Thank you very much. I had not noticed that section (section 1.3)
before.
I was doing further googling on this matter this morning, and found a
very old TechNet post. Here is a snip. It shed a lot of light on this
for me.
This posting was from May 1, 1996.
{whew-12.5 years ago - the TechNet list must have been around since the
dawn of email...are there any original technetters still on the list?}
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...
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.
Thanks for everyone's responses.
Genny.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ted Tontis
Sent: October 28, 2008 11:31 AM
To: [log in to unmask]
Subject: Re: [TN] IPC-610, 8.2.5.5
Genny,
Take a look at IPC-A-610C 1.3 specialized designs.
In a nut shell it states
1. The document can not cover all components.
2. A decision/agreement needs to be made between the customer and the
supplier on acceptability of that component.
3. If there are similar characteristics to a component already in the
document, you could use 610 as a guideline to start from.
I do not know what the end use application is but I would do some
testing to verify that solder on the component body would not have a
negative impact on the over all reliability of the component or solder
joint. I work with automotive lighting applications and we are
constantly testing our customer's new designs and processes for
reliability due to the fact there is little or no documentation on the
assembly of new components/materials.
If there are issues or concerns prior to launch they are addressed with
the customer when exceptions can be made.
Regards,
Ted T.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Green, Mike
Sent: Tuesday, October 28, 2008 11:53 AM
To: [log in to unmask]
Subject: Re: [TN] IPC-610, 8.2.5.5
I would think that you would have to take an exception on the drawing
until IPC -A-610 provides direction for each special case design.
Solder touching the component is a defect because most components are
not designed to withstand the stress internally of molten solder
temperatures.
In addition, the solder joint in contact with a case puts the joint
subject to the CTE excursions of that case. For example, as a plastic
case expands, it pushes against the solder joint causing thermal stress
Mike Green
Electronic Packaging Design
LMCO-Sunnyvale
408-743-1635
One Corporation, One Team
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Monday, October 27, 2008 10:13 AM
To: [log in to unmask]
Subject: Re: [TN] IPC-610, 8.2.5.5
Hi Genny!
Sorry it took me a bit to get your picture posted, but you know how
Monday mornings can be. I've got it up now though, it's at:
http://stevezeva.homestead.com/files/tsfp-3.GIF
Steve
-----Original Message-----
From: Genny
Sent: Monday, October 27, 2008 9:58 AM
To: TechNet E-Mail Forum; Gumpert, Ben
Cc: Steve Gregory
Subject: RE: [TN] IPC-610, 8.2.5.5
I don't know. I've included a graphic. Steve could you post it please?
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Gumpert, Ben
Sent: October 27, 2008 5:10 AM
To: [log in to unmask]
Subject: Re: [TN] IPC-610, 8.2.5.5
Genny,
It sounds like you have something that has terminations similar to a
QFN/DFN but where the lead frame is not trimmed flush to the component
body. Is there exposed metal an the bottom side of the component, or are
the leads really coming out of the side of the component?
Are you sure that section 8.2.13 is not more applicable?
Ben
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Genny Gibbard
Sent: Friday, October 24, 2008 6:22 PM
To: [log in to unmask]
Subject: [TN] IPC-610, 8.2.5.5
Question for the TechNet gurus.
The spec in the subject says that solder touching the component body is
a defect. But it states that it is allowed for SOTs.
We use a component in a TSFP (thin small flat package). The
configuration like a 3 lead sot, but the leads are not gullwing - they
come straight out of the device and the whole package mounts flat onto
the board. It is much smaller than a SOT, on the order of ~1.2mm sq in
total area.
Does this fit in the definition of a SOT?
The recommended layout actually has the pads start under the device
body. I'm not sure how you could possibly avoid solder touching the
body.
In general, why is it a defect for solder to touch the component body
for other component types?
Thanks so much for your help.
Genny
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