Passivation coatings for micro-channel coolers

Many high heat flux electronics applications have surpassed the limits of air cooling and are moving towards liquid cooling as a method to remove waste heat directly from electronics packages. In applications such as power electronics, high liquid velocities along with highly corrosive coolants (DI water in particular) limit the reliability and performance capability of many liquid cooling solutions. Engineering solutions include the use of stainless steel in place of better performing copper or aluminum materials and the use of costly nickel and gold plating where the performance of copper is required. The problem is particularly difficult with copper micro-channel coolers (MCCs), as conventional plating techniques are not capable of creating conformal coatings in the micro-channels. In this paper, preliminary results on the passivation capability of nano-scale alumina coatings deposited by atomic layer deposition (ALD) are presented. ALD coatings are deposited in the vapor phase, one atomic layer at a time, resulting in unmatched conformality and coating thickness uniformity on almost any geometry. Experimental results for thermal cycling, erosion and corrosion passivation performance with salt water are presented for a baseline (copper), gold plated copper, and ALD coated copper micro-channel cooler. In all cases the ALD coated samples demonstrated superior passivation properties.