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in tin pest and pest free Monika Leodolter-Dvorak and Ilse Steffan
Trace analysis in tin pest and pest free SnCu0.5 solder material Monika Leodolter-Dvorak and Ilse Steffan Inst. of Analytical Chemistry and Food Chemistry University of Vienna COST 531 Meeting May 2007
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Tin Pest: General Aspects and Context with Lead Free Solders
based on: W. J. Plumbridge, “Tin pest issues in lead-free electronic solders”, J Mater Sci: Mater Electron (2007) 18: Trace Analyses of SnCu0.5 Solder Material Method of ICP-OES Sample Preparation Method Validation Results Comparison of the elemental composition: “pest sample” – “pest-free sample”
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Tin: allotropic forms: -Sn 13.2°C -Sn 161°C -Sn 232°C Sn(l)
“grey tin” 13.2°C -Sn “white tin” 161°C -Sn 232°C Sn(l) -Sn: typical metallic properties: conductor, ductile crystal structure: body centered tetragonal d = 7.29 g/cm3 -Sn: semiconductor, non-ductile crystal structure: diamond cubic d = 5.77 g/cm3
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Tin Pest (tin disease, tin plague, devil´s disease):
first reported: 1851; responsible for the disintegration of tin dishes, organ pipes, … is the product of the conversion: -Sn -Sn at T<13.2°C volume change leads to the total disintegration of the sample W.J.Plumbridge
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Factors influencing the formation of tin pest*:
temperature thickness of the specimen cold work impurities or alloyed elements effective lower limits? *W. J. Plumbridge, “Tin pest issues in lead-free electronic solders”, J Mater Sci: Mater Electron (2007) 18:
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Lead Free Solders and Tin Pest:
before RoHS: solder Sn/Pb (63/37) never shows tin pest formation lead free solders: some (e.g. SnCu0.5) show formation of tin pest: Can elemental analysis down to the lower ppm-range assist clear-up? Is a forecast possible?
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Tin Pest nucleation: growth: incubation: months – years
inoculation with -Sn: days growth: linear rate: 0.06 mm/d (max) at T=-40°C mm/d at T=-18°C W.J.Plumbridge
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Do metallic impurities (ppm-range) influence the formation of tin pest?
Where are the limits of the method? 3 test samples (SnCu0.5): region without pest: 2,3 g (whole piece) adjacent to pest wart: 0,3 g one pest wart: 0,09 g sample preparation: digested with HCl conc. at 80°C and filled up to volume matrix concentration: up to 1 g Sn/10 mL
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ICP-OES: excitation liquid sample polychromator introduction detector
(Inductively Coupled Plasma –Optical Emission Spectrometry) excitation (Argon-Plasma, 6000°C) liquid sample introduction h polychromator aerosol detector data processing (ICPWinLab) statistical evaluation A.Schiffkowitz
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Criteria for the element selection:
inhibiting formation of tin pest: Bi, Pb, Sb promoting formation of tin pest: Al, Mg, Zn potential contaminants from handling ???
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Instrumental Parameters:
Perkin Elmer Optima 3000XL, axial view nebulizer: conespray (GemCone) spray chamber: cyclone sample uptake rate: 1.4 mL/min torch: Fassel type, Al2O3 injector Argon flows: nebulizer: 0.8mL/min outer gas: 15 mL/min inner gas: 1 mL/min RF-power: W, free running spectrometer: Echelle based detector: SCD (Segmented array Charge-coupled Device)
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Method validation: spike test:
solution of pure tin shot (purity %) spiked with: Al, As, Bi, Cd, Fe, Ga, Ge, In, Mn, Ni, Pb, Sb, Ta, Te, Ti, Tl, Zn Recoveries: 98 – 103% method of internal standard (Lanthanum): f=1.02 ± 0.03
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Effects: sample matrix causes an increase of spectral
background intensities but no influence on the net intensities: measurement against aqueous standard solutions numerous spectral interferences were detected after line selection: measurement of all analytes at interference free lines
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Line selection: all lines 2-sided background corrected
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Analysis of Samples (SnCu0.5)
without tin pest (3 different areas) 2. complete disintegrated (4 samples at random) with the same “thermal history”: stored at –18°C for several years
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Sample Preparation: samples rinsed with 1 M HCl, water and methanol
0.8 – 2.5 g dissolved in 6 M HCl at 80°C and filled up to volume resulting solutions were diluted prior to measurement with ICP-OES
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Results: *confidence interval: =0.02, n3
red: statistically significant difference of mean values
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Statistically significant differences
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Conclusion: ICP-OES is an appropriate method for the
trace analysis in tin based alloys. No local differences concerning trace impurities were found. The results could be an indication for the influence of trace impurities on the formation of tin pest.
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Thank You For Your Attention!
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