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. 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