Heat sinks re:reflow pad design

The padsfor large heat sinks are being designed on our boards with large copper ground planes surrounding them by our engineers. I am having great difficulty keeping the reflow temperature below 230 degrees in order for the temperature of the copper plane to reach the desired temperature for reflow. ( the therocouple is registering a local heat of 205 degrees celcuis for the heat sink pad. What I am asking is 1. What pad designs are there I could use provided I don't restrict current flow to ground? 2. Any reflow tricks ( apart from adding more zones to the four I already have ) to enable the soldering of heat sinks in RF applications.

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