SMD soldering for non production (amatuer, one offs,etc)

[watchmaker]

I watched some videos and purchased several $2 practice kits.  I have a flux pen and tacky solder.

I tried a shortcut using a hot plate, big fail.  No way to maneuver without getting burned.  I guess reflow means reflow!

The most success is with the ball end tip, flux pen, tacking one leg down and then doing the others.

Most of these kits do not have printed material or PDFs so it will be interesting to see what I wind up with.

I think the Pinecil is easier than my I-Con 1.  Yes, AO zoom scope and lots of light.

I desolder with the wick and vacuum gun; ordered a yihua heat gun (will use it for heat shrink now instead of my butane tool).  I would rather not take up space with a tweezers station.

Any other thoughts and hints?

Regards,

Dewey

[Whales]

> I tried a shortcut using a hot plate, big fail.  No way to maneuver without getting burned.  I guess reflow means reflow!

Did you use solder paste or solder wire?  I've found paste + hotplate to be really easy, but I'm not sure of the latter.

[armandine2]

I watched some videos and purchased several $2 practice kits.  I have a flux pen and tacky solder.

I think a practice kit is ok - but for want of a pcb and a schematic that could be a half decent piece of bench kit or other useful/desirable electronic device. Where all these other kits and at what cost needs to be determined.

[Psi]

For quick one-off i just use the syringe the solder paste comes in plus a dispensing needle.
I hold the syringe and push the plunger with my thumb while touching the needle to a pad to deposit a tiny blob of solder paste on each pad. I do all the pads that way and then populate the parts with tweezers making sure to push them flat onto the pcb. (The paste helps hold them in place)
Then I reflow with hot air.

Note: Sometimes the solder paste syringes don't come with a plunger. You ideally want one that comes with the plunger and a dispensing needle.

[watchmaker]

These hints are very helpful.  Need to get solder paste.

THANKS!

[Whales]

The paste I buy comes in a plastic syringe with a plunger and a small plastic tip.  I keep it in a small bag in the fridge (the flux in it is supposed to have a shelf life).

Checkout sparkfun's guide to skillet reflow https://www.sparkfun.com/tutorials/59

It's worth mentioning that you apply the paste only approximately.  For chips with lots of pins you don't paste the pins individually, instead you draw a single line of paste across all the pins together.  One the solder melts it divides itself up amongst the pads using surface tension.  You only need quite small amounts of paste, but I've found the process is quite tolerant of my cack-handed application anyway.

Stick to parts with 1mm pin pitch or above.  Once you get smaller than that you start to have solder bridges, want a microscope and/or want a solder stencil for consistency. 

If you want to start using SMD passives then start with 1206 size and see how you go.  They cost a bit more than smaller sizes but it's still peanuts.

[Solder_Junkie]

These hints are very helpful.  Need to get solder paste.

THANKS!

Er, no... don't waste your time and money. I used to use hot air and solder paste for home made boards but since seeing this instruction video I moved to using an ordinary iron and conventional solder. Paste is tricky to use, often results in microscopic solder balls appearing between IC pins, has a short shelf life and is just plain tedious for home users.

Where a part needs to be soldered underneath, such as some types of SMD power MOSFETs, I just tin the pads, apply a little gel flux and heat with a hot air soldering unit (one of the Chinese "858D" types).

This is the YouTube video: https://youtu.be/eZtPR8_x0nc?feature=shared

SJ

[dietert1]

Only a year ago i ordered a Chinese heat gun (YIHUA 959D II, less than 100 bucks at amazon). A useful tool, my recommendation. I can use it working under the stereo microscope to make sure the part sits exactly where it belongs.
We also have a T962A reflow oven, but that one required some safety mods and it requires some patience until reasonable results.

Regards, Dieter

[Psi]

If you want to solder SMT with an iron and solder wire put a blob of solder on one of the pads only to start with.
Then you can position the parts with tweezers and melt that one pad with the iron so the part sinks into place.
Then you can quickly solder the other pad.  But you want the first pad to totally cool down first. If you try and solder it too soon it will heat the other pad up to melting temp too soon and the part will move. 

This is why I go around adding solder to one pad on every footprint first. Then I go around placing parts.
Then finally I go around one last time to add the solder to the other pads.

If you need to solder IC's you can do it as above, but its often faster to learn how to drag solder,
You will need a small-ish iron tip (not crazy small) and some gel flux, and some good quality solder wick.

[tautech]

If you want to solder SMT with an iron and solder wire put a blob of solder on one of the pads only to start with.
Then you can position the parts with tweezers and melt that one pad with the iron so the part sinks into place.
Then you can quickly solder the others pad.  But you want the first pad to totally cool down first. If you try and solder it too soon it will heat the other pad up to melting temp too soon and the part will move. 

This is why I go around adding solder to one pad on every footprint first. Then I go around placing parts.
Then finally I go around one to add the solder to the other pads.

If you need to solder IC's you can do it as above, but its often faster to learn how to drag solder,
You will need a small-ish iron tip (not crazy small) and some gel flux, and some good quality solder wick.

Mostly this ^^^^
Although the one pad only needs a sorta heavy tinning and certainly not a blob as you can come back to it when the other pad is soldered and add more to create a decent solder fillet.

Prototypes will require rework just as repairs will where a K style Hakko tip becomes invaluable and saves the need to get the hot air station out on many occasions.
For all but the bigger SMD components a K style tip can span it and heat both pads where it can be removed with tweezers or just swept off the pads with the iron.

While not the gospel for SMD technique, there's some good tips here:
https://www.eevblog.com/forum/beginners/so-surface-mount-it-is/

[Psi]

Although the one pad only needs a sorta heavy tinning and certainly not a blob as you can come back to it when the other pad is soldered and add more to create a decent solder fillet.

Yeah, i usually don't care much about making it look pretty because I'm prototyping and it will probably get ripped off later on and swapped to a new value anyway. 

But yes that is the right way to do it 

[trilerian]

I am an amateur at best, lol, and have only been doing this for a year or so.  But in that time I have soldered over 500 pcb's across 5 designs that I have made.  This has been my soldering evolution.

I started out using plain old 63/37 solder, I got one of those magnetic helping hands type boards that have standoffs you can hold a small pcb with.  I would take my iron and dab a small amount of solder on each pad of the pcb then place my part with tweezers and apply hot air, the solder would melt and apply a little force with the tweezers and the part goes onto the pcb.  This worked really well for 63/37 solder.  For smaller foot prints with lots of pins like a tqfp64, I would have to use flux.  After doing 25 or so like this I bought a cheap hot plate.  The first time I tried the hot plate I thought, "what a waste of money", we'll come back to that.  After that I decided I wanted to try solder paste.  I got some leaded solder paste and used small dabs on each pad except multi pin foot prints where I made a line and then place all my components with tweezers and used hot air to melt the solder.  This method works pretty well with really small part count pcb's.  The more components you add the the less efficient this process becomes. Then I designed my next board which has 60 smb components.  Still not a lot, but over twice as many as my last board.  And I can probably assume my next board will have more.  For prototyping I still used the last method as it is very user friendly and if you create solder bridges they are easy to clean up with solder wick.   But after prototyping I knew I was going to expand to selling overseas, so I needed to go lead free.  At this point I started ordering my pcb's with the ENIG finish and went lead free with my solder paste and solder. 

What I quickly learned with unleaded solder paste and big components or multi pin components is that cold joints happen easily with my previous method as the solder needs a much higher temp to melt and solidifies at a higher temp as well.  This would create joints where the pin would be on top of the solder instead of in the solder and make debugging circuits a pita.  So my next order of pcb's I ordered a stencil with it.  OMG, this is so stupid cheap and totally worth the money...  Just a note here, make the stencil the size of your pcb and get it sanded or whatever the premium finish is.  They end up being around $15, so worth it... 

Now I'll move on to the next evolution and the current way I solder pcb's.  Back to the hot plate.  So now, I get my stencil out and tape my pcb down, and tape the stencil down over the pcb.  I smear solder paste over all the pads. I pull the stencil off and wipe it with 99% IPA and a tooth brush.  I place the components, put it on the hot plate with a temp of 250°C.  Now in a perfect world this would melt the unleaded solder paste I use, however my last pcb design uses 2oz copper plane for the ground on the bottom and some big 2oz pads on the top, but I didn't fill the rest of the top with a 2oz plane, so my pcb warps a bit during the process, this means the edges come up about 1mm and the outer components don't get soldered down at that temp.  What I did at first was to take my tweezers and press the board down on the edges and let the paste melt.  Now I use my heat gun.  Once the bed temp gets to 200°C, I start going over the board with my heat gun, at this point the big 2oz copper plane is already hot so I don't have to worry about cold joints.  Once you get the pcb heated up, you are honestly just going over it with the heat gun, it liquifies right away.  I will say that if you are using leaded solder paste and 1oz copper pcb's, you can just get away with the hot plate, and it is really cool to watch.  Blink and everything is melted. 

The next step in my soldering evolution is going to be a reflow oven.  I don't know if I am going to build my own or buy one, or even when that will happen, as right now I can prep, paste, get the components on my 60 component board, and solder it in 20 minutes.  What I can tell you though, I hate through hole components now.  What a time sink they are...