Browsing by Author "Zhan, Chau-Jie"

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A new failure mechanism of electromigration by surface diffusion of Sn on Ni and Cu metallization in microbumps
(2018-04-12)
Chang, Yuan-Wei
;
Hu, Chia-chia
;
Peng, Hsin-Ying
;
Liang, Yu-Chun
;
Chen, Chih
Microbumps in three-dimensional integrated circuit now becomes essential technology to reach higher packaging density. However, the small volume of microbumps dramatically changes the characteristics from the flip-chip (FC) solder joints. For a 20 mu m diameter microbump, the cross-section area and the volume are only 1/25 and 1/125 of a 100 mu m diameter FC joint. The small area significantly enlarges the current density although the current crowding effect was reduced at the same time. The small volume of solder can be fully transformed into the intermetallic compounds (IMCs) very easily, and the IMCs are usually stronger under electromigration (EM). These result in the thoroughly change of the EM failure mechanism in microbumps. In this study, microbumps with two different diameter and flip-chip joints were EM tested. A new failure mechanism was found obviously in microbumps, which is the surface diffusion of Sn. Under EM testing, Sn atoms tend to migrate along the surface to the circumference of Ni and Cu metallization to form Ni3Sn4 and Cu3Sn IMCs respectively. When the Sn diffuses away, necking or serious void formation occurs in the solder, which weakens the electrical and mechanical properties of the microbumps. Theoretic calculation indicates that this failure mode will become even significantly for the microbumps with smaller dimensions than the 18 mu m microbumps.
Bump Resistance Change Behavior due to Cu-Sn IMCs Formation with Various Solder Diameters
(2015)
Hsieh, Wan-Lin
;
Lin, Chung-Kuang
;
Zhan, Chau-Jie
;
Huang, Yu-wei
;
Chen, Chih
Theoretical calculation and simulation of FEM were proposed to explain the decline of change in resistance in Cu-Sn microbumps during the electromigration test. The IMC transformation from Cu6Sn5 to Cu3Sn was supposed to be the reason. Being aware that the dimension keeps shrinking, the behavior for various solder diameters was also investigated.
Effect of Joint Shape Controlled by Thermocompression Bonding on the Reliability Performance of 60 mu m-pitch Solder Micro Bump Interconnections
(2014-01-01)
Huang, Yu-Wei
;
Zhan, Chau-Jie
;
Juang, Jing-Ye
;
Lin Yu-Min
;
Huang, Shin-Yi
Three dimensional integration circuits technology has received much attention recently since the demands of functionality and performance in microelectronic packaging for electronic products are rapidly increasing. For high-performance 3D chip stacking, high density interconnections are essential. In the current types of interconnects, solder micro bumps have been widely used and thermocompression bonding process are well adopted to form the connection between bumps. However, the prefect joint contour is difficult to obtain and control by such kind of bonding process in solder micro bump joints. For fine-pitch solder micro bump interconnections, the effect of joint shape on the reliability performances of the solder micro bump joints is not concluded yet till now and needs to be clarified. In this study, the effect of joint shape controlled by thermocompression bonding on the reliability performance of solder micro bump interconnections with a pitch of 60 mu m was discussed. The chip-to-chip test vehicle having more than 4000 solder micro bump interconnections with a bump pitch of 60 mu m was used in this study. A solder micro bump structure of Cu/SnAg having a thickness of 7 mu m/10 mu m was fabricated in both the silicon chip and substrate. To evaluate the effect of joint shape, four types of joint shape were controlled and made. The first type had a conventional shape of micro joint. Compared to the first one joint structure, the second type of joint structure showed the compressed shape. The third type of joint structure was the pillar-like micro joint while the fourth type of joint structure presented a neck shape having the highest joint height among all the joint structures tested. We used the fluxless thermocompression bonding process to form these four types of micro joints. After bonding process, the chip stack was assembled by capillary-type underfill. Reliability tests of temperature cycling test (TCT), high temperature storage (HTS) and electromigration test (EM) were selected to assess the effect of joint shape on the reliability properties of those four types of solder micro bump interconnections. The reliability results presented that all the types of joint structures could pass TCT of 1000 cycles and HTS of 1000 hours but high variation of daisy chain resistance more than 15% would happen in the neck-shape micro joint after TCT. For the neck-shape micro joint, the high variation of daisy chain resistance after TCT resulted from the cracking propagated along the interface of Cu UBM/Cu6Sn5 IMC and across the tin solder. The cracking situation was more serious as compared to the other three tested micro joints. The results of HTS revealed that resistance variation mainly depended on the micro structural evolution within micro joints tested. Electromigration test was conducted under the testing condition of 0.56 A/150 degrees C. A daisy chain structure was adopted. For both the pillar-shape and neck-shape micro joints, Cu UBM consumption and formation of large void were the major microstructure evolutions within the micro interconnections during EM testing. The conpressed-shape showed the longer electromigration lifetime among all the types of micro joints tested.
Electromigration in microbumps with Cu-Sn intermetallic compounds
(2016)
Chu, Yi-Cheng
;
Zhan, Chau-Jie
;
Lin, Han-Wen
;
Huang, Yu-Wei
;
Chen, Chih
The electromigration test of the microbump interconnects with Cu/Cu6Sn5/Cu structure is reported in this study. This Cu6Sn5 intermetallic compound layer was single-crystal like. The diameter of the microbumps in die-to-die stacking was 30 mu m. Test vehicles were applied by a current density of 2.2x10(5) A/cm(2) and settled on a hotplate at 150 degrees C. The resistances of the microbumps were simultaneously monitored by the four point probe during the test procedure. The Cu6Sn5 transformed into Cu3Sn in the early stage and porous Cu3Sn generated in the Cu6Sn5 layer at later stages. The morphology of porous Cu3Sn could be caused by the current direction. The decomposition of Cu6Sn5 into Cu3Sn and Sn occurs during the EM test. The migration of Sn atoms to the periphery of the under-bump-metallization was forced by the current stress, which may be the mechanism of the pore formation with the pore volume of 41.4%. More porous Cu3Sn was found in the cathode end which was an evidence of the EM effect. Finite element analysis was used to do some calculation based on theoretical stoichiometry and microstructures in the test results. The resistivity of porous Cu3Sn structure which was about 30 mu Omega-cm which was three times larger than that of Cu3Sn. The porous Cu3Sn may threaten the reliability issues of microbumps.
Failure mechanism of Cu/SnAg/Ni microbumps in three-dimensional integral circuits under electromigration
(2014)
Lin, Wan-Hsuan
;
Chao, Shu-Han
;
Zhan, Chau-Jie
;
Huang, Yu-wei
;
Chen, Chih
In this study, we use the Cu/SnAgiNi/Cu joint with a thickness of 7 mu m/8 mu m/2 mu m /5 mu m and 7 mu m/16 mu m/2 mu m /5 mu m. The diameter of the solder joint is about 30 mu m and the UBM opening is 18 mu m in diameter with 60 pm pitches. In order to measure the resistance changes, it was fabricated which constitute four probes. By using this method we can measure the resistance changes in microbump excluding the resistance changes in the wiring trace to make it more sensitive to subtle microstructure changes. We investigated the mechanisms of electromigration in microbumps with different stages when resistance increased 20%, 50% and 100% of the initial resistance. Solder joints were stressed with 0.56 A on 150 degrees C hot plate. The average current density is 8 x 10(4) A/cm(2), calculated based on the UBM opening. We ground the samples with 1000, 2000, and 4000 sand paper and then polished them with 1 mu m, 0.3 mu m, and 0.05 mu m Al2O3. We observed their morphologies with SEM and measured their component with EDX. In the bump with electron flow upward, we observed that microbumps were transformed into Cu6Sn5 IMCs and Cu3Sn IMCs joints. In addition, voids were formed at the interface between nickel and solder. We found that both void formation and UBM dissolution were occurred. In the bump with electron flow downward; microbumps were transformed into IMC joints without void formation. To sum up, this study provides a better understanding on the relationship between the behavior of resistance curve and the morphology changes in microbumps.