Aluminum is a very common material to bond to, although it is a little tricky to solder to with traditional methods. The method that we prefer for large area solder coating is fluxless, messy, and actually kind of fun!
First, make sure you have the proper safety equipment. You’ll want a full face mask as well as a full length lab coat, and good heat-resistant gloves.
Next, heat the aluminum on a hot plate. The temperature at the top side of the aluminum should be ~50°C above the solidus temperature of the solder you plan to use. Once the aluminum has reached the correct temperature, you can add enough solder to form a thin layer over the entire aluminum surface.
With a wire brush, you can now ‘scrub’ the solder into the aluminum surface. (We speed things up a bit and use a rotary brush bit, hence the need for the added safety equipment.) The solder is generally repelled by the oxides on the aluminum surface, but as you break through the oxide layer molten solder can form intermetallics with the aluminum.
After a base layer of solder is applied to the aluminum surface, more solder can be added until you reach a desired thickness.
Finally, when the solder-coated aluminum has cooled it is ready to be machined to flatness specifications.
We use this method every day in our target bonding facility, as a step in the NanoBond® process. Let us know if you’d like to discuss this procedure in greater detail with one of our engineers.
* This post is part of the NanoFoil® Do-It-Yourself Tips and Tricks series