http://www.stencilsunlimited.com/TDS%20SynTECH.pdfhttp://www.stencilsunlimited.com/TDS%20NWS-4200-LF.pdfThe first is a datasheet for tin/lead paste; the second for tin/silver/cu.
The reflow profile is on page two of each. Flux activation happens around
140^C. Reflow doesn't begin until much higher, at 219^C for Sn/Ag/Cu. The
spec'ed peak profile temperature is higher still, ∗minimum∗ 235^C. Full
reflow will not be complete until 60 seconds after reaching 219^C.
I suspect the residue is spent flux (?) and the shiny material might be
unalloyed Sn in the paste reflowing at a lower temp. Just guessing. My paste
is in the mail; I have nothing to do the next few days but kibitz your
thinking.
----- Original Message -----
From: "Stefan Trethan" <stefan_trethan@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Monday, November 21, 2005 2:59 PM
Subject: Re: [Homebrew_PCBs] Re: Tinning the board? - reflow
> Nah, doesn't fit.
>
> If i heat with hot air from above the powdery stuff must be hotter than
> the board.
>
> ST
>
>
> On Mon, 21 Nov 2005 21:46:59 +0100, Alan King <alan@...> wrote:
>
>>
>>
>> Think of having your board right at the melt point, and taking a solid
>>
>> lead pencil and writing on the traces. Pencil stays solid, but where
>>
>> you're touching the traces is melting. Traces are above the melt temp,
>>
>> but you're only getting melt when you make it touch. For sure it is
>>
>> melting some, just not a lot. Remember it takes a lot more energy for
>>
>> the phase change, so right near the melt temp you'll melt the surface
>>
>> but not have near enough extra heat to melt the rest of the solder
>>
>> balls. Might also be doing something with the flux at a higher temp, as
>>
>> someone else noted recently it stays on much longer just at the melt
>> temp..
>>
>>
>> Think of how you draw on your iron tip with solder, as the iron is
>>
>> just heating up, leaves a nice shiny path. And won't melt the rest of
>>
>> the solder very fast yet, because it doesn't have enough extra heat.
>>
>>
>> Things well above the melt temp uaually oxidize much faster than
>>
>> things right at it, part of the reason a temp controlled soldering iron
>>
>> is a good thing too..
>>
>>
>> Alan
>>
>
>
>
>
>
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