Ray I know your pain, I started off life as a designer, then a layout engineer and after working with a lot of sub contractors did my bit in process engineering, then in service/manufacturing doing failure analysis and feeding that back to design where I ended up (again) and due to the experience I had stayed there doing a better job (IMO anyway) than I did in the first place.
But I think your frustrations are getting to you a bit, or my long response tipped you over the edge (sorry), but as you mentioned in your reply below, you had issues with data sheets and also manufacturing, because of library/footprint issues, so as I said, a library has to be more than it looks. And you cannot rely on the data sheets 100% unless it has a report attached to it with all manufacturing details, Motorlola and NSC do a lot of this, but most passive companies do not. Best Regards John A. Ross RSD Communications ltd Email [EMAIL PROTECTED] WWW http://www.rsd.tv ================================== > -----Original Message----- > From: Ray Mitchell [mailto:[EMAIL PROTECTED] > Sent: Thursday, March 11, 2004 7:48 PM > To: Protel EDA Forum > Subject: Re: [PEDA] Common PCB footprint specifications > > Everyone, > > Thanks for all the responses on footprints. This whole issue > is pretty sickening actually. Since we produce low > quantities of diverse products we have no dedicated PCB > layout people. All engineers do their own circuit designs > and parts specification and ultimately are expected to do > tiny PCB layouts of everything and get them to work. The > thing that gets me is that it seems like it would be > extremely simple for parts vendors to provide land patterns > for their parts along with the mechanical drawings of the > parts themselves. Some do but most don't. I just talked to > Maxim about this and they said they simply don't provide this > information. They recommended IPCSM782. Of course a good > percentage of the parts you need are not listed in this > document and a lot of them that are there do not match the > recommendations of the vendors of the parts. I asked Maxim > how they layout their own eval boards since they provide no > guidelines and no guidelines exist in IPCSM782. They didn't > have an answer but I suspect they rely on rules of thumb and > intuition, which is what we end up doing with our designs > here most of the time. After enough bad yields and scolding > from our PCB fabricators we manage to stumble into something > that seems to work. I did find what I thought was a good > layout for 0402, 0603, etc. from AVX capacitors. Upon closer > inspection, however, I found that their recommended > footprints violated their own guidelines given on a > different page of the same document. Go figure! > > Ray Mitchell > > > At 04:59 PM 3/11/2004 +0000, you wrote: > > > -----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 > > > > > > Ray Mitchell > Engineer, Code 2732 > SPAWAR Systems Center > San Diego, CA. 92152 > (619)553-5344 > [EMAIL PROTECTED] > * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * 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] * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
