As mentioned in a separate post, uniform pressure across a NanoBond® interface is critical for maximum solder bond strength. Uniform pressure is much easier to achieve with flat, coplanar bonding surfaces.
If you are in the design stage of your NanoFoil® application, now is the time to make sure that the parts you will be bonding are flat – so you can apply even pressure to the entire bondline. This may necessitate machining, or otherwise conditioning, the parts so they are flat, smooth, and clean.
The obvious question I would assume you will ask is, “How flat should these surfaces be?” For target bonding and other large area bonding applications, we use this general rule: ≤1mm/m. For thinner parts, the pressure during assembly may help compensate for surface variations.
As far as the surface roughness, parts definitely don’t need to be polished – I’ve even used coarse-grit emery paper to flatten surfaces before bonding. Remember though, it’s recommended you clean your surfaces with isopropyl alcohol to remove oils and debris after any sanding/grinding operation.
*This post is part of the NanoBond® Process series