1 Thermal Analysis of Sn, Cu and Ag Nanopowders Pavel Brož, Jiří Sopoušek, Jan Vřešťál Masaryk University, Faculty of Science, Department of Chemistry, Kotlářská 2, , Brno, Czech Republic

2 Masaryk University Campus (Brno-Bohunice)

3 Outline Introduction Introduction - nanoparticles - Netzsch STA 409 CD/3/403/5/G Apparatus (thermal analysis (TA), Knudsen cell MS ) differential scanning calorimetry (heat flow DSC) Studies Studies - Lead free solders (DSC testing, CALPHAD calculations) - Nanopowders of pure metals: Sn, Cu, Ag (DSC, surface effects, CALPHAD calculations) Conclusions Conclusions

4 Melting point depression Introduction  Promising materials for lead free solders Equation and Diagram showing melting point depression in dependence on particle diameter J. Liu (SMIT,Göteborg) Development of Nano Lead Free Solders – Challenges and Future Research Topics, MP0602, Joint Working Group meeting, Brno,2007 Sn - 0,5wt%Cu - 4wt%Ag Nano alloy particles

5 Laboratory of Thermal Analysis (Dept. of Chemistry, Faculty of Science, Masaryk Univ. Brno) Research project: Physical and chemical properties of advanced materials and structures Introduction

6 1…Furnace (0.1 – 20 K min -1, ºC) 2…QMS range amu resolution 0,5amu IE = eV 3…Turbomolecular Pump 4…TA System Controller (TASC) 5..Vacuum Controller, (cca 9·10 -6 mbar) 6…QMS Controller 7..Purification Column (oxygen) (Argon 99,999) Mass Flow Controller (MFC) DSC/KC/QMS Apparatus (Netzsch STA 409 CD/3/403/5/G ) Introduction

7 Lead free solders (Ag-Cu-Sn system) COST MP0602 Advanced Solder Materials for High- Temperature Application- their nature, design, process and control in a multiscale domain Example for Sn-0,7wt%Cu-3,5wt%Ag alloy (bulk) 4… liquid + BCT_A5 + ETA Phase diagram of the Sn - 0,7wt% Cu - Ag system Studies liquid BCT_A5 + Ortho + ETA liquid + Ortho 4 BCT_A5 + Ortho + Cu 6 Sn 5 _P

8 Detection of two phase transitions, the appearance of the first one visible at the beginning of the peak for Sn based material Pure Sn chosen as convenient standard Onset DSC curves for ― solder Ag-Cu-Sn and ― pure Sn Studies Lead free solders (Ag-Cu-Sn system)

9 Sn nanopowder Studies Complications due to existence of oxide layer can be expected (massive oxidation) – melting point temperature of Sn Phase diagram of the Sn - O system 232ºC

10 Studies Sn nanopowder DSC curves for ― ― Sn nanopowder and ― pure Sn cooling heating Flat curve  oxidized sample Sn packed  no particle coagulation, in oxide layer melting point depression Wide low peak indicates solidification of oxidized particles of various distribution Temperature decrease due to nucleation process

11 Studies Sn nanopowder SEM of Sn nanoparticles before heating 100 nm

12 Studies Sn nanopowder Distribution of particle size before heating N particles V particles / nm 3 Diameter of particles / nm

13 Studies Sn nanopowder SEM of Sn nanoparticles after heating 100 nm

14 Studies Sn nanopowder Distribution of particle size after heating N particlesV particles / nm 3 Diameter of particles / nm

15 Studies Cu nanopowder Complications due to existence of oxide layer can be expected but with more optimal stoichiometry than that for Sn (less massive) – melting point temperature of Cu Phase diagram of the Cu - O system 1083ºC

16 Studies Cu nanopowder DSC curves for ― ― Cu nanopowder Flat curve  oxidized sample Cu packed  no particle coagulation, in oxide layer melting point depression bulk melting point ºC cooling heating Particles coagulate  macroscopic object forms having behaviour like bulk material  effect of undercooling Number of small peaks indicates existence of coagulated microsized particles. Higher udercooling indicates absence of nucleation centre. Partial coagulation thanks to instability of oxide layer

17 Studies Ag nanopowder No existence of oxide layer can be expected – melting point temperature of Ag Phase diagram of the Ag - O system 962ºC ~200ºC

18 Studies Ag nanopowder DSC curves for Ag nanopowder Deoxidation, melting and coagulation (sintering) (waiting for analyses) Oxidation – – – … first, second and third run

19 Studies Ag nanopowder DSC curves for ― ― Ag nanopowder cooling heating bulk melting point ºC Partially oxidized sample becomes deoxidized during the heating and particles coagulate Coagulated material  no melting point behaves like bulk depression Behaviour like bulk material  effect of undercooling

20 Even oxygen traces cause formation of massive and compact oxide cover layer which disables coagulation of Sn nanoparticles Concerning Cu nanoparticles the oxidation process is less dramatic. Coagulation in liquid phase is observed. Ag nanoparticles do not undergo oxidation at higher temperatures and coagulation (sintering) takes place. These facts follow from nobility of the elements. Nanopowders are promising materials for preparation of lead free solders applicable at higher temperatures but there are problems with oxygen affinity for currently used basic materials (Sn, Cu) or with coagulation (Ag). Chemical and phase analyses on samples from the measurements are currently performed in order to support results of thermal analyses. Conclusions

21 Acknowledgement: This work has been supported by the Ministry of Education of the Czech Republic under the project MSM Any cooperation is welcome

22 Netzsch STA 409 CD/403/5/ SKIMMER Introduction

23 Construction detail of DSC/KC/QMS instrument. The instrument is not equipped with Skimmer but with a ceramic disc with orifices of various diameters enabling or disabling enter of effusing particles from studied sample Configuration of Knudsen cell and ion source Ion source, 3. shutter, 4. radiation shields, 5. particle beam, 7. sample crucible with a lid, 8. sample, 10. heating shield, 11.thermocouple Introduction Knudsen effusion method coupled with a mass spectrometer

24 STA 409 CD/3/403/5/G - details Iontový zdroj DSC sample carrier Ion source Knudsen cell Introduction