David,
Please send me a copy of your paper.
Thanks,
Dioscoro A. Merilo
Corporate R and D
ST Assembly Test Servives Ltd.
Singapore
David Suraski <[log in to unmask]>@IPC.ORG> on 01-06-2001 01:04:24 AM
Please respond to "Leadfree Electronics Assembly E-Mail Forum."
<[log in to unmask]>; Please respond to David Suraski
<[log in to unmask]>
Sent by: Leadfree <[log in to unmask]>
To: [log in to unmask]
cc: (bcc: DIOSCORO Merilo/Engr/STATS/ST Group)
Subject: Re: [LF] What is lead free...
I agree with Doug that the approach of utilizing a lead-free alloy with
tin/lead coated parts as a first step in lead-free processing is being
considered/taken by many.? Unfortunately, this is an approach that could
have?negative results for some assemblies.
Unfortunately, in the past the presence of lead in lead-free alloys has
been presumed to be acceptable.? The logic behind this often was that tin
and lead are soluble in a lead-free system.? However, what has been
overlooked is that the intermetallic crystalline structures in lead-free
systems are not soluble and will precipitate at lead boundaries.? Thus,
when using a lead-free alloy to solder to Sn/Pb coated component leads, Pb
can actually create voids in the solder joint that can result in joint
failure.
To avoid problems related to this, the most prudent course of action is to
eliminate/reduce the lead-free transition period to as short as possible.
In other words, when a company implements a lead-free solder alloy, it
should also implement lead-free component terminations and circuit board
coatings.? If these above guidelines are not followed, the reliability of
the solder joint is risked.
We've just completed a paper discussing the dynamics of this and showing
real-world examples of failures caused by lead contamination of lead-free
solders.? This will be presented a Nepcon East/SMTA Boston this June, but
if anyone would like to receive a copy of the paper before hand I'll be
happy to send one along at your request.
PS- I'm not advertising here, nor am I suggesting that anyone SHOULD go
lead-free- just offering some research to the community!
Best regards,
David Suraski
AIM
T: 800-CALL-AIM / 401-463-5605, F: 401-463-0203
www.aimsolder.com
----- Original Message -----
From: Romm, Doug
To: [log in to unmask]
Sent: Thursday, May 31, 2001 12:36 PM
Subject: Re: [LF] What is lead free...
Greg,
You will probably get different inputs but here's mine.
Many OEMs are stating that they will implement 'lead-free' in a staggered
approach.? The order of priority will be
First: solder materials
Second: printed circuit board finishes
Third: components
This is based on the % contribution of SnPb of each of the subsets
(solder, pcb finishes, components) to the total solder joint (I believe).
This approach is also being reflected in some end users roadmaps which
show the requirement for 'high-temperature' capability of components and
pcbs most immediately and then 'lead-free' as a follow-on step.? This
timing sequence is based on the fact that OEMs will convert to lead-free
solders first (which may have a higher reflow temp requirement) and then
will follow with lead-free PCBs and components.
The goal (of those who choose to pure lead-free) is total lead-free in the
entire system, but I believe the staggered approach is being followed by
many.
Doug Romm
-----Original Message-----
From: Greg Vance [mailto:[log in to unmask]]
Sent: Thursday, May 31, 2001 10:46 AM
To: [log in to unmask]
Subject: [LF] What is lead free...
Silly question, what defines lead free?? Does this imply that there will
be
no lead in the assembly or we will use no lead solder, but PCB finish and
some/all of the components may have SnPb plating on them... get my point?
I ask this from the perspective of:
1) printed circuit board finishes
2) components
3) solder materials
Greg Vance
Rockwell Automation
(330)487-6036
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