Microfiber dielectrics which facilitate laser via drilling

Abstract

This invention concerns electronic substrates comprising a non-woven filler material and a resin material. The present invention also includes electronic products manufactured from the electronic substrates of this invention including, but not limited to prepregs, metal clad laminates, and printed wiring boards with and without lased via holes. The present invention further includes a method of manufacturing printed built-up wiring boards including the steps of forming a prepreg and forming at least one via in the prepreg.

What we claim is:  
     
         1 . A lasable prepreg for use in fabrication of build-up multilayer printed wiring boards comprising: 
 a. a non-woven reinforcing material consisting primarily of micro-fiber glass; and    b. a partially cured polymer.    
     
     
         2 . The prepreg of  claim 1  wherein the non-woven reinforcing material includes less than 40 wt % of a supplemental reinforcing material selected from organic fiber, organic pulp and mixtures thereof.  
     
     
         3 . The prepreg of  claim 1  wherein the polymer is selected from a thermoplastic polymer a thermosetting resin and mixtures thereof.  
     
     
         4 . The prepreg of  claim 1  including from about 5 to about 45 wt % of non-woven reinforcing material and from about 55 to about 95 wt % polymer.  
     
     
         5 . The prepreg of  claim 1  wherein at least 80% of the micro-fiber glass has a diameter of less than about 1 micron.  
     
     
         6 . The prepreg of  claim 1  wherein the polymer is a thermosetting resin that is cured from between 10 and 50% of full cure.  
     
     
         7 . The prepreg of  claim 1  wherein the prepreg includes a first surface and a second surface wherein at copper foil is adhered to at least one prepreg surface.  
     
     
         8 . A prepreg of  claim 7  wherein the copper foil rough surface is adhered to the prepreg surface.  
     
     
         9 . A method for manufacturing a multiple layer electronic circuit that includes a plurality of lased vias comprising the steps of: 
 (a) applying a prepreg having a first surface and a second surface and comprising a non-woven reinforcing material consisting primarily of micro-fiber glass impregnated with a partially cured polymer to a substrate consisting of a first layer of circuitry located on the surface of the substrate such that the first surface of the prepreg is contacts the first layer of circuitry;    (b) exposing the laminate to elevated temperatures and pressure for a period of time sufficient to fully cure the partially cured prepreg polymer to give a laminate including a dielectric surface layer; and    (c) lasing a plurality of micro-vias into the dielectric surface layer.    
     
     
         10 . The method of  claim 9  wherein a conductive material is applied to the via.  
     
     
         11 . The method of  claim 9  wherein a conductive metal foil is applied to the prepreg second surface prior to step (b).  
     
     
         12 . The method of  claim 11  wherein the lased vias include vias that extend from the conductive metal foil layer to the first layer of circuitry.  
     
     
         13 . The method of  claim 11  wherein a second circuit pattern is created on the conductive foil layer  
     
     
         14 . The method of  claim 11  wherein the micro-vias are formed by laser drilling holes through both the conductive metal foil layer and the dielectric surface layer.  
     
     
         15 . The method of  claim 9  wherein the substrate includes an embedded circuitry layers that is separated from the first circuitry layer by a dielectric layer wherein at least one of the lased vias extends from the dielectric surface layer to the embedded circuitry layer.  
     
     
         16 . The method of  claim 9  wherein a plurality of holes are formed in the conductive metal foil layer prior to laser via formation and wherein the micro-vias are lased in the exposed holes.  
     
     
         17 . The method of  claim 9  wherein at least 95% of the plurality of micro-vias are acceptable.  
     
     
         18 . The method of  claim 9  wherein a circuit is formed on the metal film layer covering the lasable dielectric layer following the lasing of at least one micro-via.  
     
     
         19 . The method of  claim 9  wherein the circuit is formed on the metal film layer before the lasing of at least one micro-via.  
     
     
         20 . The method of  claim 9  wherein the laminate is processed by the further steps of: 
 (i) applying a layer of sputtered metal onto the dielectric surface layer and into the micro-vias of the laminate to give a sputtered metal surface;  
 (ii) applying a resist layer to the sputtered metal surface, imaging the resist layer to define wanted and unwanted resist layer portions, and removing the unwanted resist layer portions to expose at least a portion of the sputtered metal surface and at least one micro-via;  
 (iii) electroplating the metal layer to fill the exposed micro-vias with electroplated metal, and to build-up a second circuit layer corresponding to the exposed sputtered metal surface;  
 (iv) removing the wanted portion of the resist layer; and  
 (v) removing the sputtered metal layer below the removed wanted portion of the resist layer.  
 
     
     
         21 . The method of  claim 9  wherein the lasable dielectric includes from about 5 to about 45 wt % non-woven micro-fiber glass and from about 55 to about 95 wt % polymer.  
     
     
         22 . The method of  claim 20  wherein 80% of the micro-fiber glass has a diameter less than about 1 micron.  
     
     
         23 . The method of  claim 9  wherein each micro-via is lased using a laser with a uniform power setting.  
     
     
         24 . A method of manufacturing a reinforced resin coated copper prepreg comprising: 
 a. coating resin onto a copper foil surface;    b. applying a reinforcing material into the resin coating on the copper foil; and    c. drying the solvent out of the resin and advancing the cure of the resin to between 10% and 50% of full cure.