soldering small SMT resistors, capacitors and transistors, I can't get them flat

CocaCola

Apr 7, 2012
3,635
What do u use to clean the pads?

if i use a solder sucker it lifts the pad and sucks the pad off of the trace

Too much heat, improper technique, wrong tool...

And again I asked how much experience do you have?

From what I'm gathering you have nil experience and likely need to practice, practice and practice some more...

danny davis

May 9, 2012
306

I just don't know how to clean the pads if they already have solder on them

Because when i use the solder sucker it just sucks the pad also

How much heat do you use on the soldering iron? I'm at 600 on my soldering iron

jhayar25

Mar 28, 2012
47
when i solder smd or flat type i used soldering iron the technique is you must solder it quick by soldering both end alternate in quick moving...

CocaCola

Apr 7, 2012
3,635

I just don't know how to clean the pads if they already have solder on them

Post #9
If you have solder on both pads, remove the solder on one pad with wick before reworking...

Post #10
Use solder wick to remove any existing solder before you replace the device.

Post #14
Use solder wick to clean up the pads. That will make your life much easier.

.........................................................

Because when i use the solder sucker it just sucks the pad also

Post #21
Too much heat, improper technique, wrong tool...

.........................................................

How much heat do you use on the soldering iron? I'm at 600 on my soldering iron

600° C or F? What type of solder, lead free or leaded?

If it's Celsius and leaded solder, for gods sake turn that down!... If it's Fahrenheit turn it up for rework so you don't have to cook the board for so long to get it flowing... Is the iron calibrated?

I primarily use 63/37 solder and run the iron at about 670° F for most small SMD stuff, I turn it up to about 725° F for rework... These are just estimates as I adjust according to the job and how the work or rework is reacting... And I can't stress the use of proper flux and a clean iron enough...

If the pads are lifting you are getting the board too hot, likely from cooking it too long... That or you are forcing the issue and pulling the pads off yourself... This assumes you are not working on some incredibly horribly cheap quality PC boards...

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(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,506
I just don't know how to clean the pads if they already have solder on them

Use solder wick

Because when i use the solder sucker it just sucks the pad also

This means you're applying *WAY* too much heat.

How much heat do you use on the soldering iron? I'm at 600 on my soldering iron

About half that. (are you talking F or C). In retrospect it has got to be F

Whatever you're using, no more than a few seconds (at most) is required to do this job. The fact that you're removing pads is an indication of seriously bad technique, far too much heat, ot both.

Rleo6965

Jan 22, 2012
585
One technique you can try was first solder small amount of lead on both pads. Then place your solder tip in such a way that both pads was touch and therefore simultaneously melt the leads on the pads. Move solder iron on side to have space for smd. Place the smd using tweezer and removed the soldering iron. Allow the work to cool down before removing the tweezer.

Don't use too much heat and too long on pads to avoid damage to etch of pcb.

Last edited:

Aug 13, 2011
1,114
The videos I linked previously SHOW correct methods. Here are more:

Hot tweezer component removal.

0402 installation.

0603 installation.

0805 installation.

1206 installation.

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danny davis

May 9, 2012
306
What do you use to clean the solder joints? Acetone or MEK?

Most of the jobs I have don't supply solder wick

So i don't know how else to remove solder from a pad beside using a solder suck which sucks up the pad

CocaCola

Apr 7, 2012
3,635
What do you use to clean the solder joints? Acetone or MEK?

Flux

Most of the jobs I have don't supply solder wick

They should if you ask, and if not it's 100% worth the few bucks to purchase it out of pocket...

So i don't know how else to remove solder from a pad beside using a solder suck which sucks up the pad

Right back to your issue with lifting pads, you need more experience and practice... You are likely still overheating the pad and/or you are attempting to pull 'cold' wick away and ripping the pad off... The wick needs to be lifted immediately after or at the same time you remove the iron so that it doesn't get soldered down itself...

Yet, again I asked how much experience do you have doing this work? Your employer might very well find it beneficial and cost effective to get you some proper hands on soldering skills and training vs letting you keep destroying boards with what I can only assume is inexperience...

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danny davis

May 9, 2012
306
not that experienced sorry

Yes cold wick is an issue with me too for pulling off the SMT pads

I think the PCB boards are just very cheap made

What is the best FLUX to use for SMT and Fine pitch?

I hate the flux that is very sticky and smells like rosin, it just makes a mess out of soldering fine pitch

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,506
You need an appropriate liquid flux (I get mine from somebody that has a large supply and I don't remember the name at the moment). You want one that doesn't need to be cleaned off after use. I

For some uses I dilute solder paste with additional flux (manufacturers will warn against this).

For smt work I use very fine solder wick, maybe 1.5mm wide. If I have to clean up a large area I will grab some 3mm wick. The size of the tip on my iron won't allow me to use anything much wider.

A cheap SMT rework station may help you. I typically use a small (4mm?) diameter tip and relatively low speed air. The main tricks are removing only the component you want to, and melting solder on all legs of a (say) SO-16 device simultaneously. These are not difficult skills to learn.

A great advantage is that you don't have flux fumes wafting up into your face.

You should never be pulling pads off. To use solder wick, place the wick on the board, place the tip on top and wait until you feel it melt through the solder. You may also see solder appear wicking through the braid. Remove the iron and braid simultaneously. The whole process should take between 1 and maybe 4 or 5 seconds. I would think 4 or 5 seconds would normally be too long unless it's a large pad that takes a lot of heat to melt the solder..

nepow

Jul 18, 2011
99
Coca Cola has the best answer... like him I have years of SMT rework. Most of my projects I build on strip board and use chip components with success. Just purchase a solder wick as he says, a fine bit and thin solder is a bonus. Get some practice on scrap boards, you'll soon master the technique.

CocaCola

Apr 7, 2012
3,635
You need an appropriate liquid flux (I get mine from somebody that has a large supply and I don't remember the name at the moment). You want one that doesn't need to be cleaned off after use.

There are dozens of people on Ebay repackaging small bottles of Kester 951, it's a no clean and has IMO a not so bad smell... I personally don't like it all that much, as it evaporates faster than fast, but it's designed to do that...

For some uses I dilute solder paste with additional flux (manufacturers will warn against this).

Since I don't use my paste rapidly or keep it frozen or even refrigerated like recommend I have been known to either dilute it back down with alcohol (or Kester 951) or hit it with some rosin flux to make it more sticky... I post clean all my PC boards after assembly (of of parts that can get wet) in an ultrasonic so any residue flux isn't an issue for me as it gets washed off...

For smt work I use very fine solder wick, maybe 1.5mm wide. If I have to clean up a large area I will grab some 3mm wick. The size of the tip on my iron won't allow me to use anything much wider.

Maybe I'm just lazy but I still do 99% of my work both smd and through hole with the same 0.5mm wedge point... Once you get the knack it can be done without much hassle, but the bigger tips are certainly easier to work with sometimes...

A cheap SMT rework station may help you. I typically use a small (4mm?) diameter tip and relatively low speed air. The main tricks are removing only the component you want to, and melting solder on all legs of a (say) SO-16 device simultaneously. These are not difficult skills to learn.

Nope not hard at all they just require you apply yourself and practice...

A great advantage is that you don't have flux fumes wafting up into your face.

I always have a small desk fan or defume fan pulling a slight negative over my work that eliminates that... Don't blow on the work as it's causes issues with heating, but pulling across the effect is nil...

CocaCola

Apr 7, 2012
3,635
I think the PCB boards are just very cheap made

More likely your lack of experience is passing the blame, until you have more experience under your belt you really can't make that call...

What is the best FLUX to use for SMT and Fine pitch?

Kester 951

I hate the flux that is very sticky and smells like rosin, it just makes a mess out of soldering fine pitch

But, it works well...

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,506
There are dozens of people on Ebay repackaging small bottles of Kester 951

My source has a large quantity of something he got from a business that was shutting down. I'll try to find out what it is. It is a very low viscosity fluid and works an absolute treat. No noticeable residue.

I post clean all my PC boards after assembly (of of parts that can get wet) in an ultrasonic so any residue flux isn't an issue for me as it gets washed off...

I have some pretty blue liquid that is designed for washing PCBs. I should go out to the workshop to read the label

Haven't tried it with an ultrasonic cleaner, but that's an interesting idea. In most cases a bit of a dip and a swirl is enough to remove any visible residue, including any muck left from rosin fluxes (typically those which were already on the board)

Maybe I'm just lazy but I still do 99% of my work both smd and through hole with the same 0.5mm wedge point... Once you get the knack it can be done without much hassle, but the bigger tips are certainly easier to work with sometimes...

My iron has a 2 to 2.5mm wedge point. I can use it for smd work, but the hot air rework tool is just plain easier. For small boards I remove the nozzle from the rework tool and use it to reflow the entire board. It's a bit like the reverse of the method used to degauss a colour CRT. It's almost faster than waiting for the regular iron to heat up. Of course, the setup time placing the solder paste on the pads isn't counted here!

Nope not hard at all they just require you apply yourself and practice...

I think that it requires less practice and skill than regular work. A colleague and I tried to use the rework tool to damage a board (just to see how easily it could be done) and we pretty much failed.

I always have a small desk fan or defume fan pulling a slight negative over my work that eliminates that... Don't blow on the work as it's causes issues with heating, but pulling across the effect is nil...

I try to have some airflow over my work. I've never invested in a "defume fan". Just as long as the smoke doesn't make a bee-line to my face, I'm happy.

CocaCola

Apr 7, 2012
3,635
My source has a large quantity of something he got from a business that was shutting down. I'll try to find out what it is. It is a very low viscosity fluid and works an absolute treat. No noticeable residue.

The Kester 951 I suggested is generally considered a professional grade flux and is generally sold by the gallon... It's water thin and hardly leaves any noticeable residue... That is why I suggested Ebay as you can get a little bottle repackaged by someone that will last a long time for a buck or two vs purchasing an entire gallon...

I have some pretty blue liquid that is designed for washing PCBs. I should go out to the workshop to read the label

Let me know what it is if you do get the name... I have tried several made for 'defluxing' cleaners and most leave me feeling blah vs their upcharged cost...

Haven't tried it with an ultrasonic cleaner, but that's an interesting idea.

It works well in a semi-production environment... When I'm doing a run of say 100 boards it's nice to just have the ultrasonic there, as I inspect and rework any issues, I just drop them in the ultrasonic and move to the next... After a few minutes rinse them off with water and they are ready to go... I have been using some cheap dollar store 'orange' degreaser as of late it works quite well... But, I have found a lot of cleaners (especially alcohol based) will leave a TON of white powdery residue on small pitch components so you need some trial an error to find a cleaner that works well in the ultrasonic...

For small boards I remove the nozzle from the rework tool and use it to reflow the entire board.

Done and still do that for one offs... But, for multiple units I have a makeshift $20 toaster oven that I converted for reflow... A timer and a few turns of the temp knob and it does the trick quite nice... Of course, the setup time placing the solder paste on the pads isn't counted here! Since you can get custom 'plastic' stencils for about$25 now I don't bother unless it's a one off and then I just do it with the iron... I'm considering getting a custom stencil that consist of many of my normal SMD packages for repair work... Just too lazy to commit...

I think that it requires less practice and skill than regular work. A colleague and I tried to use the rework tool to damage a board (just to see how easily it could be done) and we pretty much failed.

I agree you do have to try really hard, but it's not impossible... The board will shift a a slightly darker color before everything falls apart giving you a clear indication to back off,,, But, you should never get that far as the solder is guaranteed molten well in advance of that stage...

I try to have some airflow over my work. I've never invested in a "defume fan". Just as long as the smoke doesn't make a bee-line to my face, I'm happy.

I have never ponied up the money for a real defume fan for home shop use, but I did use one when I worked in a commercial shop it was nice but IMO not worth the cost vs a \$5 desk fan...

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,506
I think we're on the same page

danny davis

May 9, 2012
306
Does anyone know any brand names that make "cordless" Infrared SMT rework or "cordless" hot air gun in the size of a pencil so I can bring to job interviews to be tested for SMT rework?

CocaCola

Apr 7, 2012
3,635
Does anyone know any brand names that make "cordless" Infrared SMT rework or "cordless" hot air gun in the size of a pencil so I can bring to job interviews to be tested for SMT rework?

Have you ever been asked to bring you own iron an heat gun to an interview? I suspect any reputable company is going to test you on their own equipment, not whatever you decide to bring in...

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