SiC Press-Pack Power ModulesDesign, Implementation and Testing

Conclusion

Jose Ortiz GonzalezResearch Assistant, University of Warwick

Layi Alatise, Li Ran, Phil Mawby, Attahir Aliyu, Alberto Castellazzi, Pushpa Rajaguru, Chris Bailey,

Adriá Junyent Ferré, Sam Aldhaher and Paul Mitcheson

Contents

• Cross-cutting research

• Project description

• Power module packaging

• SiC Schottky diode Press-Pack Prototype

• Characterisation of the Prototype

• Finite Element Analysis

• Power Cycling and Thermal Impedance

• Multiple Chip Packaging

• Publications

Cross-Cutting Research

Advanced Materials &

Devices

Components & Packaging

ConvertersElectric Drives and

Systems Integration

• Cross-cutting research connects the individual themes funded by the centre

• The project is addresses a challenge that requires research cutting across the

different themes.

Cross-Cutting Research

Research Team

University Partner Personnel

GreenwichProf. Chris Bailey

Dr Pushpa Rajaguru

ImperialProf. Paul Mitcheson

Dr Sam Aldhaher

Dr A Junyent-Ferre

NottinghamDr Alberto Castellazzi

Dr Attahir Aliyu

Warwick

Dr O Alatise

Mr J Ortiz Gonzalez

Prof Li Ran

Prof Phil Mawby

Project Aims and Objectives

● To develop and demonstrate SiC Power Devices in

Press-Pack

● Evaluate the Reliability and Performance of SiC in Press-

Pack

● Develop a design methodology using Finite Element

Analysis for SiC technology in Press-Pack

● Evaluate Condition Monitoring techniques for operational

management of SiC Devices in Press-Pack

Traditional Packaging Systems

● Traditional power module (most common):

Semiconductor devices (die)

DBC

Wirebonds

Base Plate

First isolated power moduleSemipack – Semikron, 1975 [1]

Si IGBT half bridgeSKM400GB17E4Semikron - 2015

SiC MOSFET half bridgeCAS120M12BM2Cree - 2014

[1] T. Stockmeier, "FromPackaging to "Un"-Packaging -Trends in Power SemiconductorModules," ISPSD 2008

Thermo-mechanical stresses

● Coefficient of Thermal Expansion (CTE) mismatching of the different

elements of the module causes additional thermo-mechanical stress

under thermal cycling conditions

● Identification of common the failure areas:

Chip solder

Wire bonds

Substrate solder

Power Cycling SiC Devices

• This has been reported in [1] and [2]• SiC has a Young’s Modulus 3 times higher than silicon• Also, the SiC die is thicker although the electrical drift region is thinner. These

two features cause more stresses on the SiC die attach

[1] Ch. Herold , M. Schäfer , F. Sauerland , T. Poller , J. Lutz , O. Schilling “Power cycling capability of Modules with SiC-Diodes” CIPS 2014

[2] Luis A. Navarro, Xavier Perpiña, Philippe Godignon, Josep Montserrat, Viorel Banu, Miquel Vellvehi, and Xavier Jorda “Thermomechanical Assessment of Die-Attach Materials for Wide Bandgap Semiconductor Devices and Harsh Environment Applications”, IEEE Transactions on Power Electronics, vol. 29, NO. 5, May 2014.

Power cycling results reported from other researchers show SiC is less reliable using traditional packaging techniques [1]

[1] [2]

Pressure Packaging

• One way of obviating theproblems of traditionalpackaging reliability issues isto use a pressure package

• No wirebond or solder isrequired, so solder fatigueand wirebond lift-off fromCTE mismatch is not areliability concern

• Mechanical pressure is usedto ensure that the device isfirmly

• Press-packs have been in usefor several decades and wastraditionally designed forwafer based thyristors in highpower applications like gridconnected converters forHVDC, FACTS etc

ABB thyristors and clamping systems

IGBT modules using pressure contacts

IXYS press-pack IGBT ABB Stakpak

Individual Belleville spring loaded contactsHermetic

External force

[1] ABB, "StakPak IGBT press-

pack modules Flyer”[2] J. Schuderer et Al., "Challenges and new approachesfor power module’s next generation packagingtechnology," presented at the IMAPS From Nano toMicro Power Electronics and Packaging Workshop, 2013.

[1]

[2]

SiC Diodes in Press-Pack

● Diode – Single die

Starting point

Φ 19 mm x 19.38mm

Press-pack Prototype

(a) Die carrier and assembled (b) Cross-section of the assembled prototype

Thermo-Electrical Properties

● Simplified analysis, removing the heatsink and clamp

𝑹𝒆𝒍𝒆𝒄−𝒄𝒐𝒏𝒕𝒂𝒄𝒕

𝑹 = 𝝆𝒅

𝑨

𝒇 𝒑𝒓𝒆𝒔𝒔𝒖𝒓𝒆, 𝒇𝒍𝒂𝒕𝒏𝒆𝒔𝒔, 𝒓𝒐𝒖𝒈𝒉𝒏𝒆𝒔𝒔

𝑽𝑨𝑲 = 𝑽𝑭𝑺+𝑽𝑹 =𝒌𝑻

𝒒𝒍𝒏

𝑱𝑭

𝑱𝑺+𝑹𝑺,𝑺𝑷𝑱𝑭

Simplified Electrical Model of the Press-Pack diode

Electrothermal Properties

Simplified Thermal Model of the Press-Pack diode

𝑹𝑻𝑯 =𝒅

𝝀𝑻𝑯 ∙ 𝑨𝑪𝑻𝑯 = 𝒄𝒉𝒆𝒂𝒕 ∙ 𝝆 ∙ 𝒅 ∙ 𝑨

𝒉𝒄 (Thermal contact conductance)

𝒇 𝒑𝒓𝒆𝒔𝒔𝒖𝒓𝒆, 𝒇𝒍𝒂𝒕𝒏𝒆𝒔𝒔, 𝒓𝒐𝒖𝒈𝒉𝒏𝒆𝒔𝒔

Intermediate contact material

● Molybdenum: Traditional intermediate contact for press-pack modules.

● Aluminium Graphite (ALG2208) is an alternative contact material to

molybdenum. Metal matrix composite – Aluminium and graphite

Impact of clamping force

● Using the forward voltage as a TSEP,

the thermal transient was extracted at

different forward currents for the SiC

Schottky diodes

Impact of contact material

● Transient thermal measurements

have been performed on SiC

press-pack diodes with 2 different

intermediate thermal contacts

● The contacts are Molybdenum

and Aluminium Graphite contacts

● Measurements were done at

different currents and the junction

temperature was measured using

the forward voltage as a TSEP

Simulation analysis – Finite Element Modelling

● Objective Develop & validate finite element models of press-pack

diode for two types of contact pad materials (Mo and ALG),

for various clamping pressure

» Junction temperature

» Current (and on resistance)

» Mechanical stress on the diode

● Modelling Methodology Electro thermo mechanical finite element modelling and

analysis

One quarter model of the press pack single diode chip

structure by exploiting the model symmetry.

● Contact Analysis Interfaces are in pressure assisted contact

Surface nonlinearities exist at the interface.

Contact analysis of the finite element code was utilised

Finite Element Modelling

Impact of load current, contact material and clamping force on temperature

Impact of load current. ALG contacts

Impact of load current. Mo contacts

Impact of the clamping force

Impact of the contact material

Finite Element Modelling

Analysis of the stresses on the chip

• Impact of the clamping force

and the intermediate contact

material on the thermal

resistance was evaluated using

special equipment which can

characterise the thermal

impedance

Thermal Impedance characterisation

• Impact of the clamping force

and the intermediate contact

material on the thermal

resistance was evaluated using

special equipment which can

characterise the thermal

impedance

• Results presented show clearly

the impact of the contact

material on the thermal

resistance. Module with ALG

contacts: reduction of the

thermal resistance of 0.339

K/W (~ 15 %)

Power Cycling

• Power cycling of the prototype wasperformed using a constantheating/cooling times strategy

• 30 A DC current, 30 seconds heating,30 seconds cooling

• Both ALG and Mo assemblies pass19000 cycles, however a TO-247 SiCfailed the same the test

• Periodic variations are observed onthe thermal resistance of the press-pack assemblies during cycling

Multiple chip modules

POSTER SESSION

Publications

● P. Rajaguru, H. Lu, C. Bailey, J. Ortiz-Gonzalez and O. Alatise, "Electro-thermo-mechanical

modelling and analysis of the press pack diode in power electronics," 2015 21st International

Workshop on Thermal Investigations of ICs and Systems (THERMINIC), Paris, 2015, pp. 1-6

● P. Rajaguru, C. Bailey, and H. Lu, "Optimising thermo mechanical behaviour of power

electronic module structures," in 2016 Pan Pacific Microelectronics Symposium (Pan Pacific),

2016, pp. 1-7.

● J. Ortiz Gonzalez, O. Alatise, N. Nobeen, J. Hu, L. Ran and P. Mawby, "Electrothermal

Considerations for Power Cycling in SiC Technologies," CIPS Conference 2016

● J Ortiz Gonzalez, L Ran, A Mohamed Motalab Ali Soli, Z Davletzhanova, O Alatise, P

Mawby, B.Hu, Z. Zeng, H. Ren, L. Hui and S. Xu "Enabling high reliability power modules: A

multidisciplinary task," 3D-PEIM Symposium 2016

● J. Ortiz Gonzalez, O. Alatise, L. Ran, P. Mawby, P. Rajaguru and C. Bailey “An Initial

Consideration of Silicon Carbide Devices in Pressure-Packages”, ECCE Conference 2016,

Montreal, September 2016

● J. Ortiz Gonzalez, A.M. Aliyu, O. Alatise, A. Castellazzi, L. Ran, P. Mawby, “Development

and characterisation of pressed packaging solutions for high-temperature high-reliability SiC

power modules”, Microelectronics Reliability, Volume 64, September 2016

Publications

● P. Rajaguru, H. Lu, C. Bailey, J. Ortiz Gonzalez, O. Alatise, “Evaluation of the impact of the

physical dimensions and material of the semiconductor chip on the reliability of Sn3.5Ag

solder interconnect in power electronic module: A finite element analysis perspective,”

Microelectronics Reliability, Volume 68, January 2017, Pages 77-85

● C. Bailey, P. Rajaguru and H. Lu, "Impact of wide band gap devices on power electronics

packaging designs," 2017 Pan Pacific Microelectronics Symposium (Pan Pacific), Kauai, HI,

2017, pp. 1-6.

● J. Ortiz Gonzalez, O. Alatise, L. Ran and P. Mawby “Impact of Temperature Imbalance on

Junction Temperature Identification for Multiple Chip Modules Using TSEPs” presented at

PCIM conference, May 2017

● J. Ortiz Gonzalez, O. Alatise, A. M. Aliyu, A. Castellazzi and P. Mawby, “Pressure Contact

Multi-Chip Packaging of SiC Schottky Diodes” presented at the ISPSD conference, May 2017

● P. Rajaguru, J. A. Ortiz-Gonzalez, H. Lu, C. Bailey and O. Alatise, "A Multiphysics Modeling

and Experimental Analysis of Pressure Contacts in Power Electronics Applications," in IEEE

Transactions on Components, Packaging and Manufacturing Technology, vol. 7, no. 6, pp.

893-900, June 2017

● J. Ortiz Gonzalez, O. Alatise, A. M. Aliyu, P. Rajaguru, A. Castellazzi, L. Ran, P. Mawby and

Chris Bailey, “Evaluation of SiC Schottky Diodes Using Pressure Contacts” in IEEE

Transactions on Industrial Electronics, vol. PP, no.99, pp.1-1, 2017

Acknowledgements

● Schunk Hoffmann Carbon Technology

Aluminium Graphite

● Roechling Fibracon

PPS and PEEK machined parts

● GD Rectifiers

Mechanical parts for the assembly (heatsinks, clamps…)

● ABTech

Copper parts

Any questions?

Thanks for your attention