Metalized Infrared Windows   SMFCo is an ITARS and SAM registered entity         Cage Code: 8FMV3  Created by Confocal Sputtering Source Configuration......... Confocal sputtering is a configuration of the sputtering chamber to provide for more uniform coatings on non-planar substrates, whereby the sputtering source(s) are strategically "aimed" at a rotating workpiece that has a complex shape.  Most of our window customers want two surfaces to be solderable, the face and the vertical edge.   Direct sputtering, where the sputtering source is parallel with the optical face, shooting straight down, is fine for coating that face, but may not be the optimal configuration for the best coverage of the vertical edges of the optic. In the direct sputtering configuration, the vertical edges of the window will receive 1/3 to 1/2 of the metal that the face receives, on average.  So, the 4500 angstroms of platinum that you have on the face of your windows, may only be 1500 angstroms on the edge.  That's where the confocal configuration comes in. With the sputtering source now aimed, or focused towards the vertical edge, the metal distribution ratio between the optical face and the vertical edge becomes much more favorable.

16mm silicon windows metalized with Ti/Pt/Au Solder coverage after solder pot dip in Sn63 solder.

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.