Hello Boys and Girls...
Today we're going to learn about SOLDERING
But not just any kind of soldering...
Surface Mount
Soldering
Here's a board I designed...
Here's a closeup of where we're going to need
a couple of chips installed
Those pads are 0.050" center to center
Here's what it'll look like when we're done
Here's my Irons.
That's a Weller Temperature Controlled dual controller with the blue wands.
The black thing to the left is a desoldering iron for when I screw up
Here's a close up of the Weller tips
And a closeup of the small tip with a #11 Xacto blade.
The small chip is an SOT8 package that has the same lead spacing
as the chips shown above.
(Notice the size of the chip relative to the Iron tip.)
Here's the solder I use
It's Eutectic Solder
That means 63% tin, 37% lead
This ratio minimizes the pasty stage that happens when solder cools and solidifies.
That was the thick stuff, this is the thin stuff.
Both are multi-core with water soluble flux.
(NOTE: Water soluble flux MUST be cleaned off.
Preferably in an ultrasonic cleaner)
I also stock No-Clean fluxed solder for board repair work
I also stock a wide variety of sizes of solder-wick
(Also, for when I screw up)
This is a Kester Flux Pen
of the water soluble variety.
This is an ABSOLUTE MUST HAVE for any kind of soldering,
but especially for surface mount soldering.
Here's the part number
You have to clean water soluble flux off your board when you're done
because the residue will absorb moisture FROM THE AIR
When the flux absorbs moisture from the air, it becomes gooey and CONDUCTIVE
Having your board coated with conductive goo is generally considered to be
A Bad Idea.
I also stock the No-Clean variety for when I do board repair.
This is my Pana-Vice.
You can see how I keep both sizes of solder handy.
(I didn't get a picture, but you can see my blue solder sucker
on the left. That's also a MUST HAVE item.
I usually have it set up like this.
This keeps the knobs from banging into each other
when I'm working on a small board
This is my ring light.
When I'm working my nose is right against the lens and
the lens is as close to the work as I can get it and still
get my hands and iron in there.
Did I mention my vision isn't all that good???
The clip-on things to the right are two and three diopters
The Magnivision magnifier is 3x and 6x.
I think the dual black thing is 10x
So here's what it all looks like...
Now, to work...
Let's solder chip U14.
First, we're going to use that flux pen to put some flux
on the pads we're going to be soldering.
Here's the chip.
It's a
Maxium MAX11613 A to D converter
That's an 8-Pin µMAX package.
The lead spacing is 0.025" center to center.
(That's half the size of the SOT8 chip seen earlier)
Here's the chip sitting on the board.
You can see the flux I put on earlier.
We also need flux on the legs of the chip
(both sides)
(The SOT8 package in the background look huge in compairason)
I used the Xacto to move the chip into position.
For scale, those through hole pads are a tenth of an inch center to center
The traces and pads have a small thickness to them.
Almost like little humps. You have to center the chip on it's pads.
Here's the view through the ring light.
I couldn't hold the iron, the solder, and the camera at the same time,
but here's the trick:
Start with the tiniest amount of solder already on the iron to help with heat transfer.
Rest the iron on the board away from the pad and slide the iron sideways
until it just touches the edge of the pad.
In this picture, the iron is touching the pad
but not the leg of the chip.
If you touch the chip during this process,
you will knock it off the pads
and have a mess to deal with.
Let the iron heat the pad, then touch some solder to the iron.
Capillary action will transfer a small amount of solder to the pad,
and then to the chip's leg.
Move the iron away from the pad without touching the chip's leg.
Here you can see the one corner leg soldered in place.
I did the same thing to the opposite corner.
Now the chip is held in place and I can be a bit more agressive
soldering the other legs and not worry about touching the chip.
Solder bridges are a bit of a pain, but not a disaster.
That's what the solder sucker and solder wick are for.
(Knocking the chip off it's pads while you're soldering the first
corner is much worse!)
Here's the soldered chip.
And a a view from the other side.
And through the ring light.
Here's the finished board.
And a closeup of U14 after all the other stuff's been installed.
