Author Topic: Surface mount soldering. I don't like it.  (Read 1281 times)

mjg

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Surface mount soldering. I don't like it.
« on: October 10, 2020, 09:28:53 PM »
I've been trying to do a bit of surface mount stuff yesterday.  I had 4 x SOT-23 chips to solder on, and that was about 30 minutes of frustration.  Tested the finished circuit today, and 3 of the 4 are working.  The other is not happy. 

So, some photos for people to laugh at, and then I'd like some advice for the best way to:

1) remove the one I've buggered, without damaging the board, and
2) how to not bugger future chips when I try again

Any good tutorials on soldering these things that people can recommend?   I'm using a tiny tip on the iron, and putting flux on with a pen before hand, but damn, it's hit and miss.

Here's one of the good ones under a microscope (next to the world's largest resistor):



And here's the not working one.  I think I had about 5 goes at it, probably cooked it?




cooder

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Re: Surface mount soldering. I don't like it.
« Reply #1 on: October 10, 2020, 10:31:13 PM »
What works for me is using a good lot of flux right on the part and board. I do use a small chisel tip, not a tiny pencil tip, and that seems to work for me alright too.
The second chip looks a bit like solder bridges, maybe try to hit is again with flux and hot iron. I actually use also a rel hot rion I guess, quick in quick out. Temp I use most of the time on mine is 390 C / 734 F.
Solder i use is Kester 63/37.
Just my two cents, hope it helps.
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PMowdes2

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Re: Surface mount soldering. I don't like it.
« Reply #2 on: October 11, 2020, 01:40:22 AM »
I've been doing loads of smd building a modular synth.

The trick is lots of flux.

 I also use solder paste, it helps hold the component to the board as well.

And lastly, hot air.  That's a real game changer.

If you don't have hot air use a wide chisel tip

And lots of flux
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mjg

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Re: Surface mount soldering. I don't like it.
« Reply #3 on: October 11, 2020, 03:10:42 AM »
Thanks for the ideas guys.  I was tying the smallest pencil tip, maybe Iíll go back to a wider one next time.  Iíve got the iron on 370, maybe Iíll bump it up a bit too.   I thought I was putting on a lot of flux, maybe itís not enough.

Funnily enough, this is also for a modular synth build.   :)

Wasnít able to find any solder bridges according to the multimeter... but when I checked all the continuity again, finally found the issue - pin 2 was meant to be grounded, and it was when I applied pressure with the multimeter probe...but if I let off the pressure a bit it disconnected.  Reflowed that one pin, and itís working now.  Success!


alanp

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Re: Surface mount soldering. I don't like it.
« Reply #4 on: October 11, 2020, 03:24:45 AM »
What module is it?

And yeah, SMD is definitely not foolproof.
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PMowdes2

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Re: Surface mount soldering. I don't like it.
« Reply #5 on: October 11, 2020, 07:07:31 AM »
I've spent most of this year building this monstrosity

Most of the smd stuff is pretty easy now except the QFN and STM packages


« Last Edit: October 11, 2020, 07:09:41 AM by PMowdes2 »
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dan.schumaker

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Re: Surface mount soldering. I don't like it.
« Reply #6 on: October 11, 2020, 08:42:19 AM »
I agree with PMowdes2, hot air is the way to go.  Here is my process:

1) Apply some flux to the SMD Pads (I use this one https://www.amazon.com/Tools-Harware-8310000186-Kester-Soldering/dp/B00YL1D3US?th=1)

2) Run a line of solder paste down the pads (using this syringe https://www.amazon.com/Clean-Leaded-Solder-Paste-Grams/dp/B017RSZFQQ/ref=sr_1_5?dchild=1&keywords=solder+paste+syringe&qid=1602426978&sr=8-5)

3) Hold the IC down with tweezers while I hit it with the heat gun.  I use my wife's embossing heat gun, and it has been a game changer (like this one https://www.amazon.com/dp/B07Z1VL1F5/ref=twister_B084G32K3J?_encoding=UTF8&psc=1)

4) Watch the solder melt, and touch up and solder joints with the iron.

This way has been a game changer for me on doing SMD IC's.  I still do JFET's and resistors by laying a solder blob on the pad and putting the part down, but for IC's, this is great.  The heat gun should help with removing the IC as well.

Muadzin

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Re: Surface mount soldering. I don't like it.
« Reply #7 on: October 12, 2020, 05:34:50 AM »
I agree with the OP, surface mount soldering ain't fun. And sadly as more and more through hole components go out of production it will become more and more the norm. As driven by the electronics industry, for whom this is both cheaper and allows for less repairs so more planned obsolescence. Kaching!

davent

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Re: Surface mount soldering. I don't like it.
« Reply #8 on: October 12, 2020, 09:44:14 AM »
... and the more you do it the easier it will get, necessary evil i need to face as well.
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TFZ

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Re: Surface mount soldering. I don't like it.
« Reply #9 on: October 12, 2020, 03:37:04 PM »
I actually quite like SMT soldering. I'm faster and it feels like a simpler process. But I have been doing it for all my electronic life.

One story from a tube old-timer comes to my mind: he told about when noval tubes were introduced. People of that time, used to octals and even larger, complained about this miniature stuff, who would want to deal with something that tiny!  ;)

CodeMonk

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Re: Surface mount soldering. I don't like it.
« Reply #10 on: October 12, 2020, 04:00:50 PM »
When I worked at JPL, about 90% of what I did was surface mount.
I modified my tips.
Had chisel tips that were just a little wider than the leads.
Then I modified them like this:

That little mod increased my quality and quantity.

You can buy tips already shaped like that now.
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alanp

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Re: Surface mount soldering. I don't like it.
« Reply #11 on: October 12, 2020, 04:25:29 PM »
CodeMonk, what are the Hakko codes for those? Do they affect your technique?

On the whole, I kinda like SMD. You don't have to clip fifty damn component leads, that's for sure! And if you want to fit a huge, complex circuit into something smaller than a shoebox, you kinda don't have much of an option.
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CodeMonk

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Re: Surface mount soldering. I don't like it.
« Reply #12 on: October 12, 2020, 04:41:41 PM »
CodeMonk, what are the Hakko codes for those? Do they affect your technique?

On the whole, I kinda like SMD. You don't have to clip fifty damn component leads, that's for sure! And if you want to fit a huge, complex circuit into something smaller than a shoebox, you kinda don't have much of an option.

I just did a quick search on Hakko's web site.
Something like this: https://www.hakko.com/english/tip_selection/type_r.html
Looks like you may have to do a bit of searching to fine tune the size (and other factors I guess).
That page shows soldering the entire component at once.
The tips I had were much smaller than that and did one lead at a time.
We also did all that soldering under a microscope.

You could always make your own I guess.
Only takes a exacto blade and a few minutes.

Shouldn't really affect technique.
But it does require a lot less time to heat things up and get solder to flow.
It basically heats up the pad and the lead at the same time, with a lot more contact with both surfaces.

I'm not currently doing any SMD, but i do have a few designs, in my head, that will require SMD. so I will be looking into this sometime next year.

« Last Edit: October 12, 2020, 05:28:19 PM by CodeMonk »
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mjg

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Re: Surface mount soldering. I don't like it.
« Reply #13 on: October 12, 2020, 11:31:12 PM »
Ok, so this has been really helpful, and has given me a few ideas to try.  Thanks all.  Iíll be looking into a hot air gun, and see how that goes.

And I guess practice is what I really need.  I do surface mount so rarely. 

Alan, you asked what module?  Itís a MIDI to CV module that Iím doing, using an AT mega and some DAC chips.  Nothing fancy, but thought it would be fun to do the board and code all from scratch.  I think the board should be generic enough that I can use it for any sort of Arduino-like stuff too. 

mjg

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Re: Surface mount soldering. I don't like it.
« Reply #14 on: October 12, 2020, 11:32:58 PM »
How does that type R tip work - does the solder paste hold the component in place?  Iíd be worried that Iíd miss and squash the chip or something.  ;D