Tom, Digital ran a set of experiments on via in lands and tangential lands a few years ago and established the following design rules. 1. Preferred design practice calls for a 0.013" of soldermask between the via land and the SMT land, 0.010" minimum. (that's a dispersion etch length of (0.013") 2. Tangential via lands that has a slight overlap with the SMT land must have a maximum via hole size of 0.020" to prevent solder paste from filling the via and starving the SMT land; your 0.015" hole size exceeds this requirement. 3. Re-reflow (when the wave solder process reflows the SMT solder joint) can be prevented by keeping the dispersion etch/soldermask bridge at least 0.030" for SMT devices a lead pitch of 0.025" or less. 4. SMT pads with holes is not recommended because of the drill sizes and Land If you have a FAX number, I'll be happy to send you a copy of the etch dispersion rules. Harry Parkinson Digital Equipment Corporation 603-884-6760 Internet [log in to unmask] From: US2RMC::"[log in to unmask]" "MAIL-11 Daemon" 27-JUL-1995 13:22:50.09 To: [log in to unmask] CC: Subj: Unidentified subject! I am looking for any information concerning the minimum distance between a via to smt land (1206, 0805, and 0603). Currently we are using a .015 hole / .030 pad non-tented via. Is anyone out there burying the via in the center of the land? The wave side is not as much of a concern as the reflow side. We are planning to run some test boards with several configurations. I would appreciate any feed back. Tom Vaillancourt Philips Consumer Electronics Co. 615-521-3482 Internet: [log in to unmask] % ====== Internet headers and postmarks (see DECWRL::GATEWAY.DOC) ====== % Received: from mail1.digital.com by us2rmc.zko.dec.com (5.65/rmc-22feb94) id AA20416; Thu, 27 Jul 95 13:11:21 -040 % Received: from miso.wwa.com by mail1.digital.com; (5.65 EXP 4/12/95 for V3.2/1.0/WV) id AA02781; Thu, 27 Jul 1995 10:06:20 -070 % Resent-Date: Thu, 27 Jul 95 12:17:30 EDT % Received: from ipc by gagme.wwa.com with uucp (Smail3.1.28.1 #8) id m0sbWMW-000FPlC; Thu, 27 Jul 95 12:04 CD % Received: by ipchq.com (Smail3.1.28.1 #2) id m0sbVl0-0000GlC; Thu, 27 Jul 95 11:25 CD % Old-Return-Path: <miso!knox.pcec.philips.com!vaillant> % Date: Thu, 27 Jul 95 12:17:30 EDT % From: [log in to unmask] (Tom Vaillancourt 3482 ) % Message-Id: <[log in to unmask]> % To: [log in to unmask] % Resent-Message-Id: <"aAjDi.0.vmA.Lux5m"@ipc> % Resent-From: [log in to unmask] % Subject: Unidentified subject! % X-Mailing-List: <[log in to unmask]> archive/latest/746 % X-Loop: [log in to unmask] % Precedence: list % Resent-Sender: [log in to unmask]