-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 09/01/2010 04:49 PM, Lorenzo Marcantonio wrote: > On Wed, 1 Sep 2010, Alex G wrote: > >> Thanks!!! This should prove very useful. I like their idea with the RMS >> sum for tolerances. > > It's actually a rule from statistic... summing the whole tolerances is > the `worst case' method. If (and only then) the tolerance have gaussian > distribution (and since we're talking about manufacturing thats probably > true) you can take their RSS (Root Squared Sum) instead, and still have > a representative value. Google for 'summing tolerances' to get copious > explanations. In other word, they simply applyed the usual rules :D > I'm (partially) familiar with statistics. I took a year-long college-level course in high-school on the matter. And then there's the common RMS measurements for AC. I like the idea of applying this idea to PCB design. :)
>> If I had the standard, I would quote the tables (with proper references >> of course). No, I'm not asking you to do it; I already have that info in >> LP Calculator. In fact, I'm not even suggesting it. It's just my way of >> saying I live on the dangerous edge of life. :-p > > Also, they are biggish (look at the list of the pin type, each pin has > a table for the three manufacturing densities with all the fillet > targets and courtyard excess) and easy to misquote. Since they would be > hand copied anyway I just offered a `reliable source'. And they copied > the `round to 0.05, 0.10, 0.15 and so on' explanation in *each table* as > `roundoff factor'. > And your source is very well appreciated. :) Don't worry, if it comes to it, I will quote the tables from LP calculator. Your help is already immense and of immeasurable value. > I'm looking in the rest of the standard for juicy bits... it's mostly > stuff like: QFN should survive reflowing at least 5 time, blah blah, or > what differ in etching if you use phototools vs laser engraving and > liquid resist vs dry resist, fixturing for panelization and so on (i.e. > very low level stuff for the people actually fabricating boards). > > Oh, and *vital* information like: Tape peel strength [they're talking > about components reel] shall be 40 grams +- 30 grams (/me imagines > a Q.A. technician measuring with a dynamometer the peeling strength of > one reel :D:D) > Ya' know what. For the stuff that I do, a 650W Bosch drill with scotch tape around the smaller drill bits does the job. The only thing that I would be crazy enough to measure its peeling strength with a dynamometer is too inappropriate to discuss on the list. Anyway, the bits relevant for kicad are the footprints, and a footprint calculator. That will allow kicad to penetrate deeper (no pun intended) into the professional market. > And of course there are IPC-7251 (i.e. through hole components, we need > it to replicate the corresponding function in the LP Calculator) and > IPC-2222 (mixed wisdom about overall PCB design, layer stacking and so > on -- including test coupons in panels and using some little resistor > clips if you need a board for the space shuttle :P). > Remember those headaches I mentioned earlier? (This is by no means an "I don't care"; it's just that I have too much stuff going on right now to dedicate CPU time to processing it). >> I say you should include a schematic for a GPS guided missile so that >> someone may send a free copy of your work to whatever entity wrote the >> standard (non-destructively, of course). :-p > > I suggest to send it to Mentor Graphics which acquired PCB Matrix (the > developer of the calculator). Or, also, to IPC itself which in the back > cover essentially says: > By the way, you should probably license your quick intro under the GFDL before we do that. > 'You have to pay because we spent a lot of time researching it and > partecipating meetings with a lot of red tape with ANSI and so on' > "And you can just imagine how dull a meeting looks without refreshments, wine, beer, and bikini girls" > They don't even offer an `upgrade license' for the owner of the old > standard, you have to pay it fully... (you only have 50% off if you have > *membership* with IPC, I don't dare to ask what they want each year:D) > Or whether they charge their membership in money or one of the last items I mentioned earlier. Alex P.S. Preemptive apologies to anyone who may find this email offensive. The truth of the matter is, I can only only be furious or sarcastic at those who make exaggerate profit from us common people. (And honestly, I think I found the most hurtful sarcasm for those old guys trying to rip us off). -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (GNU/Linux) Comment: Using GnuPG with Fedora - http://enigmail.mozdev.org/ iQIcBAEBAgAGBQJMfmNoAAoJEL0kPHNPXJJKx0IQAJEelhawiGargHV5XPwnGZyn XGpn2jAWekFzjwsGKtgzyC5ATAqcdJh0FZIg9xL6VLxXA+T9FUOY/b/jhPllw2aa NooLKC/ICtHKn9vMR+CCzASD+3JmprWfif3VUIa9VnCk5/FxAY1JZxedrGykZX5C DLIc/W22hZpNneZ6kacS1YsD1S3ek07wRrtmNYLungt4cTa9AghIXYYtr/Xo+A5Q +AzyqLbmfkFSxk4391AejcpkeHbo8Ls5WW4JHkI/+Tt329zPdO3Id3sIBEUkTv95 wCqaFAfE0+NFrAy7iumFWGmrufGpTNXGKX5PPHUZbEB+C2WEaOYaAjKX3zVNLn64 73DF7lZErcuHnC1vUCdLHwI/PY8AQ7mtC5wFciQKDHtZrpNWs9qtvBOo6rsRP+X/ xEDjOhFsQc2dcFSd8Z6pseAWCy8OU5r7Vcb7hcz9Xga0E8z87HUuLcwhE6xs2lQH JRGcL4u93nMEcdZV13PVPDnYZU67gCaTZ4bP0RtuIVsJXhomJ8FlLt6KxTLcloRf hSu71rhnIGCwyA2PlF6x7/ghsvoJFIEGfhS6KLdrZhD+aLdIUtqSpOvmru2o5U9J X/z3dIhf3YbMjhc/hTy7xjOQaVBeS9RPWkuz2T7dUn27fsb+gaOyluL2fgePyOPC NIu/XoFVNuh+3QJnq9FR =DndZ -----END PGP SIGNATURE----- _______________________________________________ Mailing list: https://launchpad.net/~kicad-developers Post to : [email protected] Unsubscribe : https://launchpad.net/~kicad-developers More help : https://help.launchpad.net/ListHelp
