--- In
Homebrew_PCBs@yahoogroups.com, "Dale Mosby" <dale@a...> wrote:
>
> I have made some printed circuit boards using common components
> requiring drilling. I would like to start using some simple surface
> mount resistors, capacitors, and transistors to reduce drilling and
> reduce space. I am wondering about the best techinque to use these
> devices on boards.
>
> I did a bit of experimenting with a board using some 1206 size
> resistors and it seems that using these components will be quite a
> useful addition to board construction.
>
> One recommendation I heard was to use just a small bit of glue to hold
> the components in place, then once all places come back and solder
> them all. I tried this and it did work, but I have some concern about
> the stability of the glue over time and how this might impact long
> term reliablity.
>
> I also tried just holding a resistor in place with some tweezers and
> soldering them. This also worked but obviously requires an extra hand.
>
> I would like to know what sort of techniques people use to place
> these. I also see mention of using flux paste and I am wondering if
> this is solder bearing paste. Does this hold a component in place such
> that it won't simply adhear to the tip of the soldering iron?
>
I've had no luck with tweezers. My choice is to place smt's using a
tooth pick with a pin head size ball of Blu Tack or Office Depot All
Stick, part number 323-609.
Solder paste is expensive with a short life.
I use a 15 watt iron with a fine tip, a head magnifier, a flux pen,
and .020 diameter solder.
Flux solves a multitude of sins. I even have good luck smearing flux
from a Radio Shack tube on the pads before soldering. But a flux pen
is cleaner.
Apply flux to the pads before soldering and let it dry.
With a small bead of solder tin one of the pads.
Place the component with the toothpick, hold in place, and heat to
tack it in place. Use a bead of solder to mount the other end.
Repeat on the tacked end. It only takes a second to solder each end.
With small components I put the bead on the tip. The solder roll
doesn't come near the chip.
If the components are old, reluctant to accept solder, I'll flux the
ends after tacking.
This is the low budget approach to simple smt's. I use it for 0805's,
SOIC, and SOT-23 packages. If you get smaller than SOIC packages you
might need more sophistication.