Several weeks ago I challenged TechNetters to get a photo of "acid trap" phenomenon. No one volunteered. Not a big sample set, but I believe that this is one of those things which was a problem at the dawn of pcb manufacture, but is inapplicable to today's processes. The closest respondents could come up with was to point out that alkaline ammoniacal etch solution has a tendency to eat more copper once it has some copper in solution. But, obviously, this process will starve itself out too: There must be a peak copper concentration in the bath for highest activity, otherwise the reaction would continue until the solution was 100% copper decomposition products. I can provide photos of the inverse phenomenon, which most pcb manufacturers are aware of: Pads spaced way out in the middle of dielectric tend to become over-etched, whereas tight lines/spaces tend to be under-etched. No big surprise there, since its harder to get aggressive fluid activity in tight areas. For cupric chloride etchant, These lone pads really take a beating because once the dielectric around them clears, the hungry acid droplets will splash sideways along the dielectric until they bump into something. As to boards continuing to etch long after they've come out of the etching machine, I think that's completely ridiculous. Wayne Thayer >>> [log in to unmask] 11/21/2006 12:35:17 pm >>> Deac, I agree, acid never stops, but if properly cleaned it is either diluted or neutralized to a point of no longer being able to effect the metal geometry. Again I emphasize the importance of good practice by the fabricator, if properly cleaned an acid trap has no acid left in it. Good design practice should be to avoid the creation of possible acid traps, but sometimes due to other circumstances (RF structures being one) they are unavoidable. If a design has acid traps then the alternatives are fixing the design (if time allows) or using good fabricators whose processes will assure removal of all acids from the PCB prior to completion. Just my beliefs, FNK Frank N Kimmey CID+ Principal PCB Designer PCB Programs Powerwave Technologies Inc Office 916-941-3159 Fax 916-941-3195 Mobile 916-670-0645 -----Original Message----- From: Deac Descoteaux [mailto:[log in to unmask]] Sent: Tuesday, November 21, 2006 9:22 AM To: 'TechNet E-Mail Forum'; Frank Kimmey Subject: RE: [TN] Acid Traps Frank, Acid is like rust.....it never sleeps! The acid will continue, albeit, at a slow rate, to eat away at the etch. It will take time, but it will happen. The biggest problem is that it is one of the most difficult failures to find on a board. Deac Deac Descoteaux PalPilot, East Coast Corporation, (PEC) Director of New Business Development 71 Spitbrook Road, Suite #307 Nashua, NH 03060 office # (603) 888-3400, ext. #10 Toll Free # (877) PALPILOT, (725-7456) Fax # (603) 888-3500 Cell Phone# (603) 557-7568 email address: [log in to unmask] www.palpilot.com PCB LAYOUT * SIGNAL INTEGRITY * PCB FABRICATION * METAL CHASSIS * PLASTIC MOLD INJECTION * BACKPLANE SOLUTION * CONNECTORS The information contained in this communication including any attachments is intended solely for the use of the individual or entity to whom it is addressed and others authorized to receive it. This communication may contain information that is privileged, confidential and exempt from disclosure under applicable law. If you are not the intended recipient you are hereby notified that any disclosure, copying, distribution or taking any action in reliance on the contents of this information is strictly prohibited and may be unlawful. If you have received this communication in error, please notify us immediately by responding to this email and then delete it from your system. No printed copies should be made or retained. Thank you. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Frank Kimmey Sent: Tuesday, November 21, 2006 12:10 PM To: [log in to unmask] Subject: Re: [TN] Acid Traps John, In todays world, if a PCB is properly cleaned after etch, deposition and prior to mask, then acid traps should not be a concern. We do a lot of weird angle stuff in the RF world and I have never seen a failure due to acid trap type issues. Bottom line is if your fabricator has good process then it should not be an issue, but to keep risk to a minimum good design practice should be followed when possible. Hope it helps, FNK Frank N Kimmey CID+ Principal PCB Designer PCB Programs Powerwave Technologies Inc Office 916-941-3159 Fax 916-941-3195 Mobile 916-670-0645 -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of John Foster Sent: Tuesday, November 21, 2006 8:53 AM To: [log in to unmask] Subject: [TN] Acid Traps I would like to ask the board fabricators if acid traps are a real issue. I normally try to avoid any feature that creates a structure that is less then 90 degrees. However I am helping out another group by reviewing their boards and there are literally hundreds of acid traps on the board. This board is class 3 and has to be high reliability. I have always been taught that they can be a real problem. But have never quite understood why. Any input on this will really be appreciated. Thanks John Foster --------------------------------------------------- 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 ----------------------------------------------------- --------------------------------------------------- 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 -----------------------------------------------------