We use these Hittite parts, too, and have been doing some studies on the effect of gold content on SAC solder joints just because of parts like this.  I'm curious what sort of board finish that you're using.  We don't have an issue with placing them and getting them to solder.  I'll look to see if we have any specific advice for these.  

For QFNs in general, we make sure the land pattern sticks out enough to be able to touch a fine soldering tip to it and to provide additional paste to the pin pad joints -- I believe this is around 15 mils.  You have to keep the pin pad joints and ground pad joint separated with a solder mask dam.   Make sure the soldermask is never on the ground pad on one side and off on the other (all off or all on so there's no teetering and consider solder mask registration specs).  Don't do one large ground pad stencil aperture or the part floats on top of the solder bubble. 

I would also like your help to ask Hittite to lower the maximum gold thickness to 50 microinches.  I would sure like them to know the high max gold is an issue for more than just us.

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