Stefan Trethan wrote:
>On Thu, 25 May 2006 11:30:00 +0200, Trevor Matthews
><trev.matthews@...> wrote:
>
>
>
>> To test my reflow profile, I've been cooking scrap pieces of PCB with
>>a small quantity of old RS electronics solder paste on the board to
>>check that the solder melts etc. The paste is best before wk 50, 2003.
>> During these reflows, I heat the board to 225C max. I have noticed
>>that the paste forms a crust on the board, which can be wiped off (as
>>per Stefans suggestion) but am concerned about the crust with respect
>>to its affect on component joints.
>> Does this crust form on in date paste on component joints??
>> Thanks for your help
>> Trev
>>
>>
>
>
>Ok, this crust must be different from the one i described when using
>plumbing paste for tinning.
>Does it seem to contain tin particles or is it flux?
>Will it reflow fully if you crank up the temperature a bit more (maybe try
>with soldering iron if the skillet doesn't go higher).
>
>I also use old SMD paste, it seems less tacky and harder to apply, but it
>doesn't form a crust. I don't really think the old age is the problem.
>
>Not sure.. but my gut feeling tells me your might have too low temperature.
>
>
My next attempt with scrap was going to let the skillet go higher and
see what happens, but I've tried to melt it with my soldering iron - I
can move it about and see bright tin underneath, but it doesn't change
the consistancy of the crust at all. I thought I might try to reflow
the paste with just my soldering iron and see what happens then as well.
Unfortunately, I can't run my skillet much higher than 180C without
leaving the lid on, which means I can't see what happens to the paste as
it melts, so I can't check to see if the crust is there straight away,
or if it forms over time (as it would if it melts, then oxidises as
temperature rises and as time increases)
thanks for your help
Trev
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