The effect of adding Ni and Ge microelements on the electromigration resistance of low-Ag based SnAgCu solder

Zhao, Xu; Saka, Masumi; Yamashita, Mitsuo; Hokazono, Hiroaki

doi:10.1007/s00542-012-1577-y

Cited by 20 publications

(7 citation statements)

References 17 publications

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“…The MTFs from this study shows that changing the solder alloy (SAC or SAC-NiGe) did not lead to statistically significant lifetimes for two sets of data: Cu UBM (as shown in Leg 1 and Leg 3), and Cu/Ni UBM (as shown in Leg 4 and Leg 5) (Figure 10), which is contrary to some other findings [11]. Thus, the amount of Ni and Ge additives must not have impacted the migration of Sn to Cu RDL nor the CuSn formation rate.…”

Section: Effect Of Sac Alloycontrasting

confidence: 84%

Electromigration of solder balls for wafer-level packaging with different under bump metallurgy and redistribution layer thickness

Hau-Riege

Keser

Yau

et al. 2013

2013 IEEE 63rd Electronic Components and Technology Conference

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Electromigratio n (EM) has b een cond ucted on lead -free solder balls in wafer-level packages for different redistribution layer (RDL) thicknesses, under bump metallurgy (UBM) schemes, and lead-free solder alloys. Two different types of EM-induced voids were observed at the electron-source side: pancake void between the solder/RDL interface and throughthickness voids in the RDL. In both cases, voids formed at the interface of CuSn intermetallic compound and solder. A Nilayer in the UBM was found to prolong EM lifetime by slowing the diffusion of Sn into the Cu RDL relative to a Cuonly UBM. The absence of UBM led to the shortest EM lifetime due to direct contact of solder to RDL. Also, a thicker RDL extended lifetime proportionately to the decrease in current density and Joule heating at the critical interface. On the other hand, adding Ni and Ge to the SAC alloy did not statistically impact lifetime. IntroductionWafer-level packaging (WLP) achieves a small-form factor and lower cost by eliminating the package substrate, and connecting the die directly to the printed circuit board (PCB) via solder balls.When materials, geometries, and/or structures change, the entire system needs to be re-characterized for board level reliability. These changes can include redistribution layer (RDL) material and thickness, underbump metallurgy (UBM) material and thickness, and solder ball metallurgy. This paper describes the impact of such changes on electromigration. Related papers investigate other aspects of board level reliability including drop shock and temperature cycle [1][2]. Fundamentally, EM is the self-diffusion of metal(s) induced by electric current, which can lead to voiding and interconnect failure, and is an area of major reliability concern for interconnects. Electromigration lifetime quickly degrades with increasing temperature and current density, as described by the well-known Black's Law established in 1969 [3]:

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Section: Effect Of Sac Alloycontrasting

confidence: 84%

Electromigration of solder balls for wafer-level packaging with different under bump metallurgy and redistribution layer thickness

Hau-Riege

Keser

Yau

et al. 2013

2013 IEEE 63rd Electronic Components and Technology Conference

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“…The sample fabrication was similar to that reported in our previous work. 18 The thin-layered Cu/solder/ Cu interconnection structures (the cross-sectional thickness was confirmed to be nearly 3 lm as discussed later) were formed on a printed board (FR4; 15 mm 9 10 mm 9 1.6 mm). The soldering temperature was 473 K, which was approximately 60 K higher than the melting temperature of the testing materials.…”

Section: Methodsmentioning

confidence: 99%

Electromigration Behaviors and Effects of Addition Elements on the Formation of a Bi-rich Layer in Sn58Bi-Based Solders

Zhao

Saka

Muraoka

et al. 2014

Journal of Elec Materi

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This study investigates the electromigration (EM) behaviors and effects of the addition elements on the formation of a Bi-rich layer in Sn58Bi-based solders including Sn58Bi (SB), Sn58Bi0.5Ag (SBA) and Sn58Bi0.5Ag0.1Cu0.07-Ni0.01Ge (SBACNG) solders. The EM tests were conducted at a relatively high temperature of 373 K and at a current density of 30 kA/cm 2 . Although the dominant diffusing atom was Bi, hillocks were formed from Sn more easily than from Bi. The electrical resistance increased in the solder during the current stressing, and the dominant factor was attributed to the formation of a Bi-rich layer. SBACNG solder showed the highest resistance to the formation of a Bi-rich layer, followed by SBA, and then SB solder. The possible addition elements enhancing the resistance of SBACNG solder are Ag, Ni and Ge. The effects of the addition elements are summarized as follows: (1) Ag distributes in the Sn phase as Ag 3 Sn intermetallic compounds (IMCs) that enhance the mechanical strength of Sn; (2) Ni distribution in Bi as Ni-Bi IMCs stabilizes Bi and suppresses its migration; and (3) Ge may distribute in Bi, stabilizing Bi, or Ge exists at the phase boundaries as a precipitate that inhibits Bi migration.

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“…SACN and SACG solder wires (diameter, 100µm) were prepared as testing materials. The sample fabrication was same as that reported in the previous work (5) . A 9µm-thick 2D Cu/solder/Cu layered-interconnection structure was formed on a printed board.…”

Section: Methodsmentioning

confidence: 99%

“…Actually, the current density near the inner corners was much higher than the average value due to the effect of current density concentration caused by structural change and discontinuity of materials (7) . It should be mentioned that the above experimental conditions were same as those used in our previous study on SAC and SACNG solders (5) .…”

Section: Methodsmentioning

confidence: 99%

“…On the other hand, recently, the development of low-Ag (e.g., 1Ag) based Pb-free solders becomes popular for reducing the product cost of solder manufacturing, of which the problem is taken by Ag content. Regarding low-Ag based solders, our previous study has demonstrated that Ni and Ge microelements-added Sn1Ag0.5Cu0.07Ni0.01Ge (SACNG) solder showed a higher EM resistance than Sn1Ag0.5Cu (SAC) solder (5) . However, it is not yet clear whether enhancing the EM resistance of SAC solder is taken by both of Ni and Ge microelements, or taken by single Ni or Ge microelement.…”

Section: Introductionmentioning

confidence: 99%

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Enhancing Electromigration Resistance of Sn1Ag0.5Cu Solder by Adding Single Ni or Ge Microelement

Zhao

Saka

Yamashita

et al. 2013

JMMP

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Our previous study has demonstrated that Ni and Ge microelements-added Sn1Ag0.5Cu0.07Ni0.01Ge (SACNG) solder showed a higher electromigration (EM) resistance than Sn1Ag0.5Cu (SAC) solder. However, it is not yet clear whether enhancing the EM resistance of SAC solder is taken by both of Ni and Ge microelements, or taken by single Ni or Ge microelement. This paper investigates the respective effect of single Ni and Ge microelements on the EM resistance of SAC solder. The EM resistances of Sn1Ag0.5Cu0.07Ni and Sn1Ag0.5Cu0.01Ge solders are experimentally compared via the morphological change, which is quantitatively investigated by measuring the ratio of the total EM-induced hillock volume to the time for current supply in a certain area in a sample. The experimental conditions are same as those used for SAC and SACNG solders in our previous study, and the result is analyzed together with the two reported solders mentioned above. It is concluded that single Ni and Ge microelements separately enhance the EM resistance of SAC solder, and adding of both Ni and Ge microelements together further enhances it. A possible mechanism is proposed to explain the investigated effects.

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The effect of adding Ni and Ge microelements on the electromigration resistance of low-Ag based SnAgCu solder

Cited by 20 publications

References 17 publications

Electromigration of solder balls for wafer-level packaging with different under bump metallurgy and redistribution layer thickness

Electromigration of solder balls for wafer-level packaging with different under bump metallurgy and redistribution layer thickness

Electromigration Behaviors and Effects of Addition Elements on the Formation of a Bi-rich Layer in Sn58Bi-Based Solders

Enhancing Electromigration Resistance of Sn1Ag0.5Cu Solder by Adding Single Ni or Ge Microelement

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