All: Our company recently received some boards that, after thermal cycling, started showing barrel cracks. The boards were ordered and inspected to IPC-6012 (class 3) with one after-thermal stress coupon on each panel evaluated. According to the manufacturer they saw no evidence of cracks in these coupons. One thing we discovered was that the supplier used a full pad stack in the coupon but the boards themselves had all non-functional pads removed. Typically there were three connections per hole. Layer 1 and 10 had pads plus one internal connection per hole - either signal or plane layer. I think this is one of those gray areas that are not fully defined in IPC-2221, 6012. 2221 states that the coupon should represent the board but... The supplier is using the coupon to detect smear, (etchback if required), annular ring, foil thickness, laminate voids etc. If they don't put a full pad stack they can't evaluate everything. On the other hand, by putting a full pad stack they are re-enforcing the barrel of the hole which may very well hide plating defects such as barrel cracks. This scenerio brings up several questions. How are you handling coupon design? Do you leave it up to the fabricator? Do you specify to the supplier how they should design the coupons. If we specified something like 'determine the average number of connections on a plated through hole and make the coupon look like the average hole' - how would would the board house evaluate the attributes where no pads exist? (or should we care - if one pad is good they're all good) If there was only one internal pad represented on the coupon is that enough to complete an evaluation? Do we ignore annular ring? I know that IPC-6012 specifies to use the "F" coupon for a-ring evaluation but the inspection requirement is somewhat unbelievable - "3.4.2 Annular ring and break out (internal) The F coupon may be used to assess annular ring...by external visual inspection..." I'd really appreciate comments from both the fabricators and OEM's. Thank you - Pete --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e 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 -----------------------------------------------------