Conformal Coatings - Selection guide

How to Select the Right Conformal Coating

Introduction to Conformal Coatings

A con­for­mal coat­ing is a thin pro­tec­tive film designed to safe­guard elec­tron­ic assem­blies from cor­ro­sion and envi­ron­men­tal haz­ards in harsh oper­at­ing con­di­tions. The term “con­for­mal” refers to its abil­i­ty to con­form pre­cise­ly to the com­plex con­tours of the sur­face it cov­ers. This coat­ing offers sev­er­al advan­tages, includ­ing pro­tec­tion from debris and dust infil­tra­tion, enhanc­ing cor­ro­sion resis­tance, extend­ing prod­uct war­ranties, and increas­ing over­all reli­a­bil­i­ty and safe­ty. In essence, apply­ing a con­for­mal coat­ing effec­tive­ly pro­longs the longevi­ty and dura­bil­i­ty of elec­tron­ic assemblies.

One of the main advan­tages of con­for­mal coat­ings is their dielec­tric prop­er­ties. These coat­ings exhib­it excel­lent insu­la­tion resis­tance, effec­tive­ly pro­tect­ing elec­tron­ic com­po­nents and assem­blies from elec­tri­cal fail­ures. Anoth­er sig­nif­i­cant advan­tage is mois­ture resis­tance, which serves as a cru­cial defense against mois­ture ingress, pre­vent­ing poten­tial dam­age and elec­tri­cal fail­ures in humid or damp envi­ron­ments. Addi­tion­al­ly, the break­down volt­age char­ac­ter­is­tic plays a piv­otal role in pro­tect­ing the com­po­nent from high volt­ages and elec­tri­cal stress­es. Final­ly, the flex­i­bil­i­ty of the coat­ing endows the sub­strate with enhanced mechan­i­cal resilience, enabling it to bet­ter with­stand exter­nal stress­es and envi­ron­men­tal fluc­tu­a­tions with­out deform­ing, crack­ing, or delaminating. 

In sum­ma­ry, the notable dielec­tric prop­er­ties and flex­i­bil­i­ty of con­for­mal coat­ings com­bine to cre­ate a robust pro­tec­tive bar­ri­er, ensur­ing the longevi­ty and opti­mal per­for­mance of elec­tron­ic com­po­nents in diverse and demand­ing applications.

30 days of expo­sure in an envi­ron­ment with H2S, SO2, and Cl2

Exposure results without Conformal coating
Fig­ure 1a. Expo­sure results with­out Con­for­mal Coating
Exposure results with Conformal Coating
Fig­ure 1b) Expo­sure results with Con­for­mal Coating 

Different types of conformal coatings

Acrylic — Acrylic-based coat­ings like Loc­tite Sty­cast PC 62 rep­re­sent the largest mar­ket share of con­for­mal coat­ings. These coat­ings are for­mu­lat­ed from sin­gle com­po­nents and pro­vide supe­ri­or mois­ture resis­tance prop­er­ties, mak­ing them high­ly suit­able for pro­tect­ing elec­tron­ic assem­blies in chal­leng­ing envi­ron­ments. The wide­spread choice of acrylic-based coat­ings can be attrib­uted to their ease of use, short cure time, and reworkability/repairability. Acrylic-based coat­ings are most often used in Engine Con­trol Units (ECUs), Avion­ics, and com­mu­ni­ca­tion equipment.

Polyurethane — Polyurethane-based coat­ings have excel­lent chem­i­cal resis­tance, ren­der­ing them high­ly effec­tive in coun­ter­ing the effects of com­pounds such as salt spray and nox­ious gas. Avail­able in both one-part and two-part sys­tems, these coat­ings are easy to apply. Com­pared to oth­er con­for­mal coat­ings, polyurethane-based coat­ings like Loc­tite Sty­cast PC 18M do have a length­i­er cur­ing time. Rework­a­bil­i­ty is a notable advan­tage of these coat­ings, and they are com­mon­ly used in demand­ing envi­ron­ments with appli­ca­tions that include indus­tri­al con­trols, marine elec­tron­ics, and chem­i­cal processes. 

Sil­i­cone — Sil­i­cone-based con­for­mal coat­ings are unique­ly char­ac­ter­ized by their excep­tion­al high-tem­per­a­ture per­for­mance. Due to this char­ac­ter­is­tic, they are suit­able for indus­tri­al min­ing equip­ment, elec­tron­ics with tem­per­a­tures greater than 150°C, and under­hood com­po­nents in the auto­mo­tive indus­try. Sil­i­cone-based con­for­mal coat­ings like Loc­tite SI 5293 offer rea­son­able mois­ture pro­tec­tion while remain­ing rework­able and repairable. They are sol­vent-free, yield­ing a 100% sol­id con­tent and good sol­vent resis­tance. More­over, these coat­ings incor­po­rate flex­i­ble elas­tomers, enhanc­ing their flex­i­bil­i­ty. This adapt­abil­i­ty allows the coat­ing to accom­mo­date mechan­i­cal stress­es and tem­per­a­ture fluc­tu­a­tions with­out com­pro­mis­ing its integrity.

UV-Based — UV Based con­for­mal coat­ings are pri­mar­i­ly select­ed for their short cure time, which occurs with­in a mat­ter of sec­onds. This expe­dit­ed cur­ing process reduces the cycle time while pro­vid­ing increased tem­per­a­ture per­for­mance to the coat­ed com­po­nents. UV Based coat­ings like Loc­tite Sty­cast PC 40-UMF exhib­it excel­lent resis­tance to mois­ture and chem­i­cals while also hav­ing high flex­i­bil­i­ty and abra­sion resis­tance. One of the main advan­tages of this type of coat­ing is that it is envi­ron­men­tal­ly friend­ly, as it con­tains no Volatile Organ­ic Com­pounds (VOCs) or sol­vents. Like Sil­i­cone Coat­ings, it is 100% sol­id con­tent. Due to the short cure time, UV Based con­for­mal coat­ings are suit­able for high-vol­ume applications. 

Rub­ber-Based — Ruber-based con­for­mal coat­ings rep­re­sent a class of sin­gle-com­po­nent coat­ings with excel­lent mois­ture resis­tance and low Mois­ture Vapor Per­me­abil­i­ty (MVP). Like oth­er con­for­mal coat­ings, they are easy to repair/rework, have a short cure time, and have excel­lent adhe­sion to var­i­ous sub­strates. The char­ac­ter­is­tic that dis­tin­guish­es rub­ber-based coat­ings is their superb flex­i­bil­i­ty and ther­mal-mechan­i­cal prop­er­ties. Specif­i­cal­ly, their low Coef­fi­cient of Ther­mal Expan­sion (CTE) and Glass Tran­si­tion Tem­per­a­ture (Tg) enable the com­po­nents to effec­tive­ly with­stand ther­mal shock, enhanc­ing over­all per­for­mance and reli­a­bil­i­ty. This qual­i­ty makes rub­ber-based coat­ings par­tic­u­lar­ly well-suit­ed for appli­ca­tions where tem­per­a­ture fluc­tu­a­tions pose a chal­lenge, pre­serv­ing func­tion­al­i­ty and integri­ty even in demand­ing environments.

Conformal Coating Selector Guide

Conformal coating selector guide for acrylic, urethane, uv, silicone, and rubber coatings
Fig­ure 2. Con­for­mal Coat­ing Selec­tor Table

SUMMARY

In sum­ma­ry, con­for­mal coat­ings are thin, pro­tec­tive films that safe­guard elec­tron­ic assem­blies from cor­ro­sion and envi­ron­men­tal haz­ards in harsh con­di­tions. They con­form pre­cise­ly to the sur­face, pro­vid­ing advan­tages like pro­tec­tion from debris, enhanced cor­ro­sion resis­tance, extend­ed war­ranties, and improved reli­a­bil­i­ty and safe­ty. The coat­ings offer excel­lent dielec­tric prop­er­ties, insu­la­tion resis­tance, and mois­ture resis­tance, pro­tect­ing against elec­tri­cal fail­ures and mois­ture ingress. Their flex­i­bil­i­ty ensures mechan­i­cal resilience, with­stand­ing exter­nal stress­es with­out defor­ma­tion or delam­i­na­tion. There are mul­ti­ple options to choose from, includ­ing acrylic, ure­thane, uv, sil­i­cone, or rub­ber-based, and each has spe­cif­ic prop­er­ties ben­e­fi­cial to dif­fer­ent appli­ca­tions. Over­all, con­for­mal coat­ings pro­vide a robust bar­ri­er, ensur­ing long-last­ing and opti­mal per­for­mance of elec­tron­ic com­po­nents in diverse applications.

Choos­ing the right con­for­mal coat­ing is crit­i­cal for improv­ing pro­tec­tion and reli­a­bil­i­ty in elec­tron­ic devices so an appli­ca­tion-spe­cif­ic assess­ment should be con­duct­ed. Con­tact us and our appli­ca­tion engi­neers and in-house coat­ing experts will help you out with prod­uct selec­tion for your appli­ca­tion requirements.

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