Base webs for printed circuit board production using the foam process and acrylic fibers

Abstract

A printed circuit board is made from at least one non-woven sheet or web layer comprising at least 50% by weight acrylic fibers, with any balance substantially electrically non-conductive fibers, filler, and binder. The sheet or web is preferably made by the foam process, and may contain 60-80% straight polyacrylonitrile fibers and 40-20% fibrillated (pulp) ones. The web or sheet is preferably compressed by thermal calendering so that it has a density of about 0.1-1 grams per cubic centimeter; and the web or sheet may have a basis weight of between about 20-120 grams per square meter. The web or sheet may also have a 1-40% of substantially electrically non-conductive organic or inorganic binder, or may be substantially binder free. A printed circuit board made using the layers of these non-woven webs or sheets is otherwise conventional, including a pre-preg material, electrically conductive circuit elements, and electronics, and has improved properties compared to woven glass and non-woven aramid products, including improved fiber consolidation, easy board construction, and improved MD/CD ratio and stability.

What is claimed is:  
     
         1 . A printed circuit board comprising: 
 a plurality of substantially electrically non-conductive substrate layers;    at least one of said layers comprising, prior to pre-preg, a non-woven layer including fibers, and at least 50% by weight of said fibers comprising acrylic fibers; and    electrically conductive circuit elements provided on or between at least one of said substrate layers.    
     
     
         2 . A printed circuit board as recited in    claim 1    wherein said acrylic fibers comprise at least about 50% high tenacity acrylic fibers from about 3-12 mm long and from about 6-15 microns in diameter.  
     
     
         3 . A printed circuit board as recited in    claim 2    wherein said fibers comprise at least about 90% polyacrylonitrile fibers.  
     
     
         4 . A printed circuit board as recited in    claim 2    wherein the fibers of said non-woven layer consist essentially of acrylic fibers.  
     
     
         5 . A printed circuit board as recited in    claim 1    wherein said non-woven layer is substantially binder-free.  
     
     
         6 . A printed circuit board as recited in    claim 1    wherein said non-woven layer includes an organic or inorganic binder comprising between about 1-40% by weight of said non-woven layer.  
     
     
         7 . A printed circuit board as recited in    claim 1    wherein said non-woven layer comprises a mixture of straight and fibrillated acrylic fibers.  
     
     
         8 . A printed circuit board as recited in    claim 1    wherein said non-woven layer includes at least 10% by weight other fibers besides acrylic fibers.  
     
     
         9 . A printed circuit board as recited in    claim 1    wherein said non-woven layer includes at least 10% by weight material comprising one or more of liquid crystalline polymers, aramid fibers, aramid pulp fibers, micro fiberglass, polyester fibers, DuPont fibrids, PEN fibers, PPS fibers, MF fibers, and phenolic fibers.  
     
     
         10 . A printed circuit board as recited in    claim 1    wherein said non-woven layer is produced by the foam process.  
     
     
         11 . A printed circuit board as recited in    claim 10    wherein said non-woven layer is densified by thermal calendering at a temperature over 200° C. and a pressure of greater than 500 psi.  
     
     
         12 . A printed circuit board as recited in    claim 7    wherein said non-woven layer comprises about 60-80% straight fibers and 40-20% refined fibrillated fibers.  
     
     
         13 . A printed circuit board as recited in    claim 2    further comprising a plurality of electronic components mounted on or between at least one of said substrate layers and electrically connected to said circuit elements.  
     
     
         14 . A method of producing a printed circuit board comprising: 
 (a) producing a non-woven sheet or web comprising at least 50% by weight acrylic fibers and the balance at least one of substantially electrically non-conductive fibers, filler, and binder;    (b) densifying the sheet or web from (a);    (c) forming a printed circuit board layer using the sheet or web from (b);    (d) combining the layer from (c) with other substantially electrically non-conductive layers; and    (e) providing electrically conductive circuit elements on or between at least one of the layers from (c).    
     
     
         15 . A method as recited in    claim 14    wherein (a) is practiced by using a mixture of both fibrillated and straight acrylic fibers.  
     
     
         16 . A method as recited in    claim 15    wherein (a) is practiced by using a mixture of about 60-80% straight fibers, and about 40-20% fibrillated fibers that may have been refined.  
     
     
         17 . A method as recited in    claim 14    wherein (b) is practiced by thermal calendering at a temperature of greater than 200° C. and a pressure of greater than 500 psi.  
     
     
         18 . A method as recited in    claim 14    further comprising (f), between (c) and (d), forming a pre-preg from the layer of (c) by impregnating the layer with resin; and (g), after (e), of curing the pre-preg to produce a printed circuit board.  
     
     
         19 . A method as recited in    claim 14    wherein (a) is practiced using polyacrylonitrile fibers from about 3-12 mm long and from about 6-15 microns in diameter.  
     
     
         20 . A method as recited in    claim 19    wherein (a) is practiced substantially without binder.  
     
     
         21 . A method as recited in    claim 19    wherein (a) is practiced using 1-40% by weight organic or inorganic binder.  
     
     
         22 . A method as recited in    claim 14    wherein (a) and (b) are practiced to produce a sheet or web having a density of 0.1-1 g/cm 3 , and wherein (a) is practiced by the foam process using a slurry having a solids consistency of at least about 5%  
     
     
         23 . A method as recited in    claim 14    wherein (a) is practiced by the foam process.  
     
     
         24 . A non-woven sheet or web comprising at least 50% by weight acrylic fibers, and any balance substantially electrically non-conductive fibers or filler or binder, or combinations thereof.  
     
     
         25 . A non-woven sheet or web as recited in    claim 24    comprising about 60-80% straight acrylic fibers and about 40-20% fibrillated acrylic fibers.  
     
     
         26 . A non-woven sheet or web as recited in    claim 24    wherein said web or sheet is substantially devoid of binder.  
     
     
         27 . A non-woven sheet or web as recited in    claim 24    wherein said web or sheet has been compressed so that it has a density of about 0.1-1 g/cm 3 .  
     
     
         28 . A non-woven sheet or web as recited in    claim 24    further comprising about 1%-40% by weight of a substantially electrically non-conductive organic or inorganic binder.  
     
     
         29 . A non-woven sheet or web as recited in    claim 25    comprising at least about 90% acrylic fibers.  
     
     
         30 . A non-woven web or sheet as recited in    claim 25    wherein the fibrillated fibers are refined.  
     
     
         31 . A non-woven web or sheet as recited in    claim 24    wherein the web or sheet is made by the non-woven process.