Scott

There are differences between the two processes.  I'm assuming that you're familiar with the concerns about ENIG. To name a few of the differences:

1)  ENIG is applied after the board is etched.  Flash gold is applied before the board is etched.  This means that (a) there is plating overhang with gold flash (not with ENIG) with a chance of the overhang breaking free and becoming conductive slivers (b) undercut is difficult to control because the nickel/gold doesn't dissolve in the etchant.  This makes line width control difficult.  With ammoniacial etchants, the undercut seems to be greater than for tin etch resists and tends to result in larger overhang, and (c) there will be plating overhang on the fingers with flash gold.
2) For flash plating: If the board contains isolated component patterns and large "plane" features, there will be a difference in gold (and nickel) thickness across the board with the isolated features being plated thicker than the "plane" features.  The board design and the design of the plating tanks affect the thickness distribution.  Isolated areas on several panels should be evaluated to determine the maximum gold thickness and if there is a chance of gold embrittlement.  For ENIG: The gold and nickel thickness is uniform regardless of feature distribution.
3) A continuation of point 1b: If you require tight line width tolerances, the only way to evaluate line width (copper) is to section conductors.
4) ENIG coats the vertical edges of the conductor, flash gold does not.

Don Vischulis

-----Original Message-----
>From: Scott Lefebvre <[log in to unmask]>
>Sent: Mar 27, 2008 11:01 AM
>To: [log in to unmask]
>Subject: [TN] Gold Flash vs. ENIG Solder finish
>
>I have a FAB house that is recommending we switch from using ENIG for
>the main body with electroplated hard gold for the edge fingers to an
>alternate finish.  They are recommending Gold Flash *Finish the entire
>board with 3-10 micro inches of hard Au over 100-200 micro-inches of Ni
>and selectively Au plate fingers with 30-50 micro-inches of hard Au.
>They reason they want us to change is it removes the step of removing
>the tie-bars on the gold edge fingers.
> 
>Would this have an affect with solderability switching to Gold Flash?
> 
> 
>Scott 
> 
>
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