3CONFORMAL COATINGSA newly manufactured printed circuit board will generally perform well but performance will quickly deteriorate.Common causes of deterioration and PCB failure include:Atmospheric moistureContamination of the surface with airborne ionic materialElectrostatic attraction of dust to the surfaceCorrosive environments, such as salt fogConformal 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.MilitaryIndustrialAutomotiveDomesticAerospace
4CONFORMAL COATINGSConformal coatings are thin coatings, typically microns, which ‘conform’ to the contours of a PCB.The ideal conformal coating will have performance requirements that include:Good electrical propertiesLow moisture permeabilityGood mechanical durabilityExcellent adhesion propertiesGood thermal resistanceAdditional properties such as flame retardance or chemical resistance may also be required.
5CONFORMAL COATING TERMINOLOGY 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 coatingIt 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 protectionIt 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
6CONFORMAL COATING APPLICATION Conformal coatings can be brushed, dipped or sprayed depending on the requirements. Customers often specify their desired application method.Brushing:AdvantagesDisadvantagesCost effectiveUneven coatingIdeal for small scale productionDifficult to get under componentsSelective coatingOnly one side at a time can be coated
7CONFORMAL COATING APPLICATION Dip Coating:AdvantagesDisadvantagesIdeal for medium scale productionInitial capital outlayUniform coating thicknessMasking essential for connectorsEasy to operate machinerySpecial extraction may be requiredBoth sides can be coated at the same timeSuitable for higher viscosity materialsCoating can penetrate under componentsOperator training required but not difficult
8CONFORMAL COATING APPLICATION Spraying – aerosol or manual spray gun:AdvantagesDisadvantagesCost effectiveOverspray can occurIdeal for bench top work and repairDifficult to get under componentsIdeal for small to medium scale productionSpecial extraction may be requiredConvenientOnly one side at a time can be coated
10CONFORMAL COATING APPLICATION Selective Spraying:AdvantagesDisadvantagesNo masking requiredInitial capital outlayUniform thicknessLow under component penetration – requires good flow properties with the coatingAutomated process – good for inline proceduresSpecial extraction may be required – but can be linked to the machine easilyIdeal for all scales of productionRequires a trained operator to set the software
13Application Conditions Temperature – Affects viscosity and evaporation rateHumidity – Contaminates dip coat tanks, blooming in hand spray and affects curing / pot life.Ventilation – Affects operators
15Considerations for Choice As 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 propertiesAdhesionFlexibilityTemperature rangeMechanical durabilityElectrical performanceEnvironmental performanceFlame retardanceMould resistanceApplicationViscosity/applicationTouch dry timeFull cure timeCuring conditionsIs re-work required?CostQualityApprovals required?
16CONFORMAL 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:Solvent-based – Evaporation CureSolvent-based – Heat CureLow VOC/Water-based – Evaporation/Heat CureNon-VOC – Moisture CureUV Cure – Dual Cure: Moisture/HeatCommon conformal coating chemistries include:AcrylicPolyurethaneSiliconeModified-silicone
17DCA (SCC3) MODIFIED SILICONE COATING DCA is a flexible, transparent & unique modified silicone conformal coating specifically designed for the protection of electronic circuitry.Key Features:Resistant to most solvents, lubricants and chemicals associated with most aerospace and automotive applications.Excellent adhesion under various climatic conditions to a variety of substrates, including high altitude/decompressionFluoresces under UV light for ease of inspection.Extreme operating temperature range (-70˚C to +200˚C)Excellent electrical properties
18DCA (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, 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 GelApprovalsDef-Stan 59/47 – Standard now obsoleteUL746 – File Number E138403
19DCA (SCC3) MODIFIED SILICONE COATING The DCA (SCC3) Range includes:DCA-FD – Fast-dry versionDCA-HT – With improved high temperature performanceDCR – Opaque red versionDCB – Opaque black versionDCRT – Opaque red, high viscosity versionDCE – Thixotropic gel version (dam and fill applications)Unique range of products based on a silicone modified alkydAvoids issues associated with silicone migrationEasier processing than standard siliconesPerformance compares with many silicone conformal coatings
20TFA – 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:Toluene free product.Fluoresces under UV light for ease of inspection.Wide operating temperature range (-65˚C to +125˚C)Excellent Dielectric propertiesClear coating with excellent resistance to yellowing when exposedto UV light
21TFA – 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 GelApprovalsUL746 ApprovedIPC-CC-830 approvedAutomatically meets MIL CAlso available: AFA – Aromatic Free Acrylic
22VOCs – THE NEED TO CHANGE 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
23EU Solvents Emissions Directive VOC DEFINITIONEU 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”
24UVCL - UV Cure Extremely rapid initial cure schedule Ideal for high volume productionIn-line process, curing equipment requiredVery high level of protection; highly cross-linked coatingExcellent chemical and solvent resistanceUsing a dual cure system can ensure that in shadowed areas under components the coating still cures and protects the PCBMoistureHeatUV cure coatings are available as 100% solids materialsNon-VOC options
25WBPS – 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.
26WBPS – WATER-BASED COATING Key Features:Environmentally friendly and eliminates hazards associated with solvent based conformal coatingsExcellent solvent resistance.Very low VOC contentNMP (N-Methyl pyrrolidone) free.Fluoresces under UV light for ease of inspection.Excellent adhesion on a wide variety of substrates.Excellent Dielectric properties and resistant to mould growth.
27PUC – 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 FeaturesExcellent adhesion to a wide variety of substrates.Fluoresces under UV light for ease of inspection.Good resistance to a wide variety of chemicals including acids and alkalis.Wide operating temperature range.Excellent mechanical properties including abrasion resistanceSolvent-based, can be sprayed, dipped or brushedShould be used with PTH thinners and removed with CCRG
29CHOOSING THE RIGHT PRODUCT High Temperature – DCA (SCC3) RangeExcellent Clarity – TFA or an Acrylic CoatingChemical Resistance – PUC or DCA (SCC3) RangeCosmetic Appearance – CPL (no UV trace)Low Solvent Content – WBP or WBPsReworkable – Acrylic Coatings or FSCUL Approved – DCA and TFAUV Cure - UVCL
33Adhesion LossIncorrect 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.
35Coating 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.
36OTHER PRODUCTSIn 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 processMasking – PCM and PCS are coating masks suitable for covering connectors duringthe coating process
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