Hi, Sefika, SM-782 offers formula at the beginning of the spec to use for calculating land patterns if your component does not have an RLP (registered land pattern) number, and the component's data sheet doesn't offer any recommendations either. Otherwise, there are a number of land pattern calculators on the Net, including IPC's own one at the following URL: http://search.ipc.org/sm782/default.asp I have found several things, though, that I'll share with you. I have found rare occasions where I have a data sheet that gives a land pattern for an RLP device that also appears in SM-782. I quickly noticed that the data sheet land pattern and the one given in SM-782 did not match. When I tried to verify one of them using IPC's formula and their on-line calculator, I got different answers again. So there is no standardised way of calculating land patterns. Even for RPL's, the "ideal" land pattern is dependant upon the soldering process you use and the nature/layout of your board. For example, wave soldering requires larger land patterns than Convection Reflow soldering in many cases, and features such as (even partially) unmasked traces and nearby via holes can act as "solder thieves" that rob your component of solder. Even with all the calculators and so on around, plenty of people are still experimenting with pad sizes and shapes to get the best, reliable solder joint. There is thus no exact science in calculating footprints. I adopted a hierarchy approach where information conflicted. First, if the data sheet gave a land pattern, I used that. If the data sheet didn't have a footprint recommendation, but quoted an RLP number, I used the SM-782 footprint, and if that too failed, I used IPC's on-line calculator to work it out from teh dimensional data that is usually given in the data sheet. There have been several, quite lengthy threads on this subject in the past year or so at least, so if you look up the TechNet archives on the IPC website and search for "land pattern", I'm sure you'll find lots of good advice. There is no "one size fits all" with footprints, though. You have to take your best shot at it and see how it works. If it doesn't, then you have to try adjusting it by experimentation and testing. Peter Sefika Ozkal <[log in to unmask]> 26/11/2002 10:32 PM Sent by: TechNet <[log in to unmask]> Please respond to "TechNet E-Mail Forum."; Please respond to Sefika Ozkal To: [log in to unmask] cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group) Subject: [TN] Footprint Hello, I have a problem about plastic small outline package type. I could not find the recommended footprint for two devices which are having SO8 and SO20 packages. Is there any one who knows to calculate the footprint values? Or, is there a standart I could use to solve this problem? I could not find aanything from IPC-SM-782A. Am I in a wrong way? I would be waiting for your answer. Best Regards, ªefika Özkal Electronics Engineer ASELSAN Inc. Microelectronics, Guidance and Electro-Optics Division Electronic Design Address : P.O. Box:30, Etlik 06011 Ankara,TURKEY Tel :+90 312 847 53 00 Ext:4698 Fax :+90 312 847 53 20 e-mail : [log in to unmask] --------------------------------------------------- Technet Mail List provided as a free 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/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a free 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/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 -----------------------------------------------------