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| Reply To: | (Leadfree Electronics Assembly Forum) |
| Date: | Tue, 27 May 2003 12:08:48 +0200 |
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In wave soldering a certain superheat is required to assure wetting within a resonable time without thermal damage of (themperature sensitive) components and board materials.
The required energy for wetting in wave soldering to a certain extend, is a product of heat (temperature) and time.
For FR2 board materials, the solder temperature is 235dC, for FR4 board materials 250dC can be used for soldering times of ~ 2 .5 seconds. The latter material has a better thermal conductivity and therefore it requires a higher soldering temperature for
an equal soldering time.
When you calculate the required soldering temperature for LF solders out of the specific heat of the alloy elements with reference to the solder time of SnPb solders, you will find a solder temperature of about 280dC for FR4 and about 260dC for FR2. But
at that temperature board materials will be detoriate.
So you have to find an optimum between an acceptable solder temperature and an increased soldering time.
In the European IDEALS LF project we found proces parameters ranging from solder temperatures between 250dC and t= 3.0 s for FR2- till 265dC and 2.5s for FR4 board materials.
Super heat is not a soldering parameter but just a nomenclature.
Regards,
Peer Langeveld
___________________
Royal Philips Electronics
Centre for Industrial Technology, EP&A, SAQ-p716
Glaslaan 2 5616 LW / P.O. box 218 5600MD
Eindhoven, The Netherlands
Phone/Fax: (+31 40 27) 37010 / 36815
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cc: (bcc: P. Langeveld/EHV/CFT/PHILIPS)
Subject: [LF] lead free solder pot temperature?
Havia Elina Classification:
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Sent by:
Leadfree
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2003-05-21 12:17
Please respond to
"(Leadfree Electronics
Assembly Forum)"; Please
respond to Havia Elina
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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