Hello Jack I see that you are with ADC. Are you in the group in Beaverton Oregon? I am with tmp.worldwide here in Portland and work with board designers. I have placed many good designers on contract. I thought I would mention that one of my clients in Beaverton will need a few designers in the near future. Would you happen to know any designers that like to work contracts? The tool of preference is Mentor, for this position. Just doing a little networking. Thanks for your time. Sharon K. Gheen Account Executive [log in to unmask] tmp.worldwide (Parent company of monster.com) 4900 SW Meadows Road, Suite 100 Lake Oswego, OR 97035 Toll Free 888-278-2272 Phone: 503-635-4658 Fax : 503-635-6067 -----Original Message----- From: Olson, Jack [mailto:[log in to unmask]] Sent: Tuesday, April 24, 2001 4:44 PM To: [log in to unmask] Subject: [DC] Minimum Via Size for .093 Thick PCB As a result of some discussion with our in-house manufacturing, we decided to re-evaluate our minimum via size for .093 board thickness. Just for fun (grin) I decided to look everything up in the latest IPC specs. If anyone enjoys poking holes in IPC logic, here is the result: (see below for supporting references) calculated IPC minimum via size = 19.7 mil drill with 41.4 mil land Can anyone think of a way to design PCBs to meet IPC with a smaller via? -=-=- Our initial parameters are: Design for Class 2 (no one is going to die if the product fails) Assume Level C producibility but prefer Level B (ha!) Many designs are >12" long Many designs are >8 layers According to IPC-2222 Table 9-6, a plated through via on a board >2mm thick for Class 2 is .5mm minimum Result: the minimum drill size is 19.68mils According to IPC-2221 Table 9-1, For a Level C board up to 450mm dimension (<18inches) and with note 2 to add .05mm to .45mm for >8 layers is .5mm minimum Result: Minimum Fabrication Tolerance is 19.68mils According to IPC-2222 Paragraph 9.1.1 minimum land = a + 2b + c where a = maximum drill diameter (19.68mils) b = minimum annular ring (1mil) c = fabrication allowance (19.68mils) Result: minimum land diameter is 41.37mils A 20 mil hole with a 42 mil pad is difficult to design with. To meet IPC even at Level C, the only thing I can see to reduce is the minimum annular ring to allow breakout, are ya kiddin me? Am I missing something? Any comments are greatly appreciated! Jack ---------------------------------------------------------------------------- ----- 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 set a vacation stop for delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------- ----- --------------------------------------------------------------------------------- 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 set a vacation stop for delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------