in the harmful emissions released in the environment are no longer required the pwb sheets obtained with use of udf fabrics result in a technological improvement in all the parameters which characterize the glass reinforced resin sheets in the categories where the fabric is the main basic element the surface roughness and waviness of the sheets is influenced by the structure of the underlying fabric the standard fabric see fig2 on account of the higher number of intersections per cm has a profile which cannot be less than the current values of 3 u03bcm the udf fabric see fig3 has a markedly more linear profile which allows the surface of the sheet to be reduced below the value of 2 u03bcm with this value the thickness of the copper which will subsequently be the track of the printed circuit may be reduced to below the value of 18 u03bcm as has already been necessary in the sector of high frequency applications it will also be possible to perform direct application of thin copper tracks with economic and ecological advantages owing to the saving in copper and elimination of the etching operation which is performed with toxic acids the dimensional stability lt 50 ppm on the x and y axes is a consequence of the perfect alignment of the yarns and the extremely easy possibility of obtaining high percentages for the glass content the perforability of the laminate improves by 50 with regard to the duration of the tips used and the significant reduction in deviation of the hole these two factors are negatively influenced by the lack of homogeneity of the resin glass ratio existing in the sheets constructed using standard fabrics on account of the high number of intersections of yarns of large relative diameter double that.