PCB Protection Conformal Coating, Potting, &

Encapsulation

Dr. Brian TolenoHenkel

Irvine, CA

Agenda

• Reasons for using PCB Protection

• Conformal Coating

• Low Pressure Molding (Macromelt®)

• Potting

PCB Protection Agenda

• Why?• What Environments?• What Method?• What Chemistry?

Purpose

• Environmental– Moisture– Harmful fluids– Dirt– Ultraviolet light

• Mechanical– Shock and Vibration

• Radio Frequency– Faraday cage

• Electrical Insulation• Proprietary Design

Possible Environments• Automotive

– Underhood– In Cabin– External

• Telecom– Proprietary Programming

• Utilities– UV protection– Moisture protection

• Military• Marine

Environments

Considerations

• Type of protection needed

• Size of board/part• Weight

requirements• Rework required?• Protection from

aftermarket modification/repair

• Design status

Options – Types of Protection• Conformal Coating

– Thin layer of material to cover all or part of circuit board

• Module sealing– Bonding or sealing two part external case

• Low Pressure Molding (Macromelt®)– Thermoplastic overmolding of entire product except for

connector

• Potting– Completely covering circuit board inside external case

except for connectors

• Microencapsulation– Expoy overmolding of specific areas or components

Conformal Coating• Various chemistries

– Acrylics – One component, highly abrasion resistant, easily repairable. Temps to 110°C.

– Urethanes – Softer systems, thermal shock resistant, somewhat repairable. Temps to 110 or 125°C

– Epoxies – Superb chemical and abrasion resistance. When reworkability is not needed. Temps to 125°C.

– Silicones – Highest temperature environments, reworkable, zero VOC’s, otherwise protected from abrasion.

Why?

“Hey Frank…better have engineering include a conformal coating on that next batch.”Www.plasmasystems.com/guide.html

Conformal Coating Applications

• Traditionally, conformal coatings were only used in high reliability applications

– military– aerospace

• Many Fine Pitch SMT designs will not operate or perform adequately in humid environments without the use of a Conformal Coating

Conformal Coating Applications

Conformal Coating Chemistry

• Acrylics (AR)

• Urethanes(UR)

• Epoxies (ER)

• Silicones (SI)

• Paraxylenes

"Gre

en"

Prot

ectiv

e

Tem

p °C

Rew

ork

$

AR - + 150 0 +

UR - 0 125 + +

ER - + 150 - +

SI + 0 200 + -

Conformal Coating Chemistry - Acrylic (AR)

• Advantages– Easy to apply– Desirable physical and

electrical properties– Easy to repair

• Disadvantages– Contain solvents– High modulus– Solvent resistance

Thermoplastic Lacquer that Cures bySolvent Evaporation

Conformal Coating Chemistry - Polyurethane (UR)

• Advantages– Solvent resistance– Electrical properties

• Disadvantages– Contain isocyantes– Hard to repair– High modulus– Two-part pot life

A thermoplastic polymer (which can be made thermosetting) produced by the condensation reaction of a polyisocyanate and a hydroxyl- containing material

Conformal Coating Chemistry - Epoxy (ER)

• Advantages– Desirable physical and

Electrical properties– Solvent resistance– Solvent free

• Disadvantages– High modulus– Hard to repair– Two-part short pot life– Shrink during cure

Thermosetting Resins Based on the Reactivity of the Epoxide Group

Conformal Coating Chemistry - Silicone (SR)

• Advantages– Low modulus– Electrical properties– Wide temperature range– Easy repair

• Disadvantages– High CTE– Low modulus– Cost

Based on Polydimethylsiloxane

Conformal Coating Chemistry - Paraxylenes (XY)

• Advantages– Coating applied in

ambient state– True conformability

around all parts– Excellent dielectric

strength– Chemical resistance

• Disadvantages– Batch process– Air tight seals required

for masking– Microblast for repair– Expensive

Chemical Vapor Deposition Process (Di-p-para-di-p-xylene)

Conformal Coating Process

(Clean) (Mask) (Cure)

Coat Cure (Demask)

Conformal Coating Process Cleaning

• Water Soluble (water washable) Fluxes– Thorough cleaning required

• No Clean Fluxes– All flux must be activated in reflow– No Washing

• Mold releases and marking inks – May cause dewetting

Applying the Coating

• Dip• Spray (Dispense)• Brush

Conformal Coating - Coating Thickness

• Coating thickness recommendations - IPC2221 and J-STD-001

• See also IPC - HDBK - 830

• Every design should be tested

Type AR Acrylic 1.18 - 5.12 milType ER Epoxy 1.18 - 5.12 milType UR Urethane 1.18 - 5.12 milType Si Silicone 1.97 - 8.27 milType XY Paraxylylene 0.394 - 1.97 mil

Conformal Coating Process Curing

• Solvent Evaporation• Heat• RT Moisture Two-Part

• UV Light Combinations– UV/Heat– UV/Moisture– UV/Two-Part

Coating Performance Qualifications

• Qualification Standards:– MIL-I-46058C (not to be used on new

procurement)– IPC-CC-830B– UL 746C includes flammability– Telcordia formerly Bellcore TR-NWT-000078– Individual company standards

Module Sealing• Silicones

– Flexible for high temp thermal cycling– Adhesion to numerous substrates– Substrates are usually not functional

electronics– Most protection provided by external

hardware (case)– Three types

• Cure in place – Apply, Cure, Assemble• Form in place – Apply, Assemble, Cure• Post assembly – Assemble, Apply, Cure

• May use material to complete faraday cage too

Low Pressure Molding

• What is Low Pressure Molding Molding?

Traditional InjectionMolding

Potting

MacromeltMolding

pres

sure

An innovative encapsulation process positioned between traditional potting and injection molding technologies. It is a complimentary technology. Does not replace all potting applications and typically doesn‘t compete with traditional injection molding.

cycle time

Low Pressure Molding

• Injection process whereby PCB is completely over-molded and encapsulated with liquid material, which forms the body of the device.

• Eliminates waste• Eliminates need for cup

or housing associated with potting

• Environmentally friendly

PCB Protection: Low Pressure Molding

Low Pressure molding process flow

Traditional potting process flow

Mold Case Palletize Insert Electronics Pre-heat

Encapsulate Settle or Vacuum Cure

Insert Electronics Overmold Test

Test

Process Flow Advantage

What is Low Pressure Molding?• Developed initially in Europe for the automotive industry in

1988.• The technology broadened out into telecommunications,

computer, white goods and general wiring harness industries• Emerging industries include medical and LED lighting.• Molds grommets and true strain relief on wires & cables due to

the adhesive nature of the molding compound• Encapsulates electronic devices, providing a water tight seal

Low-Pressure Molding

• Thermoplastic materials, U/L 94 V-0• Based on natural raw materials• Cure by cooling - no toxic fumes• Application viscosity from 1,000 to 10,000 cP• Application pressure from 20 to 500 psi• Performance temperatures from -40C to 140C

continuous operation based on material choice.

• Excellent adhesive properties• Amber and Black

Polyamide Molding Resins

Polyamide Hot Melt Resins

• Polyamide Resin is a reaction product of a polybasic functional group and a polyamine.

• There are two different polyamide resin families– linear family: widely known as the nylon family

• high viscosity, fiber forming, high molecular weight

– non-linear family: non-fiber forming types based on vegetable oil based fatty molecules.

• low viscosity, lower molecular weight

Traditional Polyamide Resin• Linear polyamide: (ex. nylon)

-R Amine

….….

will continue as long as reactants are available

linear PA’s exhibit great strength, toughness, flexibility, relatively high MW and have excellent

self-lubricating features

Macromelt® Polyamide Resin

• Concept of unbalancing used

• Introduction of mono and tri-functional reactional groups

• Introduction of non-functional additives– adhesion promoters– UV stabilizers– pigments– anti-oxidants

Macromelt® Polyamide resin

• Non-Linear Molecule

-R Amine

Non-linear exhibit good flexibility, low MW and most importantly, low

viscosity

The Materials – OverviewProperties A B C D E

Color Amber / black

Amber / black

Amber / black

Amber / black

Amber / black

Chemical Base

Polyamide Polyamide Polyamide Polyamide Patented Polyamide

Operating Temperature

-40/+100°C -40/+130°C -40/+140°C -20/+140°C -40/+140°C

Cold flexibility

-40°C -40 °C -40 °C -40 °C -40°C

Applicating Temperature

180-220°C 200-230 °C 210-230 °C 200-230 °C 220-240 °C

Shore hardness

A 77 A 90 A 90 D 40 A 88

Elongation at rupture

400 % 400 % 400 % 800 % 600 %

Flammability UL94-V0 UL94-V0 UL94-V0 UL94-V0 UL94-V0

Low Pressure Molding

Telecom Applications

Macromelt

Li-Ion batteries

Antennas

Mobile Phone Applications

Automotive Applications

The Equipment

• High capacity• Small foot print• Simple to operate• User friendly & safe • Easy set-up with

touch screen• Injection profiles

available• Made in the USA

Tooling• Lower cost aluminum

used instead of hardened steel

• Macromelt® materials are non-abrasive, allowing softer metal tooling

• Aluminum tooling helps facilitate heat transfer away from PCB quicker.

• Cross-drilling of mold- set not necessary as mold-station platens are chilled.

Potting

Potting Materials

• Chemistries– Epoxy: one and two component compounds– Urethanes: two component compounds– Silicones: one component systems

• Applications– Adhesives – Biomedical – Filters (Air, Oil, and Water)– General potting and encapsulation– Telecommunications Encapsulants– LED Lighting– Doming

• Packages– Range from less than one ounce per part to over 300lbs per

part

Epoxy Systems• Room Temperature Cure

– Aliphatic Amine/ Polyamide/ Amidoamines Cures– Good for wide variety of general use systems

• Heat Cure – Cycloaliphatic Amine/ Anhydride

– Used in applications where higher heat resistance is required

• One Component– Dicyandiamide, BCl3 /Anhydride, Mod. Aliphatic Amine– Used in applications where quick cure is preferred or no mixing

is required

• UV Precure/Cure

EpoxiesEpoxies

• Diglycidyl Ether of Bisphenol A • Most common• Low cost

• Diglycidyl Ether of Bisphenol F• More expensive

• Cycloaliphatic• More expensive• High performance

• Amines• Aromatic-elevated temp cure• Aliphatic-room temp cure

• Polyamides

• Anhydrides-high temp cure

• Dicyandiamide-typically used in 1 components

RESINS HARDENERS

Hardener Type vs. PropertiesAminesAliphatic

AminesAromatic

Polyamides Anhydrides

Appearance Rigid, Brittle Rigid, Tough Slightly to very flexible

Rigid to flexible

Operating Temperature,°C

105°C (221 °F)

155 – 180°C (302-356 °F)

105°C (221 °F)

To 200°C (392 °F)

Potlife, hrs. 0.5 – 0.75 8 2 – 3 20 hrs +

General Uses Modules, small castings, adhesives

Solvent resistant apps, thermal

cycling

Thermal cycling, low

stress adhesive

Excellent electricals,

module potting, coil potting

Urethane Systems

• Mix ratios from: 1:1 to 1:7.7 • Mix viscosity from: 400 cP to 25,000 cP• Hardness from: 60 (OOO) to 85 (D) • Gel time from: 2 to 360 minutes @ 25°C• Dielectric Constant from: 3 to 7• Dissipation Factor from: 0.01 to 0.2• Dielectric Strength: up to 1200 volts/mil

(20mil thickness)

Urethane 2 part Systems

• Urethanes are produced through reaction of isocyanates (R-NCO) with polyol

• (HO-R-OH) or a prepolymer (pre-reacted polyol and excess Isocyanate) with a polyol

Urethanes

• Polyethers– Polyoxypropylene Glycol

(PPG)– Polytetramethylene Ether

Glycol (PTMEG)• Polybutadiene (Poly BD)

* restricted for export*• Polyesters

– Adipates– Polycaprolactones– Castor Oil

• Aromatic– Toluene Diisocyanate– 4,4’ Diphenylmethane

Diisocyanate (Pure MDI)– Crude (Polymeric) MDI

• Aliphatic– Hexamethylenediisocyante

(HDI)• Cycloaliphatic

– Isophorone Diisocyanate (IPDI)

– Methylene Bis (4- cyclohexylisocyanat4e) (HMDI)

POLYOLS ISOCYANATES

Urethane vs. Epoxy

Property Epoxy Urethane

Operating Temperature, °C

<200 <125

Thermal Shock Good Better

Exotherm Varies, can be high Low (<50°C)

Moisture Sensitivity During Processing and

Storage

Less sensitive Very sensitive

Electrical Properties Good Good

Strength Best Good

Elongation <100% >100%

Tg, °C 0 to 160+ -65 to 80

Hardness Shore D >35 Shore A <90

FillersDesired Effects

Improved Machinability

Improved Thermal Conductivity

Improved Abrasion Resistance

Improved Impact Strength

Improved Electrical Conductivity

Improved Thixotropic Response

X-Ray Opaque

Fillers Calcium Carbonate

Alumina Chopped Glass

Mica Metallic fillers Colloidal Silica Barytes

Calcium Silicate

Flint powder Alumina Silica Alumina Bentonite clay Iron

Powdered aluminum or copper

Carborundum Powdered or flaked glass

Carbon fiber

Silica

Molybdenum dissulfide

TradeTrade--off: Abrasiveness / Hardness of Fillersoff: Abrasiveness / Hardness of Fillers

MOH Hardness

ABRASIVENESS 1 10Least

Most

TalcCaCO3

Silica

SiliconDioxide

Alumina

Diamond

ATH

Applications

Voltage regulator (off-road vehicles)Urethane

Applications

Sprinkler SolenoidUrethane

Applications

Automotive Light SocketsUrethane

Applications

Windshield Washer Fluid Heater

Camshaft Position Sensor

Urethanes

Applications

Telephone Connector BlocksUrethane

Applications

Ignition Coils Automotive Brake Sensor

Epoxies

Applications

TPMS Remote TransmitterUrethanes

Applications

Automotive ECMUrethane

Applications

Automotive LED Tail LightEpoxy

Circuit Board Protection

• Potting• Gasketing• Conformal Coating

– Epoxy (Hard, Abrasion resistant)– Acrlylic (low-VOC)– Urethane (reworkable)– Silicone (High-temp, UV/dual cure)

• Low Pressure Molding

Solutions Across the Board and Across the Globe

Thank You