Jay, I think that you should make clear what kind of blind via you are referring too - sequentially laminated vs. laser ablated blind via. Anyway, the IPC-6012 spec. does not distinguish between the various cases when it refers to the minimum annular ring allowed. And so, officially, the 1 mil minimum requirement bounds also the case of an internal layer of a blind via. This - when you are seeking conformance with spec. Now, if you are a manufacturer than I cannot agree enough with Wayne. I think that he got the laser via perfectly covered and wish to ad a word or two about the sequentially laminated board. In the sequential lamination, the layers go through several lamination sequences that cause the layers to "shift" and if your annular ring in the sub-assembly is only 1 mil, than you must be extremely good or extremely lucky to keep this 1 mil in the final product. Therefore manufacturers try to make the inner layer lands larger in case of blind vias (as much as the minimum spacing allows). Yours, Yehuda Weisz -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Wayne Thayer Sent: Monday, July 17, 2006 4:32 PM To: [log in to unmask] Subject: Re: [TN] Blind Via Internal Annular Ring No, it should be bigger! If a blind via is made by a laser as a controlled depth job, the target pad acts a bit like a "backstop" for the laser. For this case "breakout" has the most horrendous consequences: The dielectric adjacent to the pad is damaged (perhaps even carbonized) and may plate during the plating step. It may be detectable as a short right away, or may have to wait a while to show up. I use minimum of 3 mil annular ring for laser blinds, and other pcb fabricators appear to be in the same ballpark. Wayne Thayer >>> [log in to unmask] 7/16/2006 2:39 am >>> IPC-6012, Class 3 requires 1 mil minimum internal annular ring for plated through holes. Is the internal layer of a blind via bound by these requirements? Jay Otts Raytheon --------------------------------------------------- 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 ----------------------------------------------------- --------------------------------------------------- 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 ----------------------------------------------------- __________ NOD32 1.1663 (20060716) Information __________ This message was checked by NOD32 antivirus system. http://www.eset.com --------------------------------------------------- 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 -----------------------------------------------------