Hi, Mell,
I'll throw a little fat into your new fire with few discussion questions:
Was the "Right way up vs. wrong way up reliability testing" carried out by
assembling virgin components the right way up and the wrong way up
intentionally and . i.e. the test pieces were not re-worked to produce the
test orientations?
If the answer to the above is Yes, the results are interesting and should
be noted - fit the resistors the right way up first time for maximum
reliability.
However, are there any similar, comparative test results of long term
reliability for components that are fitted the right way up only after they
were re-worked to make them the right way up? Are they still more reliable
than if they were left the wrong way up and undisturbed?
Peter
Mel Parrish
<mparrish@SOLDERIN To: [log in to unmask]
GTECH.COM> cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST
Sent by: TechNet Aero/ST Group)
<[log in to unmask]> Subject: Re: [TN] Upside down chip resistors
02/09/02 09:22 AM
Please respond to
"TechNet E-Mail
Forum."; Please
respond to Mel
Parrish
Agree with MoonMan, but for discussion, this criteria was included in the
standards some time ago and was a carry over from the Mil Specs. The
testing
was accomplished then to determine if there was justification to consider
orientation of these components. The tests for a particular program proved
that there was a very significant increase in component operational life if
the component was face up.
We didn't look at the "why" although there was speculation concerning
entrapment of process chemistries, or thermal issues for the film close to
the board.
IPC-A-610C calls this a Process Indicator for Class 2 and 3 which wouldn't
support rework. If the long term reliability of the component was a
concern, you might look at effective methods to correct it (not point to
point soldering). Best option is to orient up if it by process if
required.
Mel Parrish
Soldering Technology International
Madison, AL
256 705 5530
256 705 5538 Fax
[log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Earl Moon
Sent: Friday, February 08, 2002 12:51 PM
To: [log in to unmask]
Subject: Re: [TN] Upside down chip resistors
The less rework, the better. When replacing or reworking any chip device,
using hand soldering techniques, chances are damage will ensue.
MoonMan
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