Basic Concepts Of Conformal Coating

The Basic Concepts of Conformal Coating An examine of conformal coating materials available today and how they perform

Summary
Definition of a Conformal coating
What the coating actually does
Why coatings are used
The types of coating available
How to select a coating
How a coating is applied
How to test for performance

It is a thin plastic protective film
“ conforms” to the surface of an electronic circuit assembly.
It is a breathing membrane that filters water vapour and solid debris
Protects the assembly from corrosion in harsh environments.

Nominally, the coating should be 0.001” to 0.008” thick (25 to 200µm)
Too thick may cause problems such as solvent entrapment, bubbling, shrinkage and cracking.
Too thin means inadequate protection

Improves reliability in humid environments
Reduces need to hermetically seal PCB
Reduces conductor spacing’s on PCB
Protects the PCB in aggressive environment
Protects the PCB against environmental particulates

Good dielectrics
Insulation & Moisture resistance
Breakdown voltage
Good flexibility so as not to stress components
Be Repairable

Is the coating waterproof?
NO! All coatings breathe. However, i t seals IN AS WELL AS OUT
Coatings permit air, which may contain moisture, to migrate in and out through the film.
If there is a soluble contaminant on the surface beneath the coating, then this may cause osmosis.

If your circuit is:
High-reliability and /or safety critical
Are operating in an aggressive environment
Fine line, fine pitch
There may be problems with long term reliability

Extended warranties on consumer electronics
Automotive, control drives, fire alarms and military / aerospace safety features & long term reliability

Increased demand on coating
Example is automotive electronics where it will soon represent 40% of the cost of the car
A great number of safety features are electronically controlled (ABS, airbag, servo)

The types of coatings available
Acrylics
Polyurethanes
Epoxies
Silicones
Paraxylylenes
Fluorocarbon

Acrylic Conformal Coatings
AR
Represent 80% of market
Single component materials
Excellent Moisture resistance
Easy to apply
Cure very quickly
Easy to repair by removal with solvent

AR
Especially suitable for:
Any application ‘in a box’
Boards with long service life
Any environment where water is main threat
Any environment without solvent exposure

AR
Examples of use include:
Engine management
Air bag controllers
Avionics
Communication Equipment
Elevator Controls

Polyurethane Conformal Coatings
UR
Very good solvent resistance
1 and 2 part systems
Easy to apply
Longer cure times
Difficult to repair

Polyurethane Conformal Coatings
UR
Especially suitable for:
Salt Spray protection
Applications where solvent resistance required
Directly mounted assemblies
Reparability is not an issue

Silicone Conformal Coatings
SR
Excellent High Temperature Performance
Limited solvent resistance
Solventless Products
Harder to apply
Can be difficult to cure
Nearly impossible to repair
EXPENSIVE

Silicone Conformal Coatings
SR
OVERKILL for all but specialist applications
Used in:
Huge, industrial drilling/mining equipment
High temperature electronics
Under bonnet electronics

Epoxy Conformal Coatings
ER
Good moisture resistance
Good dielectric resistance
Excellent chemical resistance
Excellent temperature resistance
Poor flexibility
Poor to repair

Paraxylylene Conformal Coatings
XY
Excellent moisture resistance
Excellent dielectric resistance
Excellent chemical resistance
Excellent temperature resistance
High cost of process
Critical processing

Fluorocarbons
Good moisture resistance
Excellent dielectric resistance
Minimal chemical resistance
Good temperature resistance
Low cost of process / Expensive set up costs
No mar resistance

Typical Coating Thicknesses
Acrylics 0.001” - 0.003” 25/75µm
Polyurethanes 0.001” - 0.003” 25/75µm
Epoxies 0.001” - 0.003” 25/75µm
Silicones 0.002” - 0.008” 50/200µm
Paraxylylenes 0.0005” - 0.0007”
Fluorocarbon 0.0005” - 0.0007”

Technologies Available
Solvent-based
Water-Based
Solvent less Silicones
Solvent less UV Curable

Solvent-Based
Advantages
Full range of chemistries available
Easy to process
Good wetting
‘ Quasi Cleaning’
Fast Cure
Disadvantages
Flammable
Odour
Extraction Required
VOC Emissions

Water-Based
Advantages
Most similar to solvent-based
Full range of chemistries available
Low odour
Non-flammable
Low VOC
Disadvantages
Longer cure times
Hard to apply by robotic equipment
More sensitive to contamination

Solventless Silicones
Advantages
Excellent high temp stability
Good flexibility
Low VOC
Disadvantages
Expensive
High Viscosity
Harder to apply by robotic equipment
Thick films required
More sensitive to contamination
Long cure times

Solventless UV Curable
Advantages
Very fast curing
High volume processing
High temperature performance
Great flexibility
Excellent adhesion and chemical resistance
Reliable secondary cure mechanism
Disadvantages
Hard to repair easily
Difficult in manual spray application
Unsuitable for dip applications
UV curing required

Summary: Technologies / Chemistries
COATING TYPES AR PU SR SB WB UV Application Easiness Dependant on tech. Dependant on tech. 2 5 2 4 Drying / Curing Time 4 3 1 4 1 5 Chemical Resistance 1 4 4 Dependant on chem. Dependant on chem. 5 Moisture Protection 5 4 4 5 4 5 Reworkability 5 3 0 4 3 2 Environmental Friendly Dependant on tech. Dependant on tech. 5 1 5 5 Main features General purpose Chem. Resis. High temp. Most common Manual application High volume

Humiseal Product Range & Codes

Humiseal Product Code 1A33 1B31 1C49 1H20AR1 1B73 2A64 UV40

Humiseal Product Code Solvent Based Number of part: 1 = 1 part system 2 = 2 part system 1 B31 2 A64

Humiseal Product Code Solvent Based Number of part: 1 = 1 part system 2 = 2 part system 1 B 31 2 A 64 Chemistry: A = PU B or R= AR C = SR

Humiseal Product Code Solvent Based Number of part: 1 = 1 part system 2 = 2 part system 1B 31 2A 64 Chemistry: A = PU B or R= AR C = SR Product number

Humiseal Product Code Solvent Based (SB) Products 1B73 1B18 1B31 1R32 1R32A-2 1A33 1A68 1A20 2A64 Technology SB SB SB SB SB SB SB SB SB Chemistry AR AR AR AR AR PU PU PU PU Cure mechanism Solvent Evap. Solvent Evap. Solvent Evap. Solvent Evap. Solvent Evap. Oxygen Oxygen Moisture Moisture MIL Yes No Yes No No Yes No Yes Yes UL Yes Yes No No Yes No No Yes No Low cost equivalent 1B18 N/A 1R32 N/A N/A 1A68 N/A N/A N/A Comments Military Reference for AR Automotive Reference Military Reference for PU

Humiseal Product Code Solvent Based 1H20 AR1 /S 1H20 UR5 /D Technology: 1H20 = water based Chemistry: AR = Acrylic UR = Polyurethane Application method: S = spraying D = dipping

Humiseal Low VOC SB = Solvent Based AR = Acrylic PU = Polyurethane WB = Water Based SR = Silicone UV = UV curable Most widely used products Products UV40 UV40 250 1C49LV 1C51 1H20AR3/S 1H20AR3/D 1H20UR5/S 1H20UR5/D Technology UV UV SR SR WB WB Chemistry PU PU SR SR AR PU Cure mechanism UV+ Moisture UV+ Moisture Moisture Heat Air Oxygen MIL Yes No Yes Yes Pending Pending UL Yes Yes Yes Yes Pending Pending Low cost equivalent N/A N/A N/A N/A N/A N/A Comments Automotive reference Spray and dip grade Spray and dip grade

Humiseal Thinners Most widely used products Products 503 535 505 521 604 600 Evaporation Rate (BuAc=1) 3.7 2.1 1.7 0.6 0.4 0.3 Flash point -1 7 14 27 11 47 Material 1B31, 1B73, 1A33 1B51 1R32 1B31, 1B73, 1A33 1B73 EPA 1R32A-2 Application method Dip, brush Dip, brush Dip, brush Spray, brush Spray, brush Spray, brush Comments Reference for dipping Reference for spraying Reduce bubbles

Humiseal Strippers Most widely used products SB = Solvent Based AR = Acrylic PU = Polyurethane WB = Water Based SR = Silicone UV = UV curable Most widely used products Products 1080A 1020 1063 1072 Chemistry to remove SB AR WB AR PU PU Coatings 1B31, 1B73, 1R32A-2 1H20 AR3 1A33 1H20 UR5, UV40 Comments Replacing previous 1080 Replacing previous 1071

Humiseal Product Range
SCH can provide:
A wide range of technologies and chemistries available
Expertise and technical support in product selection and application
Process solution for each challenging requirement

Humiseal Product Range
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Basic Concepts Of Conformal Coating

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