Repairing Cernox sensor Pt leads

The following information was provided via email with the disclaimer, "We are ultimately not responsible for what happens if the attempted repair is unsuccessful"

Suggestions:
• Do not remove the residual piece of Pt wire on the bond pads, but look to the side of it where there is open pad space.
o If this is really beat up, do not attempt repair. Order replacement.
o If there is good bondable metallization on the remaining bond pad, then that is where you want to make a new weld.
• If re-weld is doable, straighten out the ribbon wires and clean with high purity Isopropyl alcohol. Dry with Kimwipe/labwipe and allow to air dry for a while. Clean the bond pads with high purity Isopropyl alcohol and acid brush. Dry in the same manner.
o Wear gloves and don’t touch parts with hands.
• Use a DC welder, something like a Unitek PECO ThinLine, with a parallel gap type tip. Select the correct tip material for precious metals.
• Dress the tip using a very flat piece of Alumina. There should be steps on web to show how to do this.
o Make sure not to touch the tip with bare hands, wear gloves. Check the tip for any FOD and remove before welding.
• Set the DCV pulse amplitude, duration (usually millisec), and downward force to apply with tip.
• Align ribbon wire in new bonding location and bring tip down to create a new weld.
o BTW, this is something that the operator usually has to build a weld schedule for. So this could take several tries. It would be much better if the customer had similar trial/scrap materials to help dial-in the weld schedule needed for proper repair.”