On Wed, 17 May 2006 02:02:59 +0200, Trevor Matthews
<
trev.matthews@...> wrote:
> Hello all,
> I just want to confirm my understanding of using plumbers solder paste.
> I beleive people are using it to tin their board before populating,
> and use several thin layers of paste to completely tin a PCB. Does
> anyone use this paste for SMD soldering?? What about down to 0.5mm
> pitch??
I tried, but it is no good. The reason is it gets runny like water when
heated, for plumbing that is a good thing because it tends to cover the
whole area more easily. For SMD it will just run off the pads and tin a
larger area, without leaving sufficient tin at the joint.
Real SMD paste is different, it hardens up when heated and stays in
position. That is, if you didn't try to thin it with anything - if you did
that it tends to explode and catapult components off like popcorn.
> I am just about to try my first SMD board, with parts down to 0.5mm
> and given that electronic soler paste has a very limited shelf life and
> the infrequent use I will have for it if I have to use regular paste for
> SMD work I may as well use it for tinining as well.
> BTW, I've run a test reflow following an 'average' profile to 225C
> using a skillet style (see sparkfun.com) of setup, unetched board and
> regular paste which was best before end 2003. The paste formed a crusty
> grey coating over nicely tinned copper. It almost looks like a nasty
> dry joint. If you scrape the crust off the solder there is a nice shiny
> tinned copper surface, I've tried several different types of solvent but
> nothing seems to dissolve it. Any ideas of what this is and how to get
> rid of it???? and before you flame me over the use of the very out of
> date paste, I knew it was out of date & I just wanted to see if the
> reflow profile worked on a scrap piece of PCB.
> Thanks heaps
> Trevor
The dry crust seems normal, i wipe it off with a paper towel.
You really will want real SMD paste for the component soldering, then
0.5mm is no problem. Not only because of the viscosity but also because it
uses less agressive flux which may be tricky to remove from under
components.
ST