We finally got our first machined prototype probe tips back from our supplier last week. We decided to go with a company that specializes in RF connectors. If they can make connectors precise enough to handle multiple GHz, they should be good enough for our application.
Our original tip was hand-made with parts from an SMA cable kit. We used a square .1 inch header pin for the tip and used an SMA crimp sleeve soldered to a male SMA connector as the body.
While crude, these first prototypes helped us prove out our design and validated our decision to use an SMA connector on the body of the oscilloscope. However, we knew hand soldering thousands of tips was out of the question. We had to design a tip that had fewest parts possible and was easy to assemble to keep costs down. Ideally, the parts would be press fit to keep assembly costs down. Enter our new design...
We got the tip down to three parts that are all press-fit together. The probe tip is gold-plated phosphor bronze for strength and durability. The body is a nickel-plated brass alloy with straight knurling on the connector side. We didn't want to use a hex-style body like on our first prototype because we were afraid people might use a wrench to tighten. While most RF connectors have hex bodies, they are only meant to enable tightening to a precise torque specification for precision measurements. We chose a straight knurl body to enable finger tightening and prevent someone from wailing on it with a wrench. The lining between the probe tip and body is PTFE. This is a common dielectric for RF connector applications and is easy for suppliers to source.