Victor, You're on the right site. IPC-2221, 6.4 provides all the information known to common man about impedance controls and associated calculations. Also, the following is one of my Master Drawing notes concerning TDR findings with MLB constructions: 7.0 Test Requirements 7.1 All electrical, including time domain reflectometry, and physical test requirements shall be met in accordance with IPC-600F, IPC-6012, and IPC-TM-650 test method requirements. 7.2 For all impedance controlled MLB?s, the fabricator shall provide x-sectional correlation to TDR findings that clearly show and define each dielectric thickness, glass style, copper foil thickness, plating thickness, and laminate area and thermal zone evaluations as received and after thermal stress ? as in 7.1. 7.3 Two photo micrographs shall be provided for each quality conformance test circuit per lot. One shall show one hole on the ?A? coupon, in an as received condition, and one shall show one hole on the ?B? coupon, after thermal stress. This shall be done for each mutually agreed upon lot. Each photo shall be taken at 40X and shall clearly verify the fabricator?s microsection report, and shall directly correlate to the report?s findings. Also, just about everything you wanted to know about TDR test methods is presented in IPC-6012, with IPC-TM-650, number 2.5.5.7, therein. Earl --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------