Author Topic: A Beginners Guide to Soldering Surface Mount Components  (Read 2291 times)

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Offline Michael Lloyd

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A Beginners Guide to Soldering Surface Mount Components
« on: March 13, 2017, 01:28:05 PM »
I'm a beginner and this is my guide  :o

When I was in my 40's I decided that SMD's were the spawn of satan and they would never catch on  :-DD Now approaching 59... that's a long way from 60 just so you know... I have decided to start using surface mount devices. It makes perfect sense really. Now that 15+ years have gone by, I can't see worth a damn and my hands shake more than they used to (but not much). I normally work on things with tubes in them but I have an OtherMill Pro and dabble in making my own boards every now and then. I use the mill to make a prototype and then order from Osh Park if I want commercial boards (like for friends or gifts). When it comes to ordering boards, size matters  :-//

This isn't the first project but it's a good for illustrating my list of things that a beginner should know about soldering surface mount devices. It's a double sided board with a bunch of 51 ohm resistors on both sides. There's also a diode and cap for rf detection. Apparently they screwed up the board somehow and the surface mount cap location is not usable.





In no certain order these are the things that I know about soldering SMD's.

 Opinions
(1) if someone tells you that you don't need a microscope to solder SMD's, poke their eyes out with a sharp stick and take their microscope (not really but that's bullshit)
(2) use the correct soldering iron and tip. A 1/4" chisel tip might work fine on that old 1948 Zenith AM radio but it's not going to cut it for SMD work
(3) make no mistake, SMD's ARE the spawn of satan. Especially if they are smaller than 0805
(4) it's best if you know at least one or two expletives.
(5) Do Not Yell Expletives at the Board While Looking Thru The Microscope. Your components will flit off into whatever dimension those little bastards come from
(6) Concerning item 5. Add Sneezing, Coughing, or in some cases, Breathing to the list of things that shouldn't be done

Laws of Physics
Law 1: If your project requires x components, buy at least two more than x. SMD's can occupy other dimensions, so if you drop one, it's gone, forever.
Law 2: If you place a component on the board you will need to either turn it or flip it or both
Law 3: If you drop a component and it stays in this dimension (lands on the bench) it will be upside down. Especially if it's a resistor or capacitor. They are top heavy
Law 4: When you solder a resistor or capacitor to a board, make sure you either solder them all such that the numbers are the opposite of the silkscreen or solder just one the wrong way around. This will drive some people batty and it can be a source of amusement
Law 5: Make up some bullshit like Law 4 to try to cover up the fact that you soldered 1/2 the resistors on your board opposite of the silkscreen
Law 6: If a kit manufacturer supplies 2 extra components you will, at a minimum, lose 2 components
Law 7: The first component that you pick up with tweezers will make a click sound and disappear never to be seen again. Proof they come from another dimension
Law 8: Resting the barrel of the soldering iron on your finger to stabilize it will result in some level of chaos and pain. Don't do that
Law 9: Once you get into a rhythm don't take a break. If you stop in the middle of a project you will come back with the coordination of a spastic ape and fling components off into the other dimension (where satan stores them), tombstone parts, and generally turn your nearly complete board into an ugly mess.
Law 10: If tweezers were the size of a small rocket we could use them to launch spacecraft on intergalactic missions. They apparently contain some form of warp drive

Feel free to add any helpful advice that you see fit. Laws can be added at will. They are like speed limits, nobody follows them.

Endeavor to persevere

 8)
« Last Edit: March 13, 2017, 01:29:48 PM by Michael Lloyd »
 
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Offline tautech

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Re: A Beginners Guide to Soldering Surface Mount Components
« Reply #1 on: March 13, 2017, 01:45:51 PM »
 :-DD
Lovely and spot on.  :-+

Nothing worthy to add........yet.  :popcorn:
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Online JoeN

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Re: A Beginners Guide to Soldering Surface Mount Components
« Reply #2 on: March 13, 2017, 05:51:32 PM »
You forgot a big one.

11.  More flux.

If you have enough flux, you can use that 1/4" chisel tip.  For parts with lots of really fine leads like QFN-48's and more, it actually becomes the principal tip to use.  Flux the legs and pads and you can just drag solder across the legs.  To clear any bridges, clean the tip, flux a little more, and use the tip's solder affinity to just pull the extra solder away - no braid needed most of the time.  Soldering discrete parts like what you have shown is actually pretty easy, a first step, show us some QFP, or at least SOIC/SOP packages now.

I find my 3x desk lamp/magnifier is good most of the time.  It affords a very nice field of vision.
« Last Edit: March 13, 2017, 05:56:39 PM by JoeN »
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Offline alsetalokin4017

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Re: A Beginners Guide to Soldering Surface Mount Components
« Reply #3 on: March 13, 2017, 06:46:59 PM »
Hah... wait until you advance to the Hot Air Station and Solder Paste level. You'll discover entire new ways to lose multiple components at once with too much airflow, to melt all kinds of stuff you haven't melted yet like the more distant parts of your vise, new levels of pain when you lose control of the air nozzle and it falls into your lap... sheer terror when the dog makes off with the solder paste dispenser, complaints from S/HWMBO about the jars of solder paste and flux in the refrigerator....    :rant:

The easiest person to fool is yourself. -- Richard Feynman
 
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Offline Avacee

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Re: A Beginners Guide to Soldering Surface Mount Components
« Reply #4 on: March 13, 2017, 07:44:32 PM »
Law 6 has a mathematical error. The number of components lost will be Delivered - Required + 1   |O
Law 11: The chance of a component disappearing off to another dimension is directly proportional to a) its cost b) replacement delivery time c) a multiplication of a * b 
 
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Offline OutbackBob

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Re: A Beginners Guide to Soldering Surface Mount Components
« Reply #5 on: March 13, 2017, 09:46:01 PM »
As a newbee looking to get in to surface mount as well, I have been looking into USB microscopes... Are the el'cheapos suitable? Any recommendations?

Don't quite have the budget for Dave's Targano :(
 
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Offline Michael Lloyd

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Re: A Beginners Guide to Soldering Surface Mount Components
« Reply #6 on: March 13, 2017, 11:30:59 PM »
You forgot a big one.

11.  More flux.

If you have enough flux, you can use that 1/4" chisel tip.  For parts with lots of really fine leads like QFN-48's and more, it actually becomes the principal tip to use.  Flux the legs and pads and you can just drag solder across the legs.  To clear any bridges, clean the tip, flux a little more, and use the tip's solder affinity to just pull the extra solder away - no braid needed most of the time.  Soldering discrete parts like what you have shown is actually pretty easy, a first step, show us some QFP, or at least SOIC/SOP packages now.

I find my 3x desk lamp/magnifier is good most of the time.  It affords a very nice field of vision.

I've used the "more" flux method when I built a clock kit a few months ago. I used my magnifying hood and a small chisel tip for that. I tacked a corner and then "strip soldered" (that's what I called it. I think it has a different name? Drag soldering?) the other side and then came back and did the same on the tacked side


Hah... wait until you advance to the Hot Air Station and Solder Paste level. You'll discover entire new ways to lose multiple components at once with too much airflow, to melt all kinds of stuff you haven't melted yet like the more distant parts of your vise, new levels of pain when you lose control of the air nozzle and it falls into your lap... sheer terror when the dog makes off with the solder paste dispenser, complaints from S/HWMBO about the jars of solder paste and flux in the refrigerator....    :rant:

I have one of those. I think it was made for cleaning circuit boards   :)

Law 6 has a mathematical error. The number of components lost will be Delivered - Required + 1   |O
Law 11: The chance of a component disappearing off to another dimension is directly proportional to a) its cost b) replacement delivery time c) a multiplication of a * b

100% correct  :-+

As a newbee looking to get in to surface mount as well, I have been looking into USB microscopes... Are the el'cheapos suitable? Any recommendations?

Don't quite have the budget for Dave's Targano :(

I had a really cheap AmScope but the field of view was poor. I happened across a YouTube guy (Louis Rossman) that repairs Apple boards (none for me thanks) and decided to go with his not as cheap AmScope with light. So far I like it.
 

Offline klunkerbus

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Re: A Beginners Guide to Soldering Surface Mount Components
« Reply #7 on: March 14, 2017, 12:11:19 AM »
...
This isn't the first project but it's a good for illustrating my list of things that a beginner should know about soldering surface mount devices. It's a double sided board with a bunch of 51 ohm resistors on both sides. There's also a diode and cap for rf detection. Apparently they screwed up the board somehow and the surface mount cap location is not usable.

Enjoyed the post. 

The resistors are actually 2200 ohms based on the 222 markings.  22 on each side puts 44 in parallel, which gives you the 50 ohms desired for a dummy load. 

On the cap, yeah, the board is generally set up so that you can use either SMT parts or through-hole parts.  The through hole pads for C1 are on the rectified voltage and ground, which makes sense. But the SMT pads for the capacitor are between RF IN and the rectified voltage, which is likely a layout error. 
 
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Offline Michael Lloyd

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Re: A Beginners Guide to Soldering Surface Mount Components
« Reply #8 on: March 14, 2017, 12:25:43 AM »
...
This isn't the first project but it's a good for illustrating my list of things that a beginner should know about soldering surface mount devices. It's a double sided board with a bunch of 51 ohm resistors on both sides. There's also a diode and cap for rf detection. Apparently they screwed up the board somehow and the surface mount cap location is not usable.

Enjoyed the post. 

The resistors are actually 2200 ohms based on the 222 markings.  22 on each side puts 44 in parallel, which gives you the 50 ohms desired for a dummy load. 

On the cap, yeah, the board is generally set up so that you can use either SMT parts or through-hole parts.  The through hole pads for C1 are on the rectified voltage and ground, which makes sense. But the SMT pads for the capacitor are between RF IN and the rectified voltage, which is likely a layout error.

 |O Yes... admittedly I prefer colored stripes and profane mnemonics to determine resistor values but you are correct.

All in all, it's a nice little board and I needed the practice, which is why I selected the SMD kit to begin with.
 

Offline jolshefsky

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Re: A Beginners Guide to Soldering Surface Mount Components
« Reply #9 on: March 14, 2017, 12:35:56 AM »
I bought a pair of Galilean 2.5x Loupes from LW Scientific that clip on to my glasses. I like to call them "super bifocals" since with a 380mm working distance, I can comfortably work on boards at a natural distance. They were fairly expensive, but I just can't afford anything cheaper, as the saying goes. (That is, I paid the price I did to have no eyestrain using them for the rest of my life which is far cheaper than suffering with junky optics.)
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Offline Michael Lloyd

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Re: A Beginners Guide to Soldering Surface Mount Components
« Reply #10 on: March 14, 2017, 12:47:06 AM »
I bought a pair of Galilean 2.5x Loupes from LW Scientific that clip on to my glasses. I like to call them "super bifocals" since with a 380mm working distance, I can comfortably work on boards at a natural distance. They were fairly expensive, but I just can't afford anything cheaper, as the saying goes. (That is, I paid the price I did to have no eyestrain using them for the rest of my life which is far cheaper than suffering with junky optics.)

Expensive... yes... but 380mm working distance! And the convenience of having them right there  :-+
 

Online JoeN

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Re: A Beginners Guide to Soldering Surface Mount Components
« Reply #11 on: March 14, 2017, 05:40:24 AM »
I bought a pair of Galilean 2.5x Loupes from LW Scientific that clip on to my glasses. I like to call them "super bifocals" since with a 380mm working distance, I can comfortably work on boards at a natural distance. They were fairly expensive, but I just can't afford anything cheaper, as the saying goes. (That is, I paid the price I did to have no eyestrain using them for the rest of my life which is far cheaper than suffering with junky optics.)

What are the main advantages of using this over say a quality desk lamp and magnifier of the same magnification?  These look interesting and I have never considered them, but my desktop magnifier has not let me down so far.
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Offline Housedad

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Re: A Beginners Guide to Soldering Surface Mount Components
« Reply #12 on: March 14, 2017, 08:17:23 AM »
Michael, I just ordered a Amscope SM-4T 7X -45X scope, a .5x barlow off ebay, and a 114 led ring light.   It will arrive Friday.   I'm the same age and have the same aging eyes problem at 58 years old as you.  I just hope when it gets in that it is comfortable to work with.   Any Issues with your eyes using your scope?

THEN I will try to solder SMD parts!  I bought a bunch of practice boards off of Ebay and will cross my fingers. 


« Last Edit: March 14, 2017, 08:22:35 AM by Housedad »
 

Offline jolshefsky

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Re: A Beginners Guide to Soldering Surface Mount Components
« Reply #13 on: March 14, 2017, 10:18:51 AM »
I bought a pair of Galilean 2.5x Loupes from LW Scientific that clip on to my glasses.  [...]

What are the main advantages of using this over say a quality desk lamp and magnifier of the same magnification?  These look interesting and I have never considered them, but my desktop magnifier has not let me down so far.

If your desktop magnifier works, then by all means stick with it. I have a cheap-ish one with a glass lens about 4" = 100mm in diameter. I had a hard time positioning it at the right spot between my hands and my work as it's basically a swing-arm lamp. It is barely big enough for both my eyes to see through, so I'd be looking through the edges of the lens where the optical distortion was worst, and also I'd have to adjust it, my head, and my work often making it a two-handed job just to look, the third hand for soldering. With the loupes, I can either look through or around with a tilt of my head just like bifocals. They are stereo and perfectly focused at my work distance with a large focal range of about ±50mm and a wide 100mm field of view. I find all this leads to less head strain and less eye strain making it much more comfortable to do SMD work or any close, small work.
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Offline Michael Lloyd

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Re: A Beginners Guide to Soldering Surface Mount Components
« Reply #14 on: March 14, 2017, 11:06:15 AM »
Michael, I just ordered a Amscope SM-4T 7X -45X scope, a .5x barlow off ebay, and a 114 led ring light.   It will arrive Friday.   I'm the same age and have the same aging eyes problem at 58 years old as you.  I just hope when it gets in that it is comfortable to work with.   Any Issues with your eyes using your scope?

THEN I will try to solder SMD parts!  I bought a bunch of practice boards off of Ebay and will cross my fingers.

I don't have any problems with mine and I didn't have any problems with the smaller one that I had other than it didn't have a ring light and it was fixed magnification (which hasn't been an issue btw). Mine had one eyepiece that could be adjusted and one that couldn't. Like binoculars. So you focus with the non-adjustable eyepiece and then adjust the other eyepiece until they match.
 

Offline Cupcakus

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Re: A Beginners Guide to Soldering Surface Mount Components
« Reply #15 on: March 14, 2017, 05:18:38 PM »
Great post! I also use a desktop magnifying lamp and it's fine for 0603 and up, I don't usually have any issues.  I do have much younger eyes though, ask me again in a few years.

 Except SOD23 diodes, those things are the devil.   Somewhere in the void under my bench there are dozens of those never to be found again.
 
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Offline Southerner

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Re: A Beginners Guide to Soldering Surface Mount Components
« Reply #16 on: August 17, 2017, 04:20:12 PM »
I, too, am a beginner but have tried a lot of different methods.

SMD soldering is a subject that I have read about with interest
for years.  I have never feared doing anything with smt parts and
neither should you.  I am old but my eyes are not too bad yet.  I do wear
progressive focals though.
I do not fear doing the job.

There are some things not really touched on in the discussion. 
I find that a handheld magnifying glass is helpful in checking
parts and traces but difficult to use for soldering.  I have many many magnifiers.
I have searched and bought many from Amazon but buyer beware.  I look for
10x and 20x but so far have never received a 20x or even a real 10x
when I order one.  They seem to actually be 10 diopter which I understand is 3X
and that matches what I see.  I do have a 4x UltraOptix (brand) and a slightly smaller
5X of that brand, both with LED lights.  They are great for inspection or identifying parts.  Also be aware that one
might say 5x/10x and you will find a small circle somewhere in the big magnifier that is 10x where the main lens is 5x or 3x.
I don't usually find the 10x little circle to be very helpful to me.  Others might disagree.

I also have one of the LED bench magnifiers (3X) and they are good for inspection but again does not have the
magnification I need for soldering serious smt parts.

I also bought a set of Harbor Freight jewelers loop set. 
The 10X loope is about the only one I use out of there. 
20X is too much magnification (for me) and the
5X is usually not enough.

I have bought the Harbor Freight and ebay over the head magnifiers and
some work and others are a poor excuse of a tool so being able to
try them before you buy is often helpful.

It was suggested to me and others that a binocular microscope would be a great tool.  I have several!
I bought a Nikon SMZ-1 and have 2 of those.  I bought a Nikon SMZ-675.  Mine are 10x and work great but do
not have the focal length like I would like as I want the lens well away from the work.  I had given up
on achieving that until someone else on one of the Amateur Radio forums suggested a specific AmScope.  I can't
find the model number but it is great!  It allows the bottom of the lens to be 6" or more above the work.  The one
problem I have with all of my microscopes, whether wearing my glasses or not
is being able to spread the lenses far enough apart to get
one view so have to close one eye but it works.

I originally tried a cheap usb microscope but it did not provide sufficient resolution and was quickly abandoned.

On the PCB or QRP-L list someone suggested getting a "docking camera" which you see in
classrooms for projecting an image from the computer or
from a paper on the bed onto an overhead projector.  Those work but take up a lot of
room and a good microscope would get used a lot more.  I do have one
but used it once and moved on.

I have an Ottlite (brand) desk magnifier as well as the Ottlite hobby stand
(has a light,  a work platform, and a magnifier on a floor mount or desk mount stand)
often found in craft and fabric stores
as many quilters use them.  They work and are good but the microscope worked
better for me.  Your mileage will vary.

You will see many methods for soldering smt parts.  I am currently trying to get a
reflow oven built
to try.  Is it worth it for a hobbyist to acquire or build one?  Probably not. 
The electric skillet method would do the same
thing and both would require use of solder paste.  To apply paste a template
is good but I have not found any cheap ones
like I would have expected to find for hobbyists.  It is amazing to watch
what happens when you hit the right temperature and
the solder paste flows.  Parts will often auto position (to some degree)
if they were place on pads but not quite straight.

You will see a lot of Chinese rework stations that often consist of a
regular soldering iron plus a hot air gun for soldering or unsoldering.
They have become quite cheap and most work well for hobbyists. 
Just be sure to use the right size air nozzle and be sure not to
have the air volume/pressure set too high or parts to be soldered will be in orbit around the
room never to be found again.

Tweezers have often been mentioned for placing parts to solder.  I use a crossed type and have
never had a part go sailing across the room but I see a lot of others mention that the tweezer is
nothing more than a catapult in disguise.  They have worked well for me but not for everyone.

A "doofus" or tool for holding smt parts in place while trying to solder them helps. 
There have been very simple ones that work well and are easy to make.  I use a steel
cookie sheet for a work surface for building my smt
projects.  The low sides make it easier to work but still keep the parts somewhat
contained.  I purchased a cheap machinists magnetic tool/dial holder and set it on the cookie sheet. 
The tool has setable articulating arms so I can
position the arm over the part.  In the hole for the end arm that normally holds the machinist
micrometer I use a knitting needle that fits the hole and the clamp
allows me to put the needle on the part with a little pressure and hold it while soldering. 
Others use a wooden chop stick or even
a toothpick.  Blue tack has been suggested but I find that to be too big for most parts.

I see suggestions to, for example, place a smt ic with several pins and then melt a blob of
solder and drag that blob across the pins on each side of the
device.  I have never like that method.  For one thing,  it reminds me of the old through
hole part days where we were always chastized and told not to
melt the solder onto a joint but to heat the joint and let the joint melt the solder. 
Also once you have dragged the blob across all the legs you them have to
get rid of that extra blob.  It always stroke me as a good way to create solder bridges
and bridges are not always easy to remove from smt parts once you get them!
One method suggests using a big solder tip that covers several pins of a part.  This
might be ok but I have always bought the 1/64" round tips for my
soldering iron and soldered each pin of even quad flat pack ic's...with the help of my microscope.

As you can see,  there are a lot of different methods for soldering surface mount parts. You will have to find the
method and tool(s) that works best for you.

73
WA7DUY

 
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Offline tggzzz

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Re: A Beginners Guide to Soldering Surface Mount Components
« Reply #17 on: August 17, 2017, 05:43:35 PM »
I'm 60, and until a couple of years ago I shared your concern about SMD; now I prefer them to PTH and find 0603/0.5mm pitch components are no problem.

Best way of soldering many small components at once is to use solder paste and "skillet" method. Well, actually I modify it by using a saucepan with a couple of mm of sand in the bottom. The sand acts as a buffer, spreading heat, preventing hotspots, and slowing down the rise in temperature (measured by a point-and-shoot non-contact IR thermometer) so that the temperature profile can be controlled by turning the knob on the gas ring. I have access to a toaster reflow oven at the local hackspace, but have never bothered to use it.

For me the best way of seeing the little darlings is to use a £20 head-mounted visor, e.g. https://www.maplin.co.uk/p/lightcraft-headband-magnifier-a87un That allows me to
  • use my normal glasses
  • instantly re-position the viewing angle for maximum effect - just move my head
  • quickly have more or less magnification depending on what I'm looking at
  • have a useful distance between magnifier and PCB/iron/tweezers
  • use them for peering into dodgy old scopes etc at very odd angles and on the floor
You might like to consider not taking components out of their strips and rehousing them in something neater: consider what happens when you drop one container, let alone several!
There are lies, damned lies, statistics - and ADC/DAC specs.
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Offline KL27x

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Re: A Beginners Guide to Soldering Surface Mount Components
« Reply #18 on: August 17, 2017, 10:48:44 PM »
For populating a board like what you posted, try this:

1. Dab liquid rosin flux over the all the pads.
2. Use a vacuum pickup tool to pickup each resistor and drop it over the pads. The flux will make the components stick, so they won't disappear into the ether if you bump the board or sneeze. Continue until all resistors are placed.
3. Put the board under the microscope.
4. Use a soldering tip which can hold/control a large bead of solder. (Anything but a pointy conical, but 2-3mm CF/BCF is probably best.
5. Lay some solderwire out over a flat surface.
6. With tweezers, align and hold the component in place over the pads
6.5 If you get the part stuck to the tweezers funny, stick the iron to the tweezers to heat up the flux, to help the component fall off so you can try again.
7. Pickup some solder onto the tip of the iron, as needed.
8. Dab one of the pads of the resistor until solder flows and forms a joint
9. Before letting go of the component, use the tweezers on the component you just tacked to center the next component in the FOV.
10. Repeat 6-9 until all the resistors are tacked.
11. Set down the tweezers, flip the board, and zip up the other end of each resistor.

If you have the right kind of tip, you can do a lot of joints without reloading. Under the microscope, this has a major advantage of being able to stay "in" the microscope for several joints without having to look away to get more solder. I reckon 3mm CF is as good as it gets, if you have the space to maneuver it. The combination of pad size and amount of tip loading/angle/maneuvering will control the amount of solder that is deposited on the board. As for loading the tip, the 2.5-3mm CF tips are pretty forgiving. But to fine tune the bead is a bit of an art. If I get too much, I just flick the bead off onto a flat surface which is coated in old flux residue (this happens naturally as you use it as your solderwire pickup board, which I call this my "rosin board"). Because the board is coated in flux, the bead of solder breaks up into little balls. Then you can pick up a lesser amount than you had before. (If you splatter a bead onto a non-fluxed surface, it will turn into a pancake).

If you manage to touch a non-fluxed part of the PCB while soldering, you might lose part of your solder bead. Pick it up with the tweezers and deposit it back onto the iron tip. If you try to pick it up with the iron, you will just leave another string of solder. The flux is what makes this work.
« Last Edit: August 17, 2017, 11:09:47 PM by KL27x »
 
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Offline tooki

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Re: A Beginners Guide to Soldering Surface Mount Components
« Reply #19 on: August 17, 2017, 11:05:19 PM »
I see suggestions to, for example, place a smt ic with several pins and then melt a blob of
solder and drag that blob across the pins on each side of the
device.  I have never like that method.  For one thing,  it reminds me of the old through
hole part days where we were always chastized and told not to
melt the solder onto a joint but to heat the joint and let the joint melt the solder. 
Also once you have dragged the blob across all the legs you them have to
get rid of that extra blob.  It always stroke me as a good way to create solder bridges
and bridges are not always easy to remove from smt parts once you get them!
One method suggests using a big solder tip that covers several pins of a part.  This
might be ok but I have always bought the 1/64" round tips for my
soldering iron and soldered each pin of even quad flat pack ic's...with the help of my microscope.
The reason -- and the only reason, really -- for not carrying solder to a joint on the iron is flux, or rather the lack thereof. (You don't want the flux to burn off before it has a chance to act on the work, and when flux-core solder is applied to the iron tip, the flux burns off practically instantly.)

In drag soldering, applying flux is mandatory, and the reduction in surface tension thanks to the flux is what stops solder bridges from forming. Additionally, remember that* molten solder flows towards heat, so the excess solder wants to stick to the tip, not the work. (No idea where you got the idea that removing solder bridges from SMT parts is hard; it's super easy. Flux, flux, flux!)

*Edit: insert here: "absent larger forces". Hyperlink also added.
« Last Edit: August 19, 2017, 07:45:54 PM by tooki »
 

Offline alanb

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Re: A Beginners Guide to Soldering Surface Mount Components
« Reply #20 on: August 17, 2017, 11:34:25 PM »
I'm also relatively new to using surface mount. My most useful tool for soldering is a cocktail stick to hold the component onto the board whilst heating with the soldering iron.

 

Offline KL27x

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Re: A Beginners Guide to Soldering Surface Mount Components
« Reply #21 on: August 17, 2017, 11:58:44 PM »
Quote
Tweezers have often been mentioned for placing parts to solder.  I use a crossed type and have
never had a part go sailing across the room but I see a lot of others mention that the tweezer is
nothing more than a catapult in disguise.  They have worked well for me but not for everyone.
As far as this part goes, this is what for you have the rosin flux and vacuum pickup tool. With a vacuum pickup tool, you can't fling the part anywhere. And once it's on the fluxed pad, there's only one way to lose it. 99% chance you will find it by turning over your soldering hand to look at the part of your hand that touches the bench.

Even if I'm placing $0.0003 resistors, I am careful to not place extra parts on the board. For example, if I have 8 resistors, and on the last one, my pickup tool gets two, I will not just drop them both on the board. I will take the time to set them down and pick up just the one. Because this is faster than trying to get rid of the extra part once it touches flux. You have to stop and wipe the part off your tweezers (on a paper towel or something). You can't lose the damn thing if you tried. 
« Last Edit: August 18, 2017, 12:00:24 AM by KL27x »
 

Offline tautech

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Re: A Beginners Guide to Soldering Surface Mount Components
« Reply #22 on: August 18, 2017, 03:41:30 AM »
For populating a board like what you posted, try this:

1. Dab liquid rosin flux over the all the pads.
2. Use a vacuum pickup tool to pickup each resistor and drop it over the pads. The flux will make the components stick, so they won't disappear into the ether if you bump the board or sneeze. Continue until all resistors are placed.
3. Put the board under the microscope.
4. Use a soldering tip which can hold/control a large bead of solder. (Anything but a pointy conical, but 2-3mm CF/BCF is probably best.
5. Lay some solderwire out over a flat surface.
6. With tweezers, align and hold the component in place over the pads
6.5 If you get the part stuck to the tweezers funny, stick the iron to the tweezers to heat up the flux, to help the component fall off so you can try again.
7. Pickup some solder onto the tip of the iron, as needed.
8. Dab one of the pads of the resistor until solder flows and forms a joint
9. Before letting go of the component, use the tweezers on the component you just tacked to center the next component in the FOV.
10. Repeat 6-9 until all the resistors are tacked.
11. Set down the tweezers, flip the board, and zip up the other end of each resistor.
Simple and practical.  :-+

Quote
If you have the right kind of tip, you can do a lot of joints without reloading. Under the microscope, this has a major advantage of being able to stay "in" the microscope for several joints without having to look away to get more solder. I reckon 3mm CF is as good as it gets, if you have the space to maneuver it. The combination of pad size and amount of tip loading/angle/maneuvering will control the amount of solder that is deposited on the board. As for loading the tip, the 2.5-3mm CF tips are pretty forgiving. But to fine tune the bead is a bit of an art. If I get too much, I just flick the bead off onto a flat surface which is coated in old flux residue (this happens naturally as you use it as your solderwire pickup board, which I call this my "rosin board"). Because the board is coated in flux, the bead of solder breaks up into little balls. Then you can pick up a lesser amount than you had before. (If you splatter a bead onto a non-fluxed surface, it will turn into a pancake).

If you manage to touch a non-fluxed part of the PCB while soldering, you might lose part of your solder bead. Pick it up with the tweezers and deposit it back onto the iron tip. If you try to pick it up with the iron, you will just leave another string of solder. The flux is what makes this work.
If you don't........then you haven't laid out the PCB with thought of how you might populate it.

This can make a PCB next to impossible to populate and solder by hand and then reflow becomes the only option.
It can't be stressed enough for a layout newbie.........do the layout with thoughts of hand population AND rework especially when prototyping.
It's much different to TH layout, that is you can't flip the PCB to get to solder joints.
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Online jmelson

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Re: A Beginners Guide to Soldering Surface Mount Components
« Reply #23 on: August 18, 2017, 06:19:09 AM »
Well, I've been doing surface mount assembly for 20+ years.  I can do 0805 parts just fine without vision aids, but for long sessions I use a magnifying hood to prevent something that happens to my vision after long sessions of close-up viewing.  For anything smaller than 0805, and for ICs, transistors, etc. there's NOTHING like doing it under a stereo zoom microscope.  Some models don't have enough working distance.  Mine has about 6" working distance, which allows plenty of room for hands and soldering irons to get under it.

My system is to put a dab of solder onto one pin of the passives, and a corner pin of the ICs.  Hold the part with bent-nose tweezers and touch the iron to the pad with the solder.  Once it has solidified, double check the alignment, then solder the remaining pads.  I add two pieces of tiny heat shrink to the tweezers where my finger tips hold it, to make it less slippery.

I've done this in production for about 10 years before getting a P&P machine.  I still do a lot of this for prototype and rework.  For fine-pitch stuff, tiny solder (.010" or .015" diameter) is a big help.

For high density chips, there is usually enough solder on the HASL PC board to make a joint.  I apply GC liquid flux with a wire along the line of leads, and then use a tiny soldering tip to relow them.  If the joint doesn't look good, I add a tiny dab of solder to it.  I do the above scheme, but with a dab of solder on two corner pins first.  If alignment is not good, I can"walk" the chip into alignment before fluxing and soldering the rest.

Jon
 

Offline KL27x

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Re: A Beginners Guide to Soldering Surface Mount Components
« Reply #24 on: August 18, 2017, 07:06:02 AM »
Quote
Additionally, remember that molten solder flows towards heat, so the excess solder wants to stick to the tip
This isn't technically true. Once molten, solder acts by a few simple laws of physics. It will "flow towards heat" in the sense that surfaces which are wettable and hot enough to keep the solder molten will suck up some solder. But it doesn't in ay way follow a temp gradient. For instance, if you use solder wick, the solder will wick away from the tip, no problem.

When you are soldering a joint on a soldermasked board, all wettable surface of the board and iron are quickly covered. Once that is finished, the remaining factors which govern where the solder ends up (as long as flux is sufficient and doesn't run out) are mostly down to surface tension and gravity. This is why tip selection is such a big thing with SMD. If you use a tip that holds a large bead, you can just imagine it as a large pcb pad. Between the small pcb pad and the large pcb pad, the large one will end up with more of the solder. Perhaps enough so that it can share solder to a lot of smaller pads without a noticeable change.

Yes, you can solder just about anything with a fine, pointy conical tip. But this is the last tip I use for soldering anything. In the case of a pointed conical tip, the bead will natural suck up, away from the tip due to larger surface area at the base of the cone. If you consider the total surface area of bead + wettable iron surface, the surface area is smaller when the bead is higher up on the tip. This is fine when you are adding solderwire with your other hand, but in a lot of SMD soldering you don't have that luxury. And even when feeding solderwire, you will notice that periodically you may have to wipe or fling excess solder off the tip, because the bead can grow out of control. It only gets bigger and bigger until it manages to either touch something it shouldn't, or it gets big enough that gravity trumps surface tension and it drops down to the tip and falls off in a huge blob. If you use a tip that can share its solder reservoir back to the board, you have a huge advantage. Hoof/chisel/knife/CF/spoon tips have a better ability to both give and take. The tinned-face only tips are especially efficient. The closer you can keep the solder to the tip/board, the better. Gravity and surface tension are working together, rather than in polar opposition in a binary struggle that ends up "bad," one way or the other. You don't really care to suck solder far up the tip, you just care what amount gets left on the pad.

A lot of us grew up with "don't use the end of the tip, use the side." This is thru hole mentality. With SMD, only a handful of tips can be used like this (BR bent conical, perhaps). With SMD soldering, you will be using just the tip (insert joke). This one reason why IMO, knife tip is mo betta than chisel tips for SMD. (In addition to the angle, one of the main differences between a knife and a chisel is that a knife tip has chrome plating covering the sides, leaving only the tip as wettable. Kinda like the difference between a CF and a C.) Yes, knife tips are huge. In fact, between the two styles of iron I have, the knife tips average 1/4". This is not a problem for most SMD work, because the components are so flat. Slightly angling the tip will keep it flat enough to work and yet clear surrounding parts in a lot of your SMD applications (such as the board that is pictured).

« Last Edit: August 18, 2017, 08:41:10 AM by KL27x »
 
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