The aimed source eliminates the glancing angle problem, resulting in better adhesion, more uniform
growth structure, denser films, and significantly better metals distribution.
What metals do I need?
Typically, the solderable metal
stack consists of three layers,
- The adhesion, or base
layer. This layer is usually Chromium, or Titanium, and is the foundation of the stack.
The solderable layer is next. This layer is often Nickel, or Platinum.
The protective layer is almost always Gold.
Platinum or Nickel, which is better for your application?
Both metals solder quite well, but Platinum tends to be somewhat more user friendly, in our opinion.
A major difference between the two metals is the dissolution rate by the solder. Tin rich solders will immediately
consume, or scavenge, the gold layer and will next begin to dissolve the underlying layer of Ni or Pt. Nickel dissolves
in molten tin at a rate of around three times that of Platinum. If your process requires relatively long dwell times (10 seconds
or more) in the liquidus phase, then Platinum is a better choice as your solderable layer. Or, if you think that you may want
or need to reflow the solder to correct for a misaligned optic or component, then platinum lends itself much better to this
situation than nickel, at least in our experience.