Conformal coatings are applied on printed circuit board assemblies (PCBAs) in order to protect the assembly from environmental influence and silicone-based coating is commonly used. A systematic study on the performance of silicone conformal coating in connection with process-related contaminants is the focus of this paper. Different test substrates such as plain laminate surface and a test PCBA with and without conformal coatings were exposed to high humid environment at ambient temperature and the performance of the coating was evaluated using various parameters such as increase in leakage current across the components, morphology of the coating, and analysis of dendrite formation due to electrochemical migration under the coating. The morphology of the coating before and after exposure was investigated using scanning electron microscopy, and energy dispersive X-ray spectroscopy. Results show that the presence of flux residues greatly influences the electrical functionality of the components and also degrades the performance of the coatings compared to the clean substrates.
IPC-HDBK-830: ‘Guidelines for design, selection, & application of conformal coatings’2002Northbrook, ILIPC.
2.
GooseyM. T.: ‘Plastics for electronics’1999Dordrecht, Springer.
3.
TobolskyA. T.: ‘Properties and structure of polymers’1960New York, Wiley.
4.
AndriotM.DeGrootJ. V. rJ., MeeksR.GerlachE.JungkM.WolfA. T.CrayS.EastonT.MountneyA.LeadleyS.ChaoS. H.ColasA.de BuylF.DupontA.GaraudJ. L.GubbelsF.LecomteJ. P.LenobleB.StassenS.StevensC.ThomasX. and ShearerG.: ‘Silicones in industrial applications’‘Inorganic polymers’2007. New YorkNova Science publishers.
5.
SwansonF. D.: ‘The use of conformal coatings to relieve encapsulation stresses’Insulation1966242–46.
6.
ZhanS.AzarianM. H. and PechtM. G.: ‘Surface insulation resistance of conformally coated printed circuit boards processed with no-clean flux’IEEE Trans. Electron. Packag. Manuf.200629217–223.
7.
JellesenM. S.MinzariD.RathinaveluU.MøllerP. and AmbatR.: ‘Corrosion failure due to flux residues in an electronic add-on device’Eng. Fail. Anal.2010171263–1272.
8.
MedgyesB. K. and RipkaG.: ‘Qualifying methods of conformal coatings used on assembled printed circuit boards’2007RomaniaProceeding of 30th International Spring Seminar on Electronics Technology429–433.
9.
GuangbinD.WebbD. P.WhalleyD. C.HuttD. A. and WilsonA. R.: ‘Current leakage failure of conformally coated electronic assemblies’2nd Electronics System integration Technology ConferenceGreenwich, UK20081213–1318.
10.
MinzariD.: ‘Investigation of electronic corrosion mechanism’PhD thesis, Technical University of Denmark, Denmark2010.
11.
HansenC. M.: ‘New developments in corrosion and blister formation in coatings’, Progress in Organic Coatings199526113–120.
AmbatR.: ‘A review of corrosion and environmental effects on electronics’DMS vintermøde proceedings, The Technical University of Denmark2006.
14.
RocakD.BukatK.ZupanM.Fajfar-PlutJ. and TadicV.: ‘Comparison of new no-clean fluxes on PCBs and thick film hybrid circuits’Microelectron. J.199930887–893.
15.
JellesenM. S.MinzariD.RathinaveluU.MøllerP. and AmbatR.: ‘Corrosion failure due to flux residues in an electronic add-on device’Eng. Fail. Anal.2010171263–1272.
16.
ReadyW. J. and TurbiniL. J.: ‘The effect of flux chemistry, applied voltage, conductor spacing, and temperature on conductive anodic filament formation’J. Electron. Mater.2002311208–1224.
17.
SmithB. and TurbiniL.: ‘Characterizing the weak organic acids used in low solids fluxes’J. Electron. Mater.1999281299–1306.
18.
WestermannP.: ‘Investigation of process related residues during PCB manufacturing’Master thesis, Technical University of Denmark, Denmark2008.
19.
TeverovskyA.: ‘Chlorine contamination diffusion in silicones’2002Houston, TexasNASA Electronics Parts and Packaging Program (NEPP).
20.
MinzariD.JellesenM. S.MøllerP. and AmbatR.: ‘Morphological study of silver corrosion in highly aggressive sulfur environments’Eng. Fail. Anal.2011182126–2136.
21.
FunkeW.: ‘Blistering of paint films and filiform corrosion’Progr. Org. Coating.1981929–46.
22.
WeldonD. G.: ‘Failure analysis of paints and coatings’2009Chichester, UKJohn Wiley & Sons Inc.
23.
RobbW. L.: ‘Thin silicone membranes-their permeation properties and some applications’Ann. N. Y. Acad. Sci.1968146119–137.
24.
WhiteM. L.: ‘Encapsulation of integrated circuits’Proc. IEEE.1969571610–1615.
25.
ArthurA. T.: ‘Coatings Technology Handbook’, 3rd edition, part 42006New YorkTaylor & Francis Group.
26.
MinzariD.JellesenM. S.MøllerP. and AmbatR.: ‘On the electrochemical migration mechanism of tin in electronics’Corrosion Sci.2011533366–3379.
27.
El-SherifR. M. and BadawyW. A.: ‘Mechanism of corrosion and corrosion inhibition of tin in aqueous solutions containing tartaric acid’Int. J. Electrochem. Sci.201166469–6482.
28.
TseleshA.: ‘Anodic behaviour of tin in citrate solutions: the IR and XPS study on the composition of the passive layer’Thin Solid Films.20085166253–6260.
29.
MinzariD.GrumsenF. B.JellesenM. S.MøllerP. and AmbatR.: ‘Electrochemical migration of tin in electronics and microstructure of the dendrites’Corrosion Sci.2011531659–1669.
30.
NohB. I.LeeJ. B. and JungS. B.: ‘Effect of surface finish material on printed circuit board for electrochemical migration’Microelectron. Reliab.200848652–656.
