. 1 and 2, a substrate  1  includes a substrate body  2 , a chip mounting portion  3 , front electrodes  4 , back electrodes  7 , a metallic layer  5 , and an etching-resistant layers  6  of, for example, filler containing epoxy resin surrounding the chip mounting portion  3 , the front electrodes  4 , the back electrodes  8 , the metallic surface  5 . The front electrodes  4  are connected to the back electrodes  7  by inner electrically conductive elements  8 . The chip mounting portion  3 , the front and back electrodes  4  and  7 , and the metallic surface  5  are formed on respective gold layers  3   c ,  4   c ,  7   c  and  5   c , the gold layers  3   c ,  4   c ,  7   c  and  5   c  are formed on respective nickel layers  3   b ,  4   b ,  7   b  and  5   b , and the nickel layers  3   b ,  4   b ,  7   b  and  5   b  are formed on respective copper layers  3   a ,  4   a ,  7   a  and  5   a . These layers and the inner electrically conductive elements  8  are stacked through plating and etching steps. 
     At least one of nickel oxide, nickel hydroxide and copper oxide K is formed on the chip mounting portion  3 , the front and back electrodes  4  and  7 , and the metallic surface  5  with a diffusion of at least one of the nickel and copper through the gold layer and/or the nickel layer. The at least one of nickel oxide, nickel hydroxide and copper oxide K deteriorates an easy removal of a cured synthetic resin from the metallic surface  5 , in other words, adheres strongly to the synthetic resin. Therefore, the at least one of nickel oxide, nickel hydroxide and copper oxide K should be removed from the metallic surface  5  on which an undesirable part of the synthetic resin is cured. 
     As shown in FIG. 3, a synthetic resin cover  9   a  of, for example, filler containing epoxy resin, is arranged on the substrate  1  to form an electric part  10  by flowing the synthetic resin along the metallic surface  5  before curing the synthetic resin. The undesirable part of the cured synthetic resin is removed from the metallic surface  5 . The cured synthetic resin adheres to the etching-resistant layer  6 . 
     A method for producing the electric part is explained on FIGS. 4-10. As shown in FIG. 4, a bonding element  11  is arranged on the chip mounting portion  3 . As shown in FIG. 5, an electronic element chip  12  with chip electrodes  13  is mounted on the bonding element  11 , and the bonding element  11  is cured by heating the substrate  1 . The heat of the substrate  1  accelerates a generation of the at least one of nickel oxide, nickel hydroxide and copper oxide K on the front and back electrodes  4  and  7 , and the metallic surface  5 . 
     As shown in FIG. 6, before curing the synthetic resin on the substrate  1 , surfaces of the chip mounting portion  3 , the front electrodes  4 , the metallic layer  5 , and the etching-resistant layers  6  are treated by plasma-etching in a plasma treating device  20 , in which an upper plasma electrode  22  is electrically grounded to a ground terminal  24 , a lower plasma electrode  21  is electrically energized by a high-frequency alternative current supplier  23 , a vacuum pump discharges an air and/or gas in the plasma treating device  20  through a vacuum pipe  25 , and a plasma material gas, for example, argon gas is supplied into the plasma treating device  2  by a gas supplier  28  through a pipe  27 . 
     In the plasma treating device  2 , the plasma material gas becomes plasma in an electric field excited by the lower and upper plasma electrodes  21  and  22 , so that the oxide and/or hydroxide is removed by ion of the plasma material gas from the surfaces of the front electrodes  4 , the metallic layer  5  and the chip electrodes  13 , and the surface of the etching-resistant layer  6  is refreshed or activated. 
     As shown in FIG. 7, the chip electrodes  13  are connected to the front electrodes  4  by wires  15 . As shown in FIG. 8, the substrate  1  with the wires  15  and the electronic element chip  12  is inserted in a cavity  33  formed between an upper mold  31  and a lower mold  32 . An uncured synthetic resin injection hole  34  is formed on the metallic layer  5 . An uncured or melted synthetic resin generated by heating a synthetic resin  9  in a cylindrical hole  35  is supplied or pressed into the cavity  33  through the uncured synthetic resin injection hole  34  by a plunger  36 . After curing the synthetic resin in the cavity  33  to form the synthetic resin cover  9 , the upper mold  31  and the lower mold  32  are separated from each other to take out the substrate  1  and the synthetic resin cover  9 a as shown in FIG.  9 . 
     An undesirable portion of the cured synthetic resin  9   b  which extended along the metallic layer  5  is removed from the synthetic resin cover  9   a  of desirable portion of the cured synthetic resin by a separating force F, as shown in FIG.  10 . 
     The substrate  1  is reversed to mount electrically conductive balls  16  on the back electrodes  7  as shown in FIG.  11 . The electrically conductive balls  16  are joined to the back electrodes  7  by being heated, so that the back electrodes  7  have respective projecting terminals  16 ′ as shown in FIG.  12 . 
     As shown in FIG. 13, a strength B against shearing separation between the cured synthetic resin  9   b  and the surface of the metallic layer  5  is decreased by the plasma etching as described above, and a strength A against shearing separation between the cured synthetic resin  9   a  and the surface of the etching-resistant layer  6  is increased by the plasma etching as described above. These similar effects A and B are obtained by removal sputtering, but the plasma etching is more preferable. The plasma etching for decreasing the strength against shearing separation between the cured synthetic resin  9   b  and the surface of the metallic layer  5  and increasing the strength against shearing separation between the cured synthetic resin  9   a  and the surface of the etching-resistant layer  6  may be performed before mounting the electronic element chip  12 , or after connecting the chip electrodes  13  to the front electrodes  4  by the wires  15 . 
     FIGS. 14 and 15 show electric parts  100  and  200 , respectively, according to further aspects of the invention. 
     The electronic element chip  12  may be replaced by an electronic element chip  112  whose chip electrodes  113  are connected to the front electrodes  4  by respective projecting terminals  114  made of gold, copper or solder as shown in FIG. 14, or by an electronic element chip  212  whose chip electrodes  213  are connected to the front electrodes  4  by respective electrically conductive plates  214  fixed to the front electrodes  4  through heat-and-pressure welding.