RE: For the coiler who has everything else? (fwd)...SMD (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Tue, 3 Jul 2007 12:15:06 +0100
From: Colin Dancer <colind@xxxxxxxxxxxxxx>
To: 'Tesla list' <tesla@xxxxxxxxxx>
Subject: RE: For the coiler who has everything else? (fwd)...SMD (fwd)

<ARROGANCE ON>
Ha!  I laugh at your 0603 resistors!  No real challenge until you get to the
bits of dust which are 0402 resistors... 
<ARROGANCE OFF>

Seriously, I absolutely agree with Bart that SMD can be a pig when you first
move from larger through hole components, but with the right tools and
techniques I think it is actually easier and quicker than with through hole
components (though a steady hand is an absolute must).

As Bart says, production boards are made using solder paste, but for
prototype work very fine cored solder (32AWG), a needle tip iron, a good set
of tweezers and a liquid no-clean flux pen is probably better.  A head
mounted magnifier and a good desk lamp are also very handy.

(Generous use of the liquid flux makes all the following processes go much
more smoothly.)

For resistors, flux both pads, tin one pad, correctly position the resistor
over the two pads using the tweezers, reheat the pretinned pad so that the
resistor sinks into the pad and the solder forms a meniscus at one end of
the resistor (while still holding the resistor in the tweezers), let go of
the now tacked down resistor, solder the other end with the iron and just a
touch of solder, come back and add a little more solder to the first end. 

The above sounds involved and time consuming, but once you get the hang of
things it's really quick with no lead bending or trimming required.

For chips, same approach, but tack down opposite ends of the chip to ensure
everything is aligned correctly.

If you need to remove small components, a bit of fluxed copper braid with
some solder on allows you to heat both ends of the part at once without a
special tool, just slipping it off the pads.

Similarly when from time to time you blob together chip leads, a bit of
small gauge desoldering braid is a god send.

For chip removal, heat the pins one at a time and lift the lead with a
stainless steel fine pointer or scraper, though make sure the solder melts
before trying to lift or you can break the track.

In all of the above more no-clean flux is a good thing.

Hope that helps,

Colin.

P.S. Work on a large sheet of clean white paper so you can see the bits
you're working with.

P.P.S. If you drop a small unmarked SMD resistor or cap on the floor, don't
bother looking for it.  If you find something the right shape it will
probably turn out to be the different value part you dropped last month
rather than the one that just got away!


---------- Forwarded message ----------
Date: Mon, 02 Jul 2007 19:20:23 -0700
From: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: For the coiler who has everything else? (fwd)...SMD (fwd)

I build boards with SMD components at work (where board real-estate is a
serious cost concern). I always start the proto board with their larger
cousins. It's important to get it right the first time. Once the SMD board
is built, replacing and even troubleshooting can be a challenge simply due
to it's size. There are irons designed for several standard SMD packages,
but each iron tip is specific to a package and it quickly gets expensive.

When it comes to coiling or other "hobbies", I personally would not use SMD
components unless I couldn't find it's larger cousin.

Tinning the smd pad is important. Use thin solder and keep the heat down.
SMD's are designed for solder paste where a template in stainless steel is
placed over the board. Holes in the template cover only the pads. A paste is
applied. The template is then removed and the board travels to a robotic
system which grabs the components and places them in their locations. The
solder paste is termed "paste" for a reason. The component literally sticks
to it. The board then travels through a heat system which heats the solder
paste and effectively solders the components to the board pads. The board
then travels to the through hole room where any through hole components are
then inserted and wave soldered. This process works great for smd
components.

I can actually see a product here. A paste and heat machine for proto smd
boards.

But if you have to replace a component for some reason on a workbench (and
you will), even the smallest pointed tip using a nice Weller station is a
real challenge. You'll find out just how steady your hand really is. Chips
are easy but those little 603 resistors and diodes are a bear.

Helpful tip: When removing a bad smd chip. Use an exacto knife to cut
through the lead (right next to the chip). Remove the chip and then desolder
the remaining leads. This prevents accidental lifting of the pads. Remove
excess solder and add a new level of solder. Install the new chip with
typical soldering technique.

Take care,
Bart

Tesla list wrote:

>---------- Forwarded message ----------
>Date: Sun, 1 Jul 2007 22:44:30 -0700 (PDT)
>From: Brett Miller <brmtesla2@xxxxxxxxx>
>To: Tesla list <tesla@xxxxxxxxxx>
>Subject: Re: For the coiler who has everything else? (fwd)...SMD
>
>Ed,
>
>Well, I'm 32 but with my glasses I guess I make the cut.  Just slightly 
>tin your pcb on both sides where the SMD component is about to go, then 
>use your left hand to hold down the little chip component with a wooden 
>toothpick.  In your right hand use your Weller 12w soldering pencil and 
>heat up the component on each side.  They come pre-tinned anyway.  I've 
>just used a little lens for magnification...but I've only dabbled.
> I'd like to work more with SMD and learn more about finding the parts 
>fast and assembling my parts list.
>I just tend to know more about finding leaded components due to 
>experience...nowdays the digikey search engine makes that stuff easy 
>though.
>
>Some guys have done some amazing stuff with SMD and solid state for 
>micro mini sstcs and drsstcs.
>
>-Brett
>
>  
>
>>     As for SMD's, all it takes is 20-year old eyes and steady hands 
>>and a good 10 power binocular microscope.
>>
>>ed
>>
>>
>>
>>
>>
>>    
>>
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> 
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