Trace analysisTrace analysisin tin pest and pest freein tin pest and pest freeSnCu0.5 solder materialSnCu0.5 solder material

Monika Leodolter-Dvorak and Ilse Steffan

Inst. of Analytical Chemistry and Food ChemistryUniversity of Vienna

COST 531 MeetingMay 2007

1.1. Tin Pest: General Aspects and Context withTin Pest: General Aspects and Context withLead Free SoldersLead Free Solders

based on: W. J. Plumbridge, “Tin pest issues in lead-free electronic solders”, J Mater Sci: Mater Electron (2007) 18:307-318

2.2. Trace Analyses of SnCu0.5 Solder MaterialTrace Analyses of SnCu0.5 Solder Material

• Method of ICP-OES• Sample Preparation• Method Validation• ResultsResults

Comparison of the elemental composition:Comparison of the elemental composition:““pest sample” – “pest-free sample”pest sample” – “pest-free sample”

Tin:Tin:

allotropic forms:

-Sn“grey tin”13.2°C

-Sn“white tin”161°C -Sn 232°C Sn(l)

-Sn: typical metallic properties: conductor, ductilecrystal structure: body centered tetragonald = 7.29 g/cm3

-Sn: semiconductor, non-ductilecrystal structure: diamond cubicd = 5.77 g/cm3

Tin PestTin 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

Factors influencing the formation Factors influencing the formation of tin pestof tin pest**::

•temperature

•thickness of the specimen

•cold work

•impurities or alloyed elementseffective lower limits?

*W. J. Plumbridge, “Tin pest issues in lead-free electronic solders”, J Mater Sci: Mater Electron (2007) 18:307-318

Lead Free Solders and Tin Pest:Lead Free Solders and Tin Pest:

• before RoHS: solder Sn/Pb (63/37) never showstin pest formation

• lead free solders: some (e.g. SnCu0.5) show formation oftin pest:

• Can elemental analysis down to the lower ppm-range assist clear-up?

• Is a forecast possible?

nucleation:incubation: months – years

inoculation with -Sn: daysgrowth:

linear rate: 0.06 mm/d (max) at T=-40°C 0.02 mm/d at T=-18°C

Tin PestTin Pest

W.J.Plumbridge

Do metallic impurities (ppm-Do metallic impurities (ppm-range) influence the formation of range) influence the formation of tin pest?tin pest?

Where are the limits of the method?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 andfilled up to volumematrix concentration: up to 1 g Sn/10 mL

ICP-OES:ICP-OES:(Inductively Coupled Plasma –Optical Emission Spectrometry)

liquid sampleintroduction

excitation(Argon-Plasma,

6000°C)aerosol h polychromat

or

detector

data processing(ICPWinLab)

A.Schiffkowitz

statistical evaluation

Criteria for the element selection: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

• ???

Instrumental Parameters:Instrumental Parameters:

Perkin Elmer Optima 3000XL, axial view

nebulizer: conespray (GemCone)spray chamber: cyclonesample uptake rate: 1.4 mL/min

torch: Fassel type, Al2O3 injectorArgon flows: nebulizer: 0.8mL/min

outer gas: 15 mL/mininner gas: 1 mL/min

RF-power: 1300 W, free running

spectrometer: Echelle baseddetector: SCD (Segmented array Charge-coupled Device)

Method validationMethod validation::

•spike test:solution of pure tin shot (purity 99.999%)spiked with:Al, As, Bi, Cd, Fe, Ga, Ge, In, Mn, Ni, Pb, Sb, Ta, Te, Ti, Tl, ZnRecoveries: 98 – 103%

•method of internal standard (Lanthanum):f=1.02 ± 0.03

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

Effects:Effects:

Line selection:

all lines 2-sided background corrected

analyte line [nm] analyte line [nm]Ag 328.068; 338.289 Ge 303.906Al 396.152 In 325.609As 193.696; 197.197 Mn 257.610; 294.920Au 242.795 Mo 202.030Bi 223.061 Ni 221.647; 231.604Cd 214.438; 226.502 Pb 216.418; 220.353Co 230.786; 238.892 Sb 217.581; 231.147Cr 267.716 Ta 226.230; 240.063Cu 221.458; 224.700 Te 214.281; 238.578

324.754; 327.396 Tl 276.787Fe 238.204; 259.940 W 207.911Ga 294.364; 417.206 Zn 206.191

Analysis of Samples (SnCu0.5)Analysis of Samples (SnCu0.5)

1. 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

Sample Preparation:Sample Preparation:

•samples rinsed with 1 M HCl, water and methanol

•0.8 – 2.5 g dissolved in 6 M HCl at 80°Cand filled up to volume

•resulting solutions were diluted prior to measurement with ICP-OES

*confidence interval: =0.02, n3red: statistically significant difference of mean values

conc [µg/g] c i *[µg/g] conc [µg/g] c i *[µg/g]Pb 431 18 283 12Bi 155,8 6,4 27,8 3,2In 96,5 8,8 14,2 0,8Fe 35,7 2,6 29,7 2,2Ge 23,7 2,5 <10Ni 23,0 1,7 5,8 1,6Tl 10,0 0,9 7,5 1,4Ag 9,1 1,1 1,3 0,1Co 7,3 0,5 1,3 0,3Cu [mg/g] 4,8 0,4 4,6 0,2Al 2,8 1,9 2,0 0,5Cd 2,1 0,2 0,9 0,1Cr 0,4 0,2 0,2 0,0Sb 0,34 0,02 0,14 0,01Mn 0,31 0,03 0,26 0,01

pest-free samples pest samples Results:Results:

Sb Cd Co Ag

pest free

pest0

2

4

6

8

10

µg/g

ultra trace elements 0.00001 - 0.001 m%

Pb Bi In Ge Ni

pest freepest0

100

200

300

400

500

µg

/g

trace elements 0.001 - 0.04 m%

Statistically significant differencesStatistically significant differences

Conclusion:Conclusion:

1. ICP-OES is an appropriate method for thetrace analysis in tin based alloys.

2. No local differences concerning traceimpurities were found.

3. The results could be an indication for theinfluence of trace impurities on the formation of tin pest.

Thank You Thank You For Your Attention!For Your Attention!