> -----Original Message----- > From: Ray Mitchell [mailto:[EMAIL PROTECTED] > Sent: Wednesday, March 10, 2004 5:36 PM > To: [EMAIL PROTECTED] > Subject: [PEDA] Common PCB footprint specifications > > Hello, > > I'm sure this is a repeat, but is there a simple > specification readily available that gives the "commonly > accepted" (if there is such a thing) dimensions for 0402, > 0603, ..., SIOC-14, etc., and all the other "standard" > footprints? I don't really want to wade through a bunch of > technical stuff to derive all of this myself and I certainly > don't want to trust a priori the patterns that come with > Protel or any other product. It's really annoying when part > manufacturers don't provide these footprints, assuming they > are common knowledge.
Ray I have accumulated quite a library of such footprints but most of them will have been optimised to suit our in house processes more than following the IPC standards. The supplied Protel IPC land patterns are not too bad, they are certainly a good basis to build your own on. But most libraries stop at the land pattern stage, which is what the IPC are looking to change. A lot of the way the IPC are trying to structure library conventions are along the lines of what I was already doing for years anyway, not because it is good, but because it make life easier for us internally if the naming conventions for footprints already match vision library footprints on placement machines (which then relates to mechanical dimensions as well, as a Murata 16V X7R 0603 will have different dimensions to a Kemet 16V X7R 0603 in same voltage) and other EDA packages we use etc. I especially like the way the new IPC recommendations take account of things like, 0 deg positions in tape or tray, if Protel could also make allowances for rotation on non-polarised chip parts (only use 0,90) to reduce un-necessary head rotations on turret head placers that would be even better as I currently use an in house utility to parse the P&P files and check for string matches on footprint & part number to identify non-polarised parts and it will replace 360 or 180 values with 0 and 270 values with 90. In DXP I planned to use a parameter for that at SCH level, so I only need to check for one match, but that's another story, no time for documenting or agreeing how this should be done internally yet. Same with pad sizes, I slightly oversize SMT pads in some cases against IPC recommendations (not much) to allow for place tolerances when reducing Z height & down pressure, Vac release and place speed, especially on Chip r/c's as well as wave flow direction and so on. Same for connector placement, especially for IDC and connector rows <2.54mm, I sometimes enlarge the pads beyond IPC recommendations in one direction to get the best out of the features on our wave soldering equipment (Vitronics-Soltec with Select-X debridging). If Protel could assign a different footprint for rotation, or side, based on some sort of logical system, then it would make life so much easier to define DFM rules even at SCH level. Perhaps that's worth a new feature request on the DXP forum :) To me a library has to be more than just a symbols collection, or the manual pre-processing required diminishes its value, very little third party libraries do this, so IMO are not worth it. I like the IPC new offerings for library recommendations very much, and would like to see it adopted, even although some of the naming recommendations may choke some placement machines offline programming software or optimisers software a bit like white space, characters, case sensitivity and a lot of other things that should be non-issues in this day/age. I prefer a direct import approach to programming these machines, Gerber import, pattern search and processing is alright, but takes to long and can be error prone. If anyone wants me to split & upload the library contents I have here, ill do it as a part time job, but I guess most people will have these things already, or prefer to use their own in-house libraries. John * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * To post a message: mailto:[EMAIL PROTECTED] * * To leave this list visit: * http://www.techservinc.com/protelusers/leave.html * * Contact the list manager: * mailto:[EMAIL PROTECTED] * * Forum Guidelines Rules: * http://www.techservinc.com/protelusers/forumrules.html * * Browse or Search previous postings: * http://www.mail-archive.com/[EMAIL PROTECTED] * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *