Behold the Floppy Emu programming board! Normally when you read “programming board” on this web site, you’d think of some circuitry on a PCB, but this time it’s a 3/4 inch thick plank of poplar wood. Ah, that kind of programming board!

Sometimes I need to reprogram a large number of Floppy Emus, and this tool makes the job much easier. My old method was to connect the Emus one at a time to an Apple IIgs, turn on the computer, push buttons to begin a firmware update, and then wait ~30 seconds for the update to finish. It was a slow and inconvenient process when dozens or hundreds of Emus needed reprogramming. With the programming board, I can slap down one Floppy Emu into a bracket, start the firmware update going, and then rotate to the next Floppy Emu. Everything is powered from a USB supply, and I use a hub with individual lighted switches to turn on power for each Emu bracket.

Updating three Floppy Emus in parallel is a big improvement, but there’s also another trick here that makes the process even better. With the old method on the IIgs, some fiddling with cables was necessary every time I connected or disconnected a Floppy Emu. Things would slide around on my desk, and I’d waste time getting the connectors lined up. The programming board uses metal pegs at each bracket to hold the Floppy Emu centered, so a short 4-inch ribbon cable can drop down perfectly aligned with the connector every time. Here’s a close-up of the alignment pegs:

If you’re wondering about those green lights on the bottom two power adapters, they’re not status indicators, but just simple power lights. I accidentally bought some high-brightness LEDs, and even with under 10 mA current they’re so bright that it’s irritating. They’re dazzling to the point of being blinding. Fortunately the LED in the top-most power adapter didn’t work due to my lousy soldering job. I covered the bottom two with 5 layers of paper, which cuts down and diffuses the brightness enough to be tolerable.

This was my 6th *@#&% attempt to assemble some ROM-inator II PCBs using reflow soldering, instead of my normal drag-soldering with an iron. I may not be too bright, but at least I’m persistent. All of the previous attempts failed in slightly different ways, resulting in boards with multiple solder bridges that needed to be cleaned up manually with an iron. This time I altered the way I created a frame for the board being reflowed, and it almost worked. It was certainly the best result so far, but still not good enough.

You can read about the previous reflow attempts here:

1. Reflow with hot air
2. Switched to a hot plate
3. With an aluminum pie pan
4. New solder paste and aluminum sheet
5. Using a stainless steel stencil

My reflow soldering adventures have been a challenge for two reasons:

1. The ROM-inator II PCB has two chips with 0.5mm pin spacing, which is very small. If my boards had larger components with more forgiving pin spacing, my earlier attempts would probably have gone much better. 0.5mm might be approaching the limit of what can be done at home without special equipment.

2. I need the PCB to be 100% perfect after reflow, with no manual touch-ups required to fix solder bridges. If this were a one-off prototype, a few solder bridges would be no big deal. But since my goal is to develop a new process that’s faster than hand-soldering, I can’t afford the time needed to do manual touch-ups after reflow.

 
Floating Stencils

In my previous attempt, I used purpose-made plastic framing pieces to hold the PCB while I applied solder paste with the stencil. These plastic pieces were a tiny bit thicker than the PCB, resulting in the stencil floating above the surface of the PCB instead of resting on it. The amount of float was less than 0.3 mm, but it was still enough to cause problems. This time I used extra PCBs to create a frame, so the thickness was an exact match with no float. The solder paste application looked pretty much spot-on, as you can see here:

Placement of the chips is still difficult. I’m doing it by hand with a pair of tweezers, and the best I can do is to drop the chip within a couple of millimeters of the correct position. Then I slide it around until it’s in the right spot, smearing a bit of the solder paste in the process. Here’s how things looked after chip placement:

After reflow on my hot plate, the results were pretty good, but unfortunately there were still several solder bridges. Here’s a typical example. It all looks decent, except for those two pins at the far left. The chip also didn’t snap to the correct alignment, as I’d been led to believe would happen thanks to the surface tension of liquid solder. The alignment is pretty good, but not quite centered, and there’s a bridge at pin 1:

I assembled ten boards this way, with two chips per board, and two sides to be soldered per chip, making a total of 40 sides. The good news was that 14 of the 40 sides had zero solder bridges. The bad news was that about half the sides had 2+ solder bridges, and I never assembled a PCB that didn’t have at least one solder bridge on it somewhere. This was the final score:

0 solder bridges: 14 sides
1 solder bridge: 7 sides
2 solder bridges: 7 sides
3 solder bridges: 3 sides
4+ solder bridges: 9 sides

I discovered that I needed to wipe both sides of the stencil clean after each use, otherwise the solder paste application grew progressively messier with each new PCB. I also found that I wasted a lot of solder paste. Dispensing the minimum possible amount from my syringe was still too much, and resulted in a lot of leftover paste on my plastic scraping tool. It was hard to reuse the paste stuck to the scraper. When I tried it a couple of times, using another scraper to clean off the first scraper, the results weren’t good.

 
End?

Is this the end of my reflow soldering saga? I think so, at least for this particular PCB. I don’t think I can improve further on these results without more effort than can be justified, yet the speed and quality of the process isn’t good enough to replace my current method of drag-soldering with an iron. I’ll revisit this again the next time I have a new PCB to assemble, and I’ll try to stay away from 0.5 mm pitch parts in my designs.