Abstract:
A method of making a connection component for a microelectronic element includes providing a sheet comprising an electrically conductive layer, a photoresist layer overlying the conductive layer and a photoimageable dielectric layer disposed under the conductive layer. The method includes lithographically forming at least one opening in the photoresist layer to uncover a portion of the conductive layer, forming a plurality of circuit features from the conductive layer by removing the uncovered portion of the conductive layer, at least some of the circuit features being leads, and lithographically forming at least one aperture in the photoimageable dielectric layer.

Description:
ROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of U.S. Provisional Patent Application with Ser. No. 60/100,378, filed on Sep. 15, 1998, the disclosure of which is hereby incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to semiconductor chip packages and more specifically to connection components for use in semiconductor chip packages. 
     2. Description of the Related Art 
     Connection components are frequently used to make semiconductor chip packages. Certain semiconductor chip packages are made by bonding the contacts on the chip to leads on the connection component. Such semiconductor chip packages include packages made using tape automated bonding techniques wherein the connection component is a copper clad polyimide tape. Other semiconductor chip packages made with connection components include certain chip scale packages which are made by bonding the chip to a flexible interposer such as those disclosed in commonly assigned U.S. Pat. Nos. 5,148,265 and 5,148,266, the disclosures of which are hereby incorporated herein by reference. 
     One of the problems associated with the use of such tape or chip carriers is the high cost of processing the polyimide. The cost of the gold that is plated onto such carriers also contributes to the high cost of such chip carriers. It is desirable, therefore, to reduce the cost of the chip carrier by eliminating the use of sheets of polyimide and by significantly decreasing the amount of gold used. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention provides a method of making a connection component for use in packaging a microelectronic element such as a semiconductor chip or wafer. The method of this aspect of the invention includes the step of providing a composite sheet comprising a photoresist layer, an electrically conductive layer and a photoimageable dielectric layer. Portions of the photoresist layer are exposed to ultraviolet light and the photoresist layer is then developed to uncover selected portions of the conductive layer. The uncovered portions are etched to form leads and other conductive elements. The remaining photoresist layer is removed. Apertures are formed in the photoimageable dielectric layer using photolithographic techniques whereby portions of the photoimageable dielectric layer are exposed to ultraviolet light. The photoimageable dielectric layer is then developed, usually by immersing such layer in or spraying such layer with a development solution and dissolving away either the light-exposed or the unexposed portions. 
     In preferred embodiments, the connection component made by the method of this aspect of the present invention includes a photoimageable dielectric layer having a plurality of apertures and a plurality of electrically conductive leads disposed on such photoimageable dielectric layer. This connection component may be used to package a semiconductor chip by juxtaposing the chip with the connection component such that each chip contact is aligned with the tip of one of the leads. In preferred embodiments, the apertures include bond windows and holes for solder balls; and a least a portion of each lead is disposed over one of the bond windows. The chip contacts are then bonded to the leads, preferably by inserting a bonding tool through the bond window. The assembly may then be encapsulated. In preferred embodiments, a solder ball is disposed in each solder ball hole and is electrically connected to one of the leads. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1-11 show side views of progressive steps in the method of making a connection component of the present invention. 
     FIGS. 12-15 show side views of progressive steps in the method of making a semiconductor chip package using the connection component of FIG.  11 . 
     FIGS. 16-21 show side views of progressive steps in another embodiment of the method of making a connection component of the present invention. 
     FIGS. 22-26 show side views of progressive steps in the method of making a semiconductor chip package using the connection component of FIG.  21 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     One embodiment of the present invention provides a method of making a connection component. Referring to FIG. 1, a composite sheet, comprised of an electrically conductive layer  5  having a first or top surface and a second or bottom surface, a photoresist layer  3  disposed on the top surface, and a photoimageable dielectric layer  4  disposed on the bottom surface, is provided. In preferred embodiments, the conductive layer is comprised of copper and is about 12 to 18 microns thick. In preferred embodiments and as depicted in FIG. 1, the composite sheet also has a first release liner disposed on the top surface of photoresist layer  3  and a second release liner  2  disposed on the bottom surface of the photoimageable dielectric layer  4 . The first release liner may be removed before the step of exposing the photoresist layer. In preferred embodiments however, first release layer  1  is not removed until after the step of exposing the photoresist layer. In such preferred embodiments, first release layer  1  is transparent to the light used to activate the photoresist layer. 
     The method of this aspect of the invention also includes the step of selectively exposing portions of the photoresist layer to light having a wavelength and intensity that is sufficient to activate the exposed portions of the photoresist layer. The specific wavelength and intensity of the light required varies depending on the specific photoresist used. In preferred embodiments of the present invention, the photoresist layer is activated by ultraviolet light. As depicted in FIG. 2, an ultraviolet light source  6  and a mask  7  are provided. Mask  7  has a plurality of openings  8  which correspond to circuit features which are to be formed on conductive layer  5 . Portions of the photoresist layer are exposed to ultraviolet (“UV”) light from UV light source  6  to form light-exposed portions  9 . As depicted in FIG. 3, first release liner  1  is removed. The photoresist layer is then developed to remove all but the light-expose portions  9  of photoresist layer  3  and thereby uncover portions of the conductive layer. In preferred embodiments and as depicted in FIG. 4, the photoresist layer is developed by exposing such layer to a developing solution which preferentially dissolves the portions of the photoresist layer which have not been uv-light exposed. Such photoresist layers are generally referred to as “negative” or “negative-acting” photoresists. “Positive” photoresist materials, wherein the developing solution preferentially dissolves the light exposed portions, may also be used. As depicted in FIG. 5, the uncovered portions of the conductive layer are then etched to form circuit features, such as leads  10 . The remaining portions  9  of the photoresist layer are then removed, as depicted in FIG.  6 . In preferred embodiments, each lead has a notch or a frange point. The frange point is a section of the lead that has been designed to preferentially break upon the application of force to the lead and to bond to a contact on a chip when heat and or pressure is applied to the frange point. The frange point is typically located between the terminal end and the tip end of the lead. Alternative or additionally, the leads may be peelable. Methods for making peelable are disclosed in commonly assigned U.S. patent applications with Ser. Nos. 09/200,100 filed on Nov. 25, 1999; 09/020,750 filed on Feb. 9, 1998; and 09/140,589 filed on Aug. 26, 1998. 
     In preferred embodiments and as depicted in FIG. 7, a bonding material, such as gold or another oxidation resistant metallic material  24  is applied to each lead  10 . More preferably, and in order to minimize the cost of the connection component by minimizing the amount of gold used, gold is spot welded, or spot electroplated, to the portion of each chip which will be bonded to one of the contacts of the microelectronic element. In preferred embodiments, gold  24  is spot welded to each lead  10  at or near the tip end  21  of each lead. 
     The method of this aspect of the invention also includes the step of selectively exposing portions of the photoimageable dielectric layer to light having a wavelength and intensity that is sufficient to activate the exposed portions of the photoimageable dielectric layer. The specific wavelength and intensity of the light required varies depending on the specific photoimageable material used. In preferred embodiments of the present invention, the photoimageable dielectric layer is activated by ultraviolet light. Preferred photoimageable polymeric materials are chemically resistant, have good thermal resistance properties and a flexible. Preferred photoimageable dielectric materials include photoimageable polymeric materials, such as, for example, photoimageable, photoimageable acrylics, and photoimageable urethanes, and mixtures thereof. More preferred photoimageable dielectric materials include Dupont&#39;s Pyralux® PC 1000 which contains a combination of acrylic, urethane, and imide-based materials, and Dupont&#39;s Riston® Photopolymer Dry Film Resists. 
     As depicted in FIG. 8, a light source  6 ′ and a mask  11  are provided. Mask  11  has a plurality of openings  12  which correspond to apertures which are to be formed in photoimageable dielectric layer  4 . As depicted in FIG. 9, the portion of the photoimageable dielectric layer  4  that is exposed to source  6 ′ form light-exposed portions  14 . As depicted in FIG. 10, second release liner  2  is then removed. The photoimageable dielectric layer  4  is then developed to form apertures by removing all of the photoimageable layer  4  except for the light exposed portions  14 . Such apertures may include bond windows  15  or holes  16  for the subsequent placement of solder balls or, as depicted in FIG. 11, such apertures may include both bond windows  15  and holes  16 . In preferred embodiments, the photoimageable dielectric layer is developed by exposing such layer to a developing solution which preferentially dissolves the portions of the photoimageable dielectric layer which have not be exposed to the UV light. Such photoimageable dielectric layers are referred to herein as “negative photoimageable” materials. “Positive photoimageable” materials, wherein the developing solution preferentially dissolves the light exposed portions, may also be used. The assembly depicted in FIG. 11 is a connection component  25 . Connection component is comprised of dielectric layer  5  and a plurality of electrically conductive leads  10  disposed on such dielectric layer. Dielectric layer  5  has bond windows  15  and a plurality of holes  16 , each of which is adapted for placement of a bonding element, such as a solder ball, therein. Each of the leads  10  has a tip end  21  and a terminal end  20 . In preferred embodiments, the terminal end  20  of each lead is disposed over one of the holes  16 . In particularly preferred embodiments, at least a portion of each lead, at or near the tip end of such lead, is coated with gold or another oxidation resistant metal or metal alloy. 
     The connection component of the present invention can be use to package microelectronic elements, such as semiconductor chips and wafers, in either batch (e.g. panel) or continuous (e.g. reel to reel) processes. Because continuous process methods tend to be less expensive, it is preferable to provide the composite sheet on a roll so that the packaging process can be conducted in a reel to reel format. 
     Another embodiment of the present invention provides a method of making a microelectronic element package using the connection component of FIG.  11 . Referring to FIG. 12, a semiconductor chip  18  having a plurality of contacts (not shown) is juxtaposed with the connection component of FIG.  11 . Elongated leads  10  are vertically extended to form vertically extended leads  19  and the tip end  21  of each lead is bonded to one of the contacts on the semiconductor chip, as depicted in FIG.  13 . In preferred embodiments the leads are vertically extended and thermosonically bonded by inserting a bonding tool through bonding window  15 . In preferred embodiments and as depicted in FIG. 14, an encapsulant layer  23  may be disposed between the semiconductor chip and the connection component to encapsulate the leads. In particularly preferred embodiments, encapsulant layer  23  is comprised of a compliant layer which is adapted to compensate for the mismatch in the thermal coefficients of expansion of the chip and the connection component. Compliant layer  23  is preferably comprised of a silicone elastomer or a flexiblized epoxy. In an alternative embodiment, compliant layer  23  is disposed directly on the connection component before the connection component is juxtaposed with a semiconductor chip or a semiconductor wafer. 
     In preferred embodiments and as depicted in FIG. 15, the microelectronic element package includes a plurality of bonding elements  22 , such as solder balls. The solder balls are typically attached to the package by disposing one solder ball in each aperture and reflowing the solder ball to electrically interconnect it with one of the terminals. 
     Another embodiment of the present invention provides a method of making a connection component using a positive acting photoimageable dielectric material. As depicted in FIG. 16, the composite comprises an electrically conductive layer  5 , a photoresist layer  3 , a photoimageable dielectric layer  4 , a first release liner  1  disposed on the photoresist layer and a second release liner  2  disposed on the photoimageable dielectric layer. As depicted in FIG. 17, the photoresist layer  3  is exposed to an UV light source  6  through mask  7 . Mask  7  has a plurality of openings  8 . Although positive photoresists may also be used, the photoresist of FIG. 17 is a negative acting photoresist. Since the photoresist used is negative acting, the light exposed portion  9  of the photoresist layer is not removed when the developing solution is applied to layer  3 . 
     The photoimageable dielectric layer  4  is exposed to an UV light source  6 ′ through a mask  11  having a plurality of openings  12 . Because the photoimageable dielectric layer  4  depicted in FIG. 17 is positive acting the light exposed portion  14  of layer  4  is preferentially removable in a developing solution. The mask used to expose the dielectric layer should, if the dielectric material is made of a positive photoimageable dielectric layer, have openings or uv-light transparent sections which correspond to portions of the dielectric layer which will have bond windows or apertures for locating solder balls. In preferred embodiments, the first release liner and the second release are transparent to UV light so that the photoresist layer and the photoimageable layer may be exposed to UV light without having to remove the liners. In preferred embodiments, the photoresist layer and the photoimageable dielectric layer are simultaneously exposed to the UV light sources. The first release liner is then removed, as depicted in FIG. 18, and the photoresist layer is developed such that all but the light exposed portions  9  of such layer  3  are removed. Portions of the conductive layer are thereby uncovered. As depicted in FIG. 19, the uncovered portions of the conductive layer are then etched to form electrically conductive circuit features such as leads  10 . As depicted in FIG. 20, the light-exposed portions  9  of photoresist layer  3  are then removed, usually using a photoresist stripping solution. The second release liner  2  is peeled or otherwise removed from the photoimageable dielectric layer  4 . The light-exposed portions  14  of the photoimageable dielectric layer  4  are then removed to create apertures  16  in layer  4  of the connection component of FIG.  21 . Portions  14  are generally removed by immersing the assembly in a solution that preferentially removes portions  14  while allowing portions  13  to remain. Alternatively, portions  14  may be removed by spraying such a solution onto layer  4 . In preferred embodiments, a bonding material, such as gold or another oxidation resistant metal is spot welded to the tip end of each lead. 
     Another embodiment of the present invention provides a method of making a microelectronic element package using the connection component of FIG.  21 . Referring to FIG. 22, a semiconductor chip or wafer  18  having a plurality of contacts  24  is juxtaposed with the connection component of FIG.  21 . The tip end  21  of each lead  10  is bonded to one of the contacts  24 , as depicted in FIG.  23 . The terminal end  20  of each lead is disposed over an aperture  16 . Elongated leads  10  are vertically extended to form vertically extended leads  19  and the tip end  21  of each lead is bonded to one of the contacts on the wafer  18 , as depicted in FIG.  24 . Methods for vertically extending the leads include, for example, methods disclosed in commonly assigned U.S. Pat. No. 5,518,964, the disclosure of which is incorporated herein by reference. In preferred methods, the leads are extended by moving the wafer  18  and the connection component away from each other in a direction having a vertical component of motion. In preferred embodiments and as depicted in FIG. 25, an encapsulant  23  is disposed between the wafer  18  and the photoimageable dielectric layer to encapsulate the leads. In particularly preferred embodiments, encapsulant layer  23  is comprised of a compliant layer which is adapted to compensate for the mismatch in the thermal coefficients of expansion between the wafer and the connection component. Compliant layer  23  is preferably comprised of a silicone elastomer or a flexiblized epoxy. 
     In preferred embodiments and as depicted in FIG. 26, the microelectronic element package includes a plurality of bonding elements  22 , such as solder balls. The solder balls are typically attached to the package by disposing one solder ball in each aperture and reflowing the solder ball to electrically interconnect it with one of the terminals. 
     The resulting wafer may be diced into individual packages including one or more semiconductor chips. In alternative embodiments, the packaged wafer may be diced before the solder balls are attached or before the package is encapsulated. Having fully described several embodiments of the present invention, it will be apparent to those of ordinary skill in the art that numerous alternatives and equivalents exist which do not depart from the invention set forth above. It is therefore to be understood that the present invention is not to be limited by the foregoing description, but only by the appended claims.