Copper plating aluminum thin film

[spigeon]

I am working on micromachined thermal actuators. These devices consists of an aluminum thin film (500 nm) deposited on an alumina substrate. The aluminum is patterned by photolithography to make electrical traces that must withstand high currents. Since the Al layer is quite resistive, I would need a thicker copper layer (at least 100 µm) on top of the Al. I believe that copper electroplating is the most efficient way to do this, but I experienced adherence problems. The poor adherence is probably caused by the thin oxide layer on the Al, because this metal is vacuum evaporated and is therefore really clean. I tried to remove the oxide with an acid solution, but it also attacked the Al layer (some traces were completely removed by the acid). I also tried a zincate treatment, but it also consumes the Al.

If you have any idea how this could be done, please let me know. The devices are 6"x6" and I am looking for a low to medium production process.

Thanks.