Hi Inge,
The solder joints per se are not a great reliability problem, depending on the alloy, it is the necessary temperature for soldering as well as the significantly greater stiffness and slower creep rates that create almost all the reliability issues I am dealing with. It is mostly PCBs that are affected, as well as wetting problems when people try to solder too cold.
Werner
-----Original Message-----
From: Inge <[log in to unmask]>
To: [log in to unmask]
Sent: Tue, May 4, 2010 4:36 pm
Subject: Re: [TN] Why not Pb-free?
You reminded me of a report from NPL-2005. In cooperation with Aeroflex, Alcatel, BAE, Bosch, Goodrich, RR, TRW and some more. A very advanced investigation with lots of solders with Pb and without Pb. The titel was: Measuring the Reliability of Electronics Assemblies during the Transation Period to Lead free Soldering. The foreword had this content:
"The work has indicated that there should be few solder joint reliability problems when mixing SnPb and LF components and solder alloys. Very few thermal cycling fatigue failures were experienced. Not one single failure was generated during the harsh vibration testing ".
I can't scan all these pages, however, if someone, not to many, are interested, I can send it offline. You can probably get it from NPL directly yourself.
Very optimistic result at that time. Just wonder how they feel today. Anyone from NPL?
Inge
--------------------------------------------------
From: "Paul Reid" <[log in to unmask]>
Sent: den 4 May 2010 20:07
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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