Conformal CoatingsEnhanced protection for enhanced PCB performance

Introduction

Why Coat?

CONFORMAL COATINGS

A newly manufactured printed circuit board will generally perform well but performance will quickly deteriorate.

Common causes of deterioration and PCB failure include:o Atmospheric moistureo Contamination of the surface with airborne ionic material o Electrostatic attraction of dust to the surfaceo Corrosive environments, such as salt fog

Conformal coatings can be applied to a PCB giving protection against the environment, extending the life of the board and therefore can be used in a vast array of electronic applications.

Domestic

Industrial

Automotive

Aerospace

Military

CONFORMAL COATINGS

Conformal coatings are thin coatings, typically 25-75 microns, which ‘conform’ to the contours of a PCB.

The ideal conformal coating will have performance requirements that include:o Good electrical propertieso Low moisture permeabilityo Good mechanical durabilityo Excellent adhesion propertieso Good thermal resistance

Additional properties such as flame retardance or chemical resistance may also be required.

Different chemistries utilised in conformal coating technology require different types of cure. It is important to understand the terms used in conformal coating in under to understand cure schedules:

‘Tack Free’ – this is the time at which the coating is no longer tacky but slight indentations may be left in the coating when pressed firmly

‘Touch Dry’ – this is the time at which the coating is dry enough to touch without leaving any fingerprints on the surface of the coating

It is important to note that some coatings are very soft and can feel tacky even when fully cured. The touch dry time in these cases is more a reference to when you can move the board without affecting the coating

‘Cure Time’ – this is the time at which the coating is fully cured and will offer protection

It is also important to note that most coatings actually reach their optimum cure level after around 7 days but they will provide protection prior to this

CONFORMAL COATING TERMINOLOGY

CONFORMAL COATING APPLICATION

Conformal coatings can be brushed, dipped or sprayed depending on the requirements. Customers often specify their desired application method.

Brushing:

Advantages Disadvantages

Cost effective Uneven coating

Ideal for small scale production

Difficult to get under components

Selective coating Only one side at a time can be coated

CONFORMAL COATING APPLICATION

Dip Coating:

Advantages Disadvantages

Ideal for medium scale production

Initial capital outlay

Uniform coating thickness Masking essential for connectors

Easy to operate machinery Special extraction may be required

Both sides can be coated at the same time

Suitable for higher viscosity materials

Coating can penetrate under components

Operator training required but not difficult

CONFORMAL COATING APPLICATION

Spraying – aerosol or manual spray gun:

Advantages Disadvantages

Cost effective Overspray can occur

Ideal for bench top work and repair

Difficult to get under components

Ideal for small to medium scale production

Special extraction may be required

Convenient Only one side at a time can be coated

SPRAYING

CONFORMAL COATING APPLICATION

Selective Spraying:

Advantages Disadvantages

No masking required Initial capital outlay

Uniform thickness Low under component penetration – requires good

flow properties with the coating

Automated process – good for inline procedures

Special extraction may be required – but can be linked to

the machine easily

Ideal for all scales of production

Requires a trained operator to set the software

SELECTIVE COATING

SELECTIVE COATING

Application Conditions

• Temperature – Affects viscosity and evaporation rate

• Humidity – Contaminates dip coat tanks, blooming in hand spray and affects curing / pot life.

• Ventilation – Affects operators

Product Choice

Coating Options

Considerations for ChoiceAs there are many different applications for conformal coatings, there are also a number of elements that must be considered as part of the selection process:

Coating properties• Adhesion• Flexibility• Temperature range• Mechanical durability• Electrical performance• Environmental performance• Flame retardance• Mould resistance

Application • Viscosity/application• Touch dry time• Full cure time• Curing conditions• Is re-work required?• Cost• Quality• Approvals required?

CONFORMAL COATING TYPES

Conformal coatings are available in a number of different chemistry types and also cure via different mechanisms.

The different types of conformal coating include:o Solvent-based – Evaporation Cureo Solvent-based – Heat Cureo Low VOC/Water-based – Evaporation/Heat Cureo Non-VOC – Moisture Cureo UV Cure – Dual Cure: Moisture/Heat

Common conformal coating chemistries include:o Acrylico Polyurethaneo Siliconeo Modified-silicone

DCA (SCC3) MODIFIED SILICONE COATING

DCA is a flexible, transparent & unique modified silicone conformal coating specifically designed for the protection of electronic circuitry.

Key Features:o Resistant to most solvents, lubricants and chemicals associated

with most aerospace and automotive applications.o Excellent adhesion under various climatic conditions to a variety of

substrates, including high altitude/decompressiono Fluoresces under UV light for ease of inspection.o Extreme operating temperature range (-70˚C to +200˚C)o Excellent electrical properties

DCA (SCC3) MODIFIED SILICONE COATING

DCA is a solvent based coating and can be sprayed, dipped or brushed.

For optimum properties, DCA should be heat cured (2hrs at RT, 2hrs @ 90˚C advised). If RT cured then the solvent resistance will be significantly reduced.

Should be used with DCT thinners and removed with CCRG – Electrolube Conformal Coating Remover Gel

Approvals

o Def-Stan 59/47 – Standard now obsolete

o UL746 – File Number E138403

DCA (SCC3) MODIFIED SILICONE COATING

The DCA (SCC3) Range includes:

o DCA-FD – Fast-dry versiono DCA-HT – With improved high temperature performanceo DCR – Opaque red versiono DCB – Opaque black versiono DCRT – Opaque red, high viscosity versiono DCE – Thixotropic gel version (dam and fill applications)

Unique range of products based on a silicone modified alkyd Avoids issues associated with silicone migration Easier processing than standard silicones Performance compares with many silicone conformal coatings

TFA – TOLUENE FREE ACRYLIC COATING

TFA is a flexible and transparent acrylic conformal coating for the protection of electronic circuitry.

It has been formulated to meet many of today’s commercial applications, meeting both Military and IPC standards.

Key Features:o Toluene free product.o Fluoresces under UV light for ease of inspection.o Wide operating temperature range (-65˚C to +125˚C)o Excellent Dielectric propertieso Clear coating with excellent resistance to yellowing when exposed

to UV light

TFA – TOLUENE FREE ACRYLIC COATING

TFA is a solvent based coating and can be sprayed, dipped or brushed.

Should be used with DCT thinners and removed with CCRG – Electrolube Conformal Coating Remover Gel

Approvals

o UL746 Approvedo IPC-CC-830 approvedo Automatically meets MIL-46058-C

Also available: AFA – Aromatic Free Acrylic

VOCs or Volatile Organic Compounds are carbon based compounds which vaporise easily under ambient conditions

VOCs contribute towards the formation of ground level ozone

Such pollution can have many detrimental effects on the environment, damaging forests and vegetation

In addition, some materials classed as VOCs can act as irritants and over exposure can lead to a variety of health problems

VOCs – THE NEED TO CHANGE

VOC DEFINITION

EU Solvents Emissions Directive “Any organic compound having at 20˚C a vapour

pressure of 0.01kPa or more, or having corresponding volatility under the particular

conditions of use”

UVCL - UV Cure

• Extremely rapid initial cure schedule • Ideal for high volume production• In-line process, curing equipment required

• Very high level of protection; highly cross-linked coating• Excellent chemical and solvent resistance

• Using a dual cure system can ensure that in shadowed areas under components the coating still cures and protects the PCB

• Moisture• Heat

• UV cure coatings are available as 100% solids materials• Non-VOC options

WBPS – WATER-BASED COATING

WBPs is a water-based conformal coating, based on polymeric materials which has been specifically formulated for the protection of electronic circuitry.

It offers an excellent blend of both physical and electrical properties in a more environmentally and user friendly package when compared to conventional solvent based conformal coatings.

Non-flammable and contains very low levels of VOC’s.

WBP is for dipping/brushing applications whilst WBPS (Sprayable) has been specifically formulated for use in selective film coater equipment.

WBPS – WATER-BASED COATING

Key Features:

o Environmentally friendly and eliminates hazards associated with solvent based conformal coatings

o Excellent solvent resistance.o Very low VOC contento NMP (N-Methyl pyrrolidone) free.o Fluoresces under UV light for ease of inspection.o Excellent adhesion on a wide variety of substrates.o Excellent Dielectric properties and resistant to mould growth.

PUC – POLYURETHANE COATING

PUC is a tough, flexible, modified polyurethane conformal coating and is specifically designed for the protection of electronic circuitry, particularly in harsh conditions.

Key Featureso Excellent adhesion to a wide variety of substrates.o Fluoresces under UV light for ease of inspection.o Good resistance to a wide variety of chemicals including acids and

alkalis.o Wide operating temperature range.o Excellent mechanical properties including abrasion resistanceo Solvent-based, can be sprayed, dipped or brushedo Should be used with PTH thinners and removed with CCRG

Modified Silicone – LFCC, FSC (Modified with acrylic; up to 125˚C)

Acrylic – HPA (MIL Approved), APL, AFA, APLSP (Sprayable version), TRV

Water-Based – WBP (Dipping Version)

Polyester – CPL

Surface Modifier – TFCF (Fluorinated)

OTHER COATINGS

High Temperature – DCA (SCC3) Range Excellent Clarity – TFA or an Acrylic Coating Chemical Resistance – PUC or DCA (SCC3) Range Cosmetic Appearance – CPL (no UV trace) Low Solvent Content – WBP or WBPs Reworkable – Acrylic Coatings or FSC UL Approved – DCA and TFA UV Cure - UVCL

CHOOSING THE RIGHT PRODUCT

Acrylic

HPA TFA

APL AFA

Modified Silicone DCA

FSCPFSC

PolyurethanePUC

PUCAF

Water-Based

WBPWBPs

OpaqueDCRT

DCRDCB

UV Cure

UVCL

Polyester

CPL

Electrolube Conformal Coating Selector Chart

Is optical clarity required?

YES

DCA

Is a fast touch dry time required?

Is low/non VOC required?UVCL

WBP(s)

YES

YES

Is easy removal for re-work required?

Is an approval required?

YES

Is chemical resistance required?

DCA/WBP(s)

YES

Is the operating temperature above 130°C?

YES

YES

Is the operating temperature below -55°C?

WBP(s)PUC

PUCAF

YES

NO

APL

HPA (MIL-I-46058C)TFA (IPC-CC-830/UL746)

AFA (UL746)FSC (IEC61086)

DCA (UL746)UVCL (IPC-CC-830)

Is an approval required?

YES

NO

NO

NO

NO

NO

NO

NO

Conformal CoatingsPotential Problems

Adhesion Loss Incorrect curing could cause adhesion loss. This could be due to

insufficient curing, i.e. the coating has not finished cross-linking.

It could also be a problem with removing masking material – ideally this should be done when the coating is still soft.

Conformal CoatingsRework Considerations

Coating Removal Products• For acrylics, a solvent based product like Electrolube ULS is ideal

for quick and clean removal of the coating.

• For coatings with a higher chemical resistance, a product such as Electrolube RRS will be required.

• For localised rework, a remover gel like Electrolube CCRG is ideal.

In order for conformal coatings to be applied correctly some complimentary products are required:

• Thinners – where applicable conformal coatings are diluted to the required viscosity, Electrolube have a range of thinners suitable for this process

• Masking – PCM and PCS are coating masks suitable for covering connectors during the coating process

OTHER PRODUCTS

Thank YouFor further information please visit www.electrolube.com