Is there a wire bond specialist listening?
I am frustrated about a MCM package, bottom Al2O3, seal frame Kovar, leadframe Kovar and conductors/mounting pads consisting of either a)one layer Au thickfilm b) Au thickfilm/blue dielectric/Au thickfilm. Problem: bondlift or bad bond yield. Automatic 25micron U/S ball bond K&S.  The Ra is from 1-5 microns. Conductor/bondpad thickness 15-20um. Surface roughness eliminated somewhat by burnishing. Recommended (duPont) Ra-value is 0.5um for good yield. Lots of Si, Bi and Cd particles but <10um large. Of course these oxides and binders are not wanted, Au should be 100% pure, but as all know that does not exist in practice for thickfilm. Now to my question, dear Mr/Mrs  Bond : if a gold thickfilm is rough, wouldn't an increase from 25 microns to 50 microns make the bond conditions a lot better? My simple logic: rougher surface>thicker wire. With all admiration for Harman's "Bible", there is nothing mentioned this way.
Manipulating the force, amplitude and capillary face are all tried with minor improvement, at least far from 6Sigma goal. Plasma cleaning or any other cleaning does not help either.
All answers are welcome, even from the small island (forgotten the name) where Aussilek tries  to live.
Ingemar Hernefjord
Ericsson  Microwave Systems

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