Re: [SI-LIST] : BGA Ni-Au platting pattern.

Brett Grossman ([email protected])
Wed, 07 Oct 1998 08:30:32 -0700


Just a couple of suggestions if I understood your question correctly.

1. DC simulation results could be affected if your core material is a
higher resistivity than Cu, something like W may skew your loss. These
results could also be impacted by the Ni and Au plating thickness vs.
the overall physical dimensions of the ball (ex. if you are simulating a
ball that is really 99% gold by volume, then assuming copper would
probably affect your accuracy ( I know this isn't really the case, but
hopefully it demonstrates the point )).

2. AC simulations could depend heavily on your plating thickness
(skin-effect comes to mind here). If you have very thick plating
(relative to the overall diameter of the ball), then more current should
flow in the plating (Au) at a lower frequency then if you had very thin
plating. The current density in the gold material could impact your
calculations here.

Regarding #2, I had a colleague who did a demonstration of transmission
lines and skin effect loss with plain old RG-58/U cable that was pretty
good. He started by building a mathematical lossless model of the cable,
and comparing it to the data from the Belden data sheet and some
measurements he performed. He then added in the skin effect(assuming a
homogenous conductor), and showed the same comparison, then added in
dielectric loss and showed the comparison again (Z vs. Freq.). The
result was that the lossless model correlation was poor, with skin
effect added it got much better, and improved very slightly with the
dielectric loss.

Finally, he made a final addition to the model by including an
approximation of the plating of the wire ( I belive it is tin plated
copper), this brought the model into almost perfect correlation
throughout the frequency range of interest for the demonstration.

I guess as with nearly everything, the effect of leaving out the plating
in your simulations will be determined by the frequency range of
interest, and your need for accuracy. Hopefully something useful could
come out of this message for you.

Good luck,


Brett Grossman        		            __          ___  
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