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. 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