Martin Euredjian wrote: > > Going beyond raw specifications I'm trying to understand some of the choices > made when designing land patterns for various types of SMT devices. > > snip < > > So, rather than actual footprints I am looking for any kind of study/paper > that looks into the consequences of varying the geometry of the patterns. > In other words: How does pattern geometry affect such areas as soldering, > rework, reliability, testing, manufacturing, etc.? Martin, The problem with footprints is the answer is in shades of grey rather than black-or-white. The change from one var- iation to another does not necessarily result in problems, but does move the yield in terms of DPMO. Having worked with IPC-SM-782 from inception as well as a number of CEM and OEM specific guidelines we've come to think of footprints in levels of qualification: generic (the part will attach, data sheet) broad concencus (IPC, "reasonable yield" nearly anywhere) narrow concencus (OEM negotiated with multiple CEMs) factory specific (CEM authored) As you move down this list you can expect higher yield if you are in the matched manufacturing environment. Aspects such as rework and inspection access are more an issue in determining whether your product is disposable post-test, while area reserved for testability prevents fixture or component damage. We try to start with JEDEC package types and confirm them to IPC (or other required) specification. The destination is really IPC-610 and/or J-STD-001. Close the loop (very important) with manufacturing dialogue and inspection. Hope this perspective is useful, -- Jeff Seeger Applied CAD Knowledge Inc Chief Technical Officer Tyngsboro, MA 01879 jseeger "at" appliedcad "dot" com 978 649 9800 Printed Board Implementation Services since 1983 ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu