MessageSo far as I understand it the EU directive exempts solders with more
than 90% lead content from the Pb ban, This is in recognition of the fact
that for high temperature soldering there is no real alternative . The
exemption is primarily aimed at power die attach and similar applications.
High leads are available in paste presentations, and represent somewhat of a
challenge to use in most areas. (but are used routinely in SMT /hybrid thick
film assembly as well as the more "traditional" areas of device
manufacture).
For example peak reflow temperatures are high at over 300C -sometimes 350C
so getting there with minimal delta T is tough on regular SMT equipment.
Most organic materials and certainly some flux resins are at or beyond
performance envelope and so need careful selection, and so on. Nitrogen
reflow is advised to reduce oxidative degradation and ease cleaning.
Regards
Mike Fenner
Applications Engineer, European Operations
Indium Corporation
T: + 44 1908 580 400
M: + 44 7810 526 317
F: + 44 1908 580 411
E: [log in to unmask]
W: www.indium.com
Pb-free: www.Pb-Free.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Dave Chapman
Sent: Tuesday, July 15, 2003 3:39 PM
To: [log in to unmask]
Subject: Re: [TN] High temp pastes for wave soldering...
Is there an exemption from Lead Free requirements for solder paste? And is
that also the case for wave soldering PCBs?
Dave Chapman
-----Original Message-----
From: Guy Ramsey [mailto:[log in to unmask]]
Sent: Friday, September 06, 2002 3:14 PM
To: [log in to unmask]
Subject: Re: [TN] High temp pastes for wave soldering...
Getting the paste isn't too hard. But, reflow (25-40 degrees above
liquidous) temperature for those alloys is hazardous for FR-4, and many
components. Ceramic chip caps and thick film resistors might be okay but
this is clearly over the top for most plastic IC packages. We have done some
experimenting with direct attach and forming-gas to ceramic using these
alloys. One day we ran an FR-4 board though the oven without thinking. What
came out of the oven would best be described as ash with body.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Friday, September 06, 2002 3:20 PM
To: [log in to unmask]
Subject: Re: [TN] High temp pastes for wave soldering...
Hi Steve,
Hope you don't mind, I put a subject in the subject box for your post...
As far as through-put issues with your dispenser, why not print your
epoxy. You would do the whole board in well less than 30-seconds, and have
much better accuracy and consistency than you could ever expect from a
dispenser.
As far as high temperature pastes go, you would need one of the
high-lead alloys in order to be above the typical solder pot temperature of
500° F (260° C). Getting these alloys in paste form is going to be challenge
as well, you can bet that it's going to be a custom order with a minimum buy
too.
A few of those alloys are:
° F ° C
Sn10Pb90 514 - 576 268 - 302
Sn10Pb88Ag02 514 - 570 268 - 299
Sn05Pb92.5 Ag2.5 536 280
My two-cents...
-Steve Gregory-
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