# SMT soldering tutorial



## Doug S (Jan 18, 2007)

I was thinking about doing a ''getting started with SMT hand soldering'' tutorial but don't care to duplicate previous efforts. Have we had such a thread here or elsewhere in the forums before? Links to good off forum for same? TIA


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## Tritium (Jan 18, 2007)

I would be interested and have not noticed a thread before on this subject.

Thurmond


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## PEU (Jan 18, 2007)

Also very interested!!

Non SMD Soldering Station, solder paste, and smd components ready!

Thanks!


Pablo


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## coldsolderjoint (Jan 18, 2007)

id be interesting in reading it! I've only had some very limited experiance removing some smt components without smt tools.


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## Ctechlite (Jan 18, 2007)

I would be greatly interested in this, I've not seen anything like it here on CPF...


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## sflate (Jan 18, 2007)

I'd be interested too.


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## kromeke (Jan 19, 2007)

From my own SMT soldering experiences with conventional irons:

I have a little experience with SMT soldering. I have done it for component replacement and also prototyping. It is pretty easy to put down compontents. It is a little harder getting them off and replacing them (rework).

1. Solder wick (AKA desoldering braid) is your friend. Especially for rework. Get several different sizes, on the smaller end of the size scale. 

2. Having 2 irons is often handy. Sometimes it is nice to have 2 different tips at the ready. Other times it is nice to have an iron in each hand (mostly rework)

3. Get a good pair of tweezers. I'm a snob, the best tweezers have "swiss-made" stamped on them.

4. you will need something to hold the circuit board. I like the Panavise circuit board holder.

I don't have any photos handy, but I will share some of my tips. 

For new work (placing components on a fresh non-populated circuit board):

Chips are the most difficult. A lot of SMT chips have a very fine pitch on the leads. usually, I put a tiny amount of solder (just enough to wet the pad) on a corner pad. Then I place the chip onto the pads. I align the chip with some tweezers. I then hold the chip down, usually by pressing the tips of the tweezer down in the center of the chip. The corner pad that was wetted is used to place the first lead, you simply remelt the solder that you already put down. Now you look to see if all the pads are aligned. If they are, I put some solder down on the opposite corner lead. If they aren't aligned, use the tweezers in one hand and the iron in the other, carefully heat the first lead, and then adjust the chip so that it is aligned. Once aligned, you can now solder the diagonally opposite lead.

Now that the chip is aligned, solder all the leads down. I use a very fine solder 0.020" diameter, but use what works best for you. On very fine pitch chips, you will often bridge the leads with solder. No big deal, now you break out the solder wick, and use it with the iron to get the excess solder removed. 

Passive components (resistors, capacitors, etc.) are usually pretty easy, once you've practiced a bit. I put some solder down on one pad, place the component down, reflow the bit you already placed while positioning it with the tweezer, then solder the other side.

Iron tip tips: screwdriver style tips work better than conical tips. Surface area in contact with the lead is important. a screwdriver tip will have a line contact, whereas the conical tip has a point contact, which results in less heat transfer. 

Chips are also hard to remove. Nowdays, I often take a small butane torch and heat up the chip itself while trying to move it with the tweezers (this assumes the chip will be trashed and not reused). Other techniques include cutting all the leads on the chip with diagonal cutters and removing the individual leads with the iron, and using fine wire to lift individual leads one at a time (the wire is carefully threaded underneath the lead). I've never actually used the last method, but I've read about it.

Passives are easiest with 2 irons, or one of those fancy tweezer iron handpieces (they rock for this). your simply take your two irons and heat up both sides and lift it using the 2 irons. The butane torch with some tweezers also works. 

Butane torch: be careful not to linger on the circuit board. It can get too hot and char. Be very quick with it. I only use it to remove bad components. 

As far as putting down LED emitters, I have no experience here (with the high wattage LEDs, the small indicator LEDs are easy, like the passives). Heat sinking an coupling are important, I hope someone else can expound more on the ins and outs of high power emitter placement.

Thats how I do it.


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## Doug S (Jan 19, 2007)

Kromeke: your post by itself is an excellent tutorial. While I haven't personally used the butane torch, I know from personal experience that all your other recommendations are good ones. I especially like that your #1 point is about solder wick. It indeed is your friend. If I get around to doing a tutorial, may I lift some of your text verbatim?


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## infinity of zero (Jan 19, 2007)

These guys wrote some tutorials about SMD soldering:
http://www.sparkfun.com/commerce/hdr.php?p=tutorials


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## Sawtooth (Jan 19, 2007)

Doug S said:


> Kromeke: your post by itself is an excellent tutorial. While I haven't personally used the butane torch, I know from personal experience that all your other recommendations are good ones. I especially like that your #1 point is about solder wick. It indeed is your friend. If I get around to doing a tutorial, may I lift some of your text verbatim?


Lots of photos would be nice too.


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## georges80 (Jan 19, 2007)

I've soldered many hundreds of SMT IC's and parts.

I use a chisel tip bit (for IC's) and a pointy type for R's and C's etc.

The KEY is the flux and solder. (I've written about this before). I HIGHLY recommend
Kester 2331ZX flux (organic) and the same flux based Kester Solder 331.

The flux will allow you to very easily solder SMT including the finest pitch IC's (0.4mm pitch is quite easy). The flux prevents the solder from balling up and shorting pins together. You only need the soldering iron tip to be wetted with solder. Usually I just dab it to a pad that has a bit of solder on it. You want very little solder, the flux will cause the solder on the tip to flow.

With the IC's the chisel tip is dragged along the tips of the pins and the solder wicks to the pins/pads (due to the action of the flux).

Solder wick is handy for the rare occasion that the solder does short across a couple of pins.

The 2331 flux MUST be washed (water) and then the board can be blown or air dryed. I prefer to blow dry with compressed air.

Here's an example of a hand solder proto board that doesn't have a soldermask (makes soldering even more challenging) - and that's my pinky in the picture and NO, I'm NOT a giant 







cheers,
george.


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## kromeke (Jan 19, 2007)

Doug,
Sure, you can quote me. 

It wasn't until after my lengthy post that I realized you were planning on writing your own tutorial. I thought at first you were looking for one.

Edit: 
Thanks for the Spark Fun tutorial link. I like to see others' tips and techniques. The <$200 hot air station is nice. I use the butane torch for now, it is cheaper, but you have to be careful as it isn't temperature controlled. I've seen the skillet trick as well. 

This is one of those things in which there are many ways to do it.


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## maglitesales.com (Jan 19, 2007)

I would like to reiterate the point made by georges80 concerning using good flux. It is also good practice to make sure that you have clean equipment, clean solder, clean component leads and clean circuit board pads/contacts. Oxidation is your enemy. Oxidation forms on component leads, circuit board pads, your solder and the soldering iron tip itself. Use the ideas below to keep things cleaned up and you won't have a problem. Once your component and board are clean, put a small amount of flux on them to help resist oxidation during the soldering process and help the solder to flow.

I keep a bit of isopropyl alcohol, Q-tips and paper towels handy for cleaning things up prior to flowing solder.

Use the Q-tips wetted with alcohol to clean the board and pads.

Use the paper towels, slightly wetted with alcohol to clean off the solder. Just wet a spot on the towel with alcohol and pinch the solder between your thumb and forefinger and pull the solder through the towel.

Keep a wet sponge handy (damp, not soaked) to run your solder tip across periodically to get rid of old solder and oxidation. The wetness on the sponge will "flash" the tip and clean it up nicely.

And finally, remember not to use too much solder. For IC's, you should be able to see the outline of the component lead through the solder, and of wire leads on transistors and such, you should be able to see the end of the wire (coated with solder, of course). It should look almost like a Hershey's Kiss. 

Less solder = better connections, less chance for cold solder joints and an overall better looking project.

Enjoy!


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## Doug S (Jan 19, 2007)

kromeke said:


> Doug,
> Sure, you can quote me.
> 
> It wasn't until after my lengthy post that I realized you were planning on writing your own tutorial. I thought at first you were looking for one.


Actually, I'm liking the idea of letting this thread become a group effort tutorial. Less work for me! :goodjob:


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## Tritium (Oct 9, 2007)

Just a note that I just picked up a hot air rework station for a great price here:

http://www.circuitspecialists.com/prod.itml/icOid/8436 $129

Sure is making things easier on builds and repairs.

Thurmond


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