Conformal Coatings
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Transcript of Conformal Coatings
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
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
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