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Worth Repeating About Soldering SMT Devices

06/28/2017 12:43 PM

As I mentioned in response to the previous topic on soldering SMT devices, there is a really good way to do this that will delight those of you who find yourselves challenged by the prospect of working on small parts. Instead of regular solder in a wire form, use one of the many solder pastes that comes in a syringe to simplify your life. It does have a limited shelf life (for ease of application) but it consists of tiny little balls of solder in a flux paste about like tooth paste. You apply a tiny amount to the surface of your printed circuit board, place the part to solder on it, and apply heat. You don't really have to use a soldering iron because very hot air works even better. The paste changes color as the solder melts and condenses on your cold copper of your PCB and legs of your circuit parts almost like magic. There are some YOU Tube demonstrations of working with solder paste like this, but I will let you find those on your own. It is so much easier to work with that the slight increase in cost is paid back in ease of use very quickly.

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#1

Re: Worth repeating about soldering SMT devices

06/28/2017 1:33 PM

Yep, solder paste and a temperature controlled toaster oven! I've made quite a few circuit boards with SMT parts this way.

Have you seen my new soldering iron? (Courtesy, Seattle Robotics Society)

Thanks for the post!

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#2

Re: Worth repeating about soldering SMT devices

06/28/2017 2:05 PM

I always appreciate better ways of fishing! Tech tips like this make the ride on CR4 a real pleasure.

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#3
In reply to #2

Re: Worth repeating about soldering SMT devices

06/28/2017 2:11 PM

Better ways of fishing, hmmmm. Try dynamite and a long handle net.

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#5
In reply to #3

Re: Worth repeating about soldering SMT devices

06/28/2017 3:24 PM

We were setting off hydrogen-oxygen 2:1 mole ratio gas in balloons out at the farm this weekend. What a blast. It is posted on YouTube, something about red balloons popping.

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#4

Re: Worth repeating about soldering SMT devices

06/28/2017 3:12 PM

Thanks for the information. I had figured that SMT devices pretty much shut out the DIY hobbyist.

Still, DIP packages are much easier to breadboard.

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#6
In reply to #4

Re: Worth repeating about soldering SMT devices

06/28/2017 3:25 PM

True, but not everything comes in a DIP, sometimes you must SMT.

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#7
In reply to #4

Re: Worth repeating about soldering SMT devices

06/28/2017 5:17 PM

You just have to have very steady hands when placing 0804 resistors!

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#8
In reply to #7

Re: Worth repeating about soldering SMT devices

06/28/2017 5:24 PM

I'm good except for the steady hands and sharp eyesight.

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#9
In reply to #8

Re: Worth repeating about soldering SMT devices

06/29/2017 9:56 AM

We are talking microscope, and screw-arm manipulators? I don't think I could even nudge one of the 0804 resistors with tweezers and get the position 100% aligned, although, I used to be a good hand at picking up tiny forensic evidence with tweezers while working under a 'scope.

I could not even read license plate at 21:00 last evening (end of dusk, beginning of night) under our street lights, only about 35-40 yards distance.

Needed binoculars, and did not bother for them.

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#10
In reply to #9

Re: Worth repeating about soldering SMT devices

06/29/2017 10:52 AM

"I could not even read license plate at 21:00 last evening (end of dusk, beginning of night) under our street lights, only about 35-40 yards distance."

Try it before the 12 pack next time!

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#11
In reply to #10

Re: Worth repeating about soldering SMT devices

06/29/2017 11:14 AM

Yeah, good point.

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#12
In reply to #9

Re: Worth repeating about soldering SMT devices

06/29/2017 12:27 PM

I solder SMD by hand. Not often, but there is plenty of help on the net and the solder paste is wonderful.

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#13

Re: Worth Repeating About Soldering SMT Devices

06/29/2017 2:41 PM

I haven't used solder paste in years as it tends to leave little (microscopic) solder balls around in weird places on circuit boards shorting out things you don't want shorted. It's not bad with some of the larger coarse pitch parts, but when leads are .020" or less, the tiniest of solder blobs can be an issue.

I find that a fine tip iron and plenty of flux I can usually place and solder some pretty small parts. I use a felt tip flux pen. My hands aren't that steady, but I've got a technique where I use a finger or two on the bench to steady the whole hand. Works pretty well for me.

The other must have is a good stereoscopic microscope. 20x to 40x is usually good enough. A wide field of view helps as well, especially to place and solder IC's.

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#14
In reply to #13

Re: Worth Repeating About Soldering SMT Devices

06/30/2017 7:39 AM

You need to be very careful with the flux, buy best quality and only using a tiny, tiny amount, less is always better.

Plus scrubbing of any rest left, away, with alcohol and a toothbrush. You may need to do that 2 or 3 times....

The look at it carefully with a high powered eyepiece, say 50x. Using a metal pointer, remove anything untoward, but thats hardly ever needed....

Never had a problem.....

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#15
In reply to #14

Re: Worth Repeating About Soldering SMT Devices

06/30/2017 8:37 AM

Good point. Conductive crud can get caught in the flux as it dries and hardens on the circuit board. Clean it well. I've seen some weird things happen that went away once the board was cleaned.

Make sure that your alcohol is fairly pure. Isopropanol works well, but make sure it's at least 91% or stronger. I buy that at drugstores. 70% medicinal grade won't work. If you're a purist or need larger quantities, chemical suppliers can supply industrial grade at 95% or better.

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#16
In reply to #15

Re: Worth Repeating About Soldering SMT Devices

07/03/2017 1:42 PM

What about using denatured ethanol? I have plenty of that around.

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