Thanks Bill...but in this case....it was just a 'bureaucratic paperwork' thing...they want all fab guidelines called out 'as per IPC-xxxx' on fab docs. I've always accounted for potential tolerance deviations, and the fab houses I use know what I'm after... I inadvertently purchased IPC-2615, but it's all good...I'm doing a GD&T certification course at the moment anyway. Always enjoy your 'rants' ;-) Tracy Brooks, Bill wrote: > Please... just be aware that the designing to the "minimum" is not > always the best 'recommended' practice... :) Some people make the > mistake of using the minimum numbers to design to and their > companies/employers/customers end up paying for it in the long run. > > And while I agree with using the IPC specs to set a standard for your > board design, I do not always agree with the IPC specs about some of the > choices that they made... for instance... in IPC-2222 9.2.1.2 they want > drill sizes expressed in a min/max definition, and not a +/- tolerance > expression... however, the nominal diameter information is lost in that > scenario... and I usually have a target hole size that is nominal, or > 'perfect' if you will, for the application that I need. To express it in > say '.188 to .210' for example... may not communicate or imply to the > board shop that I really want a .200 hole and I want the vendor who is > making the board to try to hit that target size. > > Main thing is to do the math, and express things in a way to get the > point across to the board vendor so that you get consistent results that > work. > The IPC standards are not rules... they are a standard way of doing > things that gets generally successful results... but they in no way > should limit the designer's options in doing things... the designer > needs to know how the board will be used, what it's service life will > be, how it will be mistreated and what expectations need to be met for > survivability, and what the cost targets and volume of production is > expected... > > Ah... I guess I'm on the soap box... I must be feeling better this week. > > > Take care... > :) > > Bill > > > James Head wrote: > >> For rigid boards, IPC-2222, section 9.2.1.2, table 9.2 lists minimum >> > non-plated hole tolerance ranges, and section 9.2.2.2 has plated hole > tolerances, given in table 9.5. > >> Regards, >> >> James >> >> James Head BEng CID MIIE MIET >> Senior PCB CAD Engineer >> Crowcon Detection Systems Limited >> 2 Blacklands Way >> Abingdon Business Park >> ABINGDON >> OX14 1DY >> >> Telephone: +44 (0) 1235 557700 extension (9) 289 >> Fax: 07092024504 >> Email: [log in to unmask] >> >> >> >> -----Original Message----- >> From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of >> > Tracy Norton > >> Sent: 30 September 2009 17:36 >> To: [log in to unmask] >> Subject: [DC] drill tolerance >> >> I just got caught in an embarrassing situation. A client pointed out >> that I don't have drill tolerance specified on my fab notes, and wants >> > > >> it added AND referred to the specific IPC standard >> I looked back at all my work as far back as to '98...and there's no >> drill dia tolerance callout! >> All I need is pointed to specific standard so I can research it and >> > add > >> to notes >> Thanks! >> Tracy Norton >> >> >> > ------------------------------------------------------------------------ > --------- > >> DesignerCouncil Mail List provided as a free service by IPC using >> > LISTSERV 1.8d > >> To unsubscribe, send a message to [log in to unmask] with following text >> > in > >> the BODY (NOT the subject field): SIGNOFF DesignerCouncil. >> To temporarily stop/(restart) delivery of DesignerCouncil send: SET >> > DesignerCouncil NOMAIL/(MAIL) > >> Search previous postings at: www.ipc.org > On-Line Resources & >> > Databases > E-mail 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 > > ------------------------------------------------------------------------ > --------- > >> ******************************************************** >> >> The information transmitted is intended only for the person or entity >> > to > >> which it is addressed and may contain confidential and/or privileged >> material. 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