On Fri, 2 Sep 2005 02:59:00 -0500, you wrote:

>Some months ago, I was able to successfully hand-solder SOIC's and 
>similar-sized parts.  Since then I do this regularly, as it lets me squeeze 
>more into my usually-limited-space applications.  I've also soldered some 
>SOT-23 transistors, which though functional, don't always visually line-up 
>perfectly.
>
>Today, I tried to solder a couple SSOP's and had success .... mostly.  On the 
>first chip, I was trying to tack one corner pin down for so long, that the 
>pad lifted off the board.  It wasn't really so long, but longer than I would 
>have the iron on the pin of a DIP package.  Also, I did have to use some 
>braid/wick to clean up the bridges (lots of them) all over.  When doing this 
>though, the chips get very hot (I couldn't keep my finger on them for more 
>than a second or 2).  Is it easy to damage chips this way nowadays?  I expect 
>these things are designed to be in ovens hot enough to melt solder and all 
>pins simultaneously, so would I fry these things easily by heating all pins 
>on one side simultaneously with some wick?
>
>BTW, are there any tips to keeping SOT-23 transistors in place when soldering 
>them?  Best technique I've come up with so far is to wet one pad with some 
>solder, but clean it off (with wick/braid) to keep it low profile, slide the 
>transistor in position (I use the tip of a mechanical pencil for this), then 
>I point the same pencil over the top of the body, and press straight down to 
>keep it in place.  I carefully swap hands holding the pencil, and then 
>tack-down the pin.  If necessary, I can twist it a bit to improve the 
>alignment.  Finally I solder the remaining pins.  But still, my alignment is 
>not the best.  I'm sure I've seen somewhere the use of glue to hold the part, 
>but I would guess lining it up to glue it would be the same hassle, and the 
>glue would probably add problems if it got on the pads.  Any better way to do 
>this?
>
>Cheers,
>-Neil.

For stuff like SOT23s, put a bump of solder on one pad, place the part over the footprint with
tweezers,  and flow the solder while seating it downt. Same method for tacking the initial corner of
ICs. 

For 2-sided ICs, putting flux on the bottom of the pins as well as the PCB helps a lot. 
If you have a wide enough bit, one method is to put solder on all the pads, put flux on the pins,
hold the part in place and reflow the whole row down onto the solder.

For braiding off excess solder, one method to minimise heat is to hold a loop of  braid over the
iron bit and then touch the braid/iron combination onto the pad. 
"Soder-Wick" brand is the only braid worth using. There is s HUGE difference between good and bad
solder braid. 

If reworking, ALWAYS clean off old flux and put fresh on. You can never have too much flux, as long
as it is fresh.
I like the chemtronics circuit works flux pens (cw8200) - the spray stuff is messy and too sticky.

A screwdriver with a blob of blu-tak on the end makes a good substitute for a vacuum pick-up tool.



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