[sdiy] moving to SMD/SMT

[Tony Clark]

   Hi John!

> Anybody here doing much with SMT?

   There are a few of us about.  :)  

> I like the idea of building small stuff, though, and those discrete 
> SMDs are so small. (Widdle baby weesistors, awww, so cute! ;-)

   Cute, but it also gives all the old-timer the willies!  ;)  Every time 
I show off my stuff, I usually get dumbfounded looks and "You really 
soldered that by hand?!"

> So, what kind of equipment do I need?

   Believe it or not, you already have all the equipment you'll _need_.  
There are certainly some pieces of equipment that make things easier in 
the "rework" department, but I see those things as more of a luxury 
item.  If you've got the cash, then by all means, have a few more toys at 
your disposal, but really, a soldering iron with a fine tip is usually 
good enough.  Oh, and some solder braid, but more on that later...

> I see the term "rework station" a lot, but I don't understand it. Is
> that the tool of choice? Does it do soldering *and* desoldering? My
> Soldapult would probably suck up an entire SMD! Maybe desoldering
> braid is better? (Or is the rework station really the way to go?)

   A rework station can have a variety of tools, usually 3.  The first 
tool is a hot-air knife.  This device shoots out a super hot stream of 
air that you can use to melt solder.  This can be handy when you need to 
adjust the placement of a component that isn't square to the pads 
(surface tension of molten solder usually aligns parts without any extra 
help!).  It can also be used around heat sensitive parts that a normal 
soldering iron would kill.
   The second tool is usually a set of tweezers, or a dual tipped 
soldering iron that comes with a variety of unusual attachments.  
Different sized blades can usually be stuck onto these so that you can 
easily grab aSMD part straight off the PCB in one shot!  Great for 
passives, a little tricky to use for ICs, and really fun if you ever have 
to remove a PLCC or some other such beast!  You really do get what you 
pay for in rework tools...
   The third item is usually a straight soldering iron with a vacuum pump 
built in.  Nuff said.
   Really, the tweezers is the only tool that I'd consider an accessory 
to the standard soldering iron.the standard DIY'ers tool arsenal.  Only 
because you can grab IC's off the PCB with ease.  There are other methods 
(if you really must save it), but usually I just sacrifice the chip.  Of 
course that was before the 3080 shortage.  :P

> If an iron with a 1/32" or 1/64" tip is good enough, that'd be nice. I
> also read here http://protoboards.theshoppe.com/ that there's a
> soldering tip that looks like a miniature ladle. Do I need one of
> these, too?

   Ladle?!  Never heard of such a thing , so 99% sure you don't need it.  
A 32nd tip is certainly nice, especially if you plan to do 0603 or 
TSSOP's or other fine pitch parts.  Otherwise, you should be fine with 
any small tipped iron.
 
> I've also read about the toaster oven reflow technique. Seems
> interesting, and I suppose that I'll try it, but it won't replace the
> need for a more focused soldering method.

   I don't recommend this.  You'll need to use solder paste (which is a 
bigger health hazard and has a very limited life-span), and getting the 
oven temps just right can be tricky (plus you'll subject your PCB to 
unnecessary heat loads which could lead to pre-mature part failure.  
Reflow is really only done for production runs.
   I will say, it's fun to try, if you've never done it, but that's about 
as far as I'd go with it!

> And since SMDs usually go on PC boards, is there anything special to
> keep in mind when making PCBs?

   Well the first and most obvious thing to keep in mind is that SMD 
parts exist only ONE side of the PCB!  That means that if you use a 
double-sided board, traces on the bottom side do eventually have to make 
it to the top before they'll connect to anything!
   Also, there's a danger of trying to make things _too_ small.  Don't 
use parts smaller than what you are comfortable with.  SOIC, 0805 sizes 
or larger are good for starting out with.  Leave TSSOPs and smaller parts 
for when you get more confident.

> Any other tips, warnings, or links?

   Solder braid.  Works wonders when you bridge adjacent pins on an IC.  
Especially if it's one of those fine pitch jobs like TSSOPs.  :)

   There are some good DIY tips for SMT on the net.  I think Old Crow may 
have one up, but I forget.  I'm sure some one else will pipe up.  In the 
meantime, you can see some of my SMT work here:

http://www.physicsenterprises.andrews.edu/~clark/emusic/diy/

   Cheers,

   Tony

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