To Al Slagle; Coupons are used to evaluate what you cannot see by examining the surface of boards. They are used to verify that the appropriate weight of copper called for in the drawing was used on specific inner layers. They are used to determine if dielectric thickness between inner layers meets drawings or specification. They are used to assess how the board will perform during assembly operations by the thermal stress test (10 seconds/550F). They are also used to assess numerous other requirements found in industry and military specifications and drawings. All of the above are things that a board manufacturer should verify prior to shipment of the boards. The use of coupons enables such testing to be performed without sacrificing actual boards. In some cases where boards are produced one/panel this is the only way. Additional coupons sent to customers are used as cross checks of the board manufacturer. Some are tested by third parties and some are only tested if there is a problem during assembly or after the boards are in use. In process testing by a board shop can supplement or be used in lieu of coupon testing, with proper correlation studies. However, there is always going to be the need to see inside a finished hole and most would much rather sacrifice coupons than boards. Susan Mansilla Robisan Laboratory