Re
> the Medtronic pacemaker failures, "separation of wires" seems to be equivalent
> to "open circuit", not short
> circuit, which might be attributed to tin whiskers.
>
>L-f solder exhibits several openor high resistance
> circuit failure mechanisms as well as tin whisker short circuits. Let's
> see, there are a) voids due to the Kirkendahl diffusion of copper and b) copper
> dissolution from PCB pads, both leading to brittle joints (http://www.metallicresources.com/pdf/SACvsNonSAC.pdf), c)
> poor wetting*, d) lower modulus of elasticity than 63-37 with temperature excursions
>(stiffness).
>
>____________________________________________________
>*Conclusions
> from <http://www.pb-free.com/pdf/university_research/Solderabiliity.pdf>:
>"An
> increase of about 50°C to the soldering temperature
>may be needed for
> lead-free solder alloys to maintain
>identical wetting to SnPb. Results with
> copper samples
>and an active flux show that using lower
> soldering
>temperatures, the wetting properties of lead-free
> alloys
>degrade with superheat in a similar way to SnPb
> alloys.
>Therefore, using lower superheat will be detrimental
> to
>performance in a similar way to that exhibited by
> SnPb
>solder.
>Lead-free solderability becomes significantly poorer
> with
>weaker no-clean and pure rosin fluxes in comparison to
>SnPb solder.
> This loss of solderability can be recovered
>by the use of nitrogen.
> Nitrogen inerting may become
>unavoidable with complex boards with a high
> thermal
>demand and a large range of temperatures across the
>board during
> reflow.
>The major conclusion to come out of the SOIC data is
> that
>lead-free alloys do not wet as well to lead-free
>terminations. The
> Pd and Au finishes always wet well
>with the SnPb alloy, but are poorer with
> any of the
> leadfree
>alloys."
>-----------------------------------------------------------------------------
>With
> regard to whisker causes, Carol Handwerker is my ultimate expert based on work
> at NIST.
>She told me that only lead is the deterrent.
>There is no cure-- where there is tin there are whiskers,
> as witnessed by failures in at least one nuclear power station, with eutectic
> solder. Might of been tin finish on the leads-- these things are not
> fully investigated.
>
>
>International Symposium on Tin Whiskers > (2009)Tin Whisker and Surface Defect Formation on
> Electroplated Films and Reflowed Joints Prof. Carol Handwerker,
> Purdue University ...
>www.calce.umd.edu/symposiums/ISTW2009.htm -
>
>
>
>
>
>
________________________________
From: Bob Landman
> <[log in to unmask]>
>To: [log in to unmask]
>Sent: Thu, February 18, 2010 1:22:23
> PM
>Subject: SPAM-LOW: Re:
> [TN] Pace maker recall URL
>
>Ian,
>
>Good question! In a
> word, no. Why? No need. Lead solved the problem.
>
>
>It would be highly one could get IR&D or government funding for
> research on why tin grows whiskers.
>An interesting phenomenon but
> there are lots of more important phenomena that need studying, are there
> not?
>
>That is until the EU decided to ban lead from eutectic tin solder
> and compounded the problem by not waiting until suffient data was in that the
> new solders (and platings) did not grow whiskers under ANY conditions or that
> if they did they were miniscule and of no consequence.
>
>Of course, at
> the same time the EU banned lead in solder, the geometries of parts had shrunk
> enormously since the 1950's, 1960's and 1970's when the studies were
> done.
>
>A perfect environment was created to grow whiskers and introduce
> all kinds of metalurgical unknowns as all these new solders are just that, NEW
> with very little real life long term experience.
>
>Now we get to go
> through the same learning curve again.
>
>And that took how
> long?
>
>And meanwhile we want to make profits and we want our products to
> be trouble free (and, oh yes, not kill anyone)?
>
>Bob Landman
>H&L
> Instruments, LLC
>
>-----Original Message-----
>From: Ian Hanna
> [mailto:[log in to unmask]]
>Sent:
> Thursday, February 18, 2010 4:08 PM
>To: Bob Landman; [log in to unmask]
>Subject:
> RE: [TN] Pace maker recall URL
>
>have a look at the
> REFERENCES:
>
>1. "Eliminate Whisker Growth on Contacts
> by Using a Tin Alloy
>Plate," R.P. Diehl & N.A. Cifaldi,
> Insulation/Circuits, pp. 37-39, Apr.
>1976.
>2. "How to
> Avoid Metallic Growth Problems on Electronic Hardware,"
>Tech Report
> IPC-TR-476, The Institute for Interconnecting & Packaging Electronic
> Circuits (IPC), 1977.
>3. "Identification of Fused Tin
> Coatings on Integrated Circuit
>Device Leads," W.G. Bader, Plating &
> Surface Finishing, pp. 56-57, Aug.
>1977.
>4.
> "Spontaneous Growth of Whiskers on Tin Coatings: 20 Years of
>Observation,"
> S.C. Britton, Trans. Inst. of Metal Finishing, Vol 52, pp.
>95-102, Apr.
> 1974.
>5. "Tin Whiskers: Causes & Remedies," N.A.J.
> Sabbagh & H.J.
>McQueen, Metal Finishing, pp. 27-31, Mar.
> 1975.
>
>
>has anybody done anything relevent since
> 1977?
>
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf
> Of Bob Landman
>Sent: Thursday, February 18, 2010 2:43 PM
>To: [log in to unmask]
>Subject:
> Re: [TN] Pace maker recall URL
>
>
>Actually, we don't know what caused
> the "separation of wires". Where did the wires separate and why? A
> connector problem? A solder problem?
>
>The FDA document is
> useless.
>
>This is interesting http://www.yourlawyer.com/articles/read/16568
>
>"Medtronic
> said it has received reports of two patient deaths where it is possible,
> but unclear, whether a wire separation issue may have been a
> factor."
>
>The Medtronic document is actually more revealing http://www.medtronic.com/crm/performance/advisories/sigma-nov2005.html
>
>Sigma
> Implantable Pulse Generators
>Original Date of Advisory: November 2005
> Potential Separation of Interconnect Wires Product
>
>A specific
> subset of Sigma series pacemakers may fail due to separation of interconnect
> wires from the hybrid circuit. Specific model and serial numbers of affected
> devices are available online at:http://SigmaSNList.medtronic.com.
>Advisory
>
>This
> subset of Sigma series pacemakers that may fail due to separation of
> interconnect wires from the hybrid circuit may present clinically as loss of
> rate response, premature battery depletion, intermittent or total loss of
> telemetry, or no output.
>
>Separation of redundant interconnect wires has
> been observed on hybrid terminal blocks. Device failure occurs only where both
> interconnect wires separate from a hybrid terminal block. In October 2005,
> testing and analysis identified the root cause of these failures and the
> affected population. Hybrid circuits used in this subset of devices were
> cleaned during manufacturing with a particular cleaning solvent that could
> potentially reduce the strength of the interconnect wire bond over
> time.
>
>No provocative testing can predict which devices may
> fail.
>
>Patient Management Recommendations
>
>Recommendation for the
> management of patients who have pacemakers affected by this advisory were
> changed in May 2009. Current recommendations are:
>
>We realize that each
> patient requires unique clinical consideration and we support your judgment in
> caring for your patients. After consultation with Medtronic's Independent
> Physician Quality Panel, Medtronic offers the following recommendations for
> patients in the 2005 Sigma advisory:
>
> * Physicians should
> advise their patients to seek medical attention immediately if they experience
> symptoms (e.g., fainting or lightheadedness).
> * Physicians
> should consider device replacement for patients who are both pacemaker
> dependent and who have been implanted with a device in the affected subsets.
> Medtronic will offer a supplemental device warranty if the device is not
> already at elective replacement time.
> * Physicians should
> continue routine follow-up in accordance with standard practice for those
>
> patients who are not pacemaker dependent.
>
>Status Update
>
>As of
> July 31, 2009, 328 devices out of approximately 40,000 devices worldwide have
> been confirmed as having experienced interconnect wire separation.
> Seventy-five (75) of these devices were returned from the United
> States.
>
>One hundred ninety-three (193) of the 328 devices (0.46%) were
> returned with information indicating a problem with the patient's pacing
> system prior to explant. The remaining 135 devices (0.32%) were returned with
> no information indicating a potential malfunction while implanted or with
> insufficient information to determine the state of the device at explant.
> Lacking definite information indicating proper operation until explant, these
> devices are conservatively categorized as having experienced interconnect wire
> separation while implanted.
>
>Our original modeling predicted a failure
> rate from 0.17% to 0.30% over the remaining lifetime of these pacemakers.
> However, updated modeling now predicts a failure rate of 3.9% over the
> remaining device life.
>
>Out of the initial advisory population of 40,000
> worldwide, approximately 13,100 remain implanted. Approximately 3,100 of these
> are in the United States.
>
>=====================
>
>Bob
> Landman
>H&L Instruments, LLC
>
>-----Original Message-----
>From:
> TechNet [mailto:[log in to unmask]] On Behalf Of Reliability
> Resources
>Sent: Thursday, February 18, 2010 12:00 PM
>To: [log in to unmask]
>Subject:
> Re: [TN] Pace maker recall URL
>
>This recall was not caused by tin
> whiskers.
>
>http://www.fda.gov/MedicalDevices/Safety/RecallsCorrectionsRemovals/List
>ofRe
>calls/ucm166344.htm
>
>Reason
> for Recall: The Kappa and Sigma pacemakers in these identified series may fail
> due to a separation of wires that connect the electronic circuit to other
> pacemaker components, such as the battery.
>
>Clayton Bonn
>Reliability
> Resources
>Ph: 714-612-9359
>e-mail:[log in to unmask]
>www.reliability-resources.com
>
>
>-----Original
> Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of Ahne
> Oosterhof
>Sent: Wednesday, February 17, 2010 1:47 PM
>To: [log in to unmask]
>Subject:
> Re: [TN] Pace maker recall URL
>
>I like this sentence in that FDA
> announcement under conclusions:
>
>Untreated tin coating should never be
> used in conjunction with electronic circuitry.
>
>Especially the
> generalization of the statement!
>That page was last updated
> 30Apr09.
>
>Ahne.
>
>
>-----Original Message-----
>From: TechNet
> [mailto:[log in to unmask]] On Behalf Of Brooks,
> Bill
>Sent: Wednesday, February 17, 2010 12:42
>To: [log in to unmask]
>Subject:
> Re: [TN] Pace maker recall URL
>
>http://www.fda.gov/ICECI/Inspections/InspectionGuides/InspectionTechnica
>lGuides/ucm072921.htm
>
>Check
> that link out...
>
>
>Bill Brooks | Datron World Communications,
> Inc.
>PCB Designer/Engineer | Office: 760-602-7004| Fax: 760-597-3777 | [log in to unmask] 1808
> Aston Avenue, Suite 230, Carlsbad, CA 92008 | www.dtwc.com
>
>Performance You Require. Value You
> ExpectTM
>
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf
> Of Roberts, Jon (SA-1)
>Sent: Wednesday, February 17, 2010 12:17 PM
>To:
> [log in to unmask]
>Subject:
> Re: [TN] Pace maker recall URL
>
>I did not readily see the root cause on
> any of the Medtronic recalls. So where is the actual report stated it was
> whiskers? I may have missed it, Thanks, Jon
>
>-----Original
> Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of John
> Burke
>Sent: Wednesday, February 17, 2010 1:37 PM
>To: [log in to unmask]
>Subject:
> Re: [TN] Pace maker recall URL
>
>Here you go:
>
>6) FDA forced
> Medtronic to recall their implanted cardiac defibrilators (from patients
> bodies) when whiskers shorted the devices.
> http://www.fda.gov/ora/inspect_ref/itg/itg42.html
>
>
>John
> Burke
>(408) 515 4992
>
>
>-----Original Message-----
>From: TechNet
> [mailto:[log in to unmask]] On Behalf Of Victor
> Hernandez
>Sent: Wednesday, February 17, 2010 9:19 AM
>To: [log in to unmask]
>Subject:
> [TN] Pace maker recall URL
>
>Fellow TechNetters:
>
> A few
> weeks back on of the subscriber share health information about a
>recall
> pace maker which I found very interesting. How, I am not
> able
>to
>locate that link now that I have a need for it. That
> subscriber share that URL site once again.
>
> In advance I thank
> you for your timely response in this
> matter.
>
>Victor,
>
>
>______________________________________________________________________
>This
> email has been scanned by the MessageLabs Email Security System.
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