I talked a little while ago about a prototype miniature low temperature LCR filter I made. Well I’m making the real things now, so I thought I’d share the process as they come together. Here is the first stage: The metalwork. This doesn’t actually take very long.
Each filter needs a base plate (top metal pieces with the crosses etched in) to secure the filter and provide the cryostat ground – which I’ll write about in a separate post, a flexible printed circuit board (the flat middle strips of Copper), a supporting wall with feedthrough holes (those ones are pretty obvious) and a lid (bottom metal pieces).
The walls are made just by bending the relatively thin copper plate around 4 times. The holes are made with a metal punch and are 3.18mm in diameter.
Let the mass production commence!! Well, I’m making 5 of these. I think I’ll need 4, and you always make a spare 🙂 I’m thinking of mounting them on the new fridge at 4.2K, 1.5K, 50mK and base temperature, but I haven’t quite decided yet.
Timewise this took a couple of hours (whilst I was waiting for the fridge dewar OVC to pump down – gotta love critical path analysis).
Here is a slightly more artsey photo of the same thing: