Dear Sir: As you have observed and reported in your note, most laminates tend to be tapered i.e. thicker in the center than at the edges. This is due to the fact the laminators put anywhere from 6 to 15 laminate books in one press opening. For very close thickness toloerance work, people often only purchase a center cut out of the master sheet to insure good thickness tolerance and therefore a good dielectric constant tolerance. The only penalty is you pay for all the drops. Another way of improving thickness tolerance is to only press 1 laminate book at a time which can also be costly. A company which produces laminates on a continuous basis in this fashion is Glasteel Industrial Laminates, Collerville, TN. In addition the dielectric constant of their normal material is 3.7 which may or may not be an advantage for you. Their numbers are 901-853-5070 for the phone line and 901-853-8664 for the fax machine. Doug Sober IPC Base Materials Committee Chairman [log in to unmask]