Copper plating air bubbles

I'm Copper plating a die-cast zinc logo plate, and did some burn test on it at 250 °C. After the test, some small bubbles are appeared on the copper plating area. My vendor claimed that copper plating can withstand at most a temperature of 150 degree, is this true. On the other hand, our die-cast vendor has done some improvements by stopping outgassing from the zinc die-cast part such as increasing the molding pressure, and running hot oil through the mold. But the air bubbles still exist. please advise how to solve this situation.

Best regards,

If your diecasting is not pressure die cast, then it may not be possible to avoid the problem entirely. You may find a better result if you brass plate instead of copper plate.