I was following our typical corporate method -
Ready, Shoot, Aim
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Whittaker, Dewey (EHCOE)
Sent: Wednesday, May 05, 2010 7:16 AM
To: [log in to unmask]
Subject: Re: [TN] Why not Pb-free?
Just cause it floats doesn't mean its palletable (think Caddy Shack). Precondition your samples per IPC-TM-650, Method 2.6.27, prior to evaluation for a more realistic assessment of the chances for success.
Dewey
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of ALLEN, LOA
Sent: Tuesday, May 04, 2010 4:09 PM
To: [log in to unmask]
Subject: Re: [TN] Why not Pb-free?
Werner,
I am not trying to disprove supplier quality - we have a couple of good fab shops & I don't want to get on their bad side. This exercise is to compare a number of solder floats at 220°C & at 260°C to prove to management the reduction in reliability.
I hope to find a large quantity of previously accepted PWBs with several coupons that we can cut up into 20 floats.
Float 2ea 5x, 7x, 9x, 11x, & 13x at 220°C & 2ea 5x, 7x, 9x, 11x, & 13x at 260°C.
Then x-section & evaluate the barrels.
The sole purpose is to demonstrate to management how the increase in temperature will affect the PWB - it is not meant to be a material/process qual or reflection on supplier quality.
Do you think this is overkill? Use less samples?
Thanks again,
Loa
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
Sent: Tuesday, May 04, 2010 3:02 PM
To: [log in to unmask]
Subject: Re: [TN] Why not Pb-free?
Hi Loa,
Please do not always blame the PCB FAB house-many of the problem PCBs I see were never properly specified for Pb-free assembly needs.
Werner
-----Original Message-----
From: ALLEN, LOA <[log in to unmask]>
To: [log in to unmask]
Sent: Tue, May 4, 2010 5:38 pm
Subject: Re: [TN] Why not Pb-free?
Paul,
Thank you very much . . . this type of information is what I am looking for. I
remember you & Werner commenting on this earlier & now wish I had paid more
attention.
Since we do test the coupons before the PWB lot is accepted it shouldn't be too
difficult to provide actual samples of failures & number of "preconditioning"
attempts then compare to the 6X for assembly & rework to determine percent of
reduction in reliability .
This forum is awesome . . . gotta go fire up the solderpot.
Thanks again,
Loa
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Paul Reid
Sent: Tuesday, May 04, 2010 11:08 AM
To: [log in to unmask]
Subject: Re: [TN] Why not Pb-free?
Werner Engelmaier has pointed out, on a number of occasions that PWB reliability
directly and profoundly affected by lead-free assembly and rework and we at PWB
Inc. concur.
We have found that in a perfectly fabricated PWB, reliability is reduced by 50%
in a lead-free application. Tin lead processing reduces reliability by 25% or
less. By that statement we mean that if the reliability of a coupon, expressed
and thermal cycles to failure, tested "As Received" is your "entitlement" the
reliability after 6X260°C preconditioning to simulate assembly and rework will
be half of the "entitlement" value. PWB failures can occur in assembly and the
end use environment.
That 50% rule of thumb for PWB reliability in a lead free application has not
changed since the adoption of RoHS. The report I completed today, for example,
suggested the reliability of the product tested after lead-free simulation, was
reduced by 70%. Since a 70% reduction in reliability is significantly higher
than we expect, there is probably a fabrication discrepancy contributing to the
early failure. Lead free assembly is at the limit of most epoxy systems.
It would be prudent to optimize your PWB fabrication requirements, material and
design (if possible) for a lead free application.
The copper failure mode tends to shift from barrel cracks to corner cracks. The
corner cracks tend to be horizontal rather than at a45° angle. Material is
degraded and is expressed has cohesive failure, adhesive delamination and
crazing. Since QC type requirements, like copper thickness, registration do not
anticipate reliability in a lead free environment many companies are using
reliability testing as a condition of lot acceptance. If you do reliability
testing you must test for both copper and material reliability or you could get
a false positive result.
Of course you must predicate all of the above comments with "It depends..."
Sincerely,
Paul Reid
Program Coordinator
PWB Interconnect Solutions Inc.
235 Stafford Rd., West, Unit 103
Nepean, Ontario
Canada, K2H 9C1
613 596 4244 ext. 229
Skype paul_reid_pwb
[log in to unmask] <mailto:[log in to unmask]>
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of LA
Sent: May 4, 2010 11:56 AM
To: [log in to unmask]
Subject: [TN] Why not Pb-free?
Until now we have not considered going to Pb-free soldering processes for any
of our products. But in trying to keep up with the latest technologies it is
becoming harder & harder to find Sn/Pb solder surface finishes, meaning we
are spending huge amounts of resources reworking components prior to
assembly.
Some management are wanting to convert the bulk of our products to Pb-free
& are tiring of my usual arguments of - Tin whiskers, unknown reliability
models, cost of running two separate processes, PWB development for higher
reflow temps, review of current component database to verify compatibility
with higher reflow temps, teaching old dogs new tricks.
Equipment is high end telecommunications mostly rack-mount office
environment.
Questions - Are my arguments still valid? Are there any recent studies
concluded indicating Sn/Pb is superior?
Thank you in advance . . .
NOTE: This email is not the opinion or desires of the sender; it is solely the
desires of the sender's company.
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