IPC-7251 & 3-Tier PTH Pad Stack Obsolete : In 2009 IPC (Dieter Bergman,...

Wed, 05 Nov 2014 10:13:18 +0000

Author: Tom H
Subject: 1463
Posted: 05 Nov 2014 at 10:13am

In 2009 IPC (DieterBergman, John Perry and Tom Hausherr) started progress on a land patternstandard for through-hole components called IPC-7251. There were meetings whereGary Ferrari attended by webcast. The 3-Tier pad stack annular ring forthrough-hole was based off the same precedent for SMD where the Least, Nominaland Most environments had a single value for Toe, Heel and Side. IPC-7251 nevergot published and progress was discontinued on October 1, 2014 by the IPC 1-13Land Pattern committee as they decided to instead add it to IPC-7351C whichwe’re currently working on.

The IPC-7251through-hole pad stack was inherently flawed due to the 3-Tier annular ringconcept that the same Annular Ring Value could be used for any hole size. Anexample of this would be: The Nominal Environment annular ring (AR) was set to8 mils. That means that a 10 mil hole had a 8 mil AR and a 20 mil hole had a 8mil AR and the 40 mil hole had a 8 mil AR and a 80 mil hole had a 8 mil AR. Theflaws are apparent in that small holes require small AR and large holes requirea larger AR for solder volume, strength, voltage current, heat, etc. Eventhough LP Wizard and Library Expert supported IPC-7251, the through-holedefault in both programs was “Proportional Pad Stacks” due to the fact thatIPC-7251 was an unreleased standard.

PCB Libraries Forum : IPC-7251 & 3-Tier PTH Pad Stack Obsolete

IPC-7251 & 3-Tier PTH Pad Stack Obsolete : In 2009 IPC (Dieter Bergman,...