Surface Mount Soldering

[rstofer]

I think I'll be trying to hand solder the SOIC chips on the board using traditional methods and save the paste and reflow methods (hot air, reflow oven, etc.) to sometime when I have a little more cash to spend and more patience.  Everything I've seen and based on comments here leads me to believe I should be fine mounting the SOICs using a heat adjustable solder iron with a reasonably fine tip and fine grade solder.  I'll use SOIC for everything I can get in an SOIC package...

Related, not related, what is the etiquitte for posting PCB design for critique?  Post a picture of the top copper layer and a separate picture for the bottom copper layer or picture of the combined top/bottom..?

You may find that you don't want a 'fine' tip for drag soldering multi-lead SMD components.  You can also use solder paste instead of solder wire.  Just run a long bead of paste perpendicular to the pins, place the parts and tack opposing corners.  Then just drag the tip across the pins.  A more conventional technique is to use wire solder and tack the corners as usual.  Then put a small dab of solder on the tip and drag it across the pins.  This works very well if you run a bead of flux perpendicular to the pins.

This is all much ado about nothing.  Soldering SMD packages turns out to be pretty easy.  SolderWick is pretty handy.  Paste flux is the secret and paste solder has a place as well.

Where solder paste is really helpful is on 0805 packages and smaller.  Place the part in the paste, press down with curved tweezers and hit the joint with the iron.  This will prevent tombstoning.

Look for videos on 'drag soldering'.

[jpanhalt]

I think I'll be trying to hand solder the SOIC chips on the board using traditional methods and save the paste and reflow methods (hot air, reflow oven, etc.) to sometime when I have a little more cash to spend and more patience.  Everything I've seen and based on comments here leads me to believe I should be fine mounting the SOICs using a heat adjustable solder iron with a reasonably fine tip and fine grade solder.  I'll use SOIC for everything I can get in an SOIC package...

Here are couple of hints for starting out:
1) A very tiny dab of rosin flux under the device will help hold it.
2) For resistors and caps, use a microdot of CA (crazy glue, cyanoacrylic) on the board between the pads. When you put chips down, you will have a little time to get it adjusted, then it is quite robust to soldering.  You can put a lot of chips in place, then methodically solder them.  The nice thing about CA is that it is heat sensitive.  At soldering temp, most of it will just vaporize (it is made by distillation of the polymer).  Try to avoid getting it on the pad.   As for the "microdot", I use a thin piece of music wire ground to a dull point.   Place an ordinary drop of CA on bare copper PCB.  The bare copper will not set it off for  quite awhile.  I dip the music wire applicator into the puddle, then touch to the board.  You will be applying <0.1 microliter (i.e., a small fraction of a milligram).
3) The CA method doesn't work as well for SOIC chips, as there is often a small gap under the IC; however, medium CA will work.   Generally, SOIC's are so easy to solder, I don't bother.
4) As an alternative to #2, I will put a thin tiny dot of solder on one pad.  Place the component, then heat the pad and it will float into place. The little wire I made for #2 can be used to position the component and/or press it down.  If you get too much solder, just use solder wick to remove it.   You don't need much more than a plating thickness.  Once one end is tacked down, then solder the other end.  Finally make a good solder joint on the tacked end.

The CA method is, of course, what is done in industry on occasion.   I simply found that hobby CA works pretty good compared the the expensive branded stuff.  I use method #2 when I have a lot of chips to solder and #4 when just a few.

Apologies, if this comment repeats comments from below.   I sort of lost tract after my first post.  I also have my usual two cups of coffee in the morning.

John

[james_s]

IMO soldering surface mount parts is easier than soldering through-hole parts for the most part, I don't know why people are so scared of them. With SMT there is no trying to wedge the part in there while you flip the board over and solder, no trimming the excess bits off, no issues with solder wicking up through plated through holes, it's just a lot cleaner. Also I can reflow solder a whole board all at once on my hotplate but that isn't really necessary. After working with quite a few 0.5mm pitch QFPs the SOIC chips feel like big chunky things, you could solder those with one of those big old Weller soldering guns. Just tin one of the corner pads with a bit of solder, then place the part there and reflow that pin, adjusting the IC as necessary until it's centered. Then solder the other pins just like you'd solder anything, take care not to use too much solder. The same technique works for chip resistors and capacitors, just don't use too much heat or you'll melt the solder on the end you already did when you solder the other end.

My favorite trick for hand soldering high density QFP stuff is to use lots of flux and put a bit of solder on the face of a wedge tip on the iron and then touch and drag away from the IC. If you get too much solder and it bridges, add a bit more flux and drag it off, wiping the iron on the cleaner between drags. If there's way too much, a bit of solder wick will remove it.

Don't fear SMT, it's really not hard. Practice soldering some cheap parts on a scrap board and you'll get the hang of it, then you'll wonder why you waited so long to try.

[mrpackethead]

2) For resistors and caps, use a microdot of CA (crazy glue, cyanoacrylic) on the board between the pads. When you put chips down, you will have a little time to get it adjusted, then it

I'd never ever go down this path. If you want to take the part off you can't!    and there is no need to take this path either.

[tautech]

Related, not related, what is the etiquitte for posting PCB design for critique?  Post a picture of the top copper layer and a separate picture for the bottom copper layer or picture of the combined top/bottom..?

If you've done PCB design most of the traps for young players will be self explanatory except when it comes to rework and the tools you might use/have for such, probably moreso for prototyping.
If you want us to have a good look, top and bottom please.

[jpanhalt]

2) For resistors and caps, use a microdot of CA (crazy glue, cyanoacrylic) on the board between the pads. When you put chips down, you will have a little time to get it adjusted, then it

I'd never ever go down this path. If you want to take the part off you can't!    and there is no need to take this path either.

You missed the point about the temperature sensitivity of CA. Most of it is vaporized once the part is soldered.  The glass transition temperature of common household/hobby versions is less than 100°C.  More specialized versions have higher Tg's, but clearly my discussion did not relate to them.

Edit:  Sorry, I was in a hurry and forgot to address your second point.  If there is no need for it, then why do manufacturers still do it?  Why is there a "glue" layer?   Ever see the little red (color doesn't matter) spots under various SMD's?

John

[eugenenine]

CA smells really good when soldering too

[mrpackethead]

Edit:  Sorry, I was in a hurry and forgot to address your second point.  If there is no need for it, then why do manufacturers still do it?  Why is there a "glue" layer?   Ever see the little red (color doesn't matter) spots under various SMD's?
John

Not for the reason you think they do.  Its to enable double sided placement for parts that wont' say put due to surface tension when the other side is reflowed.  Ever notice that the glue is only on one side of the pcb

[tooki]

Edit:  Sorry, I was in a hurry and forgot to address your second point.  If there is no need for it, then why do manufacturers still do it?  Why is there a "glue" layer?   Ever see the little red (color doesn't matter) spots under various SMD's?
John

Not for the reason you think they do.  Its to enable double sided placement for parts that wont' say put due to surface tension when the other side is reflowed.  Ever notice that the glue is only on one side of the pcb

And for SMD on wave-soldered boards.

[tkuhmone]

To the OP, I am self-taught as far as soldering (a lot of watching YouTube and reading this forum), recently made the jump to trying SMD.

I bought myself a few Chinese SMD soldering kits to practice ($2 each on EBay), like this one: http://www.ebay.com/itm/SMD-Components-Solder-Practice-Plate-for-Training-DIY-Module-Electronic-Kit-/281916872729

could I ask how much did it took time for the PCB set to deliver ? I have wait mine for a bit over one month now, tracking did only show "Shipping info received". Not any tracking details visible, like packet locations...

EDIT: I also bought the angled weller PT-series tips (for drag solder practise). Got them new for fairly good price, two tips cost 0.8€ (without VAT)

[LaurentR]

could I ask how much did it took time for the PCB set to deliver ? I have wait mine for a bit over one month now, tracking did only show "Shipping info received". Not any tracking details visible, like packet locations...

I don't think I have used this particular vendor, but he's got good feedback. ePacket from China is 2-3 weeks to the US, but there is a very long tail. I had one over xmas that took 2 months, mostly stuck in China.

If it says "shipping info received" and not "Acceptance..." or "Processed through facility" in China, there is an issue right at the start. Contact your seller.

[TheDane]

Microscope. Microscope........ (Optical Stereo is best, USB Digital the worst)

If you can't see what you've soldered, are you willing to risk your work by powering it?
- or check for shorts with your huuuuuge multimeter probes, and then creating small shorts whiule doing so..... (pushing the solder to the sides, it's sooo easy to do on 0.4 and 0.5 pitch devices if not extremely careful)

Practice (on a scrappy lot) before doing high-cost devices, and get used to the difference in hand-eye body action department.
And yes, it's a LOT easier to rework a simple mistake than replacing the power supply, the device you tried to solder, and all the thin copper traces that acted as a fuse. It might not be as fast initially due to the extra tenderness, but in the long run it will save you time if you do it 'enough' - it does for me anyway, and I repair stuff for a living 

So lastly from me - Practice, and various forms of feedback - -get's it done right.
- don't try to save time or cost, at least if you want quality

[james_s]

I use an inexpensive illuminated loupe to inspect soldering on fine pitch stuff. A 3D microscope is an expensive piece of gear for most hobbyists, I don't need one enough to justify the cost.

[TheDane]

    Yeah.

Tools. Tools, Tools tools....  Me - I either love them, or need them and have a love-hate relationship.
I love my Metcal soldering station, and I would never go back to my Well-hellish iron without a fight.
It's hot faster, it delivers more heat and I could go on. Yes, it's pricy - but worth it

I have an Andonstar V160 2MP USB Digital Microscope at home, it does the job - but it lags and details can be hard to see.
It's not great, and I really miss the microscope I have at my workplace. If just the price was right......
- but at home I have more time, and I guess it's true: Time is money

[ebastler]

thanks for link, today I also ordered couple of boards. So I could try soldering with hot air, with flux etc etc.

Please don't bother with solder paste stencils and hot air, hot plates or whatever for now! Throughout this whole thread, ebclr has been the only one suggesting that approach, and several users have already contradicted him.

Hand soldering is the way to go for SOICs and smallish PCBs. You will not even need extra flux for 1.27mm pitch pins; the resin core in the solder is perfectly fine. Just make sure that to use sufficiently thin solder: 0.5mm diameter is fine; thicker stuff makes it more difficult to dose it right.

Even 0.5mm pitch can be hand-soldered nicely, but then the technique becomes a different one, and you will need to add extra flux to make sure the solder ends up where you want it to go. Others have suggested youtube channels to watch which do a great job demonstrating these advanced techniques -- but that's for later... 

Have fun with your SOIC-based layout -- and yes, I would suggest to use SOIC parts throughout. For practice, because it looks nice and consistent, and because you will enjoy the soldering!

[mrpackethead]

thanks for link, today I also ordered couple of boards. So I could try soldering with hot air, with flux etc etc.

Please don't bother with solder paste stencils and hot air, hot plates or whatever for now! Throughout this whole thread, ebclr has been the only one suggesting that approach, and several users have already contradicted him.

Hand soldering is the way to go for SOICs and smallish PCBs. You will not even need extra flux for 1.27mm pitch pins; the resin core in the solder is perfectly fine. Just make sure that to use sufficiently thin solder: 0.5mm diameter is fine; thicker stuff makes it more difficult to dose it right.

Even 0.5mm pitch can be hand-soldered nicely, but then the technique becomes a different one, and you will need to add extra flux to make sure the solder ends up where you want it to go. Others have suggested youtube channels to watch which do a great job demonstrating these advanced techniques -- but that's for later... 

Have fun with your SOIC-based layout -- and yes, I would suggest to use SOIC parts throughout. For practice, because it looks nice and consistent, and because you will enjoy the soldering!

A stencil, paste and some way to reflow is a very valid option.   Its not the only option but it a valid one.

[ebastler]

A stencil, paste and some way to reflow is a very valid option.   Its not the only option but it a valid one.

Sure. Obviously reflow soldering has its place, and at some point (pitch) it even becomes the only alternative.

But for a beginner in SMD, who owns and knows how to use a soldering iron, and wants to get first experience using SOICs? Why bother buying new equipment and materials, getting a stencil made, and familiarizing yourself with an entirely new process? That creates an unnecessary hurdle, and I strongly advise against it.

[tkuhmone]

thanks for link, today I also ordered couple of boards. So I could try soldering with hot air, with flux etc etc.

Please don't bother with solder paste stencils and hot air, hot plates or whatever for now! Throughout this whole thread, ebclr has been the only one suggesting that approach, and several users have already contradicted him.

Hand soldering is the way to go for SOICs and smallish PCBs. You will not even need extra flux for 1.27mm pitch pins; the resin core in the solder is perfectly fine. Just make sure that to use sufficiently thin solder: 0.5mm diameter is fine; thicker stuff makes it more difficult to dose it right.

Even 0.5mm pitch can be hand-soldered nicely, but then the technique becomes a different one, and you will need to add extra flux to make sure the solder ends up where you want it to go. Others have suggested youtube channels to watch which do a great job demonstrating these advanced techniques -- but that's for later... 

Have fun with your SOIC-based layout -- and yes, I would suggest to use SOIC parts throughout. For practice, because it looks nice and consistent, and because you will enjoy the soldering!

I plan to go ahead with simple setup first... And also with the equipment I currently own. I do have already 0.5mm SnPb solder wire (stannol).
In the soldering iron, I have approx 1.5mm wide chisel tip - that should be ok soldering practises now (for typical 0805 size).

I do not currently own hot air soldering equipment, for the moment that is not on my list to purchase.

I have an access to optical stereo microscope with sturdy base platform . The column used to adjust eyepiece height, that is around 50..60mm diameter and feels very solid. If correctly remember there is approx 20cm of work space between base platform and objective lens.  That could be very useful equipment later on :-)

[mrpackethead]

But for a beginner in SMD, who owns and knows how to use a soldering iron, and wants to get first experience using SOICs? Why bother buying new equipment and materials, getting a stencil made, and familiarizing yourself with an entirely new process? That creates an unnecessary hurdle, and I strongly advise against it.

And as someone whos done a lot of SMD, i'd say its well worth the effort to tool up with some new gear, and learn the new process.. Because its a skill that is *well* worth learning.. Just as much as learning to hand solder SMD parts.

[james_s]

I do reflow and have used stencils a couple times but sometimes I just hand solder. Not worth the expense of a stencil until you are positive that your layout is good, so I always at least build one prototype by hand or if I reflow then apply solder paste with a toothpick.

[LaurentR]

You _will_ need manification, at the very least to inspect. If you have good, young eyes, soldering should be possible without magnification in many cases.

I personally use a couple of Optivisors, one at 1.5x with good working distance and enough magnification to be able to solder most everything, and one at 2.75x with much shorter working distance but enough magnification for inspection. Needs strong lighting too.

https://smile.amazon.com/Donegan-OptiVisor-Headband-Magnifier-Magnification/dp/B0068OSIIS/

I use my wife's microscope on rare occasions. The visors are much friendlier to use for occasional soldering/inspection. If you are going to spend hours doing boards, a microscope is a much better (and much more expensive) option. You can work with the Optivisors for hours, but if you need large magnification, the small working distance becomes a liability and you need fancier optics than a single lens to move your head away from your hands.

[james_s]

Most stuff I just inspect visually without magnification. The 0.5mm pitch ICs I use an inexpensive illuminated loupe, it works fine. I can just about do it without a magnifier but it's easy to miss a bridge that way.

[mrpackethead]

I do reflow and have used stencils a couple times but sometimes I just hand solder. Not worth the expense of a stencil until you are positive that your layout is good, so I always at least build one prototype by hand or if I reflow then apply solder paste with a toothpick.

At least for me the cost of a stencil is much lower than the cost of the time it takes to place the parts by hand and then hand solder..   An unframed stainless stencil for a small pcb starts at just $10.

[Rick Law]

So I've only ever done through-hole device soldering, and I think I'm... pretty okay at it.  But now I'm working on a prototype that uses a couple chips that only come in surface mount packages.  I've been watching a lot of videos about hand soldering SMDs and it doesn't look too scary... I guess there has to be a first time for everything.

So two questions; first is related to package selection.  I'm leaning towards SOIC... the relatively large 1.27mm pin spacing seems attractive to me as a first timer.  Am I on the right line of thinking, or are smaller pin spacing deceptively easier?  My other question is around the other chips being used... coincidentally all of the chips have a SOIC package.  Should I have everything on the board be SOIC, under the theory that I might get "good" at it (about 8 chips on one board, plan to make 2 prototypes) or should I stick to through-hole for those that come in that package?

RJDog,

I understand the uneasy you are feeling.  I am a merely an inexperienced hobbyist and I felt the same when I considered stepping into SMD soldering.  The tasks just appeared to be so damn impossible. Your questions and reluctance are so similar to my questions and reluctance then.  So, allow me to share the story of my venture into SMD...  Hopefully, it will help you kick start your venture.

I kicked around the idea of dipping into SMD soldering for what seemed like ages.  I watched a few SMD soldering videos and kicked around it some more ever so reluctant because it looked so hard.  I found one of my old dead cell phone (StarTac) and started removing parts, and putting them back, and removing them, and putting them back...  Did that for may be a couple of weeks (dozen or so 1/2 hour workout), may be more.  But the phone was dead before I start, so I never knew if the replacement was correct or if I cooked the part and didn't even know.  I did "solder" one IC for so long the pin felt out.  So I kick around the idea a while longer.

I have a couple of SMD's I managed to send to electrocution.  I need to replace them but they were 1mm pitch and 0.5mm pitch .  It look damn near impossible to me.

Finally, I decided to have a go.  Dig out that cell phone again, this time, I practice the work flow to cut down the solder-iron contact time.  I recall I set a 2 seconds (per pin) target and 5 seconds limit.

After another hour or two of practice, the next day, I decided - time to have a go!

What I was glad I had at hand:
 - good flux
 - good solder sucking braid (when I applied too much)
 - a couple of magnifying glass (4x and 10x loupe)
 - a small screw driver (to help position and to hold the part)
 - 1mm solder (would have prefer smaller, but that's what I got)
Nothing fancy, I think you probably have everything I had in that list.

The technique I was most glad I learned (from the videos) before I start:
 - flux well
 - start with a corner pin (so it hold in position), then inspect carefully, then opposite corner, then inspect carefully again, then the rest of the pins, then inspect carefully again. 

First shot, 0.5mm pitch (10 pins) VSSOP.  Got it on, it works!  Second shot, 1mm pitch (6 pins) SOT23-6, got it on, it works.  Two successes in the space of an hour or so.  I was so pleased by it I wrote this:
_{https://www.eevblog.com/forum/beginners/some-times-things-work-out-the-way-they-should/}

It was beginner's luck.  As beginner, I was extra careful.  After that first day, SMD doesn't scare me anymore.  It doesn't look so impossible any more.  I have since improved - now SMD is just another chip to me.

Put your doubts in a jar, screw the lid shut and keep your doubts in that jar; then, with your doubts contained, have a go at it.  Practice some, practice some more, then start with some cheap IC's...  (I started with the ADS1115 which was a $6 chip if I recall... it worked out well but it was not smart.)

Good luck!

By the way, luck tends to favor the well prepared...

[james_s]

At least for me the cost of a stencil is much lower than the cost of the time it takes to place the parts by hand and then hand solder..   An unframed stainless stencil for a small pcb starts at just $10.

Cheapest I found was $20 by the time I paid shipping. It did save some time when I built several identical boards but I still had to place the parts one at a time and that was a longer part of the process than dabbing solder paste on the pads with a toothpick.

SOIC though, one could hand solder those with one of those comically huge soldering irons used for stained glass or a Weller soldering gun if that's all they had. The solder joints are not that much smaller than for a DIP.