When MIL-STD-2000A was written, the issue of the SOT's didn't arise because at that time, Military didn't allow use of non-hermetic ICs and thus we didn't consider criteria for these parts. I recall as I chaired the Acceptance Criteria Committee for the DoD for MIL-STD-2000A and am still having nasty flashbacks!!!! What you see in 2000A was a general requirement that solder not contact the part body lead seal for reasons of thermal transfer (4.23.7.5 Lead heel fillet.); this wasn't a defect as the idea was that the part's functionality was 100% checked AND solder may wet up to near/abut lead if the lead is solderable (e.g. gold). The part about not touching the bottom of the part was in 4.23.7.7 (J-leaded and V-leaded device) and had to do with solder under the device acting as a stress loading point during low temp exposure. Remember, we were talking hermetic (ie. ceramic) devices. When ANSI/J-STD-001A was being developed (A rev), it was noted,as you point out, that solder contacting the sides of the part (on SOT/SOICs) is fairly common and no failures were noted, thus the condition was allowed in ANSI/J-STD-001A in table 9-2 note 1. Call if you have questions. Jim Maguire Senior Principal Engineer Boeing Defense & Space Group PO Box 3999 M/S 3W-97 Seattle, WA 98124-2499 Phone 206-657-9063 FAX 206-657-8903 Email: [log in to unmask] ______________________________ Reply Separator _________________________________ Subject: ASS- X S Solder on SOT-23 Author: [log in to unmask] at esdigate Date: 4/30/96 2:32 PM Mail*Link(r) SMTP ASS: X S Solder on SOT-23 Kenny, Your response of "no response" I find very interesting. IMO, I would not allow the filling of the strain reliefs in the component leads for any "serious" Class 3 product. The following are my concerns/thoughts: 1) With solder against the component body, significant heat has been transfered through the component lead(s) through the lead and into component body seal. This could have degraded the adhesive bond between the lead and plastic body molding compound. 2) Differences of thermal expansion coefficients between the component and the printed board interconnection substrate during thermal/power cycling/shock will strain the (assumed weakened) bond between the component lead and component body. Re-occuring cyclic reverse-stress could lead to component failure. 3) Mechanical shock/vibration will likewise subject the component lead and component body to the same type of possible failure mode as in concern/thought 2). However it may be acceptable, depending on the life-cycle environment (as you will read, this pun was not intended) for the poroduct. If the component were mounted on an assembly that was a medical implant, such as a heart pacemaker, it would probabibly be acceptable, because if the inside of the ol' human body is subjected to thermal shock/cycling or mechanical shock/vibration to damage the assembly/component, I think some other part of the 'ol body will deteriorate functionality before the SOT-23's soldered connection. Disclaimer - this is my opinion, and would most probably not endorsed by my employer. Ralph Hersey e-mail: [log in to unmask] -------------------------------------- Date: 4/30/96 7:17 AM From: Kenny Bloomquist On Friday, April 26th I wrote: We are discussing excess solder on a SOT-23 for a critical DOD application per MIL-STD-2000A. The condition is solder contacting the body of the component between the PWB and the body, also solder contacts the lead seal. Per 2000A this "shall not" be done but it is not in Table 1 as requiring disposition. My real question is, what is the risk for this condition and does anyone have any supporting data (good, bad or otherwise)? I was suprised that no one sent a response. I know this is a touchy subject but any information would be greatly appreciated. Thank you in advance for all responses. [log in to unmask] ------------------ RFC822 Header Follows ------------------ Received: by quickmail.llnl.gov with SMTP;30 Apr 1996 07:15:30 -0700 Received: from ipc.org by simon.ipc.org via SMTP (940816.SGI.8.6.9/940406.SGI) id IAA11945; Tue, 30 Apr 1996 08:54:36 -0700 Resent-Date: Tue, 30 Apr 1996 08:54:36 -0700 Received: by ipc.org (Smail3.1.28.1 #2) id m0uEF6w-0000CSC; Tue, 30 Apr 96 08:04 CDT Resent-Sender: [log in to unmask] Old-Return-Path: <[log in to unmask]> Message-Id: <[log in to unmask]> X-Sender: [log in to unmask] X-Mailer: Windows Eudora Version 1.4.4 Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Date: Tue, 30 Apr 1996 06:09:41 -0700 To: [log in to unmask] From: [log in to unmask] (Kenny Bloomquist) Subject: ASS: X S Solder on SOT-23 Resent-Message-ID: <"VhA0C1.0.lO7.o_WXn"@ipc> Resent-From: [log in to unmask] X-Mailing-List: <[log in to unmask]> archive/latest/3726 X-Loop: [log in to unmask] Precedence: list Resent-Sender: [log in to unmask]