Homebrew PCBs

Leon,

You are comparing apples and bananas. He said in his original 
message he was using Radio shack solder paste. This is identical to 
the plumbers paste for use on copper pipes, I have both, It is not 
the refined version for smt pcb's and has none of the 
characateristics.

The plumber's paste is designed to be reflowed with a propane torch.

The only apparent advantage for the plumber pastes is that it is 
very cheap.

Myc


--- In Homebrew_PCBs@yahoogroups.com, "Leon Heller" 
<leon.heller@...> wrote:
>
> ----- Original Message ----- 
> From: "Trevor Matthews" <trev.matthews@...>
> To: <Homebrew_PCBs@yahoogroups.com>
> Sent: Saturday, May 27, 2006 4:16 AM
> Subject: Re: [Homebrew_PCBs] Qu about old reflow solder paste
> 
> 
> > On Fri, 26 May 2006 03:06:21 +0200, Trevor Matthews
> >
> >><trev.matthews@...> wrote:
> >>
> > I've tried a couple of things and here are my results:
> >    1) I placed a couple of blobs of paste on my scrap PCB and 
melted
> > them with my soldering iron - success, the flux burnt off, and 
nice
> > shiny paste.  Even the paste I did not heat directly did the 
right thing.
> >
> >    2)  Heated the scrap PCB in the skillet to about 250C.  No 
change to
> > the previous - grey looking surface to the reflowed paste.  Took 
the lid
> > off while it was still very hot and there was a puddle of grey 
surfaced
> > paste with a brown/yellow liquid (?flux) mixed in and 
surrounding it.
> >
> >    3) Tried again without the lid on.  Noticed at about 120-150C 
the
> > paste seemed to partially melt - there was small balls of bright 
solder
> > inside the grey muck.  Over the next 20-30C the balls seemed to
> > disappear under the grey stuff.  The flux did not obviously 
activate, no
> > fumes. Continued to let the board heat up. Got the board so hot 
that the
> > substrate started to smoulder and the binding glue bubbling out 
the
> > sides of the board.  Still no joy.  Thought I'd try adding my 
soldering
> > irons heat to the process to see what happened.  Flux activated 
and the
> > paste seemed to do the right thing.
> >
> >  Theory:  Skillet not transferring enough heat to the paste.  
Would it
> > have anything to do with the board being unetched????
> >
> >  Don't know how to fix the problem.  Should I try a toaster 
oven??
> > sparkfun.com document lots of problems with melting SMD 
connectors using
> > an oven and I've already tried to hand solder one compact flash
> > connector to a board - I'd prefer to reflow it with the other smd
> > devices if I could.
> >
> >  What do those experts out there think???
> 
> I just repeated your experiment. Not having a suitable skillet I 
just used 
> the hotplate on the electric stove (don't know the temp, I just 
guessed the 
> setting), and it worked perfectly! I just put a couple of blobs of 
solder on 
> a small scrap of polished SRBP PCB material (easier to cut than 
FR4) and put 
> it on the hotplate. In a couple of minutes or so the blobs 
liquified and 
> spread out, then the flux burnt off leaving little puddles of nice 
shiny 
> solder, surrounded by flux residue. Your paste must be knackered, 
you need 
> to buy some new good quality new stuff. I used Warton Metals 
Microprint 
> P2004, in a syringe.
> 
> Suitable electric skillets are difficult to get hold of here in 
the UK, so I 
> might try using the stove hotplate for a real board. I do have a 
toaster 
> oven, but haven't tried it yet.
> 
> Leon
> --
> Leon Heller, G1HSM
> leon.heller@...
> http://www.geocities.com/leon_heller 
> 
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