Tests - Results Sample Preparation The solder joints tested in this study were composed of a Sn-Ag-Cu alloy of Sn-3.0Ag-0.5Cu wt.% (SAC 305). To construct these polycrystalline specimens, Cu blocks were cut to dimensions of 11mm x 13mm x 6mm, and their broad faces were polished to 4000 grit. After the blocks are soldered they are cut into sheets. These sheets are then polished with various slurries to produce a damage free surface suitable for examination under a Polarized Light Microscope (PLM) or Electron Backscatter Diffraction (EBSD) . Abstract The restriction of toxic leaded solders by recent policies has made Sn-Ag-Cu alloys the prevailing replacement for solder systems. However, the electromigration damage they must withstand poses a major reliability issue. In order to quantify the electromigration damage a simple and efficient testing apparatus was built to conduct electromigration tests under desirable conditions. Joule heating, temperature gradients, and current crowding in the solder joints contribute and complicate the analysis of electromigration. Thus, this project attempted to build an electromigration testing apparatus that provided constant temperatures and current densities through a solder sample. Results showed that porcelain mounts were great electrical insulators but had a low thermal conductivity which retained heat in the system, proving detrimental to the experiment. Glass on the other hand proved to be an adequate base for the mount since it did not retain heat in the system as much. We expect future electromigration tests will utilize glass mounts with three mechanically braced Cu heat sinks. Acknowledgments • J.W. Morris, Jr., Ph.D., & Xioranny Linares – Mentors • Rhonda La Grande, Aaron Chan, & Linda Dada – Lab partners • Cal NERDS Staff and Scholars – Support & Encouragement • Cal NERDS & UC Leads program – Funding Tests - Results • Prepared samples are connected to the anode and cathode using silver paste. • Current applied to the system varies between 20A – 25A, in order to achieve a current density of 11.5 kAcm -2 across the sample. • The sample is placed in an oven until thermal equilibrium is sustained at about 100°C. • Constant current is applied for 2 days. Conclusions • Although both the porcelain tile and glass have a low thermal conductivity, using a glass mount proved a lot more beneficial because it dissipates heat a lot faster than the traditional ceramic. • Leveled heat sinks are vital for support and help prevent the sample from deformation. • Mechanically bracing the system alleviates stresses on the JB Weld epoxy and extends the apparatuses’ lifetime. Alejandro Cota, Xioranny Linares, Rhonda La Grande, Aaron Chan, J.W. Morris, Jr., Ph. D. Department of Materials Science and Engineering, University of California, Berkeley, CA 94720 References Linares, Xioranny, et al. 2013. The Influence of Sn Orientation on Intermetallic Compound Evolution in Idealized SnAgCu 305 Interconnects: An Electron Backscatter Diffraction Study of Electromigration>. Accessed 2013 Aug 2. Figure 2: Simple schematic of testing a sample. Figure 6: Current design uses a glass base, but lacks mechanical braces on cathode and anode. For further information Please contact [email protected] or visit: http://www.mse.berkeley.edu/groups/morris/Research.html. Alejandro Cota is a Mechanical & Materials Science Engineering major at UC Berkeley. Step 1: Polish block faces, coat with flux, and match together while separated by 250μm spacers. MAKING A TESTING APPARATUS FOR C ONDUCTING ELECTROMIGRATION TESTS Background Many efforts to study electromigration in the past have proven unsuccessful due to the lack of a competent electromigration testing apparatus. The goal of this experiment is to build and improve a test apparatus capable of upholding a constant temperature, and constant current density during the length of the sample testing period. Achieving these constant conditions allow us to isolate and study the effects of specific electromigration parameters, such as the effects of varying current densities. Future Work Figure 7: Ideal Electromigration testing apparatus with a glass base. e - j e Z D C J Sn kT Sn Cu EM Sn Cu Sn Cu * , , , C Cu,Sn : Atomic density of Cu in Sn D Cu,Sn : Diffusivity of Cu in Sn Z* : Effective charge e : Electron charge ρ : Resistivity j : Current density k : Boltzmann Constant T : Temperature Electromigration Equation Three types of drill bits can be successfully used on glass: tungsten carbide spear-tipped drill bits, diamond-tipped drill bits, or diamond-coated drill bits. Obtain appropriate drill bit to build five testing apparatuses, all with mechanical braces and Cu heat sinks. Use an Infrared Camera to evaluate the thermal gradient of the entire apparatus including the specimen. Step 2: The composite block was placed in molten Sn-Ag-Cu at 375°C for 30 seconds. Step 3: Quickly quench in ice- water until block cools. Figure 4: New and modified testing apparatus uses porcelain tile base. Figure 5: Five samples were tested using the new apparatus. Figure 3: Glass base, cathode and anode, missing a failed idealized Cu||Sn||Cu interconnect due to failure after running the sample through the experimental procedure. • Glass base electrically insulates the experiment from the oven. • Both anode and cathode use a Cu heat sink. • Samples failed due to uneven heat distribution. • An additional Cu heat sink must be introduced to the system. • JB Weld epoxy becomes brittle causing cathode and anode to fall off. • A mechanical brace would reduce stresses on JB Weld. Step 4: Once cooled, all blocks were cut into sheets roughly 500μm thick. Figure 1: Sample preparation diagram. • Porcelain base electrically insulates the experiment from the oven. • Applied a third Cu heat sink. • Machined a bronze-coated sheet metal brace for both anode and cathode. • Samples deformed as they softened from high heat and unleveled heat sinks. • Extracting samples required an additional 4-6 hours compared to glass base due to porcelain’s high heat insulation and low thermal conductivity. • Porcelain tiles acted as a radiant heat source and generated unwanted thermal profiles throughout the system. • Cu heat sinks were made level. Twice as much JB Weld epoxy aids in heat distribution away from the sample. • Design proved successful. Addition of mechanical brace will further improve the design. • Samples survived the two day experimental procedure, and have been extracted for further analysis.
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Tests - Results
Sample Preparation The solder joints tested in this study were composed of a Sn-Ag-Cu alloy of Sn-3.0Ag-0.5Cu wt.% (SAC 305). To construct these polycrystalline specimens, Cu blocks were cut to dimensions of 11mm x 13mm x 6mm, and their broad faces were polished to 4000 grit. After the blocks are soldered they are cut into sheets. These sheets are then polished with various slurries to produce a damage free surface suitable for examination under a Polarized Light Microscope (PLM) or Electron Backscatter Diffraction (EBSD) .
Abstract The restriction of toxic leaded solders by recent policies has made Sn-Ag-Cu alloys the prevailing replacement for solder systems. However, the electromigration damage they must withstand poses a major reliability issue. In order to quantify the electromigration damage a simple and efficient testing apparatus was built to conduct electromigration tests under desirable conditions. Joule heating, temperature gradients, and current crowding in the solder joints contribute and complicate the analysis of electromigration. Thus, this project attempted to build an electromigration testing apparatus that provided constant temperatures and current densities through a solder sample. Results showed that porcelain mounts were great electrical insulators but had a low thermal conductivity which retained heat in the system, proving detrimental to the experiment. Glass on the other hand proved to be an adequate base for the mount since it did not retain heat in the system as much. We expect future electromigration tests will utilize glass mounts with three mechanically braced Cu heat sinks.
Acknowledgments • J.W. Morris, Jr., Ph.D., & Xioranny Linares – Mentors
• Rhonda La Grande, Aaron Chan, & Linda Dada – Lab partners
• Cal NERDS Staff and Scholars – Support & Encouragement
• Cal NERDS & UC Leads program – Funding
Tests - Results • Prepared samples are connected to the anode and cathode using
silver paste. • Current applied to the system varies between 20A – 25A, in
order to achieve a current density of 11.5 kAcm-2 across the sample.
• The sample is placed in an oven until thermal equilibrium is sustained at about 100°C.
• Constant current is applied for 2 days.
Conclusions • Although both the porcelain tile and glass have a low
thermal conductivity, using a glass mount proved a lot more beneficial because it dissipates heat a lot faster than the traditional ceramic.
• Leveled heat sinks are vital for support and help prevent the sample from deformation.
• Mechanically bracing the system alleviates stresses on the JB Weld epoxy and extends the apparatuses’ lifetime.
Alejandro Cota, Xioranny Linares, Rhonda La Grande, Aaron Chan, J.W. Morris, Jr., Ph. D. Department of Materials Science and Engineering, University of California, Berkeley, CA 94720
References Linares, Xioranny, et al. 2013. The Influence of Sn Orientation on Intermetallic
Compound Evolution in Idealized SnAgCu 305 Interconnects: An Electron
Backscatter Diffraction Study of Electromigration>. Accessed 2013 Aug 2.
Figure 2: Simple schematic of testing a sample.
Figure 6: Current design uses a glass base, but lacks mechanical braces on cathode and anode.
For further information Please contact [email protected] or visit:
http://www.mse.berkeley.edu/groups/morris/Research.html. Alejandro Cota
is a Mechanical & Materials Science Engineering major at UC Berkeley.
Step 1: Polish block faces, coat with flux, and match together while separated by 250μm spacers.
MAKING A TESTING APPARATUS FOR CONDUCTING ELECTROMIGRATION TESTS
Background Many efforts to study electromigration in the past have proven unsuccessful due to the lack of a competent electromigration testing apparatus. The goal of this experiment is to build and improve a test apparatus capable of upholding a constant temperature, and constant current density during the length of the sample testing period. Achieving these constant conditions allow us to isolate and study the effects of specific electromigration parameters, such as the effects of varying current densities.
Future Work
Figure 7: Ideal Electromigration testing apparatus with a glass base.
e-
jeZD
CJ SnkTSnCu
EM
SnCu
SnCu *
,,
,
CCu,Sn : Atomic density of Cu in Sn DCu,Sn : Diffusivity of Cu in Sn Z* : Effective charge e : Electron charge ρ : Resistivity j : Current density k : Boltzmann Constant T : Temperature
Electromigration Equation
Three types of drill bits can be successfully used on glass: tungsten carbide spear-tipped drill bits, diamond-tipped drill bits, or diamond-coated drill bits.
Obtain appropriate drill bit to build five testing apparatuses, all with mechanical braces and Cu heat sinks.
Use an Infrared Camera to evaluate the thermal gradient of the entire apparatus including the specimen.
Step 2: The composite block was placed in molten Sn-Ag-Cu at 375°C for 30 seconds.
Step 3: Quickly quench in ice-water until block cools.
Figure 4: New and modified testing apparatus uses porcelain tile base.
Figure 5: Five samples were tested using the new apparatus.
Figure 3: Glass base, cathode and anode, missing a failed idealized Cu||Sn||Cu interconnect due to failure
after running the sample through the experimental procedure.
• Glass base electrically insulates the experiment from the oven.
• Both anode and cathode use a Cu heat sink.
• Samples failed due to uneven heat distribution.
• An additional Cu heat sink must be introduced to the system.
• JB Weld epoxy becomes brittle causing cathode and anode to fall off.
• A mechanical brace would reduce stresses on JB Weld.
Step 4: Once cooled, all blocks were cut into sheets roughly 500μm thick.
Figure 1: Sample preparation diagram.
• Porcelain base electrically insulates the experiment from the oven.
• Applied a third Cu heat sink.
• Machined a bronze-coated sheet metal brace for both anode and cathode.
• Samples deformed as they softened from high heat and unleveled heat sinks.
• Extracting samples required an additional 4-6 hours compared to glass base due to porcelain’s high heat insulation and low thermal conductivity.
• Porcelain tiles acted as a radiant heat source and generated unwanted thermal profiles throughout the system.
• Cu heat sinks were made level. Twice as much JB Weld epoxy aids in heat distribution away from the sample.
• Design proved successful. Addition of mechanical brace will
further improve the design.
• Samples survived the two day experimental procedure, and have been extracted for further analysis.
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