Blahetová, Marie

Drápala, Jaromír

Lasek, Stanislav

Vrbický, Jiří

English

DSpace at VSB Technical University of Ostrava

ITltJLIB Sborník vědeckých prací Vysoké školy báňské - Technické univerzity Ostrava číslo 3, rok 2009, ročník Lil, řada hutnická, článek č. 154 8  Stanislav LASEK 1 , Jaromír DRÁPALA 2, Marie BLAHETOVÁ 1, Jiří VRB!CKÝ3 ELECTROCHEMICAL CORROSION PROPERTIES OF LEAD-FREE SOLDERS KOROZNĚ ELEKTROCHEMICKÉ VLASTNOSTI BEZOLOVNATÝCH PÁJEK Department o/ materia/s engineering, VŠB-Technica/ University Ostrava, 17. listopadu 15, Ostrava­Poruba, 735 64, Czech Republic - stanislav./asek@vsb.cz Department o/non-ferrous meta/s, rafining and recycling, VŠB-TU Ostrava, Czech RepublicDepartment o/ matematics and descriptive geometry, VŠB-TU Ostrava, Czech RepublicAbstract In the contribution the electrochemical corrosion p�operties of selected and/or new tin base lead-free solders with additions of Ag, Bi, Cu, ln, Sb are compared and evaluated by means of potentiodynamic cyclic method using O,lmol/1 NaCl water solution and by standard salt spray test. For testing were used these solders: Sn-0,5Ag-56Bi, Sn-2,5Ag-2Bi, Sn-3,lAg-6,l Bi, Sn-3,4Ag-4,8Bi, Sn-3,5Ag-7Bi, Sn-3,5Ag-10Bi, Sn-3,3Ag-4,8Bi; Sn-5Ag-8,6ln, Sn-3,3Ag-4,8In, Sn-0,5Ag-5ln, Sn­l ,5Ag-5In; Sn-5Bi-lln; Sn-l ,5Ag-3Cu-5In, Sn-0,5Ag-3Cu-5In, Sn-0,5Ag-l Cu-5In, Sn-l ,5Ag-l Cu-5In; Sn-3Ag-2Bi-2Sb, Sn-0,5Ag-l ,5Bi-3Sb, Sn-2,5Ag-l l ,2Bi-5,5In, Sn-2Ag-7,5Bi-5,5In, Sn-2,9Ag­l ,9Bi-2,9In, Sn-2Ag-7,5Bi-0,5Cu. The samples were made of casted rods 010-12 mm in the shape of discs. According to potentiodynamic test and pitting potentials (depassivation, repassivation) values, the solders with addition of Bi and/or Bi-Ag are more resistant in comparison with indium containing ones. The interpretation of individua! alloying elements influence is difficult with respect to their low content and distribution among different phases and areas, as confirmed by metallography and microanalysis. Application of statistical methods made a possibility to compare the influence of individua! elements on the corrosion parameters, e. g. the linear regression relation has been used for depassivation potential values: Ed = -388  +18,0.Ag +o,35.Bi -5,0.Cu -11,1.In -16,3.Sb, where Ag and Bi have shown positive and In or Sb negative influence. The similar relation were obtained for corrosion mass loses after the salt spray test and gravimetrie measurements. For a better interpretation of results, the pure metals for solders were also tested and ranking in pitting resistance based on potentiodynamic testing was confirmed in the order Ag, Bi, Cu, Sb, Sn and ln. The dark spots, pits, matt surfaces and coloured areas on solders were observed by microscopy after corrosion tests. Abstrakt V práci jsou porovnány a zhodnoceny korozně elektrochemické vlastnosti vybraných anebo nových bezolovnatých pájek na bázi cínu s přídavky Ag, Bi, Cu, ln, Sb na základě potenciodynamické cyklické metody s použitím vodného roztoku O,lM NaCl (25°C) a expoziční zkoušky v komoře solné mlhy. Pro zkoušení byly použity tyto pájky: Sn-0,5Ag-56Bi, Sn-2,5Ag-2Bi, Sn-3,lAg-6,l Bi, Sn-3,4Ag-4,8Bi, Sn-3,5Ag-7Bi, Sn-3,5Ag-10Bi, Sn-3,3Ag-4,8Bi; Sn-5Ag-8,6In, Sn-3,3Ag-4,8In, Sn-0,5Ag-5ln, Sn-l ,5Ag-5In; Sn-5Bi-l ln; Sn-l ,5Ag-3Cu-5In, Sn-0,5Ag-3Cu-5In, Sn-0,5Ag-l Cu-5In, Sn-l ,5Ag-l Cu-5ln; Sn-3Ag-2Bi-2Sb, Sn-0,5Ag-l ,5Bi-3Sb, Sn-2,5Ag-l 1,2Bi-5,5In, Sn-2Ag-7,5Bi-5,5ln, Sn-2,9Ag-l,9Bi-2,9In, Sn-2Ag-7,5Bi-0,5Cu; vzorky byly vyrobeny z odlévaných tyčí 010-12mm. Podle hodnot potenciálů bodové koroze (depasivace, repasivace) odolnější jsou pájky obsahující Bi, případně Bi-Ag, naopak méně odolné jsou pájky s indiem. Interpretace výsledků s ohledem na vliv jednotlivých přísad je poměrně obtížná z důvodu jejich nízkého obsahu a rozdělení do různých fází a oblastí, jak potvrzují výsledky metalografického rozboru a mikroanalýzy. Aplikace statistických metod umožnila porovnat vlivy jednotlivých prvků na parametry koroze, např. pro potenciál depasivace byl zjištěn regresní vztah: Ed =. -388  + 18,0.Ag 129 The application of statistical methods made possible the comparison of individua) elements influence on the corrosion parameters. For example, by the means of linear regression model the relation for depassivation potential was calculated (with correlation index I= 0,91 ): Ed = -388 + 18,0.(Ag) + 0,35.(Bi) - 5,0.(Cu) - 11, l.(ln) - 16,3.(Sb), (I) where positive influence have shown Ag and Bi, and negative other element {ln, Sb). Tin as base elements was not incorporated into regression model and the content of alloying elements is given in % wt. The similar relation were found olit for other potentials (E,., Econ Ed-Eco,), e.g. Ei = -4, 1 + 3,9.(Ag) + 1,64.(Bi) - 3,9.(Cu) - 8,34.(ln) - 16,3.(Sb), (I= 0,87) (2) The stated influence of elements is in good agreement with their resistance to pitting corrosion as pure metals by potentiodynamic method. The sequence of pitting resistance was determined: Ag, Bi, Cu, Sb, Sn and In. This order also corresponds to standard potential (E0) values: Ag +0,80V; Bi +0,30V; Cu +o,34V; Sb +0,15V; Pb -0,13V; Sn -0,14V a In -0,34V (HSE). The galvanic corrosionbetween lead-free solders and base metals (Cu, brass) is also possible and could be tested. Theintermetallic phases rich in Ag, Bi and Cu can initiate microgalvanic corrosion of tin base matrix.The example of typical structure of solders (FI: Sn-2Ag-7,5Bi-5,5In) is documented in Fig. 3, where the dendritic grains with differert orientations and heterogeneities are evident. Fig. 3 Microstructure of sol der (F I) after polishing and etching Fig. 4 Surface of solder (El4, 012) after salt spray test, exposition 240 h 4.2 Salt spray test After exposition test the spots, pits and mat surfaces were observed, and on same samples the coloured areas have occurred, Fig. 4. The results of gravimetrie method are compared in Fig. 5, where the positive influence of Ag and /or Bi (solder E3, F25, F42, F47, Q) is indicated but negative effect ofin (see solders: EI 1, F51, F52, F55). 14 �-----------------------, 12 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -,r E 10 s � 8 � 6 E3 E5 E11 E1◄ E19 F1 F9 F17 F23 F25 F34' F36 F41 F◄2 F44 F45 F47 F51 F52 F55 F56 01 lead-fi"ee solder Fig. 5 Corrosion weight losses after salt spray test 133 

Korozně elektrochemické vlastnosti bezolovnatých pájek

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Korozně elektrochemické vlastnosti bezolovnatých pájek

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