FYI, from a practical manufacturing point of view, I normally will ask that the clearance be at least 15 mils, ID to OD of thermal relief. Anything less than 5 mils has a good chance of turning into a direct connect. kb Ted Tontis wrote: > I am still fairly new to PCB design and I am studying for the IPC > design cert. I cam across IPC -2222 9.1.2 Thermal relief in conductor planes > which states the relationship between the hole size, land and web area is > critical. Typically, divided 60% of the minimum land area diameter by the > number of webs desired to obtain the width of each web in accordance with > the following example: > I understand this with no problem but where does it state the air > gap or expansion size? Is it the same value all the way around the land > area? or does the current control the distance? > > Thank you, > > Ted Tontis > Engage Networks Inc. > [log in to unmask] > PH 414.273.7600 Ext. 7607 <http://www.engagenet.com> > > --------------------------------------------------------------------------------- > Technet 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 Technet > To temporarily halt delivery of Technet send the following message: SET Technet 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 > --------------------------------------------------------------------------------- --------------------------------------------------------------------------------- Technet 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 Technet To temporarily halt delivery of Technet send the following message: SET Technet 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 ---------------------------------------------------------------------------------