Some other SM considerations: Suitability to coat insides of via's without cracking - some of the newer LPI materials are actually good for this. Via tenting - small <0.25mm drill via's - again there are LPI materials that can achieve a fill or coat depending on hole size, both without voiding and cracking if the design has enough gap between drill sizes. Method of application, typically curtain coat or spray. Fabricator specific, and limits what can be achieved. Matt or gloss, lower solder balling or higher surface resistance? Thermal, flux and cleaning withstand, aging, moisture absorption, Dk and Df (more so Df) etc etc. There are so many factors, some more relevant than others for a specific design. Unfortunately the generality of the constraining implied by SM-840 is far too wide to properly specify materials for all but "consumer" applications. A bit like slash sheets, but worse. As an aside, I regularly, and 100% successfully, probe thru soldermask with blunt scope probes and little pressure. Not really a functional insulator ,but happily the ATEX certification people think it is Best Regards David Greig ______________________________ GigaDyne Ltd 5 Albany Business Centre Gardeners Street Dunfermline KY12 0RN United Kingdom t: +44 (0)1383 624 975 www.gigadyne.co.uk ______________________________ -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Jeffrey Bush Sent: 29 January 2007 12:45 To: [log in to unmask] Subject: Re: [TN] Soldermask Types implied in IPC-D-325A FYI - .0015" is not an accurate callout. I suggest using the IPC-SM-840 specification in lieu of this. To obtain .0015" minimum on all feature geometries you may need more than 1 coat. The "wet" weight of most LPI coatings target .0012", which after curing result in thickness less than this. Many OEM specifications of old required a minimum of .0006", which was based on epoxy, deposited masks. Minimum thickness needs to be based on that material's DWV, rather than a arbitrary thickness value. Jeffrey Bush Director, Quality Assurance and Technical Support VERMONT CIRCUITS INCORPORATED 76 Technology Drive - POB 1890 Brattleboro, Vermont 05302 Voice - 802.257.4571 ext 37 Fax - 802.257.0011 <http://www.vtcircuits.com/> -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier Sent: Saturday, January 27, 2007 2:11 PM To: [log in to unmask] Subject: Re: [TN] Soldermask Types implied in IPC-D-325A Hi Andrew, That FAB note has a number of shortcomings. "Construction to be SMOBD, using liquid photoimageable (LPI) solder mask material, type XXXX. Apply to both external layers in accordance with IPC, (Type B, Class 2). Use appropriate solder mask artworks for each side of board." I would thing SMOBD should be SMOBC. I have never heard of a solder mask material Type "anything;" why put anything like this "down" if it does not have an accepted technical meaning? "...in accordance with IPC" is meaningless without giving an IPC document number-IPC-D-325 is a 'documentation' document; for specification purposes you should be using IPC-SM-840. (Type B, Class 2) also do not correspond to any accepted way of specifying solder mask. I would recommend a FAB Note like this: "SOLDER MASK OVER BARE COPPER ACCORDING TO IPC-SM-840, CLASS H, TYPE LIQUID PHOTO IMAGEABLE (LPI), 0.0015 MAX THICKNESS, COLOR: GREEN, BOTH SIDES OF THE BOARD. ALL FIDUCIALS, LANDS AND HOLES, EXCEPT VIAS, SHALL BE FREE OF SOLDER MASK MATERIAL." If you are in the process of wring a specification document for your PCBs, my White Paper in the subject may be helpful-I am sending the details in a separate e-mail. Werner --------------------------------------------------- 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 ----------------------------------------------------- -- Virus scanned by Lumison. --------------------------------------------------- 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 -----------------------------------------------------