John- Unfortunately, there are lots of exceptions nowadays to any "rule" like this you try to set up. There are just too many different packages and different kinds of packages to make blanket statements. The first package family which comes to mind for this application is the "FN" styles: "DFN" and "QFN". The "N" is for no- lead (that's not "lead" as in Pb, but as in legs). These packages often have a large contact under the body of the part for either thermal dissipation or good RF ground. I think they would be more appropriately called "ball-less BGA's" because that is essentially what they are--the manufacturers (and consumers) spend a considerable amount of money doing ball attach on BGA parts, so industry has discovered that you can get away without the ball for smaller parts under certain conditions. These "FN" styles all have body heights less than 6mils and you MUST put solder beneath them to make proper electrical contact. Other components which violate the "rule" you are asking about are the "leadless" devices. These use "castellations" (vias sawn in half--see ceramic crystal packages) or end-wrap terminations (such as most SMT resistors and capacitors) for contact. Again, you want solder to go beneath these parts. So I'm actually having trouble imagining where the "rule" might make sense! Perhaps it was made because of people complaining about shorts under "FN" packages which are actually due to the manufacturers not assigning a pin number to the big pad used for thermal/RF reasons--when these get entered into the CAD library, many CAD operators aren't sure how to handle them without a pin number, so maybe they left the pad off the library model and thus the opportunity for a short occurs. Wayne Thayer >>> [log in to unmask] 12/9/2006 1:20 pm >>> Hello I was wondering if some manufacurers could comment on the following. I have been using a footprint calculator and it recently added a new feature. The calculator asks for the height of the component body from the board. If the height is less then 6 mils then it will not allow the pads to go under the body of the IC. This makes sense to me as then when the paste is deposited the body of the IC is not setting in the solder paste. In the old calculator and quite frankly in almost every decal tool or baseline I have seen the pads run up under the body of the IC. I think most board deigners tend to make the paste layer identical to the surface mount pad. I have not personally had problems with this. But I don't assembly circuit cards for a living. I am building a lot of new decals and am running with this new thought because it makes sense from a common sense standpoint. However I worry about heel fillets. DOES IT REALLY MATTER. Any input will be appreciated Thanks John Foster --------------------------------------------------- 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 -----------------------------------------------------