Kitty, While it is more comfortable for a fabricator to have these parameters you mention pre-specified... really they are determined and design driven requirements that depend on the intent and requirements for operation of the circuit under the environmental conditions it will be exposed to and tested against. People tend to get caught up in specifications and rules... don't get me wrong, I like rules and standards and specifications... but they do not restrict what a designer can do. The design goals do. You have to determine that...based upon the specific design and its needs. If all things were designed based on past specifications and standards... there would be no innovation or "anything new under the sun... " (to borrow a quote from a somewhat famous passage...) The power and responsibility the PCB designer has that the manufacturer does not is in the designer's ability to balance the electrical, thermal, mechanical, circuit board design requirements against the standards and find a solution that can be manufactured and tested and assembled economically while surviving the intended conditions the circuit must operate in for as long as it is intended to survive. (Wow, I need a deep breath after that one...) :) Believe me, there are many boards that are successful that do not meet the specs. New ideas are being tried all the time that there is no spec for. While that really gives you nothing substantive to tell them, it should indicate that you are not restricted in your designs unless it is self or company imposed or contractually imposed on your project. The limits are really... whatever can be fabricated and still work under the conditions it must... Some board houses cannot fabricate cutting edge technology, while a smaller number of manufacturers can and do regularly and in fact set the 'cutting edge'... Some assembly houses have trouble placing 0805 resistors while others are happy to place 0201's or smaller... it just depends on what your operating budget is and what vendors capabilities you want or need to work with and how much your product can cost once it is built... etc... etc... I really don't think IPC has put a restriction similar to what you appear to suggest on board designs. The closest thing to a restriction would be a voluntary compliance with IPC-7351 the land pattern standard for example. It does set some spacing and land size standards that we can follow if we want to avail ourselves of the common economic benefits that come from adopting them. However your manufacturing department may need to set guidelines for you to agree with in order to guarantee that THEY can build your designs... or if you exceed their abilities in your designs, you may have to have your product built outside your facility at a more advanced assembly house or ask your company to invest in more capable assembly equipment so they can build the tighter, more advanced technologies... its all in the balance criteria... if you can balance everything you get the best results for the least cost... but not everyone is designing to those goals... some don't care what it costs... it MUST WORK and ANY COST... so the designer needs to understand that and design accordingly. Sorry for the long winded response... your message caught me during lunch time and well.. I could not help myself. :) Best regards, Bill Brooks - KG6VVP PCB Design Engineer, C.I.D.+, C.I.I. Datron World Communications, Inc. 3030 Enterprise Court, Vista, CA 92083 http://www.dtwc.com Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510 e-mail:[log in to unmask] _______________________________________ IEEE Member Member IPC Designers Council Instructor at Palomar College http://dcchapters.ipc.org/SanDiego/ http://www.palomar.edu http://pcbwizards.com -----Original Message----- From: Kitty Hines [mailto:[log in to unmask]] Sent: Tuesday, August 28, 2007 11:53 AM To: [log in to unmask] Subject: [DC] Spacing Requirements Hi, I'm trying to revamp some of the spacing requirements that our Manufacturing Dept. has decided upon and need some documented proof that the spacing they "require" is unnecessary. I tried to find specific requirements in IPC-2221, but wasn't able to find them. What I'd like to find is spacing requirements for pad-to-pad, pad-to-trace, smd land-to smd land. I'd like to find requirements for solder wave and reflow processes. Does anyone know what IPC spec I should be looking at? Or a reliable reference I can find? These requirements would only take Manufacturing rules into consideration, disregarding any electrical rules. Thanks for any help you can be, Kitty --------------------------------------------------------------------------------- DesignerCouncil Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF DesignerCouncil. To temporarily stop/(restart) delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL/(MAIL) Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail 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 ---------------------------------------------------------------------------------