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