pcb protection - la/oc smta · • various chemistries – acrylics – one component, highly...
TRANSCRIPT
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PCB Protection Conformal Coating, Potting, &
Encapsulation
Dr. Brian TolenoHenkel
Irvine, CA
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Agenda
• Reasons for using PCB Protection
• Conformal Coating
• Low Pressure Molding (Macromelt®)
• Potting
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PCB Protection Agenda
• Why?• What Environments?• What Method?• What Chemistry?
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Purpose
• Environmental– Moisture– Harmful fluids– Dirt– Ultraviolet light
• Mechanical– Shock and Vibration
• Radio Frequency– Faraday cage
• Electrical Insulation• Proprietary Design
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Possible Environments• Automotive
– Underhood– In Cabin– External
• Telecom– Proprietary Programming
• Utilities– UV protection– Moisture protection
• Military• Marine
Environments
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Considerations
• Type of protection needed
• Size of board/part• Weight
requirements• Rework required?• Protection from
aftermarket modification/repair
• Design status
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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
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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.
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Why?
“Hey Frank…better have engineering include a conformal coating on that next batch.”Www.plasmasystems.com/guide.html
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Conformal Coating Applications
• Traditionally, conformal coatings were only used in high reliability applications
– military– aerospace
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• Many Fine Pitch SMT designs will not operate or perform adequately in humid environments without the use of a Conformal Coating
Conformal Coating Applications
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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 + -
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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
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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
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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
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Conformal Coating Chemistry - Silicone (SR)
• Advantages– Low modulus– Electrical properties– Wide temperature range– Easy repair
• Disadvantages– High CTE– Low modulus– Cost
Based on Polydimethylsiloxane
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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)
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Conformal Coating Process
(Clean) (Mask) (Cure)
Coat Cure (Demask)
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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
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Applying the Coating
• Dip• Spray (Dispense)• Brush
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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
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Conformal Coating Process Curing
• Solvent Evaporation• Heat• RT Moisture Two-Part
• UV Light Combinations– UV/Heat– UV/Moisture– UV/Two-Part
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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
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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
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Low Pressure Molding
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• 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
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• 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
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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
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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
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• 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
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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
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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
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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
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Macromelt® Polyamide resin
• Non-Linear Molecule
-R Amine
Non-linear exhibit good flexibility, low MW and most importantly, low
viscosity
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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
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Telecom Applications
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Macromelt
Li-Ion batteries
Antennas
Mobile Phone Applications
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Automotive Applications
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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
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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.
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Potting
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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
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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
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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
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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
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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)
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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
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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
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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
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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
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TradeTrade--off: Abrasiveness / Hardness of Fillersoff: Abrasiveness / Hardness of Fillers
MOH Hardness
ABRASIVENESS 1 10Least
Most
TalcCaCO3
Silica
SiliconDioxide
Alumina
Diamond
ATH
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Applications
Voltage regulator (off-road vehicles)Urethane
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Applications
Sprinkler SolenoidUrethane
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Applications
Automotive Light SocketsUrethane
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Applications
Windshield Washer Fluid Heater
Camshaft Position Sensor
Urethanes
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Applications
Telephone Connector BlocksUrethane
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Applications
Ignition Coils Automotive Brake Sensor
Epoxies
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Applications
TPMS Remote TransmitterUrethanes
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Applications
Automotive ECMUrethane
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Applications
Automotive LED Tail LightEpoxy
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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
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Solutions Across the Board and Across the Globe
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Thank You