At 07:29 AM 5/5/2010, ALLEN, LOA wrote:
>I was following our typical corporate method -
>
>Ready, Shoot, Aim
You say that like it's a bad thing. :-)
Hey, we got downrange guidance these days don't we?
>-----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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