In article <
bivsu4+9hlp@...>,
aussiedude36 <
aussiedude@...> wrote:
> I have recently decided I need to utilize SMT resistors on one of my
> designs as there simply isn't room for regular thru hole resistors.
> From reading recent posts it seems as if I would simply use solder
> paste to glue/hold the SMT res. in place then heat it to melt the
> solder. Can I do this with a soldering iron or do I need an expensive
> hot air type machine? What stops the solder paste from bridging the 2
> pads beneath the SMT Resistor? Any suggestions would be appreciated.
I've tried solder paste but haven't been terribly happy with it. The paste
actually contains the solder in tiny beads, rather like small ball
bearings and the "ball bearing" effect made it quite difficult to hold the
component exactly where I wanted it. This may have been a property of the
particular paste I used, I don't know, but the beads were clearly visible
through the microscope I was using. I know you can get pastes which
specify very small particle sizes, which may have been better, but they
are (to me) prohibitively expensive.
Even though the paste was supplied in a small syringe I found very precise
application to be difficult, both in terms of quantity and geographically,
requiring careful cleaning up afterwards.
Commercially I believe they use a UV curing adhesive to hold the
components in place before soldering.
My own technique is to "tin" the pads and then apply flux from a flux pen
dispenser. Holding the component in position with a dental probe I then
"tack" it into place at one end before soldering the other end properly.
I use an Antex 15W iron with a 1mm tip and, against conventional wisdom, I
touch the tip with solder before applying to the joint to be "tacked".
As far as solder bridging the gap between pads, components are coated with
a substance that repels solder to make this less likely; though it is
possible if you apply too much solder and heat.
Stuart.
>
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