Causes and Cures of Delamination, Cracks and Blisters in

Europe – Asia – Americas www.zestron.com Copyright – V 02

Causes and Cures of Delamination, Cracks and

Blisters in Conformal Coating Layers

iNEMI

Board Assembly Tech Topic Series

Freddy Gilbert, Technology Analyst, ZESTRON Europe

[email protected]

June 30th, 2021

Watch the recorded webinar: https://youtu.be/0WkbAfN-1KA

mailto:[email protected]

https://youtu.be/0WkbAfN-1KA


ZESTRON Portfolio

Cleaning

Technical support

Process monitoring

R&S – Services


Zestron Reliability & Surfaces



ZESTRON R&S Coaching

– When and what for?


Mechanical

e.g. vibrations, acceleration, crash

Electrical

e.g. moisture, flux, impurities,

overvoltage effects

Corrosive

e.g. humidity, climate

change, salt spray,

harmful gases

Thermal

e.g. temperature

variation,

extremely high/low

temperature

Stress on electronic assemblies


Coating or potting to protect the

assemblies

Coating protects against

mechanical stress

Coating protects against

moisture-induced failures:

Creeping currents

Electrochemical migration

Corrosion

Signal distortion in high

frequency circuit

… if the surface is sufficiently

clean


Introduction – about faults


Coating defects – Delaminations

Easy peeling off of the coating at the edges and components

due to insufficient adhesion

Recognizable through the apparition of light areas at the surface of the coated

assembly

Potential causes: contamination at the surface prior to coating, too thick coating

layer, insufficient curing…


Contamination influences on coatings,

potting and moulding compounds

Contamination reduces adhesive forces and leads to delamination effects

Contaminants

Improvement of surface cleanliness minimize the risk of delamination


Coating defects – Cracks

Conformal Coating after Ageing (e.g. temperature cycles)

Potential causes:

Too thick coating layer (heterogeneous mechanical/thermal properties

between the upper coating layer and the bottom layer

Presence of the contamination with a very different coefficient of thermal

expansion

Coating material not suited for the test / application (brittleness)








Coating defects – Blisters (during curing)

Potential causes:

Evaporation of moisture of residual solvent from flux

Drying performed too quickly and/or at too high temperature

Entrapment of air under component (spraying application pattern)


Other defects

Electrochemical

migration (ECM),

triggered by defects in

coating

Delamination of

silicone lens on

LED components

Delamination / curing

issues of

2K-polyurethane-potting


Other defects

Insufficient wetting under

components

Immediate dewetting

during coating

Incomplete crosslinking

(e.g. crosslinking blocked by

organotin compounds,

sulphur and ammonium

compounds)


Preventive measures –

Have a clean surface

47

0

25

72

1 0

20,5

21,5

50

9,5

27,5

87

7

3

23,5

33,5

67,5

32

32,5

132

4,5

8,5

20,5

33,5

0

20

40

60

80

100

120

140

Delamination

uncleaned

Cracks

uncleaned

Bubbles

uncleaned

Total Defect

uncleaned

Delamination

cleaned

Cracks cleaned Bubbles

cleaned

Total defect

cleaned

Total error curve over test cycles - uncleaned vs. cleaned

100 cycles 400 cycles 500 cycles


Surface evaluation

before Conformal Coating

Optical cleanliness inspection

Ionic contamination: ROSE-Test, Ion Chromatography

Testing for flux activators

Testing for resin residues

Testing for cross-linking disruptors

Measurement of surface energy


Quality tests for Conformal Coating and

Potting

Inspection of fluorescent coatings

Adhesion tests: X-Cut Tape Test, Cross Hatch Tape Test

Differential Thermal Analysis (DTA)

Environmental simulation tests (e.g. harmful gases with mixtures of

SO2, H

2S, NO

2and Cl

2)

Complete life duration testing (e.g. according to IEC-68-2 or EN

60068-2-60)


Conventional harmful gas testing:

drawbacks

Expensive and complex experimental set-up necessary (climate

chamber, test chamber, cylinders, taps…)

Harmful gases (H2S, Cl

2,…) High effort and high costs to ensure

operational safety

Long test duration No quick statement possible about the quality of

the Conformal Coating or Potting


Requirements for extended quality tests

Tests should be carried out quickly, i.e. within a few hours

It should be possible to carry out tests with as little equipment as

possible and at the same time with as high an operational

reliability as possible

Tests should enable a qualitative assessment of the protection

system

Tests are shall be able to be used according to the points 1-3 as

production-accompanying quality monitoring tools


New, extended quality tests

Quality tests for coatings and potting:

Coating Reliability Test (CoRe-Test) according to GfKORR

Quality test with iodine vapour

ZESTRON®

Coating Layer Test


Quality tests for protective systems:

Coating Reliability (CoRe) Test

Simplified, accelerated “climate test“ give

examples to the following questions:

Is a protective coating against moisture

necessary?

Is the existing coating sufficient to provide

protection against moisture?

Is the coating quality/adhesion negatively

influenced by contaminants?

Are there defects or weak points in the

coating?

Could the quality of the coating be

improved after optimizing the coating

process?


Quality tests for protective systems:

Coating Reliability Test (GfKORR)

Gas development

at imperfections

(02

and H2

as a

result of electrolysis

of water)

+

–

- 5 V

- 12 V

- 24 V

Dendrite growth

= ELECTROCHEMICAL MIGRATION (ECM) at defects

Standby current

over time

R protection


Coating Reliability (CoRe) Test –

Current characteristics (examples)

Not fully crosslinked coating layer

- broken through

Coating layer –

- Resistant to short term condensation



Objective for a new and fast quality test for potting and

molding compounds:

Localization of cracks and penetration paths in molds and potting

compounds

Localization of adhesion weaknesses between assembly surface

and molding/potting

Focus on power electronics encapsulation (especially DCB

substrates)



Test specifications/ performance iodine vapor test:

Further development of the “Pressure-Cooker-Tests” (IEC 60749-

33:2004), which is used as an accelerated humidity test for

encapsulated (molten) components without power supply

Iodine is reactive but also easy to handle (as solid or saturated aqueous

solution)

Test equipment: Beaker/autoclave; fume cupboard with suitable filter

system; optical microscope with polarizing filter (interference contrast)

Iodine evaporates from the saturated solution at elevated temperature -

a saturated iodine vapor atmosphere is established (resublimation of

the iodine on cooling)

Combined humidity and humidity pressure test possible (adjustable via

test temperature)



Test conditions: ~60 °C; 1-3 h

Optical evaluation via microscope transparent systems are preferred

Saturated

iodine solution

Iodine and/or

water vapour



Test result: case study

- Cu-DCB power electronics module (chips soldered on; Al Bonds)

- Silicone potting: 1-1.5 cm layer thickness

Before the test:

Clear, transparent silicone

After the test:

Turbidity of the silicone



Test results: Case study

Inorganic substances (salts, ...) can be made visible via the interference

contrast in the light microscope

In areas with insufficient potting adhesion - especially in the immediate

vicinity of the chip solder joints - copper iodide has formed

Copper

iodide


Application area

Localised detection of protective coating

layer defects on electronic assemblies

black coloring

No fluorescent tracer necessary

Reacts with metal surfaces:

Tin

Copper

Nickel or nickel containing

compounds

Other less precious metals such as

ferrite (Fe, Fe/NiZn, Fe/Mn)

Other less precious alloys


Easy and fast application with a test

result within minutes

1. Apply test indicator 2. Wait for max. 3 minutes

3. Optical analysis 4. Rinse off or dab off


Conformal Coating


Conformal Coating after Ageing

(e.g. temperature cycles)


Coating Layer Test


Summary

Quality Management/

Safety

Drying

Coating

Application

Machine

Geometry of

PCB

Surface

PCB Production

Picture courtesy of GfKORR


Where do I find support?

Technical articles

GfKorr Handbook

IPC – Guide-

line – 830

NASA Handbook


Thank you!

Do you have questions?


Topic Date

PCBA Cleaning – Stefan Strixner July 8th, 2021

iNEMI

Board Assembly Tech Topic Series


Contact

Zestron Reliability & Surfaces

ZESTRON Europe

Freddy Gilbert

Technology Analyst

Phone : +49 841 635 115

Email : [email protected]

mailto:[email protected]

Documents

Causes and Cures of Delamination, Cracks and Blisters in