Over Caffeinated Adventures in SMD Madness

[somnif]

Well, that was miserable....


So,  back in August, member NFX released a clone board of the old boss CS-2 compressor. I'd always been a fan so I jumped on board. The problem is, and the reason why the effect is fairly rare in the DIY scene, is Boss used a proprietary Roland OTA, the BA662. And this chip is the better part of 100$ on the market, when you can find it.

Thankfully, Synth Addicts are a somewhat insane lot, and they banded together to figure out the bloody circuit in the integrated circuit, and designed a clone using SMD matched pair transistors. Fantastic! Clone "chips" are available for sale! But... 20$ with shipping..... Um....

Ok, one last piece of the puzzle, they made public the Eagle files for the clone board! So, to OSH park I went and bought myself a handful of boards! They were worryingly cheap. I placed an order for the 9 transistor pairs and 2 resistors, and sat back to wait.... Only to realize the trannys were on back order. Until this week.

So I finally got the parts and... oh my god I am in over my head.



My hands shake. I'm caffeinated to the gills to stay coherent grading lab reports. My eye sight isn't fantastic. And I have resistors the size of Lincoln on a penny. Oh boy....

So, no fantastic lighting. My only magnifier is a little 2in hand lens, and I only have standard gauge solder on hand. LETS DO THIS! (Though I'm not completely insane, I did buy some fine pointed tweezers for this)

5 hours later......



Yes its ugly and flux soaked. I know some pins are blobbed together, its ok, those are linked on the schematic anyway. I don't have anything to test it in, so I'm a bit nervous about it,  but my continuity tester shows things are linked which should be linked, and not where not. Assuming I didn't toast anything while assembling it should work...  I hope... (sockets won't fit it in a 1590B enclosure so its going straight on the board. Gulp....)

Now I just need some MPSA18's to arrive and I can finally finish the damn pedal that's been laughing at me for 4 months. Also learned it is surprisingly tricky to get a decent picture of a board this size. Between flux glare and poor lighting, this was the best I could do.

[rockola]

These days I won't even thread a needle without one of these. In case the link is borked, it's a magnifying glass slash desk lamp.

https://www.reichelt.com/de/en/Magnifying-Lamps/LL-FP-45268/3/index.html?ACTION=3&LA=2&ARTICLE=136455&GROUPID=4515&artnr=LL+FP+45268&SEARCH=%252A

Good luck on your quest. It wouldn't be a challenge if it was easy.

[EBK]

Well, that was miserable....

Sure, but...

5 hours later......

You've multiplied your wealth by 10!

[midwayfair]

Jeez, that's some dedication right there to saving $20

But awesome work. Did you do the PCB yourself?

[somnif]

But awesome work. Did you do the PCB yourself?

No, I'm still trying to learn how to use Eagle, with marginal success. It was designed by some folks who are fans of old Roland Synths, and they kindly made their eagle files publicly available. There is also another version on OSHPark with a built in trimmer for DC offset voltage tinkering, bits taller and wouldn't fit in the enclosure.

http://wiki.openmusiclabs.com/wiki/BA662

Their picture is much prettier than mine 

[stringsthings]

SMD is 100% easier with the right tools.   

1. A decently small tip for your iron.  ( It doesn't have to be super small, you can use the same tip for your thru-hole PCB work )
2. Flux, flux, flux! ( some folks like flux pens.  I currently have a small bottle and dispense it with a plastic bottle with a fine needle tip )
3. Small diameter solder.  ( I use .015".  For comparison, I use .032" for thru-hole )
4. Decent pair of tweezers.
4. Good lighting.
5. Some kind of magnification, especially for checking for shorts/bridges/cold joints.
     ( I've also got one of those magnifying lamps, but I get a lot of use out of one of those headband-glasses-with magnifier lenses )
6. Flux cleaner or iso-alcohol for cleaning up the flux.  Very important to clean up the flux.  Leftover flux can cause shorts and other problems.

I took the SMD plunge about a year ago and it wasn't too hard with some practice and repetition.  There's some very helpful vids
on youtube that show various methods of SMD soldering.  I got one of those SMD practice kits on ebay for 99 cents to start out with.
When you purchase components, get plenty of extras.  ( they're usually not expensive )
It's inevitable that a few of your components will end up on the floor/carpet ... never to be seen again. 

[somnif]

I do have a needle point for my Iron (thank goodness for that impulse purchase), and it did help (given how tightly packed the board was).

I did use flux, though without a pen I instead used a fine point paint brush. Haven't cleaned the residue off yet, may pick up something to do so before I install it.

I ended up sort of... sharpening my solder at times. I'd give it a clip with my snips to thin it at the tip to fit it on just one pad. NOT the best solution.

Magnification and lighting were Definitely the biggest issues, especially in determining the which was pin 1 on the tranny pairs. A little 2 inch hand lens, a reading lamp, and a Harbor Freight LED flashlight with dying batteries were what I had (also used my phone's LED to shine through the board to ensure I didn't have bridges). I made it work, but I probably looked a little crazy bobbing and weaving my head around to get the glare to settle on the chip just right for me to see the little dot.....

And yes, one of the chips did end up on the carpet. I bought a spare (they were 50 cents a piece, so just 1 spare) but I ended up finding it after a minute of frantic scrounging. Thankfully my cheap apartment has terrible carpet, so it stayed on the surface 

I imagine SMD wouldn't be quite as frustrating on a board with fewer chips/more passives, and with a bit more breathing room. A lot of the frustration was just due to needing to get my iron around 9 SOT363 chips on a 20mm x 6mm space.

[culturejam]

That's awesome! 

[selfdestroyer]

Dang.. I would shake way to much for that.. I barely can do a FV-1 in one go. So cool

[somnif]

 Yeah my shaky hands were a problem.  I've got lots of practice working around it with micropipetters at work, but those tricks aren't really practical with a 700F bit of metal. (Though I nearly burned myself several times before catching myself because of muscle memory )

[pickdropper]

Very cool.  I actually enjoy SMT work.

Although today at work I have to deal with reworking 0402 diodes with pads underneath the component.  Components with pads underneath are a lot less fun (at least for me).

[mjg]

And yes, one of the chips did end up on the carpet. I bought a spare (they were 50 cents a piece, so just 1 spare) but I ended up finding it after a minute of frantic scrounging. Thankfully my cheap apartment has terrible carpet, so it stayed on the surface 

I admire your dedication - well done for sticking it out!

My one attempt at SMD was hilarious.  I've only got a big thick tip on my iron, at one point the chip I was trying to solder stuck itself on the end of the iron, instead of the PCB.  Yeah, I think that one probably got too much heat.  Also lost one in the carpet for a few hours.   

[stringsthings]

Haven't cleaned the residue off yet, may pick up something to do so before I install it.

I would definitely recommend cleaning the flux residue off.  Some iso-alcohol from the drug store will work perfectly fine.

I forgot one thing in my previous pos:  solder braid.  For chips with fine pitch, ( like those SOT-363 ), if you get a solder bridge
between two pins, just put a bit of flux over the bridge and use the wick to suck up the excess solder.  Works extremely well and still
leaves a good connection between the pins and the pads.

[peAk]

ugh.....ugh.....ugh......

nope.

[Micpoc]

Thankfully, Synth Addicts are a somewhat insane lot, and they banded together to figure out the bloody circuit in the integrated circuit, and designed a clone using SMD matched pair transistors. Fantastic! Clone "chips" are available for sale! But... 20$ with shipping..... Um.... over my head.

Yeah, I think I paid about $10+ shipping here in the US when I started the CS-2 clone, i.e. more than the chip itself... should have checked their price before starting the project.

Nevertheless, congrats, it looks great!