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1、Electronic Module Conformal Coating and Potting,MPC-T-1,2,Training Objectives,Explain what coatings and pottings are and why they are used Describe coating and potting application methods and controls Provide examples of coating and potting within Delphi Provide resources for additional information,
2、3,Outline,Definitions Coating Reasons for coating Material types Application methods and Delphi examples Quality issues Potting Reasons for potting Material types Application methods and Delphi examples Quality issues Additional sources of information,4,What Is It?,Conformal Coating A thin layer of
3、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. Potting (also referred to as encapsulation) A process of filling a complete electronic assembly with a solid compound for
4、 resistance to shock and vibration, and for exclusion of moisture and corrosive agents.,Transparent coating on a populated printed circuit board,Opaque potting material in an electronic module cavity,Transparent “gel” potting material in an electronic module cavity,5,Additional Definitions,Ion: An a
5、tom 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. Ionic contamination: Surface debris that contains ions Electrochemical migration (ECM): Also known as Dendritic Growth, is the growth of conductive
6、 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. Tin whiskers: A crystalline metallurgical phenomenon involving the spontaneous growth of tiny, filiform hairs from a meta
7、llic surface. The mechanism is encouraged by compressive mechanical stresses Silicone: 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. Acrylic: Thermoplastic made by polymerizin
8、g acrylic acid or methacrylic acid . Acrylics are used for cast and molded parts or as coatings and adhesives Polyurethane: 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 dens
9、ities,Coatings,7,Why 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 an
10、d 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 conditioning Provide physical protection to the circuitry and components by preventing surface scrat
11、ches under normal handling and use Mitigate the effect of tin whiskers,8,Encapsulating Contaminants,Thin layer of water or water vapor,Various types of contamination,Circuit board laminate,Without Conformal Coating,Thin layer of water or water vapor,Conformal coating keeps moisture away and encapsul
12、ates contamination and circuitry,Contaminants dissolve in water and become mobile ions,9,What is Dendritic Growth?,It 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
13、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 electrolyte,Image from www.npl.co.uk,Direction of Growth,- +,10,What is De
14、ndritic Growth?,Electricity + Water + Contamination = Dendrites,11,Dendritic Growth,Conditions 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
15、 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!,12,Dendritic Growth,Applied correctly, Conformal Coating will prev
16、ent 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 dissolved,1. Bias is present ( 1 to 2 volts) 2. Water is presen
17、t. 3. Ionic contamination cannot dissolve and become mobile ions. Therefore no dendritic growth!,13,Dendritic Growth A Cautionary Note!,Conformal 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
18、to the surface relatively quickly Small Chip Capacitors have been shown to be very sensitive to this condition,Verification of coating coverage and thickness during process set-up is critical,Dendrite across capacitor terminals where coating is thin / missing,14,Another Case Where Coating Does Not H
19、elp,Circuit board laminate,Contamination bridges circuitry,Coating layer,Continuous contamination layer is in place prior to coating application,15,Is the product in a sealed case, potted, or gel encapsulated?,Coating recommended by MTT,Product remains uncoated,Is the product a mission critical or s
20、afety related device?,Try validating with no conformal coating,Product passes validation with no ECM,Product fails validation,Try validating with no conformal coating,Does the product have pure (99%) tin finishes on the circuit board or any component surface, including connectors, surface mount comp
21、onents and through hole components?,Conformal Coating recommended,Failure due to cause other than ECM or moisture susceptibility,Failure due to ECM, corrosion, moisture susceptibility,Validation requires condensing moisture while under power or a “dewing test”,Product passes validation with no ECM,P
22、roduct remains uncoated,Product fails validation due to ECM, corrosion, moisture susceptibility,MTT Recommended Coat/No-Coat Decision Tree,Customer requires coating regardless of case design,MFGE RP 9.3 Appendix A,16,Key Coating Decision Factors,Customer Requirement Specifically required regardless
23、of product design or technology Build-to-print Validation test specifications Product 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 n
24、ot 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 board In all cases MFGE RP 9.12: Liquid Water Immunity Test can be used to identify sensitive circuitry that will require coating,1
25、7,What Coating Materials Are Used?,Delphi-E&Ss current menu of conformal coatings has selections from most coating types: Commonly used Silicones 5 approved materials available Acrylic 1 approved material Application specific materials Polyurethane Typically used in Europe Parylene Must be applied b
26、y a 3rd party (single source) Before 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 usage,18,Silicone Coating Mater
27、ials,Silicone: 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 Advantages Wide temperature range: Compliant to most environmental restrictions (WEEE, RoHS, REACH) Low m
28、echanical stress Concerns 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 housings Material Suppliers Dow Corning Shin Etsu,Material High Temp
29、Flexible to Silicones +150 to 200C -45 to -115C Epoxies +150 to 180C n/a Urethanes +115 to 125C -60C Acrylics +85C n/a,19,Acrylic Coating Materials,Acrylic Resin: Thermoplastic or thermosetting plastic substance derived from acrylic acid, methacrylic acid or other related compounds Advantages No ris
30、k of silicone volitiles Fast ambient curing Capable of applying very thin layer (0.001”) Concerns Not approved for high temperature applications Max temp: 85C Solvent based, therefore may not satisfy REACH requirements Not a low VOC (volitile organic compounds) material Material Suppliers Elantas /
31、PD George,20,Polyurethane Coating Materials,Polyurethane: A family of polymers that offer a range of hardness values. They have good strength and environmental resistance properties Advantages 2-part curing systems can be adjusted for application Vary catalyst to resin ratio to modify hardness Good
32、moisture resistance Concerns Limited service temperature (120C) Not easily repaired Suppliers Primarily supplied to European manufacturing sites Lackwerke Peters Hunstman,21,Coating Application Methods,Lean, Selective Spray Coating Also have Jet Pulse precision coating Dip Coating Dispense Coating O
33、nly approved for use in specialized cases Manual Brush Coating Not recommended by the MTT for general use,22,Spray coating,The preferred method for applying conformal coatings in manufacturing Spray heads are mounted on 3-axis robot gantries. The system has natural tolerances and capability limitati
34、ons.,Selective coating spray valves,Spray coater,23,Spray Coating Details,Example 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 / SZ
35、M (multiple programs) Silicone coating can be applied by both systems Acrylic coating is best applied by Nordson-Asymtek system Why used / preferred Controlled application of coating Reduced material and utility usage Fits “Lean” principles Prevent material from coating “keep-out” zones without mask
36、ing Reduced board to board cross-contamination Common Issues Nozzle clogging Thickness variation or streaking Overspray into keep-out areas Shadowing around larger components,24,Precision Spray Coating,Also known as Jet Pulse Spray Coating Special application of Selective Spray Coating when tighter
37、spray tolerance is required Standard clearance to non-coated areas is 3.2mm Precision Coating clearance is 1.0mm,25,Dip Coating,Board is dipped in a bath of coating Example of usage Suzhou Equipment Cheng Hua Material DC 4097 (Silicone) Delnorte Equipment Knoedel, Paintline Material DC 4097(Silicone
38、) Equipment 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 coating,26,Dip Coating,Why used Apply coating quickly across an entire board Floods areas where small components may reside under connection system E
39、conomical for high volume production Common 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, a
40、t least 20% of the material must be used or replaced per week If solvent borne coating, need to add solvent to maintain viscosity Drawbacks Large equipment size Not scalable for lower volume Cannot dip coat with non-underfilled BGAs Underfilled flip-chips are OK,27,Cure Processes,Depending on their
41、chemistry, coatings can be cured by Heat UV energy Moisture Ambient air,28,Coating Guidelines,DDS27 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 areas From MFGE RP 9.9 Coating Thickness Guidelines For
42、Circuit Board Environment With Condensing Moisture,29,Quality,Quality defects are identified by their effect on adhesion, coverage, or coating homogeneity Does it compromise the coatings ability to protect the circuit? Does it compromise downstream operations? Examples: Always refer to released prod
43、uct workmanship standards for specific criteria,Bubble exposes PCB,Excessive Bubbling,Insufficient Coverage,Overspray,30,Quality,IPC 610D is the primary source for coating quality Additional quality guidelines available through the Coatings and Adhesive Web Page http:/ link The amount of coating and
44、 coverage required is product dependent and will be determined by validation requirements,31,Quality,The addition of UV dye to the coatings makes defects easily visible under a blacklight,32,Assembly Stacking Error Assembly Sliding On Work Surface Error,Both the coating and the components can be dam
45、aged by mishandling,Assembly Handling Errors,Pottings,34,Why Use Potting?,Encapsulate and immobilize ionic contamination Provide physical protection to the circuitry and components without need for a cover Provide mechanical stability to components with respect to vibration and shock,35,What Potting
46、 Materials Are Used?,Silicone based gels Hard potting Epoxy Polyurethane Silicone adhesives,36,Selecting a potting Material,Before use, materials must pass comprehensive compatibility testing (including Surface Insulation Resistance) and solder joint reliability testing RP-9.21 defines the test plan
47、 and methods Materials COE approval required In addition, pottings must meet thermal and mechanical requirements for the product Cannot impart undo thermal stress on components Should not create excess voids or expansion within a constrained space,37,Cure Processes,Pottings are applied to products b
48、y 1-part or 2-part dispense 1-part materials Heat Moisture Oxidation 2-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
49、frequent change of mix tubes is required to prevent clogging Material mixing can be done “statically” or “dynamically”,38,2-part mixing techniques,Static Mixing Material is combined as it flows through a specially designed mix tube Dynamic Mixing Mixing equipment uses moving parts to combine the potting components prior to dispensing,39,Product Example,SDM Fluid Research equipment di