Lead free solders for aerospace applications
The factors controlling the reliability of Pb-free solders when subject to thermomechanical regimes relevant to the harsh aerospace environment have been studied. Ball grid array (BGAs) typical of microelectronic devices have been manufactured in-house and subjected to isothermal ageing and thermal...
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| Format: | Thesis |
| Language: | English |
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2010
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| _version_ | 1797079598743158784 |
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| author | Farinha Marques, VM |
| author2 | Grant, P |
| author_facet | Grant, P Farinha Marques, VM |
| author_sort | Farinha Marques, VM |
| collection | OXFORD |
| description | The factors controlling the reliability of Pb-free solders when subject to thermomechanical regimes relevant to the harsh aerospace environment have been studied. Ball grid array (BGAs) typical of microelectronic devices have been manufactured in-house and subjected to isothermal ageing and thermal cycling. The BGAs comprised both Cu and Ni-Au metallizations, Pb-free Sn-Ag-Cu 400 and 600μm solder balls, FR4 and Al<sub>2</sub>O<sub>3</sub> boards, and included circuits to measure resistance changes due to damage in the joints during thermal cycling. Microstructural evolution within the solders balls and complex interfacial reactions were studied in all configurations using various types of electron microscopy. The mechanical properties of the different phases formed within solder joints were studied using nanoindentation at room and elevated temperatures up to 175°C for the first time. Intermetallic compounds (IMCs) were stiff, hard and brittle with very low creep rates, while the softer primary Sn, eutectic regions and Cu metallization readily underwent creep. Two-dimensional finite element analysis (FEA) of nanoindentation was used to understand better the physical meaning of nanoindentation creep data. Reliability experiments comprised both thermal cycling and FEA of BGAs. The difference in coefficient of thermal expansion (CTE) in the BGA materials caused interfacial fatigue damage in the solder joints, which was detected primarily at the solder/metallization interface of the outermost, most strained solder joint. Accumulated creep strain per cycle at this interface was evaluated using 3D FEA of the stress-strain state of the BGA and results calibrated against experimental BGA mean lifetimes using the Coffin-Mason relationship. Nanoindentation combined with FEA has been shown to be a viable route for the rapid assessment of creep performance and lifetime in lead-free solders under aerospace thermal cycles. |
| first_indexed | 2024-03-07T00:48:15Z |
| format | Thesis |
| id | oxford-uuid:85707054-bc46-44f3-b9c6-9fd29358ad25 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-07T00:48:15Z |
| publishDate | 2010 |
| record_format | dspace |
| spelling | oxford-uuid:85707054-bc46-44f3-b9c6-9fd29358ad252022-03-26T21:57:37ZLead free solders for aerospace applicationsThesishttp://purl.org/coar/resource_type/c_db06uuid:85707054-bc46-44f3-b9c6-9fd29358ad25MetallurgyElectronicsMaterials modellingAlloysStructure of interfacesPhysical metallurgyFatigueMaterials processingMicroscopy and microanalysisEnglishOxford University Research Archive - Valet2010Farinha Marques, VMGrant, PJohnston, CThe factors controlling the reliability of Pb-free solders when subject to thermomechanical regimes relevant to the harsh aerospace environment have been studied. Ball grid array (BGAs) typical of microelectronic devices have been manufactured in-house and subjected to isothermal ageing and thermal cycling. The BGAs comprised both Cu and Ni-Au metallizations, Pb-free Sn-Ag-Cu 400 and 600μm solder balls, FR4 and Al<sub>2</sub>O<sub>3</sub> boards, and included circuits to measure resistance changes due to damage in the joints during thermal cycling. Microstructural evolution within the solders balls and complex interfacial reactions were studied in all configurations using various types of electron microscopy. The mechanical properties of the different phases formed within solder joints were studied using nanoindentation at room and elevated temperatures up to 175°C for the first time. Intermetallic compounds (IMCs) were stiff, hard and brittle with very low creep rates, while the softer primary Sn, eutectic regions and Cu metallization readily underwent creep. Two-dimensional finite element analysis (FEA) of nanoindentation was used to understand better the physical meaning of nanoindentation creep data. Reliability experiments comprised both thermal cycling and FEA of BGAs. The difference in coefficient of thermal expansion (CTE) in the BGA materials caused interfacial fatigue damage in the solder joints, which was detected primarily at the solder/metallization interface of the outermost, most strained solder joint. Accumulated creep strain per cycle at this interface was evaluated using 3D FEA of the stress-strain state of the BGA and results calibrated against experimental BGA mean lifetimes using the Coffin-Mason relationship. Nanoindentation combined with FEA has been shown to be a viable route for the rapid assessment of creep performance and lifetime in lead-free solders under aerospace thermal cycles. |
| spellingShingle | Metallurgy Electronics Materials modelling Alloys Structure of interfaces Physical metallurgy Fatigue Materials processing Microscopy and microanalysis Farinha Marques, VM Lead free solders for aerospace applications |
| title | Lead free solders for aerospace applications |
| title_full | Lead free solders for aerospace applications |
| title_fullStr | Lead free solders for aerospace applications |
| title_full_unstemmed | Lead free solders for aerospace applications |
| title_short | Lead free solders for aerospace applications |
| title_sort | lead free solders for aerospace applications |
| topic | Metallurgy Electronics Materials modelling Alloys Structure of interfaces Physical metallurgy Fatigue Materials processing Microscopy and microanalysis |
| work_keys_str_mv | AT farinhamarquesvm leadfreesoldersforaerospaceapplications |