80/20 Au/Sn Solder and Proper FLux Selection

All:

I am reaching out to get some suggestions on the right flux to use as well as a recommended cleaning process for soldering a KOVAR RF shield using 80/20 Au/Sn solder to a ceramic hybrid.

The recommended profile is 4-5 min at 280C and at least 1 min over 310C from the preform vendor. We are able to hit this profile.

Our process is to flux a ceramic board (2 mils thic of flux), place a 3 mil 80/20 preform and then place the KOVAR shield.

The issues we have seen are excessive flux residue then cannot be cleaned (no clean tacky flux) or the flux burns a re dark black and then cannot be removed (water soluable).

1. Does anyone have a recommended flux that can withstand these profile temps? 2. Does anyone know how to clean flux residue from Kovar?

BWET

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