Populating SMD Components is Slow

Wow is it slow. I spent most of BDO plodding along soldering down LEDs, resistors and capacitors. I breezed through as many or more through-hole solder joints for the vias in a tiny fraction of the time I spent on the SMDs.

It as slow as point-to-point soldering on a perfboard. I prefer home-etched through-hole boards to point-to-point because of the time difference. If there is a major error in the board it is easy to start over. On a point-to-point board there is a lot of time invested in the assembly.

With my current technique for populating SMDs, I might as well be doing point-to-point. I need to up my game somehow. I'm going to look into solder paste, a reflow skillet and some sort of suction device to manipulate the devices into position.

Toner Transfer

My skill level is increasing with Toner Transfer. I'm really careful to scrub the snot out of the of board with a Scotch Brite and acetone while wearing gloves. I rinse with only water, still wearing gloves. I'm careful to wrap the board with exactly two layers of bounty. I've gotten the hang of minimum trace widths and separations. I know what I can drill.

Usually, when I go for a dense board, the densest area always gets massive transfer failures. But this time, with all my skills and experience working with me, I transferred a really dense board with very few easily correctable errors. Its pretty darn satisfying to be able to transfer a board like this one.

Transimpedance Amplifiers!

Thanks to my buddy Tom I have discovered Transimpedance Amplifiers. These chips wrap up the entire functionality of the circuit I was trying to mimic. They work great. A little expensive at $4.50 but worth it. I'm using TI's OPA380A. Digi-Key has them in single quantities. So, I've now quite successfully breadboarded my IR detection circuit and am ready to commit the design to DipTrace.

I learned a little something about FETs tonight. After getting the detector working well, I tried to up the amperage on my LEDs. At some point I pulled the wire off the gate of the FET to connect it in a different way to the MCU. Suddenly my invisible light LEDs became visible light LEDS. Then they turned black and smoke actually escaped the plastic housing! Apparently I pulled the FET just at the moment the gate was charged. Since the gate is a kind of capacitor, it had no way to discharge once I pulled the wire and thus the FET remained on long past 10us. Since the LEDs are only rated for that amperage for 10us at a time, they promptly smoked. Lesson learned! Anyway the 1.32 amps should be fine. I'll just go with that.