There are three types of vias defined in IPC-4761 that are part of a protection strategy. There is a filled and covered via (Type VI-b Via); a filled and capped via (Type VII Via); and a tented and covered via (Type II-b Via). The covering of Type VI-b and Type II-b Vias shall be per the application of SMOBC LPI solder mask per IPC-SM-840 in accordance with the requirements of 3.7 of IPC-6012. The Type VII Via may or may not be covered. It is dependent on final surface finish and functional implications (via in pad). Dewey -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Chris Mahanna Sent: Tuesday, April 14, 2009 8:15 AM To: [log in to unmask] Subject: Re: [TN] Info on LPI tenting of vias, both sides Kevin, No big deal- Just making sure that we are on the same page. IPC-4761 is a laundry list circa 2007, not preferred, not necessarily common. Consensus at the time was scarce, not much better today. IPC-6012 still has no explicit via protection requirements. We might get bare copper to explicitly apply to the vias in 6012C, but I doubt it. The majority of industry, including class 3, still seems to be very much split. That said, via protection is a real world everyday risk. Our most common flavor: single sided plug -> trapped nickel pretreat -> circumferential isolated thin hole wall copper -> z axis differential CTE during soldering = barrel cracks as infants. It is a horrible defect as it usually very random (at least thin Cu or poor tensile/elongation is easy to find). Any other etching/corrosive/ionic material trapped in the via can yield similar, or other bad results. A breached double sided plug/tent will certainly trap better, if the bad guys get in. Keep in mind the relative count of opportunities (percentage of tent failures is usually low). But 'cosmetically' those tent failures can be a little too obvious. Mask isn't fond of -65/125 shock, but hey vias aren't either. More common hi-rel choices: Double plug + cover ENIG/ENEPIG first then mask HASL first then mask (requires mask over meltable metal waiver) Fill Fill and cap As far as I know, the jury is still out on ImAg, ImSn as final via finish. Considering creep, tarnish, whiskers, porosity... I wouldn't go there. Chris -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Kevin Glidden Sent: Monday, April 13, 2009 2:32 PM To: [log in to unmask] Subject: Re: [TN] Info on LPI tenting of vias, both sides It is for via protection. We have documented failures of assemblies where UR conformal coating pin holes and/or break-down allowed moisture ingress to a via and resulted in corrosion and ultimately shorting of an inner layer to an adjacent non-functional pad. Kevin -----Original Message----- From: Whittaker, Dewey (EHCOE) [mailto:[log in to unmask]] Sent: Monday, April 13, 2009 1:56 PM To: TechNet E-Mail Forum; Kevin Glidden Subject: RE: [TN] Info on LPI tenting of vias, both sides You must first decide if this is a functional requirement, such as part of a via protection strategy or simply a manufacturing aid, then we can talk. Dewey -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Kevin Glidden Sent: Monday, April 13, 2009 10:45 AM To: [log in to unmask] Subject: Re: [TN] Info on LPI tenting of vias, both sides Yes, it was my mistake. I intended to say dry-film tenting of vias on both sides. I have IPC-4761, and it basically covers an LPI tented via as Type I. What is not clear is if by inclusion in the specification that this is a preferred format or not, or was simply included because it is common practice, right or wrong. In section 3.2 there is also a statement "Plugging of vias from both sides of the hole results in manufacturability and reliability issues". I have heard warnings that tenting both sides can be problematic in that if the seal is not perfect or somehow compromised (adhesion loss / puncture) moisture or other contaminants can make their way in and the results can be more catastrophic then a blind or single-side-tented via. I have also been warned that at one time LPI tenting was "verboten" in MIL-STD-2000, so that alone is questionable whether it was a scientifically derived requirement, as some of the old requirements did not have the benefit of today's research. Thanks, Kevin -----Original Message----- From: Chris Mahanna [mailto:[log in to unmask]] Sent: Monday, April 13, 2009 1:25 PM To: TechNet E-Mail Forum; Kevin Glidden Subject: RE: [TN] Info on LPI tenting of vias, both sides Kevin, Generally LPI and Tent don't go in the same sentence unless there is a secondary cover. Is your intent via protection? Does your solderable final finish process follow the mask? Chris Chris Mahanna Robisan Laboratory Inc. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Kevin Glidden Sent: Monday, April 13, 2009 12:45 PM To: [log in to unmask] Subject: [TN] Info on LPI tenting of vias, both sides Hello everyone, I am looking for information on the potential pitfalls of using LPI via tenting on both sides, leaving an air pocket in the vias. Application is NOT Pb-Free. I located this article description, and wanted to see if anyone had it, but other information, inputs, or articles are also welcome: Title: An Evaluation of Via Hole Tenting with Solder Mask Designed to Pass MIL-P-55110D Thermal Shock Requirements Author(s): J.J. Davignon, F. Gray Journal: <http://www.emeraldinsight.com/0305-6120.htm> Circuit World Thanks! --------------------------------------------------- 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 ----------------------------------------------------- --------------------------------------------------- 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 ----------------------------------------------------- --------------------------------------------------- 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 ----------------------------------------------------- --------------------------------------------------- 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 ----------------------------------------------------- --------------------------------------------------- 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 -----------------------------------------------------