elimination of s n in spacecraft assemblies presentation to the emaps workshop 17 th february 2010
TRANSCRIPT
Elimination of SElimination of Snn in in Spacecraft AssembliesSpacecraft Assemblies
Presentation to the EMAPS Presentation to the EMAPS Workshop Workshop
1717thth February 2010 February 2010
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Spur Electron specialises in:-Spur Electron specialises in:-
All aspects of High Reliability component All aspects of High Reliability component engineering and procurement engineering and procurement
Component Assessment and Failure Component Assessment and Failure Analysis…Analysis…
Manufacture of hardware to ESA, NASA and Manufacture of hardware to ESA, NASA and Military StandardsMilitary Standards
Spur Electron OverviewSpur Electron Overview
Spur Electron OverviewSpur Electron Overview
Spur Electron specialises in:-Spur Electron specialises in:-
All aspects of High Reliability component All aspects of High Reliability component engineering and procurement engineering and procurement
Component Assessment and Failure Component Assessment and Failure Analysis…Analysis…
Manufacture of hardware to ESA, NASA and Manufacture of hardware to ESA, NASA and Military StandardsMilitary Standards
>
Spur Electron OverviewSpur Electron Overview
>
Spur Electron specialises in:-Spur Electron specialises in:-
All aspects of High Reliability component All aspects of High Reliability component engineering and procurement engineering and procurement
Component Assessment and Failure Component Assessment and Failure Analysis…Analysis…
Manufacture of hardware to ESA, NASA and Manufacture of hardware to ESA, NASA and Military StandardsMilitary Standards
The Spur input to EMAPSThe Spur input to EMAPS
The title proposed for this input was:The title proposed for this input was:
““The elimination of SThe elimination of Snn in Spacecraft Assemblies.” in Spacecraft Assemblies.”
I would suggest a subtle change of title to :I would suggest a subtle change of title to :
““The minimisation of SThe minimisation of Snn in Spacecraft Assemblies” in Spacecraft Assemblies”
The complete The complete eliminationelimination of pure S of pure Snn in Spacecraft Hardware, even in Spacecraft Hardware, even today, is virtually impossible and will become even more difficult today, is virtually impossible and will become even more difficult in the future.in the future.
What does ESA say What does ESA say about pure about pure SSnn ??
ESCC – 60 - 6.2.2.2 ESCC – 60 - 6.2.2.2 d1, “Pure Sd1, “Pure Snn used as a finish on leads, used as a finish on leads,
terminations and external surfaces of terminations and external surfaces of components and packages shall not be components and packages shall not be used”used”
e, “The use of pure Se, “The use of pure Snn in internal cavities in internal cavities may be authorised, on a case by case basis, may be authorised, on a case by case basis, based on a demonstration there is no based on a demonstration there is no alternative product alternative product and there is no and there is no risk!!risk!!””
Minimisation of pure SMinimisation of pure Snn in in Spacecraft HardwareSpacecraft Hardware
We have already heard that we face We have already heard that we face two major problems using pure Stwo major problems using pure Snn..
Tin Whiskers & Tin PestTin Whiskers & Tin Pest
Photo courtesy of Goddard Space Flight Center
Tin Whiskers & Tin Pest Tin Whiskers & Tin Pest
Tin WhiskersTin Whiskers are probably correctly are probably correctly seen as the greater evil, in that, they seen as the greater evil, in that, they occur in equipment operating under occur in equipment operating under normal conditions and can very easily normal conditions and can very easily cause short circuits in electronic hardware.cause short circuits in electronic hardware.
Tin PestTin Pest should not be ignored even should not be ignored even though it is thought to occur at very low though it is thought to occur at very low temperatures. Much of our hardware sees temperatures. Much of our hardware sees low temperatures, which is one reason low temperatures, which is one reason that we qualify electronic components that we qualify electronic components from -55 to +125.from -55 to +125.
History Whisker FailuresHistory Whisker Failures During WW2 Cadmium whisker failures were During WW2 Cadmium whisker failures were
causing serious problems.causing serious problems. 1950’s Change to tin, resulted in same problems!1950’s Change to tin, resulted in same problems! The Whisker growth methodology still accepted The Whisker growth methodology still accepted
today was predicated in 1954.today was predicated in 1954. In 1975 a certain Mr. B.D. Dunn published the In 1975 a certain Mr. B.D. Dunn published the
Worlds 1Worlds 1stst paper containing high quality SEM paper containing high quality SEM micrographs of Whisker growth. He micrographs of Whisker growth. He recommended Srecommended SnnPPbb as the preferred finish for as the preferred finish for components.components.
Even in Commercial applications the US, NEMI Even in Commercial applications the US, NEMI state ”Pure Tin is unacceptable”.state ”Pure Tin is unacceptable”.
History - Tin PestHistory - Tin Pest Tin Pest or Plague was known in the early 19Tin Pest or Plague was known in the early 19thth
Century and was, at one time credited with the Century and was, at one time credited with the French defeat in 1812, because the French tin French defeat in 1812, because the French tin uniform buttons literally disintegrated in the uniform buttons literally disintegrated in the extreme cold!extreme cold!
It was also blamed for the collapse of fuel cans It was also blamed for the collapse of fuel cans along Scott’s return route!along Scott’s return route!
The major problem that we face today is that The major problem that we face today is that under extreme cold conditions tin will disintegrate under extreme cold conditions tin will disintegrate as an insulator but become conductive if it warms as an insulator but become conductive if it warms up!up!
Minimisation of pure SMinimisation of pure Snn in in Spacecraft HardwareSpacecraft Hardware
The complete elimination of pure SThe complete elimination of pure Snn in Spacecraft Hardware is in Spacecraft Hardware is virtually impossible. However, Spur have become experts in virtually impossible. However, Spur have become experts in minimisingminimising its inclusion by:- its inclusion by:-
Careful control of Component Selection.Careful control of Component Selection. Detailed Component Assessment of non-qualified devices.Detailed Component Assessment of non-qualified devices. Specifying SSpecifying SnnPPbb whenever possible in Procurement Specs. whenever possible in Procurement Specs. Routinely carrying out lead / termination testing at R.I.Routinely carrying out lead / termination testing at R.I. Re-processing SMD SRe-processing SMD Snn components to inhibit whisker growth components to inhibit whisker growth Stripping and SStripping and SnnPPbb dipping of leaded components to dipping of leaded components to
minimise risk of whisker growthminimise risk of whisker growth
Even these precautions cannot guarantee pure SEven these precautions cannot guarantee pure Snn exclusion! exclusion!
Component Selection ControlComponent Selection Control Component Lists need to be reviewed for a wide range of Component Lists need to be reviewed for a wide range of
potential problems including:- Qualification , current and potential problems including:- Qualification , current and future availability & Quality history amongst others. future availability & Quality history amongst others.
However, with respect to Lead finish it is essential to:-However, with respect to Lead finish it is essential to:-
Maximise the use of components which are controlled by a Maximise the use of components which are controlled by a specification which offers Sspecification which offers SnnPPbb or A or Auu lead finish. lead finish.
Check that these components are still supplied in that Check that these components are still supplied in that finish, but don’t always expect a truthful answer from finish, but don’t always expect a truthful answer from stockists.stockists.
If pure SIf pure Snn is the only option offered then an alternative is the only option offered then an alternative component should be sought.component should be sought.
Where no alternative exists action must be taken to Where no alternative exists action must be taken to minimise the risks. minimise the risks.
Component AssessmentComponent Assessment Where no, or inadequate, previous knowledge of a Components Where no, or inadequate, previous knowledge of a Components
quality of assembly, is available, Component Assessment needs to quality of assembly, is available, Component Assessment needs to be carried out.be carried out.
WRT minimising SWRT minimising Snn it is natural to concentrate on the leads / it is natural to concentrate on the leads / terminations, but increasingly we are finding pure Sterminations, but increasingly we are finding pure Snn being used being used as an internal plating in cavity devices.as an internal plating in cavity devices.
Device found to have lid with pure tin finish
Sample component termination Sample component termination testingtesting
As a standard activity during Receiving Inspection, Lead / As a standard activity during Receiving Inspection, Lead / Termination EDAX Inspection is carried out as standard on a small Termination EDAX Inspection is carried out as standard on a small sample of all date codes.sample of all date codes.
Photos of EDAX SPhotos of EDAX Sn n & S& SnnPPbb
Re-processing pure SRe-processing pure Snn devices. devices. Spur have developed a means whereby Pure SSpur have developed a means whereby Pure Snn SMD’s can SMD’s can
be reprocessed such that the Pbe reprocessed such that the Pbb content exceeds 3% content exceeds 3% throughout the re-made joint, thus inhibiting whisker throughout the re-made joint, thus inhibiting whisker growth. growth.
pure tin re-processed jointpure tin re-processed joint
Spur process to mitigate pure tinSpur process to mitigate pure tin
1st re-flow showing pure tin remains on top of termination
Back Scatter image shows pure tin (no PPbb present) on top of termination
Spur process to mitigate pure tinSpur process to mitigate pure tin
2nd re-flow showing entire termination and solder fillet comprise of tin/lead mixture
Back Scatter image showing good amalgamation of tin and lead – even on top of termination
Stripping / TinningStripping / Tinning Most of us are aware of the process of stripping and Most of us are aware of the process of stripping and
reprocessing of pure Sreprocessing of pure Snn or A or Auu leaded components, and the leaded components, and the need to avoid overheating glass or ceramic body seals.need to avoid overheating glass or ceramic body seals.
The problem with SThe problem with SnnPPbb solder coated leads is that S solder coated leads is that Snn whiskers whiskers can still grow from the untreated area at the top of the lead.can still grow from the untreated area at the top of the lead.
Controlled Solder Dipping Process
•Pre-Heat Hot Plate
•IPA cleaner
•Flux
•De-Golding Pot
•Solder Dip Pot
•Controlled Immersion
Chemical StrippingChemical Stripping Spur believes that it has identified a means by Spur believes that it has identified a means by
which the entire lead can be chemically stripped which the entire lead can be chemically stripped of pure Sof pure Snn and can then be re-plated to within a and can then be re-plated to within a safe distance of the case.safe distance of the case.
The methodology needs to be assessed through a The methodology needs to be assessed through a properly controlled study managed by an properly controlled study managed by an accredited agency such as ESA.accredited agency such as ESA.
Spur would be prepared to offer its proposed Spur would be prepared to offer its proposed solution to its customers but unfortunately it has solution to its customers but unfortunately it has no evidence based results to demonstrate the no evidence based results to demonstrate the reliability of the procedure. reliability of the procedure.
Space Grade Press Fit ConnectorsSpace Grade Press Fit Connectors EDX Analysis EDX Analysis
identified identified potentially potentially dangerous mix dangerous mix of termination of termination finishesfinishes
SummarySummary
Tin Whiskers and Tin Pest have been known Tin Whiskers and Tin Pest have been known problems that remain with us.problems that remain with us.
In spite of the serious implications of banning SIn spite of the serious implications of banning SnnPPbb solders and finishes, Brussels has handed us a solders and finishes, Brussels has handed us a time bomb!time bomb!
Unless we are extremely vigilant we Unless we are extremely vigilant we willwill lose lose spacecraft to electrical failure caused by Sspacecraft to electrical failure caused by Snn related problems. related problems.
SummarySummary
All of us involved in the design and manufacture All of us involved in the design and manufacture of Spacecraft hardware must ensure that we of Spacecraft hardware must ensure that we minimise the inclusion of Pure Tin within our minimise the inclusion of Pure Tin within our equipment, using the controls identified above.equipment, using the controls identified above.
We must also look for the means of removing SWe must also look for the means of removing Snn from our hardware to the maximum extent from our hardware to the maximum extent possible, using known inspection techniques and possible, using known inspection techniques and investigating new methods of removing the investigating new methods of removing the hazard that pure tin poses.hazard that pure tin poses.
End of showEnd of show
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