SiliconWitchery's Raj Nakarja Pushes the Envelope on Hand Assembly with an Ultra Tiny Bluetooth FPGA
Packed with components, including four BGA ICs and passives as small as 0201 package, the tiny modules are soldered using a homebrew oven.
Engineer Raj Nakarja has really pushed the limit of what can be achieved through hand assembly, putting together some Bluetooth-equipped FPGA modules considerably smaller than a microSD card.
The tiny SiliconWitchery modules, built with castellated edges for soldering onto a separate PCB as a daughterboard, are jam-packed full of surface-mount components on both sides — from the FPGA itself to a Bluetooth radio module, plus a whole mess of surface-mount passive components, any one of which would be near-impossible to find if dropped. "Smallest [parts] are 0201," Nakarja explains, "but there’s also some 0402 for the larger caps and inductors.
"There will need to be a slot in the board to allow clearance of those [reverse-side] components. Overall it halves the size of the module and saves volume and thickness in the overall design."
The module is designed for high-performance signal processing and neural network operation at the edge. "This FPGA includes two hardware I3C/I2C/SPI ports (which you can use in various combinations)," Nakarja explains. "This lets you hook up two chains of sensors for example and process data in true parallel. On a CPU this would be threaded and then you’d need some extra overhead if you wanted to combine or compare this data."
"All that is great, but these days, data is no good if it can’t go anywhere. The Bluetooth chip lets it talk to the outside world and handles all the network things, configuration, sleep settings, etc."
A Twitter thread walks through the process of hand assembly: Solder paste is applied using a stencil, the bottom side populated with components carefully positioned with tweezers, then baked in a homebrew reflow oven. The process is then repeated for the other side — which includes four ball-grid array (BGA) packages.
More details are available in Nakarja's Reddit post.