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Working with SMD devices

post #1 of 29
Thread Starter 
How do you folks solder/use SMD chips/etc? (and "I don't" is *not* a valid answer )

The reason I ask is because I think a micro-miniature SMD Cmoy would be *sweet*... Imagine, an amp that's the same size as the battery...
post #2 of 29
Soldering and reworking SMDs requires almost a leap of faith once you get past the two-pin (Rs & Cs) that require solder tweezers - to remove a device you have to melt all the solder on one side and then bend it up before melting the other side. If you have a four-sided device then you have to melt all of them at once or else you may as well junk the board. At this point, if you don't have some hot-air reflow or at least specially-shaped tips, you are in trouble.

If you only care about the board and not the part you can sometimes shear off the legs close to the part and then desolder them one by one but your side cutters and hand had better be very good, or you will lose pads. Soldering these devices onto a board is another matter...

Once a long time ago I was building my first prototype modem using a device in a PQFP144 package. I spent almost an hour soldering one row of pins with a magnifying glass and the finest tip I could find before the lab technician took pity on me. He took over the iron, fitted a big tip and applied some solder, then squirted liquid rosin all over the next row and just wiped the iron down the whole row in one steady motion. Surface tension took care of the rest - with the exception of one pair of bridged pins, easily fixed, the whole row was done perfectly.

If you really want a tiny cmoy it's possible. Why not get AD825 modules from L C Audio to prototype in DIP-form and then make a board for the SMDs?
post #3 of 29
You're absolutely right, and the technique you mentioned is what I've heard and used as well. Also as you say, if you need to remove the part, you can say bye-bye to the board except maybe if the part has only a few pins. If you saw my thread on Headwize from last week, you could see how I destroyed a board - that took me a while to make mind you - by desoldering a part I managed to destroy while testing. But the whole idea today is that it's not worth replacing - human time is expensive. So just trash the board, write it off and use another instead. Very nice for big corporation, unacceptable for DIY'er.
post #4 of 29
Eric, you can do it. Just remember there's SMD and then there's SMD. Stay away from stuff that requires a professional assembly station if you don't have one or the skills... you'll just get mad.

Remember the first time you saw a DIP and were wondering if your hands were stable enough and eyes good enough to hit just one pin?

re: amp the size of a battery, HEY SKIPPY! Get in here! And this isn't SMD, it's just well planned and executed SkippyBuild(tm)

I was whining about this problem over at our other home last month... you might find something useful in that thread. http://headwize.powerpill.org/ubb/sh...num=3&tid=1726

There's others like it on both sites, do searches in both DIYs.
post #5 of 29
Thread Starter 

It's also a very good example of soldering parts to eachother's pins, I've heard of people that using SMD parts and some *really* steady hands have built bugs (of the spy variety) the size of PEARLS.
post #6 of 29
I really miss the building side of R&D. Anyone have a job involving design and building that they would like to hire a C programmer to do?
post #7 of 29
I just built a current boosted Cmoy with a 4132 SOIC surface mount opamp. I etched the board by using the Radio Shack dey transfers and cutting them with a scalpel. Take one of the long trace pieces lay it at 90 degrees to the chip, attach it and then carefully cut the gaps between the opamp pins and lift them off. I used very small metal film CMF 50 resistors instead of Smt devices. The back of the board was left as pure copper unetched. Whenever a part needs to go to ground just drill a hole and solder it. Resistors not needing grounding are simply soldered standing vertically trimmed to a very short wire flattened sideways.
The final amp is 3/4"X 1 1/2" complete. Which is small for a current boosted amp comprised of four opamps in one (ALA Headroom designs). The reason I did this was to try a few surface mount parts I already had from wrong part number orders. Also I wanted to know if they sound as good as the bigger parts and they do in this application.
It took some thought to figure out a way to etch the little lines, but this method works very well. You just need a really fine very sharp blade. It would be great if you could get dry transfers the size of these little parts. That may come as more and more of these are being made.
This amp will easily fit in a very small box with one 9V or a small Pactec with up to three 9V batteries, and yes it makes a difference as these chips like +-15V which could be four 9V batteries as they are usually less than 9 anyway.
I will take photos when I can.

post #8 of 29
Thread Starter 
BTW, Apheared, what did you mean by
Just remember there's SMD and then there's SMD

You mean there are two types of SMD?
post #9 of 29
There definitely are different types of SMD. Some are just smaller than DIP, yet they can still be worked with relatively easy. For example, SOIC components. Some are yet smaller than that and hard to even see let alone solder. I think SOT-23 belongs there, I don't know if there are even smaller things around. Resistors/capacitors can be also very tiny but at least they have only 2 pins on the opposite sides.

What apheared probably meant is that there are two ways to achieve "SMD form factor" (i.e. small device size) - either using actual SMD parts, or using regular parts but carefully choosing ones that are small and using intelligent layout techniques to pack many of them in a small space - like in the amp above...
post #10 of 29
Thread Starter 
How is it possible to solder components that small?
post #11 of 29
exactly... SOIC is "surface mount" considering the only other term is "through hole". While no SMDs go thru a hole, they vary in size greatly... re: aos's SOT example if you sneezed on the board while tryin to tack a SOT-23 device, not only will it fly off the board but you'll never find it. Sometime you'll look at the tweezers and think you dropped it, only after 20 double-takes do you notice nope it's still in the tweezer jaws.

Some things were only intended for machine assembly and "repair" involves swapping a machine populated circuit board.

eric, go read that rant thread I linked... you'll laugh.
post #12 of 29
Hmmm... I *was* planning to use one 5-pin SOT-23 inverter in my DAC, just because I haven't found anything in intermediate size... I suppose I know know who's NOT going to be making my project, eh?
post #13 of 29
I don't know why SOT23 has been singled out but its measurements are more reasonable than (T)SSOP and LQFP. I think SOT23 is about the limit for workable packages. DIP is huge, SOIC is nice, SOT23 is ok but anything smaller is nasty.

I watched a sales demo involving SMD rework. As long as you have decent tools (hot air gun), it isn't that bad. The only other tool needed is a suction cup tool for the chip itself.
post #14 of 29

getting started with SMD

Working with SMD parts is not as hard as it seems. I'm no expert, but have taught myself to remove and replace SMD
parts, even large QFPs.

Good tools help, but I'm noticing that you don't really need
a lot of expensive stuff. The main thing you need is a good
temperature regulated soldering iron. The higher wattage ones
work best. Then you need the finest gague solder you can
get, liquid flux, solder braid, fine stainless wire, two or three
sizes of precision tweezers, and a set of solder probes or
dental picks. And it sure helped my confidence to have a
good heat gun with a reducing nozzle. Even though I think
it overheats the active components, you can use it for
preheating the board and you can get anything off the
board, although you risk destroying the parts in the process.

You will find that as soon as you start practicing, working
with SMD parts gets less mysterious. Start on boards you
salvage from broken appliances, which you can get from the
Salvation Army or the trash or your own broken computer
peripherals. I took apart a dead HP laser printer and an old cell phone to get started.

Have fun! Keith
post #15 of 29
I started Surface mount by working with old boards removing and resoldering parts. I am saving parts for later projects too. Yes, there are some sizes which are impossible but these are usually chips I will not be working with in audio. It just seems important to be able to work with this technology as it is here to stay, and many newer components are not available in the old bigger types. Just one look at available parts will show this. It also makes dip work so easy.
I admire Jewelers who work on and repair watches. The old mechanical type. After seeing the size and details of this type of work circuit work becomes a "piece-of-cake". Darn, I found a resistor in a batch of Vishay CMF 50 that was a standard through hole, but was incredibly tiny.
The heat gun is a great idea too. I don't yet have one. Removing parts from, and assemblying components can also be accomplished with a carefully used toaster oven I hear. Some boards have the parts glued before being soldered though.
The etching I do is done the old traditional way with acid. Board traces can also be hand routed using a Dremel with an engraving bit, free hand or with a router base. Set the bit to just pierce the copper.
I am just trying to help find ways that we DIYers can work with surface mount. Another very useful thing is the use of reading glasses as magnifiers. I use 3.5X and sometimes two sets to increase this as my upclose vision is going.
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