三防漆与灌封.ppt

Delphi ProprietaryManufacturing EngineeringElectronic Module Conformal Coating and PottingMPC-T-1Delphi ProprietaryManufacturing EngineeringTraining ObjectivesuExplain what coatings and pottings are and why they are useduDescribe coating and potting application methods and controlsuProvide examples of coating and potting within DelphiuProvide resources for additional information2Delphi ProprietaryManufacturing EngineeringOutlineuDefinitionsuCoating –Reasons for coating–Material types–Application methods and Delphi examples–Quality issuesuPotting–Reasons for potting–Material types–Application methods and Delphi examples–Quality issuesuAdditional sources of information3Delphi ProprietaryManufacturing EngineeringWhat Is It?uConformal Coating–A thin layer of a dielectric (electrically insulating) chemical compound that is applied to the surface and serves to protect the electronic circuitry. The material can be transparent or opaque.uPotting (also referred to as encapsulation)–A process of filling a complete electronic assembly with a solid compound for resistance to shock and vibration, and for exclusion of moisture and corrosive agents. Transparent coating on a populated printed circuit boardOpaque potting material in an electronic module cavityTransparent “gel” potting material in an electronic module cavity4Delphi ProprietaryManufacturing EngineeringAdditional DefinitionsuIon: An atom or molecule where the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge.uIonic contamination: Surface debris that contains ionsuElectrochemical migration (ECM): Also known as Dendritic Growth, is the growth of conductive metal filaments on or in a printed circuit board (PCB) under the influence of a DC voltage bias. The filament growth is facilitated by the movement of ions on the circuit board.uTin whiskers: A crystalline metallurgical phenomenon involving the spontaneous growth of tiny, filiform hairs from a metallic surface. The mechanism is encouraged by compressive mechanical stresses uSilicone: Inert, man-made polymer compounds that include silicon, carbon, hydrogen and oxygen and some other chemical elements. Silicones can be used over a wide temperature range.uAcrylic: Thermoplastic made by polymerizing acrylic acid or methacrylic acid . Acrylics are used for cast and molded parts or as coatings and adhesives uPolyurethane: Any polymer consisting of a chain of organic units joined by urethane (carbamate) links Polyurethane formulations cover an extremely wide range of stiffness, hardness, and densities 5Delphi ProprietaryManufacturing EngineeringCoatingsDelphi ProprietaryManufacturing EngineeringWhy Do We Coat?uEncapsulate and immobilize ionic contaminationuPrevent electrochemical migration (ECM), also known as dendritic growthuPrevent further contamination of circuitry by environmental salts, soils, dust, smoke, and water vaporuPrevent circuit leakage between conductors and possible arcing in high current situations–For example the UL94V0 standard require that coatings survive 1000V for one minute without breakdown»At minimal coating thickness»After prescribed thermal conditioninguProvide physical protection to the circuitry and components by preventing surface scratches under normal handling and useuMitigate the effect of tin whiskers7Delphi ProprietaryManufacturing EngineeringEncapsulating ContaminantsThin layer of water or water vaporVarious types of contaminationCircuit board laminateCircuitCircuitWithout Conformal CoatingCircuit board laminateCircuitCircuitWith Conformal CoatingThin layer of water or water vaporConformal coating keeps moisture away and encapsulates contamination and circuitry Contaminants dissolve in water and become mobile ions58Delphi ProprietaryManufacturing EngineeringWhat is Dendritic Growth?uIt is a form of “Electro-chemical Migration (ECM).”–Conductive metal filaments grow on the surface of a Printed Wiring Board (PWB) or component under the influence of a DC voltage bias –ECM (or Dendritic Growth) is very similar to electro-plating. –Metallic ions migrate from the anode (+) to the cathode (-) of a circuit»Under the influence of an electrical bias and in the presence of sufficient water or other electrolyteImage from www.npl.co.ukDirection of Growth - +19Delphi ProprietaryManufacturing EngineeringWhat is Dendritic Growth?Electricity + Water + Contamination = Dendrites10Delphi ProprietaryManufacturing EngineeringDendritic GrowthuConditions for Electrochemical Migration –An electrical potential (voltage) between the electrodes is needed to establish an ionic current in the water layer.–Water or other electrolyte must be present to dissolve the ionic materials and sustain them in their mobile ionic state. –Electrical carriers (such as ions) must be present. 1. Bias is present (> 1 to 2 volts) 2. Water is present. 3. Ionic contamination is present. Therefore dendritic growth!ANODE +CATHODE -11Delphi ProprietaryManufacturing EngineeringDendritic GrowthuApplied correctly, Conformal Coating will prevent Electro-Chemical Migration! –Provides additional dielectric material to reduce the electrical potential (voltage) between the electrodes –Creates a barrier between water or other electrolyte and ionic contaminants so that ions are not dissolved1. Bias is present (> 1 to 2 volts) 2. Water is present. 3. Ionic contamination cannot dissolve and become mobile ions. Therefore no dendritic growth!ANODE +CATHODE -12Delphi ProprietaryManufacturing EngineeringDendritic Growth – A Cautionary Note!uConformal coating is not a barrier to standing water–Over time water molecules will penetrate silicone and acrylic coatings–When the coating is thin water migrates to the surface relatively quickly–Small Chip Capacitors have been shown to be very sensitive to this conditionVerification of coating coverage and thickness during process set-up is criticalDendrite across capacitor terminals where coating is thin / missing13Delphi ProprietaryManufacturing EngineeringAnother Case Where Coating Does Not HelpCircuit board laminateCircuitCircuitContamination bridges circuitryCoating layerContinuous contamination layer is in place prior to coating application14Delphi ProprietaryManufacturing EngineeringIs the product in a sealed case, potted, or gel encapsulated?Coating recommended by MTTProduct remains uncoatedIs the product a mission critical or safety related device? Try validating with no conformal coating YesYes NoProduct passes validation with no ECMProduct fails validationTry validating with no conformal coatingDoes the product have pure (99%) tin finishes on the circuit board or any component surface, including connectors, surface mount components and through hole components? No YesConformal Coating recommendedFailure due to cause other than ECM or moisture susceptibilityFailure due to ECM, corrosion, moisture susceptibilityValidation requires condensing moisture while under power or a “dewing test” No NoProduct passes validation with no ECMProduct remains uncoatedProduct fails validation due to ECM, corrosion, moisture susceptibility YesMTT Recommended Coat/No-Coat Decision TreeCustomer requires coating regardless of case designMFGE RP 9.3 Appendix A15Delphi ProprietaryManufacturing EngineeringKey Coating Decision FactorsuCustomer Requirement–Specifically required regardless of product design or technology–Build-to-print–Validation test specificationsuProduct Design and Application Requirements–Liquid water condensing on circuits generally drives the decision to coat»Result of product validation »A function of product usage or location –Sealed case design typically does not require coating–Poor component or board cleanliness or exessive water absorption drives need to coat–High failure mode “severity” can be mitigated by coating circuit boarduIn all cases MFGE RP 9.12: Liquid Water Immunity Test can be used to identify sensitive circuitry that will require coating16Delphi ProprietaryManufacturing EngineeringWhat Coating Materials Are Used?uDelphi-E&S’s current menu of conformal coatings has selections from most coating types:–Commonly used»Siliconesu5 approved materials available»Acrylicu1 approved material–Application specific materials»PolyurethaneuTypically used in Europe»ParyleneuMust be applied by a 3rd party (single source)uBefore use, materials must pass comprehensive compatibility testing (including Surface Insulation Resistance) and solder joint reliability testing–MFGE RP-9.21 defines the test plan and methods–Materials COE (Hank Sanftleben) must approve usage17Delphi ProprietaryManufacturing EngineeringSilicone Coating MaterialsuSilicone: An entirely synthetic polymer containing a Si-O backbone. –Organic groups are frequently attached to the backbone via a Si-C bond–Note: Silicon is a metal and Silicone is a polymer uAdvantages–Wide temperature range:–Compliant to most environmental restrictions (WEEE, RoHS, REACH) –Low mechanical stressuConcerns–Customer sensitivity to Silicone contamination–Some relays and brush motors are sensitive to silicone volitiles »Only when silicone is within 1 cm or so of the arc current»Only on relays with poorly sealed housingsuMaterial Suppliers–Dow Corning–Shin EtsuMaterial High Temp Flexible toSilicones+150 to 200°C -45 to -115°CEpoxies+150 to 180°C n/aUrethanes+115 to 125°C -60°CAcrylics +85°C n/a18Delphi ProprietaryManufacturing EngineeringAcrylic Coating MaterialsuAcrylic Resin: Thermoplastic or thermosetting plastic substance derived from acrylic acid, methacrylic acid or other related compoundsuAdvantages–No risk of silicone volitiles–Fast ambient curing–Capable of applying very thin layer (0.001”)uConcerns–Not approved for high temperature applications »Max temp: 85C–Solvent based, therefore may not satisfy REACH requirements»Not a low VOC (volitile organic compounds) materialuMaterial Suppliers–Elantas / PD George19Delphi ProprietaryManufacturing EngineeringPolyurethane Coating MaterialsuPolyurethane: A family of polymers that offer a range of hardness values. They have good strength and environmental resistance propertiesuAdvantages–2-part curing systems can be adjusted for application »Vary catalyst to resin ratio to modify hardness–Good moisture resistanceuConcerns–Limited service temperature (<120C)–Not easily repaireduSuppliers –Primarily supplied to European manufacturing sites–Lackwerke Peters–Hunstman20Delphi ProprietaryManufacturing EngineeringCoating Application MethodsuLean, Selective Spray Coating–Also have Jet Pulse precision coatinguDip CoatinguDispense Coating–Only approved for use in specialized casesuManual Brush Coating–Not recommended by the MTT for general use21Delphi ProprietaryManufacturing EngineeringSpray coatinguThe preferred method for applying conformal coatings in manufacturing uSpray heads are mounted on 3-axis robot gantries. uThe system has natural tolerances and capability limitations. Selective coating spray valvesSpray coater22Delphi ProprietaryManufacturing EngineeringSpray Coating DetailsuExample of usage–PVA equipment spraying DC 3-1953 (silicone coating)»Kokomo plant 7 - BCM for GMT900 truck»Delnorte (multiple programs)–Nordson-Asymtek equipment spraying PD George 5026-21 (acrylic coating)»Delnorte / DDM / SZM (multiple programs)–Silicone coating can be applied by both systems–Acrylic coating is best applied by Nordson-Asymtek systemuWhy used / preferred–Controlled application of coating»Reduced material and utility usage»Fits “Lean” principles »Prevent material from coating “keep-out” zones without masking»Reduced board to board cross-contaminationuCommon Issues–Nozzle clogging–Thickness variation or streaking–Overspray into keep-out areas–Shadowing around larger components23Delphi ProprietaryManufacturing EngineeringPrecision Spray CoatinguAlso known as Jet Pulse Spray CoatinguSpecial application of Selective Spray Coating when tighter spray tolerance is required–Standard clearance to non-coated areas is 3.2mm–Precision Coating clearance is 1.0mm24Delphi ProprietaryManufacturing EngineeringDip CoatinguBoard is dipped in a bath of coatinguExample of usage–Suzhou»Equipment – Cheng Hua»Material – DC 4097 (Silicone)–Delnorte »Equipment – Knoedel, Paintline»Material – DC 4097(Silicone)uEquipment Differences–Knoedel system raises a small tub of coating to the board–Paintline and Cheng Hua systems bring boards down to a larger tub of coating25Delphi ProprietaryManufacturing EngineeringDip CoatinguWhy used–Apply coating quickly across an entire board–Floods areas where small components may reside under connection system–Economical for high volume productionuCommon Issues–Keep-out areas must be masked–Coating in dip bath can become contaminated with flux or other residues»DC 4097 neutralizes flux residues»Solvent borne coating is effected by flux–Need to monitor and prevent viscosity changes in the bath »For DC4097, at least 20% of the material must be used or replaced per week»If solvent borne coating, need to add solvent to maintain viscosityuDrawbacks–Large equipment size–Not scalable for lower volume–Cannot dip coat with non-underfilled BGAs»Underfilled flip-chips are OK26Delphi ProprietaryManufacturing EngineeringCure ProcessesuDepending on their chemistry, coatings can be cured by –Heat–UV energy–Moisture–Ambient air27Delphi ProprietaryManufacturing EngineeringCoating GuidelinesuDDS27 defines the minimum clearance between “must be” coated and “must not be” coated areas is 3.2mm–Allows for some slump or overspray around coated areasuFrom MFGE RP 9.9–Coating Thickness Guidelines For Circuit Board Environment With Condensing Moisture28Delphi ProprietaryManufacturing EngineeringQualityuQuality defects are identified by their effect on adhesion, coverage, or coating homogeneity –Does it compromise the coating’s ability to protect the circuit?–Does it compromise downstream operations?–Examples:uAlways refer to released product workmanship standards for specific criteriaBubble exposes PCBExcessive BubblingInsufficient CoverageOverspray29Delphi ProprietaryManufacturing EngineeringQualityuIPC 610D is the primary source for coating qualityuAdditional quality guidelines available through the Coatings and Adhesive Web Page linkuThe amount of coating and coverage required is product dependent and will be determined by validation requirements30Delphi ProprietaryManufacturing EngineeringQualityuThe addition of UV dye to the coatings makes defects easily visible under a blacklight 31Delphi ProprietaryManufacturing EngineeringAssembly Stacking Error Assembly Sliding On Work Surface ErrorBoth the coating and the components can be damaged by mishandlingAssembly Handling Errors32Delphi ProprietaryManufacturing EngineeringPottingsDelphi ProprietaryManufacturing EngineeringWhy Use Potting?uEncapsulate and immobilize ionic contaminationuProvide physical protection to the circuitry and components without need for a coveruProvide mechanical stability to components with respect to vibration and shock34Delphi ProprietaryManufacturing EngineeringWhat Potting Materials Are Used?uSilicone based gelsuHard potting–Epoxy–Polyurethane–Silicone adhesives35Delphi ProprietaryManufacturing EngineeringSelecting a potting MaterialuBefore use, materials must pass comprehensive compatibility testing (including Surface Insulation Resistance) and solder joint reliability testing–RP-9.21 defines the test plan and methods–Materials COE approval requireduIn addition, pottings must meet thermal and mechanical requirements for the product–Cannot impart undo thermal stresson components–Should not create excess voids orexpansion within a constrained space36Delphi ProprietaryManufacturing EngineeringCure ProcessesuPottings are applied to products by 1-part or 2-part dispenseu1-part materials–Heat–Moisture–Oxidationu2-part materials will generally cure upon mixing–Can take 24 hours or more for full cure–Additional minimum hold time may be required before validation testing »Up to several days–Process can be accelerated by heat–System purge and frequent change of mix tubes is required to prevent clogging–Material mixing can be done “statically” or “dynamically”37Delphi ProprietaryManufacturing Engineering2-part mixing techniquesuStatic Mixing–Material is combined as it flows through a specially designed mix tubeuDynamic Mixing–Mixing equipment uses moving parts to combine the potting components prior to dispensing38Delphi ProprietaryManufacturing EngineeringProduct ExampleuSDM–Fluid Research equipment dispenses PD George UH510S »two part urethane39Delphi ProprietaryManufacturing EngineeringQualityuUV dye in a transparent gel can make it visible for automated error proofinguSome level of bubbling is to be expected –Air escapes from under large components–Some air entrapped in processuExcessive bubbling and foaming can occur if material change-over not completed properlyuSample Workmanship Standard: 40Delphi ProprietaryManufacturing EngineeringBad Product Potting DesignuPartial fill of an “inverted cup” will apply excessive stress on solder joints–Gel shrinks during cool down after cure–Solder Cracking occurred at t=041Delphi ProprietaryManufacturing EngineeringSummaryuCoatings or pottings are required for the electrical and mechanical protection of many automotive electronic circuit boardsuThere are a number of MTT approved materials that are applied by a variety of methods uContact the MTT if new materials are being considered for applicationuVisit the Coatings and Adhesives MTT web page to learn more about the application Building Blocks: Delphi ProprietaryManufacturing EngineeringHow to acces the MTT webpage43Delphi ProprietaryManufacturing EngineeringHow to access the MTT webpage44Delphi ProprietaryManufacturing EngineeringHow to access the MTT webpage45Delphi ProprietaryManufacturing EngineeringQuiz Questions46Delphi ProprietaryManufacturing EngineeringQuestion 1____?_____ + Water + Contamination = Dendrites47Delphi ProprietaryManufacturing EngineeringQuestion 1Electricity + Water + Contamination = Dendrites48Delphi ProprietaryManufacturing EngineeringQuestion 2uConformal coating provides a water tight seal for electronics–True–False49Delphi ProprietaryManufacturing EngineeringQuestion 2uConformal coating provides a water tight seal for electronics–True–FalseuConformal coating is not a barrier to standing water–Over time water molecules will penetrate silicone and acrylic coatings–When the coating is thin water migrates to the surface relatively quickly–Small Chip Capacitors have been shown to be very sensitive to this condition50Delphi ProprietaryManufacturing EngineeringQuestion 3uDDS27 defines the minimum clearance between “must be” coated and “must not be” coated areas is ___?___mm51Delphi ProprietaryManufacturing EngineeringQuestion 3uDDS27 defines the minimum clearance between “must be” coated and “must not be” coated areas is 3.2 mm52Delphi ProprietaryManufacturing EngineeringQuestion 4uAcrylics can be used for coating underhood electronics–True–False53Delphi ProprietaryManufacturing EngineeringQuestion 4uAcrylics can be used for coating underhood electronics–True–FalseuAcrylics are limited to +85°CMaterial High Temp Flexible toSilicones+150 to 200°C -45 to -115°CEpoxies+150 to 180°C n/aUrethanes+115 to 125°C -60°CAcrylics +85°C n/a54Delphi ProprietaryManufacturing EngineeringQuestion 5uHow do you determine whether to coat or not?55Delphi ProprietaryManufacturing EngineeringQuestion 5uHow do you determine whether to coat or not?uConsider the key coating decision factors:–Customer Requirements–Product Design »Sealed case?–Application Requirements»Underhood, high humidity location?–Ability to pass the Liquid Water Immunity Test56Delphi ProprietaryManufacturing EngineeringQuestion 6uWhy Do We Coat?57Delphi ProprietaryManufacturing EngineeringQuestion 6uWhy Do We Coat?–Encapsulate and immobilize ionic contamination–Prevent electrochemical migration (ECM), also known as dendritic growth–Prevent further contamination of circuitry by environmental salts, soils, dust, smoke, and water vapor–Prevent circuit leakage between conductors and possible arcing in high current situations–Provide physical protection to the circuitry and components by preventing surface scratches under normal handling and use–Mitigate the effect of tin whiskersCircuit board laminateCircuitCircuitThin layer of water or water vaporConformal coating keeps moisture away and encapsulates contamination and circuitry 58Delphi ProprietaryManufacturing EngineeringQuestion 7uIPC 610D is the primary source for coating quality–True–False59Delphi ProprietaryManufacturing EngineeringQuestion 7uIPC 610D is the primary source for coating quality–True–False–Link to IPC 610D is provided through DWS 1.00060。