Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

----- 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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