Wrinkle finished on solder joint

I'm running intrusive reflow. What happened was when the board went thru' the first reflow ( which is secondary side ), at Post reflow, I can see the solder joint quality is very good smooth and shiny. But when we proceed with the 2nd reflow, at Post reflow, whenever I fliped and look back at that good, smooth and shiny joint, they are no longer as they were. The joints turns to hv kind of wrinkles finished.

What could be the possible cause? Is it because of the temperature set for the second reflow is too high ? Pls advsie.

Steve Vai

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