# Presentation: 439891

## KINETICS OF INTERMETALLIC LAYER GROWTH FOR SOLDERED COPPER AND COPPER-NICKEL ALLOYS

**E. K. Ohriner**
**Metals and Ceramics Division**
**Oak Ridge National Laboratory**
**TMS Annual Meeting**
**San Francisco, CA**
**Multicomponent Multiphase Diffusion Symposium**
**In Honor of John E. Morral**
**February 15, 2005**

## INTERMETALLIC LAYER GROWTH FOR SOLDERED COPPER AND COPPER-NICKEL ALLOYS

**Materials and Procedures**
**Intermetallic Growth Kinetics**
**Structures and Chemistry of Intermetallics**
**Discussion of Multicomponent Diffusion**
**Conclusions**

## Base Metal Compositions from 0% to 23% Nickel by Weight

## Solders Include “High-Tin”, High-Lead”, and “Tin-Lead”

| Type | Wt. % | Solidus, °C | Liquidus, °C |
| --- | --- | --- | --- |
| High-tin | 100 Sn | 232 | 232 |
|  | 95Sn-5Sb | 232 | 240 |
|  | 95Sn-5Ag | 221 | 241 |
| Tin-lead | 60Sn-40Pb | 183 | 190 |
|  | 30Sn-70Pb | 183 | 255 |
| High-lead | 10Sn-90Pb | 268 | 299 |
|  | 10Sn-88Pb-2Ag | 268 | 302 |
|  | 5Sn-95Pb | 305 | 312 |

## Copper-Tin Phase Diagram

## Nickel-Tin Phase Diagram

## Scanning Electron Micrograph of Soldered Joints with 95Sn-5Sb Exposed 4000 h at 150°C

- Pure copper				Cu-15Ni-8Sn

- Cu3Sn

- solder

- solder

- Cu6Sn5

- (Cu,Ni)6Sn5

## Scanning Electron Micrograph of Soldered Joints with 95Sn-5Sb Exposed 4000 h at 150°C

- Cu-1.9Be-0.4Co			Cu-9Ni-6Sn

- solder

- solder

- (Cu,Ni)6Sn5

- Cu3Sn

- Cu6Sn5

## Parabolic Layer Growth With 95Sn-5Sb Solder at 150°C

## Effect of Nickel Content on Parabolic Growth Rate Constant

## Effect of Composition on Kinetics of Layer Growth for High-Tin Solders 

**Nickel-free alloys have low and nearly uniform activation energy**
**Alloys with 6 or 9% nickel exhibit high activation energy in the temperature range 150 to 175°C **
**Alloys with 15% nickel or more exhibit high activation energy in the temperature range 175 to 200°C**

## Arrhenius Plots for Layer Growth with 95Sn-5Sb Solder

## Arrhenius Plots for Layer Growth with 95Sn-5Ag Solder

## Arrhenius Plots for Layer Growth with 60Sn-40Pb Solder

## Arrhenius Plots for Layer Growth Cu-15Ni-8Sn with Various Solders

## Tin Depletion In 60Sn-40Pb Solder in Region Adjacent to Cu-15Ni-8Sn After 500 hours at 175°C

- (CuNi)6Sn5

- Cu-15Ni-8Sn

- Pb-rich

- 60Sn-40Pb

## Parabolic Rate Constants for 10Sn-90Pb Solder Vary Little with Base Metal Alloy Composition

## Cu3Sn Observed only in Alloys not Containing Nickel

## Structures and Chemistries of Intermetallic Layers With High-tin Solders

**Cu****3****Sn and Cu****6****Sn****5**** intermetallic layers in nickel-free alloys**
**Only (Cu,Ni)****6****Sn****5**** intermetallic layers in nickel-containing alloys**
**At temperatures of 150°C and 175°C distinct layers corresponding to approx. (Cu****4****Ni****2****)**** ****Sn****5**** adjacent to base metal and (Cu****5****Ni)**** ****Sn****5**** adjacent to the solder**

## Composition Profile for Cu-15Ni-8Sn with 95Sn-5Sb Shows Two Regions of (Cu,Ni)6Sn5

## Composition Profile for Cu-9Ni-6Sn with 95Sn-5Sb Shows Two Regions of (Cu,Ni)6Sn5

## Compositions of Intermetallic for Cu-15Ni-8 Sn Base Metal (1500 hrs)

## Compositions of Intermetallic for 95Sn-5Sb Solder

## Compositions of Intermetallic Layer

## Discussion of Multicomponent Diffusion

**At higher temperatures the intermetallic formation can be treated as a pseudo-binary system when there is no segregation of nickel and copper**
**At temperatures where there are distinct regions on high- and low-nickel content (Cu,Ni)****6****Sn****5 ****the system can only be treated as a ternary**

## Ternary Effects With Segregation in the Intermetallic (Cu,Ni)6Sn5

**Kinetics of layer growth are controlled by rate limiting diffusion through nickel-rich intermetallic**
**In binary diffusion couple kinetics of compound growth in one phase layer does not effect others**
**Layer growth of the lower-nickel content intermetallic layer is limited by the requirement of mass conservation**
**Low activation energy in temperature range of 150 to 175° C associated with presence of nickel-rich intermetallic**
**“****Uphill diffusion” of copper**

## Effects of Crystal Structure

**Ni****3****Sn****2**** has hexagonal **
**  ****B8****2**** structure with **
**  ****structural vacancies **
**  ****at nickel sites**
**Cu****55****Sn****45**** analogous **
**  ****hexagonal B8****1**** structure**
**  ****with copper atoms at **
**  ****these same sites**
**Both phases show **
**  ****ordering at low **
**  ****temperatures**

## Discussion of Crystal Structure, Ternary Diffusion, and Layer Growth

**Nickel-rich intermetallic has lower tin content which is consistent with lower tin content in the binary Ni-Sn intermetallic as compared to the Cu-Sn intermetallic**
**Nickel-rich intermetallic is formed adjacent to the base metal consistent with the tin diffusion gradient**
**Lower diffusion rates in nickel-rich intermetallic are consistent with reduced vacancy content**
**The initial increase in layer growth rate with small additions of nickel does have a simple explanation on the basis of crystal structure**

## Discussion of Quarternary Diffusion and Layer Growth

**Increased Rate of Layer Growth for Tin-Lead Solders as compared to High-Tin solders**
**Low levels (about 0.2) of Pb detected in intermetallics**
**	****formed with high-lead solders at 225°C****	**
**Low levels of Pb not detected but likely present in**
**	****intermetallics formed with tin-lead solders at 175°C**
**Low levels of Pb may effect ordering, segregation of nickel and resulting defect structures resulting in the observed increased rate of intermetallic formation in Cu-15Ni-8Sn **
**Ag and Sb in High-Tin Solders have little effect on layer growth**
**Observed addition of 2% Ag to 10Sn-90Pb solder reduces intermetallic layer growth in nickel-containing alloys**

## CONCLUSIONS

**Intermetallic layer growth has parabolic kinetics and depends on base metal and solder compositions**
**For low-tin content solders intermetallic layer growth is controlled by tin diffusion through the solder and is sensitive to solder composition**
**For high-tin and eutectic solder intermetallic layer growth is very sensitive to nickel content of the copper alloy**

## CONCLUSIONS (continued)

**Intermetallic layer growth for these solders show a maximum growth rate at 6 to 9 % nickel, as much a 35 times greater than other compositions**
**Reduced layer growth rates are associated with two distinct layers of (CuNi)****6****Sn****5**** with differing nickel contents**
**At low nickel contents and/or at increased temperature the layer growth can be treated as a pseudo-binary**
**Segregation within the (CuNi)****6****Sn****5**** requires that the layer growth be treated as a ternary diffusion**