James Bowman has come up with a technique even impressing Ladyada. He says:
PCB fabrication has changed a lot in the last couple of years, at least for me. Steel stencils, paste and reflow ovens used to be out of reach. Not any more! The construction steps for PCBs are:
- apply paste to PCB through stencil
- place parts by hand
- put it in a cheap IR reflow oven and press ‘start’
- go for a 7.5 minute walk
Hand placement works surprisingly well. Surface tension works to your advantage, centering the parts on their pads.
He’s been looking at ways of speeding up hand placement, especially for very small pitch parts. And found a great way:
It’s two acrylic sheets, sandwiched together. The lower is a frame for the PCB. The upper is a guide for the component placement. With the board pressed into the lower frame, the upper layer exactly places the larger components. Actually placing the parts is now laughably easy. The slots are precisely cut for each one, so it’s not even necessary to use a microscope. It’s possible to place 5 parts in a few seconds – not bad for a human!
After placement the PCB pops out of the frame leaving the parts firmly stuck in place in the paste. While this setup has been working really well for large parts, small components haven’t worked out — they tend to get lost in the holes in the acrylic.
You can check out his post which includes an Eagle script for converting a mnt file into an SVG file to cut out the acrylic.