Improvements of partial discharge screening for …...2018/01/10 · Improvements of partial...

Improvements of partial discharge screening for product testingW. Frank, M. StecherInfineon Technologies

Copyright © Infineon Technologies AG 2018. All rights reserved. Infineon Proprietary 2

Agenda

From where does partial discharge originate?

Partial discharge test circuit according to VDE 0884-11

Partial discharge test results

Summary

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2018-01-10


Agenda




Summary

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2018-01-10

Isolations protecting against supply network voltages are exposed to tough environments

› Short term spikes occur over lifetime due to switch mode operation.

› Temporary overvoltages < 5s occur randomly.

› Transient overvoltage <1ms occur due to atmospheric influences, particularly lightning.

› All systems have to prove that they can resist these threats.

VIORM VIOTM,60664-1Vtemp.OV,60664-1

log(t)

100 s

1010 s

107 s

102 s

103 s

VIN

T1

T2

D1iD(t)

vG2

42018-01-10 Copyright © Infineon Technologies AG 2018. All rights reserved. Infineon Proprietary

Isolations protecting against supply network voltages are exposed to tough environments

VIORM

log(t)

100 s

1010 s

107 s

102 s

103 s

Partial discharge free safe operating area

Area to ignite partial discharge

What does that mean to isolated

couplers?


VIOTM,60664-1Vtemp.OV,60664-1

Partial discharge paths of Infineon Coreless-Transformer Couplers

› Electric field between die pads is relatively low.

› Distance between LF paddles is large

› Even larger voids in mold compound do not result in partial discharge.

› The electric field between bond wire and chip is very high.

› Very small distance

› Even small voids in the mold compound can trigger partial discharge

Distance between lead frames Distance chip/bond wire



Agenda




Summary

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2018-01-10

Background of partial discharge

Vinc,max

time

Vinc

Vext

Partial discharge

starts.

Partial discharge stops below this

limit.

Peak of applied AC voltage

VDUT

Measurement area for PD. The selection of the measurement voltage level has a

strong impact on the screening results.

Used for isolation test


Partial discharge measurement setup as per VDE 0884-11

VPDmax

HV AC source

DUT

Low pass filter to avoid source influences

Measurement impedance

Measurement equipment



Partial discharge test timing profile accordingVDE 0884-11

› Inception voltage Vinc is higher than extinction Vext voltage

› Isolation test voltage Vpd(ini),x is above inception Vinc voltage

› PD measurement level is below extinction voltage

2018-01-10

time

Vinc

Vext

VDUT

tini

tm

Vpd(ini),x

Isolation test interval

PD measurement interval

Vpd(m)

VIORM

Comparison between magnetic coupler PD timings and opto coupler PD timings

Magnetic C

ouple

rs

VD

E 0

884-1

1O

pto

Couple

rsIE

C 6

0747-5

-5

The measurement happens immediately after the HV stress.

Optocoupler allow also physically incorrect test routines.



Agenda




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Forcing partial discharge by intentional delamination and voids in mold compound

› 5 Groups have been processed

› Group AA is the reference group

Void size Group BB (small), CC (medium), DD (large)

Delamination Group EE

IFX standard: to be delam-free after TC 1000 + PD


Copyright © Infineon Technologies AG 2017. All rights reserved. 14

Diameter of voids influences the PD results (Cross-Sections group CC – medium void size)

› CC-sample with low PD has several voids compared to the CC-sample with high PD.

› The larger the void the larger is the PD effect.

2017-05-26 restricted

qpd >5 pC

qpd <5 pC

Bond wires

Bond wires

PD Test results as a function of initial HV test voltage Vpd(ini)

› Group CC is the worst one with respect to PD.

› Group EE is the worst one respective shorts.

› The higher HV/PD product test voltages are, the more weak devices are screened out.

Peak voltage at DUT 10.2kV 5.5 kV

Short qpd >5 pC

AA (POR) 3 0

BB (min voids) 7 1

CC (med voids) 14 33

DD (worst voids) 8 12

EE (Delam at MSL1) 149 0

How critical is the partial discharge screening for the lifetime?


Results of reference group AA

› Acceptance criterion: qpd <5 nC

› The reference group shows consistent PD test results and lifetime results

AA

< 5 pC @ 5.5 kVp



Higher PD test level increases test confidence and screens out all bad systems of group CC!

› Measurement results at 2.5 kV


› Lifetime sensitivity on PD

2018-01-10

Group CC

<[email protected]

Group CC

>[email protected]

HV storage @6kVrms!

+1 Outlier outside the

diagram


diagram


Higher PD test level increases test confidence and screens out all bad systems of group CC!



› Lifetime sensitivity on PD

2018-01-10

Group CC

<[email protected]

Group CC

>[email protected]

HV storage @6kVrms!


diagram


diagram

Infineon Technologies applies >4.5 kV peak as PD measurement voltage to ensure the

highest quality of shipped products.


Agenda




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Summary

Partial discharge is a key test methodology in VDE 0884-11 to screen out for good insulation quality.

Infineon Technologies performs a 100% PD-test for all certified couplers with much tougher test conditions than requested by theVDE 0884-11.

The partial discharge measurement voltage level plays an important role for the HV robustness needed in the field. The higher the test voltage, the better the screening.


Improvements of partial discharge screening for …...2018/01/10 · Improvements of partial...

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