EYE ON NPI - 3305 Series Open Bottom Low-Profile Receptacles #EYEonNPI #DigiKey @MillMaxMfg @digikey
Channel: Adafruit Industries
Date: 2021-06-10

This week's EYE ON NPI is all in on keyboard hacking, just like us! The Mill-Max 3305 series open bottom, low-profile, solder mount receptacles are specifically designed to make mechanical key switches hot-swappable. The 3305 series is designed to be soldered into a 0.060” (1.50 mm) minimum mounting hole with an ultra-thin retention shoulder so plugged-in components sit nearly flush to the board surface. The open bottom design is meant to accommodate varying lead lengths, making this a very versatile receptacle.

These sockets are popular in the keyboard building and modification community for allowing folks to have PCBs that allow socketing or direct-soldering of switches without any height changes or PCB layout changes. Compared to previous sockets manufactured by Mill-Max, the 3305's are lower profile and have gold plating for long-life reliable contacts.

Cherry MX switches (https://www.digikey.com/en/products/detail/cherry-americas-llc/MX1A-E1NW/20180) have a standardized pinout, with a large center hole - two optional side-stability holes and two normally-open contacts. Cherry offers a wide range of switches with the same pinout/physical shape but with different mechanical attributes - some are smooth/linear, some are loud and clicky. Of course, many people like to customize what the switches are on a keyboard. Now, hopefully your keyboard manufacturer comes with different options for keys. but maybe you're doing a build or its an older design you want to update. You can carefully de-solder switches to replace them, but it's much better to socket them like we do with chips. (https://www.adafruit.com/product/2203)

Sockets do exist for MX switches, (https://www.digikey.com/en/products/detail/adafruit-industries-llc/4958/13997772), at this time both Gateron and Kailh make em. The good news is they work quite well - but they do require a new PCB layout for the SMT pads. All good for folks making new designs. But, sometimes you don't have the ability to change the design - or for some constraint reason you don't want to use these sockets.  That's where the Mill-Max 3305's come in! (https://www.digikey.com/en/product-highlight/m/millmax/3305-series-open-bottom-receptacles)

These ultra-slim ferrules can be soldered into existing plated through holes that are made in a PCB design. After soldering them in, two per switch, they accept the rectangularish contacts on MX and compatible switches. Best of all, they come in pick-and-place tape so you can integrate these into your manufacturing process or solder by hand. Now, you might be thinking "this seems really specialized to a specific purpose, why bring this up on EYE ON NPI?" Aha, because while these are designed for use with MX switches, these could be used to socket all kinds of through hole parts without changing PCB layout or height. For specialized parts, sensors or tubes or specialized displays, there may not be a plug-and-play ready to go socket available. But you still don't want to solder it right into your PCB? Check the lead sizes...you may be able to use these inexpensive sockets! Best of all, since they're open-bottom you can go with any length chip lead.

Various lengths of Mill-Max 3305 sockets are in stock right now at Digi-Key for immediate shipment. (https://www.digikey.com/short/45bfzdj7) Order today and you can start socketing securely by tomorrow morning!

See at Digi-Key at https://www.digikey.com/short/45bfzdj7

See the Mill-Max video at https://www.youtube.com/watch?v=6Ig6UFJOF5g