Yes, I agree, and I have a confession to make as well... I asked an IPC dude (Gary) about the difference between the registered pattern dimensions and the calculated results, and he said the calculator was in the process of a significant re-design, but then I never heard anything about it since then. (Does anyone know if there is a newer version on the way? or is that what we are using now?) The confession is, sometimes I am lazy and just look it up in my SMTplus library, since they have every SMT part under the sun. (my original post said "If I was starting OVER again") After being frustrated by seeing 4-5 "suggested" patterns for the same darn part from every vendor and data sheet, I still maintain it is preferable to START with a standard. As for your statement about "permutations in board design, materials, assembly processes, component package styles, materials and contents, operating conditions..." well, this getting into the area where your knowledge and experience is leading you towards a modification, which is GREAT!, All I say is DOCUMENT THE REASON so the next bozo to come along won't change it and lose all the benefit of your work. And I still stick by my statement that if you DON'T know what you are doing, USE A STANDARD, don't use a component data sheet. Jack [log in to unmask] 16Apr2002 08:02 PM To: "TechNet E-Mail Forum." <[log in to unmask]> "Jack C. Olson" <[log in to unmask]> cc: Subject: Re: [TN] IPC SMT FOOTPRINT DESIGN GUIDLINES VS SUPPLIERS Retain Until: 05/16/2002 Retention Category: G90 - Information and Reports Caterpillar Confidential: Green Jack, I had great difficulty in getting land patterns to "conform to IPC". If you have a registered land pattern and it's in IPC-SM-782, but you then check/compare it using the calculator/formula in the same spec, you get two different results. Where is the conformity, I ask? Also, there are more instances of no-land-pattern-information-availability than there are guidelines or recommendations. As was said, component manufacturers do their own thing, maybe loosely centred around "standard" package types, but they often differ enough from the standard to make one suspicious about using the "standard" land patterns for them. As I said (provocatively) in my last reply posting, there are too many permutations in board design, materials, assembly processes, component package styles, materials and contents, operating conditions and so on, to have a concise "standard" for all occasions - unless each parameter in the overall CCA universe becomes standard/fixed. What we have are workable compromises that suit most groups of parameters. It's towards the more extreme CCA applications and environments that these compromises start to break down. I believe there's still a ways to go before 'art' changes to 'science'. Peter "Jack C. Olson" To: [log in to unmask] <OLSON_JACK_C cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST @CAT.COM> Aero/ST Group) Sent by: Subject: Re: [TN] IPC SMT FOOTPRINT DESIGN TechNet GUIDLINES VS SUPPLIERS <[log in to unmask] ORG> 04/16/02 10:53 PM Please respond to "TechNet E-Mail Forum."; Please respond to "Jack C. Olson" Great question! We have wasted SO much time designing custom libraries for specific vendors, its to the point of being ridiculous. Here is what I would do if I was starting over: - Design to IPC unless I had a GOOD reason not to. - NEVER use a component data sheet. can't trust 'em. - If a vendor had a reason supported by SCIENTIFIC DATA to suggest a change, DOCUMENT IT! The ideal (in my opinion) would be to say "All footprints conform to IPC with the exception of..." and for those exceptions explain WHY YOU CHANGED IT. (including high density versions, wave solder alternates, whatever) best wishes, Jack -----Original Message----- From: Earl Moon [mailto:[log in to unmask]] Sent: Sunday, April 14, 2002 2:03 PM To: [log in to unmask] Subject: [TN] IPC SMT FOOTPRINT DESIGN GUIDLINES VS SUPPLIERS Folks, Just a simple question really. How many folks use IPC SMT footprint guidelines compared with supplier recommendations? There often is quite a difference. As everyone on this planet uses IPC acceptance criteria, why shouln't everyone use IPC design guidelines but for component supplier liability issues? MoonMan --------------------------------------------------------------------------------- Technet 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 Technet To temporarily halt delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL 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/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 --------------------------------------------------------------------------------- [This e-mail is confidential and may also be privileged. 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