Phil,

I can find little mention of surface roughness in my very small wire
bonding library.  I suspect that surface roughness doesn't matter that much
unless the roughness feature size starts to interfere with the bonding
tool's ability to make good contact with the substrate surface.  The tool
won't transfer as much energy, creating a weak weld.

Sometimes thick film bond pads are "coined" to make a smoother bond area.
This is essentially tapping the surface without wire in the bonding tool to
compact the area where the substrate bond is placed.  Thick film is usually
much  rough and less dense than plating, and coining is often not necessary
even on this surface finish.

Remember that pure gold is very soft (hence the term "soft gold").  It will
tend to deform during the bonding process.  If the layer of gold is thick
enough, it should be fairly forgiving.

I have little data to back up my opinion, and I would be interested to see
other people's comments.

Dave Anderson



>>> <[log in to unmask]> 08/14/97 10:15am >>>
A question came up on what the surface finish (smoothness/roughness) should
be for wire bond on a land.  The plated finish is typically nickel and a
covered with a soft gold finish.  Will hills and valleys in the surface
make
any difference in the bond strength.

Phil Hinton
hintpwb1@aol,com