John,
Just as an aside, the flame would not actually be contacting the
paste. The system I had mentioned has extremely directional pinpoint
thermal energy and does not need to have the flame contact the physical
point of the connection....
Mike
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Vivari, John
Sent: Friday, September 12, 2003 9:18 AM
To: [log in to unmask]
Subject: Re: [TN] LED Soldering Query
Peter,
As to processing options, I see two paths to choose from if your goal is
to stick with soldering. As was said already, silver epoxies have
several undesirable qualities when mixed with HASL and "rigid"
substrates so I too am discounting them as a preferred option.
I'm not clear as to whether the LEDs are the only part on the board in
question so adjust to fit.
1) Solder pastes exist that are designed to withstand the temperature
cycling typical of iron and laser heating without explosive vaporization
issues. They can be dispensed or printed depending upon the processing
options available to you. Flame, as a heat source, can ignite solvent
vapors and rosin in the flux so I, personally, would stay away from them
unless you could avoid said ignition.
2) You could also try pre-pasting the pads, along with the rest of your
standard board assembly (if there is any), and later using a tacky flux
for component attach and reflow. The likelihood of solder balls is
exceptionally low regardless of heating method (as there are none to
wash free with the flux).
Depending upon production quantities and accuracy requirements, such
systems as tabletop automation, with integrated dispensing and heating,
might be a more cost effective solution than manual alternatives. Only
a cost comparison will answer that question.
John Vivari
Technical Service Engineer
Solder Paste Operations
EFD Inc.
[log in to unmask]
www.efdsolder.com
Ph: 401-333-3800
Fx: 401-333-4954
-----Original Message-----
From: Peter Swanson [mailto:[log in to unmask]]
Sent: Friday, September 12, 2003 4:57 AM
To: [log in to unmask]
Subject: [TN] LED Soldering Query
We have a customer who is looking at assembling some surface mount LEDs
to a FR-4 board. We are told that the parts will not stand conventional
reflow temperatures (they themselves are made with a LMP solder, and the
lens is temperature sensitive). At this stage, I don't know much more
detail.
The query is whether he could print conventional paste, place the
devices and then reflow each joint individually, by using a robot. But a
soldering iron applied the paste will cause spitting, solder balls, etc.
Perhaps a thermode could be applied to the joint and a temperature ramp
up applied, which will safely reflow the paste, if such a thing exists
and can be mounted to a robot.
I would be interested in general thoughts on how to process these parts.
Maybe not even solder...
TIA,
Peter
--
--------------------------------------------------------
Peter Swanson [log in to unmask]
INTERTRONICS http://www.intertronics.co.uk
Tel: +44 1865 842842 Oxfordshire, England
INTERTRONICS is dedicated to providing quality material, consumable and
equipment solutions to high technology assembly industries, with the
highest levels of technical support and customer service.
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