Sn Deposit Microstructures Depending on the Deposition

Current Density

Kil-Won Moon, Soo-Kil Kim, Maureen Williams, and William Boettinger

Metallurgy DivisionNIST

Gaithersburg, MD 20899

Contents

• Background• Experiments• Results & Discussion

– Grain size – Defect (Hillock) density– Microstructure: SEM and FIB – Crystallographic: XRD

• Summary

2

Relation of Electrodeposit Microstructures to Deposition Conditions

• Grain sizes will be finer when;– higher current density– higher polarization (voltage) – more additives– less metal ion concentration – lower temperature– slower rotating speed

• Equiaxed grains grow to relatively larger sizes than columnar grains do.

• Dendritic-type grains result from mass-transport-controlled growth

3

Objectives

• Investigating the effect of deposition current density on deposit structures– on the competition between nucleation

rate and deposit growth rate– potential operating mechanism to reduce

the deposit strain energy– finer, equiaxed, and random oriented

grain

4

5

Electrodeposition

• Cu substrate• 99.999% Sn sheet anode• 200 rpm rotating cathode• Current density range: 30

- 200 mA/cm2 @ 25 ºC• Commercial bright

methanesulfonate (MSA) with D/I water (18.3 MΩ-cm)

Results

6

45

55

65

75

85

95

105

0.01

0.02

0.03

0.04

0.05

0.06

0.07

20 70 120 170 220

Efficy (%)

mg/cm^2 sec

Effic

y (%

)

mg/cm

^2 sec

mA/cm^2

Current Efficiency & Deposit Rate depending on the Current Density

7

0.25

0.45

0.65

0.85

1.05

1.25

1.45

1.65

1.85

20 70 120 170 220

mA/cm^2

um

Current Density vs. Grain Size

8

Grain Shapes Depending on the Deposition Current Density

9

30 mA/cm2 60 mA/cm2 90 mA/cm2

120 mA/cm2 150 mA/cm2 200 mA/cm2

Cross Section Microstructures: FIB

10

30 mA/cm2

90 mA/cm2 200 mA/cm2

0

1000

2000

3000

4000

5000

6000

20 70 120 170 220

mA/cm^2

# /

cm

^2

Hillock Density Depending on Deposit Current Densities

11

Hillocks Depending on the Deposition Current Density

12

30 mA/cm2 60 mA/cm2 90 mA/cm2

120 mA/cm2 150 mA/cm2 200 mA/cm2

02 03 04 05 06 07 08 09 001 011 021 031 041

)ged( atehT-owT

5k2

0k5

5k7

Inte

nsity

(Cou

nts)

0

XRD Results Depending on Deposition Current Densities

13

0

2

4

6

8

10

12

30 60 90 120 150 180 210

011121031112321420312013332123303323143532512

PF

Current Density

Preference Factor Changed depending on the Deposition Current Density

14

PFhkl =Ihkl

Ir,hkl1n

∑ IhklIr,hkl

Stereograph with Preference Factors of Sn Deposits

15

texture determined by EBSD

slip plane closest packed

plane

twin basal plane

• At low stress and long time, stress relief occurs by creep processes

• At a high stress and short times, plastic deformation (slip /twinning) might be important for stress relief mechanisms

• Changes of PF might correspond to the plastic deformation

Summary• The effect of deposition current density from 30 to 200

mA /cm2 was investigated. • Below 90 mA/cm2, hillocks (a low aspect ratio variant of

whiskers) were formed; however, above 90 mA/cm2, no surface defects were observed on the Sn electrodeposits.

• As the current density increased;– the columnar grain diameter decreased, – above 90 mA/cm2, the plating efficiency dropped from

99 % to 54 %, and the grain boundary shape changed from wavy to faceted.

– the most preferred orientation was changed from Sn (332) to Sn (112)

16