PERFORMANCE AS A FUNCTION OF COATING THICKNESS FOR ULTRATHIN FLUORINATED POLYMER COATINGS Molly Smith, Greg Marszalek 3M Company msmith7@mmm.com
Topics Purposes of coatings in electronics Performance tests Thickness versus performance - data analysis Application method affects thickness Remarks
Purposes of coatings on electronics Environmental protection Inhibit corrosion Electrical integrity Moisture protection Corrosion protection of metal
Common protective coating technologies for printed circuit boards: Common coating types Acrylic Epoxy Urethane Silicone Parylene Fluorinated polymer* * Fluorinated polymer coatings were used in the testing in this presentation * Coatings were applied by different methods with variable target thicknesses * Small thickness variations can make a difference in application processes and ultimate performance.
Topics Purposes of coatings in electronics Performance tests Thickness versus performance - data analysis Application method affects thickness Remarks
Performance Tests DWV* - IPC-TM-650 2.5.7.1 Water immersion* IPX7 Flowers of Sulfur* ASTM B809 Salt Spray ASTM B117 * Modified - details on following slides
Topics Purposes of coatings in electronics Performance tests Thickness versus performance - data analysis Application method affects thickness Remarks
Increasing Dielectric WIthstanding Voltage (Vac) Electrical Integrity Dielectric Withstanding Voltage vs Average Coating Thickness of Each Sample Dip Coated Spray Coated IPC-TM-650Test Method/Test # 2.5.7.1 Dielectric Withstand Voltage (DWV) Polymeric Conformal Coating Qualification 1500 VAC (Voltage), 60 Hz for 1 minute between positive points (1,2,3) and negative points (4,5) on test board. Modification: For boards passing 1500 VAC, voltage was ramped until breakthrough (arcing) occurred. Increasing Average Coating Thickness Thicker coating resulted in greater electrical insulation
Average Current Leakage over 1 hour at 3V or 6V (Log(amps)) Salt Water Immersion Protection IP7 Test Method Submerge unpowered sample under 1 meter of water for 30 minutes Remove from water, test Modification: IPC B25-A test boards were powered to 3VDC or 6VDC Powered boards were submerged under ~4 inches of 5% salt water solution for 1 hour Current leakage was measured across the open comb pattern throughout the entire test. Average Current Leakage versus Average Coating Thickness in Salt Water Immersion Test Increasing Average Thickness of Each Sample (microns) Dip Coated, Tested at 3VDC Dip Coated, Tested at 6VDC Spray Coated, Tested at 3VDC Spray Coated, Tested at 6VDC Uncoated This is evidence that a thicker coating allows for less current leakage in salt water
Cumulative Amount of Failed Resistors out of 30 total Corrosion Protection ASTM B809 Flowers-of-Sulfur Test method Samples placed in a desiccator containing elemental sulfur Desiccator placed in oven at elevated temperature. Infinite resistance reading across the resistors indicates an open circuit ( failure ). Modifications 105⁰C rather than 50⁰C No humidity control 14 12 10 8 6 4 2 0 Failure of 499 Ohm Resistors Per Time in FoS at 105 C 0 days 5 days 10 days 20 days 30 days 40 days 50 days Time 1 Spray, 4% Concentrate 3 Sprays, 4% Concentrate Uncoated Performance is not linear to thickness: E.g. tripling coating thickness extended time to initial failure by 5X
Corrosion Protection - Examples ASTM B809 Flowers-of-Sulfur with IPC suggested modifications for silver Uncoated, 5 Days FOS (105C) Uncoated, 51 Days FOS (105C) 1 pass spray, 51 Days FOS (105C) 3 Pass spray, 51 Days FOS (105C)
2015 3M Company Salt Spray (fog) Protection ASTM B117 Salt Spray Test method: 96 hour test duration unpowered ImAg IPC B25-A test boards Chamber temperature ~35 ⁰C; salt mist ph ~6.5 to 7 ASTM B117, 3.2: Prediction of performance in natural environments has seldom been correlated with salt spray results when used as stand-alone data Modification: None Uncoated Non-atomize Spray with 1% Concentrate Non-atomize Spray with 4% Concentrate Non-atomize Spray with 8% Concentrate
Topics Purposes of coatings in electronics Performance tests Thickness versus performance data analysis Application method affects thickness Remarks
Process Conditions Affect Coating Thickness Dip Impacted by: Solvent properties Coating viscosity Removal rate of substrate from dip bath Size and shape of substrate and components Multiple coating dips Spray Impacted by: Solvent properties Coating viscosity Spray nozzle shape and size Machine settings (e.g. speed, z-height, fluid pressure and atomization) Size and shape of substrate Multiple spray passes
Dip coating Background Wafers etched to expose trenches Etched wafers dip coated in ultrathin fluorinated polymer coating Cross sectional (SEM) shows coating thickness variation Fluoropolymer coating: 127nm on top of trench 94nm on corner ~190nm in trench Etched wafer dip coated in 4% solids fluorinated polymer solution Very thin fluoropolymer coating conforms to very small geometries when dip coating
Spray coating Coating Wafers etched to expose trenches Etched wafers atomized spray coated with ultrathin fluorinated polymer coating SEM cross sectional analysis Fluoropolymer coating completely fills the trench: Coating was about 5 microns across the entire wafer Etched wafer atomized spray coated with 4% fluorinated polymer Very thin fluoropolymer coating conforms to very small geometries when spray coating
Spray Parameters Must be Carefully Setup Process Condition 1,2,3 Process Condition 4 Parameters contributing to good result in process condition 4: Percent solids 4% Distance to surface 65mm Atomizing at 2psi Fluid pressure at 5psi
Resistor Cross Section - Comparing Dip to Spray Dip 499 Ohm resistor Spray Hand soldered 499 Ohm resistors cross sectioned lengthwise for SEM / elemental analysis
Elemental Analysis SEM pictures of dip coated cross-sectioned resistor Fluoropolymer coating conforms to larger geometries when dip coated
Elemental Analysis SEM pictures of spray coated cross-sectioned resistor Fluoropolymer coating conforms to larger geometries when spray coated
Topics Purposes of coatings in electronics Performance tests Thickness versus performance - data analysis Application method affects thickness Remarks
Remarks Protection of printed circuit boards and their components are an increasing concern as electronics are used in more environmental conditions. Different customer applications require different levels of coating thickness to provide appropriate protection. Ultrathin fluorinate polymer coatings can provide sufficient protection from moisture, sulfur and other environmental contaminants for many applications. Different coating application methods can provide various thicknesses and should be chosen based on user performance requirements, production needs and overall costs.
Thank you Contact us with Questions Greg Marszalek 3M Electronics Materials Solutions Division Office: 651.733.1815 gjmarszalek@mmm.com Molly Smith 3M Electronics Materials Solutions Division Office: 651.733.2619 msmith7@mmm.com
Important Notice Regulatory: For regulatory information about these products, contact your 3M representative. Technical Information: The technical information, recommendations and other statements contained in this document are based upon tests or experience that 3M believes are reliable, but the accuracy or completeness of such information is not guaranteed. Product Use: Many factors beyond 3M s control and uniquely within user s knowledge and control can affect the use and performance of a 3M product in a particular application. Given the variety of factors that can affect the use and performance of a 3M product, user is solely responsible for evaluating the 3M product and determining whether it is fit for a particular purpose and suitable for user s method of application. Warranty, Limited Remedy, and Disclaimer: Unless an additional warranty is specifically stated on the applicable 3M product packaging or product literature, 3M warrants that each 3M product meets the applicable 3M product specification at the time 3M ships the product. 3M MAKES NO OTHER WARRANTIES OR CONDITIONS, EXPRESS OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, ANY IMPLIED WARRANTY OR CONDITION OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE OR ANY IMPLIED WARRANTY OR CONDITION ARISING OUT OF A COURSE OF DEALING, CUSTOM OR USAGE OF TRADE. If the 3M product does not conform to this warranty, then the sole and exclusive remedy is, at 3M s option, replacement of the 3M product or refund of the purchase price. Limitation of Liability: Except where prohibited by law, 3M will not be liable for any loss or damage arising from the 3M product, whether direct, indirect, special, incidental or consequential, regardless of the legal theory asserted, including warranty, contract, negligence or strict liability. Electronics Materials Solutions Division 3M Center, Building 224-3N-11 St. Paul, MN 55144-1000 1-800-810-8513 www.3m.com/novec 3M and Novec are trademarks of 3M Company. Please recycle. 3M 2016. All rights reserved. 10/2016
IPC-CC-830 Handbook Three classes of electronics: Class 1: General Electronic Products (extended use is not required) Class 2: Dedicated Service Electronic Products (extended use is expected and uninterrupted service is desired) Class 3: High Performance Electronic Products (extended use is required and uninterrupted service is critical to life) So what thickness you actually need will be dependent upon which of these classes, and their resulting performance requirements, are needed.