Using superheat is a very useful method for comparing the wetting of
different alloys, and is used as a method for comparing performance on a
level playing field. However, it should not be forgotten that the actual
temperatures are not the same for the same superheat, so in a process
situation it might not be surprising that this extra temperature for the
lead-free case has some additional effects.

Chris Hunt

> -----Original Message-----
> From: Havia Elina [mailto:[log in to unmask]]
> Sent: 21 May 2003 11:18
> To: [log in to unmask]
> Subject: [LF] lead free solder pot temperature?
>
>
> The wave soldering pot temperature needed for SnAgCu solder is between
> 255-270 C (based on the experiments). The solder pot
> temperature used with
> SnPb is approximately 250 C, which is about 70 degrees over
> the melting
> temperature. With SnAgCu the superheat (= heating over the melting
> temperature) is only approximately 40 degrees.
>
> C. Hunt, NPL, Apex 2000 has compared the wetting times of
> different solders:
> with equal superheat the wetting times are similar between
> SnPb and SnAgCu.
> But with SnAgCu even lower superheat works as the
> experimental test series
> has shown.
>
> On the other hand increase on the solder pot temperature can
> be detrimental
> to the flux. For fluxes and for component heat tolerance it
> is good that
> lead free solders does not need so high superheat.
>
> Anybody having an explanation for  this? Why lead free solder
> does not need
> so high superheat (= heating over the melting temperature) as
> SnPb solder?
>
>
>   Best regards,
>
>         Elina Havia
>
>
> --
> Ms Elina Havia
> Elektroniikan 3K-tehdas
> Laitaatsillantie 3
> FIN-57170 SAVONLINNA
> Finland
> tel. +358 15 571 4034
> gsm  +358 50 461 5572
> fax. +358 15 571 4029
>
> e-mail: [log in to unmask]
> http://www.3ktehdas.com
>
>
>
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