SLID bonding for thermal interfaces - IMAPS IV/IV-2.pdfTechnology for a better society Outline Background and motivation – The HTPEP project – Solid-Liquid Inter-Diffusion (SLID)

Technology for a better society

SLID bonding for thermal interfaces

Thermal performance


Outline

Background and motivation

– The HTPEP project

– Solid-Liquid Inter-Diffusion (SLID)

– Au-Sn SLID

– Cu-Sn SLID

– Reliability and bond integrity

– Alternative HT TIM technologies

comparison

Case study

– HT (>200 °C) power controller

– Stationary performance

Conclusions

Acknowledgements


The HTPEP project – objectives

Develop a reliable packaging technology for power electronic systems

operating at temperatures up to 250 °C.

– Know-how on SiC component technology.

– Processes for packaging of SiC and passive

components for HT application.

– Knowledge on failure mechanisms

occurring in interconnects and

materials during HT operation.

– Demonstrator.


www.bxpl.com

Application

• Demonstrate the packaging technology in a

power controller for a brushless DC motor

for downhole applications.

• Packaging solution should enable the

controller to operate for at least 6 months at

an ambient temperature of 200 °C and a

junction temperature of 250 °C.


Die attach and Thermal interface materials (TIM)

Typical components – Die attach: Fix components to substrate. Low thermal resistance. Electrically conductive.

– TIM 1: Fix substrate mechanically to a support structure. Ensure low thermal resistance.

– TIM 2: Low thermal resistance between support structure and external housing.

TIM 1

TIM 2

Die attach


Substrate technology

Silicon nitride, Si3N4

– Thermal conductivity: up to 90 W/mK

– CTE: ~3.2 ppm/K @ 250-300 °C

– Flexural strength: 750-900 MPa

– Durable and robust

during thermal cycling

Cu conductors

SiC BJT


Die attach/interconnect technology: SLID

SLID – Solid-Liquid Inter-Diffusion

Creates a bond that is stable at higher temperature than the initial

process temperature

– Au-Sn SLID: up to 500 °C

– Cu-Sn SLID: up to 670 °C

Au-Sn SLID – As bonded Cu-Sn SLID – As bonded

~10 µm


Solid-Liquid Inter-Diffusion (SLID)

Uses a two-metal system: – One HT and one LT melting metal.

– At process temp. above the lower

melting point. Inter-diffusion

causes IMCs to form.

– E.g.: Cu-Sn SLID, where a

Cu – Cu3Sn – Cu bond is created.

This bond is stable up to 676 °C

(process temp of 250-300 °C).

Before

bonding

at RT

During

bonding

at TB

After

bonding

at TB

Hi Tm

Hi Tm

Liquid

Thin low Tm

interlayer

sandwished

between high Tm

joint parts

Melting of low Tm

interlayer and

interdiffusion

Homogeneous

joint / IMC

formation where

solidification is

isothermal

Hi Tm

Hi Tm

Lo Tm

Hi Tm

Hi Tm

IMC


Okamoto. H.. Au-sn (Gold-Tin). J. Phase Equilib. Diffus.. 2007. 28(5): p. 490-490.

Liu. H.S.. C.L. Liu. K. Ishida. and Z.P. Jin. Thermodynamic modeling of the

Au-In-Sn system. J. Electron. Mater.. 2003. 32(11): p. 1290-1296.

Au-Sn SLID

Advantages:

– HT stability and reliability.

– Oxidation resistant.

– Relatively low processing temp.

– Mechanically robust.

– Au has three functions:

– Bonding.

– Diffusion barrier.

– CTE mismatch absorption.

Disadvantages:

– Novel system – relatively

unexplored.

– High cost.


Die attach processing – Bond Characterization

90 at% Au10 at%

Sn

ζ

Au

100 at% Au

90 at% Au10 at% Sn

The bond interface is a uniform Au-rich phase. identified by EDS

to be the ζ phase (with a melting point of 522 °C).

T.A. Tollefsen et al.. "Au-Sn SLID bonding for high temperature applications". HiTEN 2011


Reliability testing – Die shear strength

Superb bond strength: >78 MPa.

0

20

40

60

80

100

Die

sh

ea

r s

tre

ng

th (

MP

a)

Unaged500 cycles (0-200°C, 10°C/min)1000 cycles (0-200°C, 10°C/min)Aged (6 months, 250 °C)

X-section

ζ

Au

Au

NiP

Cu

SiC

Hotplate

Substrate

Chip

Clamp

MIL-STD-883H

T.A. Tollefsen et al.. "Au-Sn SLID bonding for high temperature applications". HiTEN 2011


HT TIM comparison chart

Name Material base Effective thermal

conductivity

(W/m·K)

Degradation

temperature

(°C)

Outgassing

@ 300°C

Expected final

layer thickness

(µm)

Estimated thermal

resistance

(mm2·K/W)

Au-Sn SLID Gold and tin 60 Tm: 522 - ~10 ~0.17

Cu-Sn SLID Copper and tin 104 Tm: 676 - <10 <0.10

Aptiv® 1000 Semi-crystalline polymer

film

0.25 200 Low 8 32

Aptiv® 1102 Semi-crystalline polymer

film filled with talc

0.43

(0.911)

200 Low 12 28

Duralco 4703 Epoxy with Al2O3 powder 2.55 330 0.33% ~50 ~20

Epo-tek® 353ND Epoxy 0.10-0.15 412 0.87% ~4-6 ~40

Epo-tek® H74 Epoxy 1.25 425 0.80% >502 >40

Epo-tek® H77 Epoxy 0.66 405 1.47 % >502 >76

Resbond 906 Silicate with magnesia 5.6 1650 Low ~100 ~17.9

Resbond 931 Silicate with graphite 8 3000 - ~100 ~12.5

Resbond 954 Silicate with stainless >2 1200 Low ~100 ~50

Staystik® 581 Silver >3 300 Low 38 12.7

Staystik® 682 Aluminum nitride >1 300 Low 38 38

1 In-plane 2 Particle size


Case study

Power controller for a brushless DC motor for downhole applications.

Motor drive key features:

– Half bridge topology

– Switching capability per phase

– 400 V, 5 A

– May be combined for 3-phase

– 3.1 kVA total power delivery

Power card key specs:

– Up to 250 °C

– 6 month operation


Power card – Parts

SiC BJT

SiC Schottky diode

Multilayer capacitors

Ceramic resistors Si3N4

substrate

Cu / Ni / Au

(Back side)

34 mm

20 mm


Power card – TIM

Au-Sn SLID

Au-Ge solder

Duralco 4703

SLID or adhesive

(Back side)


Power card – Dissipation

10 W

10 W

700 mW

10 mW

350 mW 900 mW

7 mW 35 mW

(Ptot ≈ 22 W) (Pwire bonds: typically 2 – 13 mW / bond)


Case study – BC

h = 500 W/m2K

h = 100 W/m2K

TIM: Graphite-oil

h = 100 W/m2K


Case study – Temperature distribution


Case Study – Temperature distribution

P = 10 W

P = 20 W

Cu-Sn SLID Duraclo 4703


Case study – Temperature drop


Case study – Temperature drop – 10 W

SiC BJT Ambient

SiC BJT

∆T ≈ 1 °C

Die attach (Au-Sn SLID)

∆T < 0.5 °C

Substrate

∆T ≈ 8 °C & 7 °C

TIM: Power card

∆T ≈ <0.5 °C & 5 °C Cu-Sn SLID

Duralco 4703

TIM: Graphite-oil

∆T < 0.5 °C Base plate

∆T ≈ 2-3 °C

Shell

∆T < 0.5 °C

Ambient

∆T ≈ 5 °C


Case study – Temperature drop – 20 W

SiC BJT Ambient

Substrate

∆T ≈ 15 °C & 15 °C

TIM – Power card

∆T ≈ <0.5 °C & 14 °C

Ambient

∆T ≈ 9 °C


Case study – Derating of TIM specs


Case study – Temperature profile


Potential life time

• A small reduction in operation temperature may provide a significant

improvement in reliability and lifetime of a device.

M. Watts "Design Considerations for High Temperature Hybrid Manufacturability". HiTEC 2008


Concluding remarks

• SLID bonding show great TIM potential for high reliability, performance and

temperature applications. Primarily due to:

– Low thermal resistance.

– Uniform joint (low "contact resistance").

– HT stability and reliability

– Mechanically robust

• Further investigations of SLID bonding as a TIM is needed.

– Applicability for larger and more irregular surfaces.


Acknowledgements

• The HTPEP project and its sponsors and partners

• My co-authors

– Torleif A. Tollefsen

– Olav Storstrøm


Thanks for your attention!

HTPEP

Andreas Larsson

SINTEF ICT. Instrumentation dept.

[email protected]

Documents

SLID bonding for thermal interfaces - IMAPS IV/IV-2.pdfTechnology for a better society Outline Background and motivation – The HTPEP project – Solid-Liquid Inter-Diffusion (SLID)