Some authors electroplate gold with a tin
cap on top. In this case, excessive gold is used. The solder
layer has to be reflowed before use in order to achieve an
eutectic alloy on top of the solder pad. This reflow step is
critical because the excessive gold can lead to dentritic
growth of z-phase before the soldering process.
Therefore, there is less eutectic left which would be
needed for the soldering process. Further, Kirkendall
voids can lead to failure of the solder joint.