2014 nepp tasks update for ceramic and tantalum capacitors · 2014 nepp tasks update for ceramic...

2014 NEPP Tasks Update for Ceramic and Tantalum Capacitors

Alexander TeverovskyAS&D, Inc.

Work performed for Parts, Packaging, and Assembly Technologies Office,

NASA GSFC, Code [email protected]

NASA Electronic Parts and Packaging (NEPP) Program

Deliverable to NASA Electronic Parts and Packaging (NEPP) Program to be published on nepp.nasa.gov originally presented by Alexander Teverovsky at the NASA Electronic Parts and Packaging (NEPP) Electronics Technology Workshop, Greenbelt, MD, June 17-19, 2014.

https://ntrs.nasa.gov/search.jsp?R=20150000205 2018-06-08T07:33:26+00:00Z

List of Acronyms and Symbols

2Deliverable to NASA Electronic Parts and Packaging (NEPP) Program to be published on nepp.nasa.gov originally presented by Alexander Teverovsky at the NASA Electronic Parts and Packaging (NEPP) Electronics Technology Workshop, Greenbelt, MD, June 17-19, 2014.

AF acceleration factor MLCC multilayer ceramic capacitorBME base metal electrode MSL Moisture sensitivity level

C capacitance PME precious metal electrodeDCL direct current leakage PV Prokopowicz-VaskasDF dissipation factor S&Q screening and qualification

DWV dielectric withstanding voltage STD Standard deviationESR Equivalent series resistance T temperatureHALT highly accelerated life testing THB temperature, humidity, biasHSSL humidity steady state low voltage TSD terminal solder dip

HT High temperature TTF time to failureHV high voltage VBR breakdown voltageIM Infant mortality VBR75 third quartile of VBR distribution

IR insulation resistance VO++ charged oxygen vacancy

LV low voltage VR rated voltage

Outline

3

Update on tantalum capacitors. MnO2 chip capacitors. Advanced wet capacitors. Polymer capacitors. Future work.

Update on ceramic capacitors. Low-voltage failures in MLCCs. IR degradation of BME capacitors caused by oxygen

vacancies. The significance of breakdown voltages for quality

assurance of BME capacitors. Effect of soldering. Future work.


New Technology Tantalum Capacitors

MnO2

KEMET F-process

AVX Q-process

Low ESL, multianode, stacked, …

microchips

embedded

Wet

SuperTan, TWA

Hybrid

Supercapacitors

Polymer

LV molded chips

HV molded chips

Hermeticallysealed

Specifications:military, SCD,

medical, automotive

Diversity is due to the variety of cathode systems.A general trend: reduction of size and ESR, increase in C, VR, and Toper.New technologies appear with increasing speed.Deliverable to NASA Electronic Parts and Packaging (NEPP) Program to be published on nepp.nasa.gov originally presented by Alexander Teverovsky at the NASA Electronic Parts and Packaging (NEPP) Electronics Technology Workshop, Greenbelt, MD, June 17-19, 2014.

4

Diversity of Tantalum CapacitorsTechnologies similar to Ta:

Nb/Nb2O5 and NbO/Nb2O5

Updates on MnO2 Tantalum Capacitors

5

Projects problems with capacitors appear with ~constant rate. Deficiencies in M55365 and new screening processes are in line with

NEPP recommendations.KEMET F-technology – importance of VBR.AVX Q- technology – Weibull grading, HT DCL, reflow…

Pop-corning and MSL.


15 uF 50 V

0

50

100

150

200

250

0 10 20 30time, min

tem

pera

ture

, oC

-1001020304050607080

defo

rmat

ion,

um

cycle 1 Tcycle 2 Tcycle 1 dcycle 2 d

0

0.3

0.6

0.9

1.2

1.5

init 1 c 3 c 10 c 30 cES

R, O

hm

CWR09 22uF 20V

Baking to avoid pop-corning.Multiple soldering cycles might degrade ESR and DCL.Recent projects’ failures (linear regulator oscillated due to increased ESR, first turn-on failures)

Updates on Wet Tantalum Capacitors

6

Reverse bias effects are similar to solid tantalum capacitors but might cause more dramatic consequences.

Ripple current testing and requirements for rating and derating for applications in vacuum.

Vibration testing of various types of capacitors is work in progress.


0102030405060708090

100

0 200 400 600 800 1000

tem

pera

ture

rise

, dee

g.C

time, sec

DWG93026 120uF 25V T1

120Hz 0.47A

120Hz 0.57A

120Hz 0.68A

Irm at 0.12 kHz =0.75A

Failure in vacuum chamber

Guidelines for S&Q have been updated to include ripple current requirements.Requirements for vibration testing should be specified.

Thermal run-away in vacuum happened at currents below Irm.

Updates on Polymer Capacitors

7

Characteristics of various types of chip and hermetic polymer tantalum capacitors are monitored since 2009.

Substantial progress in performance and quality, especially for HV capacitors.


50

70

90

110

130

-150-125-100-75 -50 -25 0 25 50 75 100 125 150

capa

cita

nce,

uF

temperature, deg.C

120 Hz

1 kHz

10 kHz

40 kHz

0.01

0.1

1

-150-125-100 -75 -50 -25 0 25 50 75 100 125 150

ES

R, O

hm

temperature, deg.C

120 Hz 1 kHz10 kHz 40 kHz100 kHz 400 kHz

Chip capacitors are still not ready for space applications. Hermetically sealed capacitors are good candidates for

space, especially for low-temperature applications. High-temperature performance still remains a problem.

10uF 35V

DCL_1000sec, A

cumu

lative

prob

abilit

y, %

1.E-9 1.E-51.E-8 1.E-7 1.E-61.E-1

5.E-11

510

50

100

1.E-1

Eng. samples 2009

DC0927

DC1008

DC1120

DC1336

Future Work on Tantalum Capacitors


MnO2 chip capacitors. Leakage currents and requirements for HT DCL. MSL issues and requirements for manual soldering.

Requirements for DCL and conditioning for soldering. High volumetric efficiency wet capacitors.

Leakage currents, gas generation, and requirements for wet. Analysis of requirements for vibration testing. Effect of HT storage.

Requirements for DCL and vibration testing. Polymer capacitors:

Evaluation of automotive industry parts. Hermetically sealed capacitors.

Assessment of performance at high temperatures.

High CV parts require improved S&Q procedures.

New Technology low-voltage MLCCs

PME

Thin dielectric

BME

“large size”(0603 and above)

“small size”(below 0402)

Embedded Flex termination

New Technology MLCCs


The electrode system in MLCCs is limited to two materials. Diversity is due to variety of ceramic compositions and processes. Two major issues with MLCC:

Cracking-related low-voltage failures; Oxygen-vacancies-related IR degradation.

Specifications:MED, AUTO, MIL(?)

BME is a mature technology in commercial world

Low-Voltage Failures

10

HSSLV testing of various types of PME and BME capacitors showed that all PME capacitors with cracks failed, compared to16% for BME.

Failed BME capacitors had much greater IR. Cracks in BME can be revealed by THB testing at V >> 1.3V.Manual soldering have a detrimental effect on MLCCs with defects.


Probability of failures for PME is greater than for BME capacitors. The difference is due to the specifics of electro-chemical behavior of Ni and Ag/Pd and formed products.HSSLV testing is not effective for BME.

BME

PME

IR Degradation


11

It is assumed that reliability of BMEs is limited by VO++.

The wear-out problem is still there, but it has been moved out of application conditions by using new materials and processes.(Life testing (1000 hr, 2VR, 125 °C) is equivalent to thousands of years at 65 °C and 0.5 VR).

Intrinsic wear-out failures due to VO++ do not affect applications.

Failures in the systems are caused by manufacturing or assembly-introduced defects.

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

1.E+08

2 4 6 8 10

time,

yea

rs

voltage acceleration constant, n

Time at 65C, 0.5VR that is equivalent to 1khr life testing

0.7eV 0.9eV1.1eV 1.3eV1.5eV 1.7eV1.9eV

−×

=

211

2 11expTTk

EVVAF a

n

1.E-06

1.E-05

1.E-04

1.E-2 1.E-1 1.E+0 1.E+1 1.E+2

curre

nt, A

time, hr

0.33uF 50V at 175C 200V

BME_CBME_APME_VPME_C

BME and PME capacitors at HALT

Detection of Defects

12

Local defects do not change C, DF and IR, but affect VBR. Majority of MLCCs with defects can pass DWV test.

defect

High values of VBR (similar to IR) provide assurance that the parts have no gross defects that might cause failures.The consistency of VBR distributions indicates stability of the

manufacturing process and quality of the product.

VBR intrinsic VBR intrinsic

VBR defect

VBRi < VBRd


Example of intrinsic breakdowns

Distributions of VBR

13

In most cases distributions of VBR for BME capacitors are bimodal. The HV mode has tight distributions (STD/Mean ~4%) indicating

intrinsic breakdown. The presence of LV subgroup is due to defects.

0.1uF 25V and 50V BME MLCCs

breakdown voltage, V

cumu

lative

prob

abilit

y, %

0 2500500 1000 1500 20001

5

10

50

99

0805 15um 25V M

0805 13um 25V A

0603 8um 50V C

1210 26um 50V C

BME capacitors with bimodal distributions


cumu

lative

prob

abilit

y, %

200 2200600 1000 1400 18001

5

10

50

99

1812 1uF 50V

0805 0.1uF 25V

0805 0.12uF 50V

1210 0.1uF 50V12 um, floating electrode

15 um

13 um

14 um


The interception point indicates proportion of defects. The spread of VBR towards low voltages indicates the

significance of defects. Lot acceptance criterion: VBRmin/VBR75 > 0.5.

Reliability of MLCCs with Defects

14

Assumptions: intrinsic degradation for a defect-free part results in failures at TTF0 and the voltage AF follows PV equation with n ~ 3 for PME and nfrom 4 to 9 for BME capacitors.

n

i

dVBR

VBRTTFTTF

×= 0

VBR intrinsic VBR

defectV0

++

TTFs were calculated based on VBR assuming for PME TTF0=50 khr, and for BME TTF0=10 khr.

0805 0.1uF 25V, life test simulation

time, hrcu

mulat

ive pr

obab

ility,

%1.E-1 1.E+51 10 100 1000 100001

5

10

50

90

99

BME, n = 9

BME, n = 3PME, n = 3

β=0.3

β=0.9

PME

β=3 to 9

BME


Wear-out degradation in BME capacitors with defects results in IM failures.

The greater the voltage acceleration constant n and the lower VBR/VBR75, the more probable IM failures are.

Effect of Soldering Stresses on VBR

15

BME 0805 0.12uF 50V Mfr.A


cumu

lative

pro

babil

ity, %

500 1500700 900 1100 13001

5

10

50

99

initialafter TSD_350

BME 0805 0.47uF 16V Mfr.Pa


cumu

lative

pro

babil

ity, %

500 800560 620 680 7401

5

10

50

99

initial

after TSD_350

BME 1825 0.47uF 50V, Mfr.A


cumu

lative

prob

abilit

y, %

0 2500500 1000 1500 20001

5

10

50

99

manual soldering

TSD_350Cvirgin

intrinsicbreakdown


Some lots are sensitive to TSD stress.Stresses related to manual soldering

can degrade VBR.VBR can be used as one of tests to

qualify MLCCs for manual soldering.

Effect of Soldering

16

It is often assumed that large size MLCCs are more vulnerable to cracking.

Out of 40 samples of 0603 size MLCCs soldered with a soldering iron set to 315°C, 10 samples had intermittent or no contact.

Failures were due to cracks along the terminations. No failures when parts were soldered onto a board preheated to 150°C.


Manual soldering can cause cracking of small size capacitors. Preheating of the board is critical to reduce the probability of

failures.

crack

Effect of Soldering, Cont’d


17

Solder

Board

Capacitor

Board

Capacitor

crackTensile stress

Board

CapacitorSolder

∆L

Project failure case.0402, 1000pF 50V X7R.

Post-soldering touch-up to improve the attachment might result in tensile stresses.

Tensile stresses can cause cracking.

To decrease the probability of fracturing during soldering, both, the reduction of the level of stress and selection of robust capacitors are necessary.

Future Work on Ceramic Capacitors

18

Defect-related mechanism of failures at HT. Requirements for screening.

Effect of manual soldering conditions on reliability. Requirements for qualification testing.

Comparative analysis of performance and reliability of PME and BME capacitors: Leakage currents. Breakdown voltages. Mechanical characteristics and the probability of fracturing. Recommendations for application.

Reliability issues related to assembly of small size MLCCs (0402 and less). Screening and qualification requirements.


2014 nepp tasks update for ceramic and tantalum capacitors · 2014 nepp tasks update for ceramic...

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