Here is the answer from the previous TechNet discussion: (Ioan, your memory is not so good...., grin) The green color of soldermask was chosen after extensive testing by the U.S. military at the National Materials and Procurement Center in Cedar Bluffs Virginia in late 1954. According to Colonel Robert Bright, Public Liason Officer, the particular shade of green was found to provide the maximum contrast to the white silkscreen ink under all tested adverse situations while still allowing a clear view of the underlying circuitry. Every other color tested failed to provide the required contrast under conditions of low / high illumination levels and various colored light sources. The quantity of Printed Circuit Boards purchased by the Defense Department established a "de facto" standard which most vendors began to follow. Usage of other colors is permitted for prototype and or pre-release boards. --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------