Cupric system are great for inner layer since this chemistry efficiently removes copper and has generally a lower etch factor/side wall attack than you will see at the slower ammoniacal rates. Curpic is by far easy to control, but a properly controlled alkaline system does have advantages with some design types. Cupric with external layers is not compatible using a tin resist and the external layers are much more prone to have design flaws creating the acid trap issue. Your CAM system should be affective in the detection and correction of these types of layout issues. Jeffrey Bush Director, Quality Assurance and Technical Support VERMONT CIRCUITS INCORPORATED 76 Technology Drive - POB 1890 Brattleboro, Vermont 05302 Voice - 802.257.4571 ext 21 Fax - 802.257.0011 <http://www.vtcircuits.com/> -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Wayne Thayer Sent: Wednesday, September 13, 2006 10:02 AM To: [log in to unmask] Subject: Re: [TN] Etchant traps Thanks a bunch Joe. That helped answer some of my questions. Does anyone out there actually have a picture of the results of an alkaline etch actually creating this "trap" problem? I use cupric chloride, and I have a calibration pattern of "square spirals" at varying line and space. The corners of these tell a lot about how the cupric chloride etches in different situations: The amount of over-etch is monotonic with the area of bare dielectric immediately adjacent to the photoresist-protected copper. This matches my experience with circuits others have built for me: Isolated pads tend to get over-etched the most. Wayne Thayer >>> [log in to unmask] 9/12/2006 10:50 pm >>> Greetings Wayne, I realized that I did not really respond fully to your message of yesterday. You are right in your thinking and observations based on current best practices and it is a detail that should be corrected/clarified/brought current. I was recounting experiences that likely don't hold well today with current chemistry and equipment. My experience was primarily been with copper ammonia alkaline etchants beginning in the early 1970s and etching equipment not up to today's quality. We observed occasions where the sharp corners when fluid exchange was not good and copper etching irregular where this occurred. One of the curious things about alkaline etch chemistry is that the etch rate of the chemistry increases with metal concentration which is the genesis of the suggestion based on the observations at the time. As you suggest, design tools are not likely to make acute angles without permission. Again, the more important reason today remains the one mentioned earlier and related to simple mechanical issues and electrical performance. A very good article on alkaline etch by Karl Deitz can be found at the following link if you have interest. _http://www2.dupont.com/Imaging_Materials/en_US/assets/downloads/techtal k/TT02 05.pdf#search=%22%22etch%20rate%22%20%22ammonium%20chloride%22%22_ (http://www2.dupont.com/Imaging_Materials/en_US/assets/downloads/techtal k/TT0205.pdf#sear ch=""etch%20rate"%20"ammonium%20chloride"") Thanks for your observations and comments. Kind regards, Joe --------------------------------------------------- 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 -----------------------------------------------------