Soldering the smallest caps/resistors?

Thread Starter

DarthVolta

Joined Jan 27, 2015
509
I never bothered to try yet, soldering/de-soldering anything super small (on purpose), on a phone, or motherboard. The parts that are sand grained size, and fine sand at that. Even with a microscope, that must be near impossible to get multimeter probes on, to find a value anyways, off the PCB. Big SMD parts get stuck to the iron so easy, and fry. Is there any such thing as a needle tipped soldering iron? Or does anyone just heat a needle tip somehow, and attemp this under a microscope, with manipulator arms ?


What about pre-placing the part, with glue, or some special solder paste, and using hot-air, or IR ? That might be do-able at home, if you ever really wanted to, I don't, just wondering....until it's cheap and easy.

What about putting the part in exactly in place, and hoping there's enough solder there, and then just have a metal rod sit on top of it, heat it up, and then let it sit there until it cools down and the solder freezes ?

What method do they use to solder them at the factory ?
 
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Travm

Joined Aug 16, 2016
323
Hot air rework station for rework, reflow solder oven for new production.
Solder is a paste emulsion with tiny solder balls in flux. You can use this paste and an iron, but professionals use hot air stations
 

nsaspook

Joined Aug 27, 2009
7,594
For the real tiny stuff you need magnification and soldering rework tools designed for SMD work.

 
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Thread Starter

DarthVolta

Joined Jan 27, 2015
509
I've never tried just placing a big iron tip right next to a part, until the whole area heats enough that way. I have junk boards here to fool around with a lot more.

In real life, if someone wanted me to repair SMD stuff, I better have replacements on hand, I'll probably fry some.

I have to get some glue like they use, what's that called ?
 

nsaspook

Joined Aug 27, 2009
7,594
I've never tried just placing a big iron tip right next to a part, until the whole area heats enough that way. I have junk boards here to fool around with a lot more.

In real life, if someone wanted me to repair SMD stuff, I better have replacements on hand, I'll probably fry some.
Practice makes perfect, this is especially true with soldering.
 

SamR

Joined Mar 19, 2019
2,590
I can solder SOT-23 on by hand but it is a bear with my shakey hands. Lots of liquid flux and a very small tip. Hot air to remove.
 

jpanhalt

Joined Jan 18, 2008
10,246
Up till now, I have done it one of 2 ways by free hand and without hot air:

1) Tin one pad. Place the component. Reheat that pad. There is just enough colder to hold the component while you solder the other pad. Solder first pad.
2) Add a micro-spot of CA adhesive. Place component. Press component with tapered piece of fine music wire (that helps set off the CA -- not necessary in all cases). Solder one pad. Solder other pad. I then reheat the first pas to relieve an stress.

System, works well down to 805 or an occasional 603. My next board is all 805 and will be my first attempt with reflow using either an oven or hot air.
 

MrChips

Joined Oct 2, 2009
21,879
Practice, practice, practice.
I can do most SMD soldering by hand. QFN packages are a pain because there are no leads to solder.

There are different techniques the DIY person can use.
1) Use a tiny drop of glue to tack the SMD on the board before soldering.
2) Use solder paste on the pads to hold all the SMD in place and then put the entire board in an oven.
3) Here is the technique I use. I put a tiny amount of solder on one pad. Butt up the SMD with tweezers and melt the solder to the SMD. Then solder the other side.

Edit: Same as John above.

You need to use the finest soldering tip and solder you can get (0.38mm).
I use a microscope for viewing.

To remove SMT resistors and capacitors I use two soldering irons heating up both ends at the same time.
Removing ICs require some practice.
 

Thread Starter

DarthVolta

Joined Jan 27, 2015
509
CA adhesive, so just superglue. Yup, soon I want to chop-up a PCB I have here, so I'll use the iron instead of the hotair, and try the super glue.

And right, if I wick away all the solder off the pads, and do 1 side 1st, using tweezrs and the scope, and then the other side. And lot's of good flux and clean tips.

If you glue something, like a piece of guitar string, to a little SMD part, and then soldered it down, and pulled on the string, what happens ?
 
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MrChips

Joined Oct 2, 2009
21,879
You don't have to wick away all the solder on a pre-soldered board, just enough to lower the bead a little.
One side of the SMD will then adhere to the solder that remains with the aid of the soldering tip.
Then go over each joint with some fresh solder.
 

SamR

Joined Mar 19, 2019
2,590
Never tried super glue. Yeah, solder one pad and remove as much as possible. Then I position the part on the one pad and (here's the tricky part) stick a well-callused finger down to hold it while I tack a bit of solder on to hold the piece on the pad. Reposition a bit if needed and solder the other pads and then reheat and fully solder the first pad. The real trick is not to burn the finger.
 

Thread Starter

DarthVolta

Joined Jan 27, 2015
509
My finger's aren't that deadened yet LOL, I've added a few more scars tho from the iron by accident.

I swear I'm going to start wearing googles, or I'll loose an eye from splashes or even using the microscope and not watching the iron tip off screen.
 

Ylli

Joined Nov 13, 2015
978
0603 and even 0402 parts I could do fairy easily by hand under a stereo microscope. Used two soldering irons (one in each hand) to unsolder the parts. To place and solder new, I just added a bit of solder to one of the parts, positioned the part with a tweezers and held it down with a fingernail. Reflowed that side, then soldered the other side.

0201 parts were a bit more difficult, but not impossible. I do have steady hands.
 

jpanhalt

Joined Jan 18, 2008
10,246
CA adhesive, so just superglue. Yup, soon I want to chop-up a PCB I have here, so I'll use the iron instead of the hotair, and try the super glue.
Some hints:
1) You probably will not b able to apply a sufficiently small dot of CA directly from whatever it is in.
2) I use a piece of PCB with copper exposed. Other surfaces will probably work too. You do not want wood. You want to use something that doesn't set off the CA. I put a small drop of CA on the board as my reservoir.
3) The "fine" wire I use is 0.035" music wire that is ground to a slight taper and blunt tip. When touched to the reservoir and then to the board, a very tiny amount is transferred. My guess is < 0.1 ul.
4) Once the chip is in place, you can wait or add a little pressure with the wire to make the CA set off.

And right, if I wick away all the solder off the pads, and do 1 side 1st, using tweezrs and the scope, and then the other side. And lot's of good flux and clean tips.
I sacrifice caps and resistors. Wick solder from both sides. If you wick from just one side, then work on the opposite end. Heat the working end and lift. I have never torn a pad from the board doing that and the component just raises up. The when you do the other end, and it is released. Final step is to clean the pads with solder wick.

If you glue something, like a piece of guitar string, to a little SMD part, and then soldered it down, and pulled on the string, what happens ?
You've ruined a good guitar string. It will detach easily from the SMD. The fine wire I mentioned could be a thinner. Just use something that is comfortable in your hands. You want something that is fine enough to make manipulations easy and apply a little pressure, but not too thin to pick up when it is laying on the table.
 

MrSoftware

Joined Oct 29, 2013
1,914
I've done down to 0402's by hand using a microscope, I have not tried 0201's or smaller but I would think a microscope and an appropriate tip on your iron would be a necessity for most people. The smaller you get the more it helps to have the right tools.

To the OP; yes there are oodles of different iron tips, depending on your brand of iron. For the small parts I actually like a pointy hooked tip, I don't know what it's called officially but it was in the collection of metcal tips at one place where I contracted. The big fat spatula of a tip that comes standard on some irons could make life difficult at best with the smaller stuff.
 

Tonyr1084

Joined Sep 24, 2015
5,081
If you have solder paste you don't need the glue. The paste will hold the part in place. If you use hot air or IR when the solder melts, capillary action will drag the component into place nicely. If you try to heat one side with an iron then the component may tombstone (flip up on one end - huge pain to get them back down). 0201 components are smaller than a single digit of the date on a dime. I had a picture somewhere but can't find it now. Done a lot of rework on SMT components as small as 0201. QFP's (Quad Flat Pack) can be fun to do with an iron. My technique is to solder one corner. Then adjust the alignment on the opposite corner. Once I have the chip properly positioned on the pads I use a wave solder technique using a big flat tip to drag solder across the leads. Plenty of flux is required. The last two or three leads may bridge, but that's easy to fix. After all leads are soldered, wick away the bridged solder. More flux. Swipe the big tipped solder iron across the pins again and you will likely drag a good amount of solder along and deposit it on the last leads without bridging.

Years ago I built a hot lamp using a focused (mirrored) lamp from a projector. The intense light and heat focused into a small space can melt solder. Of course it's blindingly bright, dark sunglasses is a must. But it's a good way to solder without making contact.

Back in the day I had very steady hands. But the first wife saw to it that my nerves could not hang steady anymore. My days of working with 0201's is pretty much limited to hot air pencils. But about 8 years ago I did some rework on some boards for Vivint. The parts were 0402's and I used dual irons to remove some resistors and replace them with different values, add some caps and add some chokes. Even the 0402's - you pretty much have to do under a microscope. But again, back in the day I could see those tiny parts without the need for a scope. The scope I like best is a stereo zoom 7 to 40 X. As an inspector people would get upset with me using the scope. But just because a defect appears larger doesn't mean the defect itself is larger. You're still looking at percentages. How much coverage (IPC-A-610 rev's C through G).

Anyway, it's been a great career. Just wish I knew more about the workings of the components and how they work together. I have a basic understanding of most of it, but there's a ton I know I don't know. Oh well. Next phase of life for me is a wood shop over the garage. Custom wood furniture and cabinets.
 

Ylli

Joined Nov 13, 2015
978
Even the 0402's - you pretty much have to do under a microscope.
I really got spoiled using my Stereo Microscope at work (retired 6 years ago). I even used it when working on larger things like good ol' standard DIP packages. So much easier to see when you have good solder flow and a fully wetted joint.
 
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