Protection des cartes électroniques avec des Revêtements ... · Résultats de tests suivant la...

Protection des cartes électroniques avec des Revêtements Ultra-Fins Fluoropolymères

Jeudi 2 Avril 2015

Julie Boizot – Ingénieur d’application 3M

2. All Rights Reserved.3 April 2015© 3M 3M Confidential.

On observe une demande croissante pour:

– appareils électroniques plus compacts, portables avec de

multiples fonctionnalités

– Utilisables dans tous types d’environnements extérieurs

– Besoin de protection des composants sensibles contre

l’humidité, les souillures

Les vernis de tropicalisation comme réponse possible:

– résine réticulable UV ou à chaud, permanents

– Polymère acrylique, PU, silicone, époxy

– épaisseur de 12,5µm ou +

La protection de cartes électroniques avec des revêtements ultra-fins

Les revêtements ultra-fins ne sont pas des vernis de tropicalisation

s

Agenda

• Description des revêtements ultra fins fluoropolymères

• Performances suivant les tests de l’IPC – CC- 830B

• Performances en conditions de corrosion à criticité croissante

• Les méthodes de mise en œuvre

• Contrôle du process

• Opérations possibles après dépôt du revêtement


La protection de cartes électroniques avec des revêtements ultra-fins fluoropolymères

• Polymère en solution dans un solvant fluoré très fluide

• Fluides porteurs diélectriques, ininflammables,

inertes, sans phrase de risque pour l’homme

• Une chimie durable: faible PRP, PACO=0

• Existent sous la gamme 3MTM NovecTM

• S’appliquent par trempage ou pulvérisation

• Sèchent à l’air ambiant en qqs secondes

• Forment une couche de protection hydrophobe

et oléophobe de l’ordre de 1µm d’épaisseur

• Protègent de l’humidité, atmosphères soufrées

• Existent avec traceur UV


Résultats de tests suivant la norme IPC-CC-830B

• Humidité : 160h de cycles à 65°C 85%HR pdt 3h / 25°C pdt 2h

A l’inspection visuelle, aucun endommagement du film NovecTM n’est

observé, la résistance électrique maintenue

• Choc thermique : 100 cycles de -65°C pdt 15min / 125°C pdt 15min => A

l’inspection visuelle au microscope ne montre aucun endommagement du

film

• Vieillissement température et humidité : 120jours à 85°C et 98%HR =>

Pas d’endommagement du film observé

• Peut supporter 175°C à 200°C pendant 24h et maintenir son

imperméabilité à une huile silicone chlorée (selon norme MIL-B81744AA)

Il existe un rapport de test issu d’un

laboratoire externe:

Trace Laboratories Test Report


Acier inox non traité

Après 16h

Revêtement fluoré ultra fin –traceur UV

• Selon ASTM B117-09

• Température : 35°C

• Humidité : 95%

• Solution saline: 5% NaCl en aspersion

• pH=6.5~7

Après 44h

La protection contre la corrosion en brouillard salin


La protection contre la corrosion en atmosphère soufrée

• Selon l’ASTM B809: FoS : Flower of Sulfur

• Test conçu pour recréer atmosphère de gaz soufrés

• et d’humidité que l’on retrouve dans de nombreuses industries

• Test sur coupons standards IPC -B-25A

• Revêtements appliqués par trempage sur coupons placés ensuite dans la chambre saturée en atmosphère soufrée

• 3 configurations testées avec le même fluoropolymère en solution dans un solvant (T°eb: 76°C):

Nom Epaisseur du dépôt % massique du polymère en solution

F-1 0,1µm 1%

F-2 0,5µm 4%

F-3 1,0µm 8%


Réduction de corrosion en atmosphère soufrée sur coupons protégés selon ASTM B809


• Finition ImSnPb –34 jours

• Finition ImAg –10 jours

Il existe un livre blanc sur le sujet

pour en savoir plus:

Coating Corrosion Protection of Metal

Surfaces from Sulfur

Protection en atmosphère soufrée

http://multimedia.3m.com/mws/media/959072O/coating-corrosion-protection-of-metal-surfaces-from-sulfur.pdf?fn=Corrosion Protection of Metal Su


Méthode de test

Milieu d’immersion

Temps(min)

Sous tension

IPX7 Eau 30 Non

3M - A Eau 60 3 Volts

3M - B Eau à 5% NaCl 60 3 Volts

La protection en milieu aqueux selon l’IPX7

• Revêtement appliqué par pulvérisation

• Dépôt de 2µm épaisseur

• Les coupons sont immergés dans l’eau ou

• dans l’eau salée pendant 30 à 60 minutes


• Méthode 3M-A:

• Immersion dans l’eau,

pendant 60min, sous 3

Volts

• Méthode 3M-B:

• Immersion dans l’eau salée,

pendant 60min sous 3 Volts

Non testé

(référence)

Non protégé Protégé avec revêtement

de 2µmIl existe un livre blanc sur le sujet pour en savoir plus:

Protection of Circuit Boards, Electronic Components from Water

La protection en milieu aqueux selon l’IPX7

http://multimedia.3m.com/mws/media/985673O/protection-of-circuit-boards-electronic-components-from-water.pdf?fn=ProtectionOfCircuitsWaterTechPap


La protection en milieu acide d’un appareil sous alimentation

• Revêtement appliqué

par pulvérisation

• appareil mis en marche

• Sueur de synthèse

appliquée sur les zones

critiques de la carte

• Durée du test: 4h

• Sur les cartes non

revêtues, on observe

une corrosion

significative en fin de

test

Non protégé

Protégé avec

un revêtement de 5µm


Les méthodes d’application en production

Flexibilité de la méthode d’application

• Trempage, pulvérisation, seringue

• On peut également revêtir intégralement une

pièce

• Les pièces peuvent être revêtues

sélectivement

• On peut appliquer plusieurs couches

• par pulvérisation

Variété de concentrations

• Différents extraits secs et/ou différents

mélanges de solvants porteurs pour optimiser

performance et process

Cartesnettoyées

Séchage à l’air ambiant*

Les cartes sontprêtes pour

l’étape suivante

Trempage

Pulvérisation* Une polymérisation à chaud peut être

requise pour certaines références


Process de mise en oeuvre

Trempage à température ambiante

• Bain non thermostaté

• Confinement des vapeurs par un circuit de

refroidissement

• Durée d’immersion de 30 sec

• Séchage à l’air ambiant en quelques secondes

• La vitesse de retrait influe sur l’épaisseur du

dépôt

Pulvérisation

• Buse spécifique

• Influent sur l’épaisseur:

• Hauteur/vitesse de la buse

• Nombre de passages

• Pas de suivi de bain

Partenariat avec:

Pour la distribution et la mise en œuvre des produits


Contrôle du process d’application

• De la couverture de la pièce

• par contrôle UV

• De la tension de surface

• par encre de test de 28 dynes

• De l’épaisseur:

• AFM, Ellipsométrie, Profilométrie, MEB coupe transversale

• Mesure de changement de masse

Revêtement

Pas de revêtement

Avec lampe UV 254 nm


Manipulations possibles après revêtement

• Pour des opérations de réparations:

• Dévernissage possible de la carte par immersion

dans bain de Fluide Novec pur

• Réparations locales par soudures possibles à travers

le revêtement

• L’épargne des connecteurs peut ne pas être

nécessaire

• Manipulations par toucher/pression

n’endommagent pas le revêtement.


Une technologie de l’ultra-fin pour la protection des cartes, des LED et des écrans

• Les revêtements ultra fins constituent une nouvelle catégorie de vernis de protection des

cartes

• Les revêtements ultra fins fluoropolymères protègent les cartes de l’humidité, des

atmosphères corrosives, de l’immersion en milieu aqueux

• Ces revêtements peuvent être appliqués sur des LED, conforme CREE - livre blanc à

paraître

• Il existe une technologie de revêtements encore plus fins (10nm) en solution à 0,1% pour

protéger les écrans tactiles

• => Revêtement hydrophobe et oléophobe pour faciliter le nettoyage des écrans

s

Merci de votre attention

s

Annexes


La gamme des revêtements 3M™ Novec™

Application Area

NovecCoating

Solids (%) Solvent

Preferred Application Methods1

Dry TimeCure Time

PCB Moisture

Protection

ACF Connection Protection

Anti-Migration Removable

UV Detectable

Anti-Smudge Easy Clean

InternalProtection

Designed to protect printed circuit boards,

solder alloys, components, metals,

composites

1700 23M™ Novec™ 7100

Engineered FluidDip

5-30 seconds No cure is required

1901 1

3M™ Novec™ 7100 and 7200

Engineered Fluids Blend

Spray or Dip

5-30 seconds No cure is required

1902 2 Spray or Dip

1904 4 Spray or Dip

1908 8 Dip

2704 43M™ Novec™ 7200

Engineered Fluid2

Spray or Dip 5-30 seconds No cure is required

2708 8 Dip

2702 23M™ Novec™ 7200

Engineered FluidSpray or Dip

30-90 secondsCure at 70-

150°C for 15-60 minutes

External Protection

Designed to protectglass, steel, aluminum,

ceramics

1720 0.13M™ Novec™ 7100

Engineered FluidDip or Spray

5-15 secondsCure at 70-

150°C for 15-60 minutes

2202 0.23M™ Novec™ 7200

Engineered FluidSpray

5-15 seconds Cure at 185°C for

60 minutes

1 All Novec coatings can be applied using spray, dip or syringe methods. For spray application, 3M recommends using engineered controls or PPE to minimize worker

exposure.

2 Contains < 5% by weight PGMEA, a VOC. See SDS for specific product information.


3M™ Novec™ Electronic Grade Coatings External Protection

Application Area

NovecCoating

Solids (%) Solvent

Preferred Application Methods1

Dry TimeCure Time

Anti-Smudge

Easy Clean

ExternalProtection

Designed to protect glass, steel, aluminum, ceramics

1720 0.13M™ Novec™

7100 Engineered Fluid

Dip or Spray

5-15 seconds

Cure at 70-150°C for

15-60 minutes

2202 0.23M™ Novec™

7200 Engineered Fluid

Spray

5-15 seconds Cure at

185°C for 60 minutes

1 All Novec coatings can be applied using spray, dip or syringe methods. For spray application, 3M recommends using engineered controls or PPE to

minimize worker exposure.


Contacts:

• Catherine Sol – 3M France

• Développement de Marché Fluides et Gaz

• [email protected]

• Julie Boizot – 3M France

• Ingénieur Support Technique Fluides et Gaz


• Jonathan Cetier – Inventec

• Responsable Grands Comptes


Les revêtements 3M™ Novec™

mailto:[email protected]




Informations complémentaires

Le montage ou l’utilisation du produit 3M décrit dans le présent document implique des

connaissances particulières et ne peut être réalisé que par un professionnel compétent.

Avant toute utilisation, il est recommandé de réaliser des tests et/ou de valider la bonne

adéquation du produit au regard de l'usage envisagé.

Les informations et préconisations inclues dans le présent document sont inhérentes au

produit 3M concerné et ne sauraient être appliquées à d’autres produits ou

environnements. Toute action ou utilisation des produits faite en infraction de ces

indications est réalisée aux risques et périls de leur auteur.

Le respect des informations et préconisations relatives aux produits 3M ne dispense pas

de l’observation d’autres règles (règles de sécurité, normes, procédures…)

éventuellement en vigueur, relatives notamment à l’environnement et moyens

d’utilisation. Le groupe 3M, qui ne peut vérifier ni maîtriser ces éléments ne saurait être

tenu pour responsable des conséquences, de quelque nature que ce soit, de toute

infraction à ces règles, qui restent en tout état de cause extérieures à son champ de

décision et de contrôle.

Les conditions de garantie des produits 3M sont déterminées dans les documents

contractuels de vente et par les dispositions impératives applicables, à l’exclusion de

toute autre garantie ou indemnité.

3

IntroductionProtection against water – both vapor and liquid – has become increasingly critical to the lifetime performance of electronic devices. This is especially true as electronics become more mobile and are used in more challenging environments.

One effective method of providing this protection is to coat the internal surfaces of the electronic device components, including its printed circuit boards and connections. To demonstrate this, tests were conducted to show the capability of 3M™ Novec™ Electronic Grade Coatings (EGC) to protect metals against moisture, liquids and corrosion under a variety of water and salt water immersion conditions.

3M™ Novec™ Electronic Grade Coatings (EGC) are thin, low viscosity coatings designed to protect printed circuit boards and electronic components from moisture and corrosion. These polymer coatings dry to thin, transparent films with excellent hydrophobic and oleophobic properties. Available in both thermal curing and non-curing versions, they are easy to apply – whether by liquid dipping, spraying (controlled) or brush. These coatings are non-ozone depleting and RoHS compliant.

The 3M™ Novec™ Electronic Grade Coatings portfolio includes a number of coatings. For this evaluation, 3M™ Novec™ 1710 and 2708 Electronic Grade Coatings were chosen for testing. These coatings are fluorinated polymers delivered as a solution in a segregated-hydrofluoroether 3M™ Novec™ Engineered Fluid. These low viscosity and low surface tension solutions allow for easy wetting over a variety of surfaces, helping to ensure outstanding coverage.

At 8% solids content, Novec 2708 coating is recommended as a final coating. A yellow-orange dye is incorporated into the polymer backbone. This dye will fluoresce under UV light, thus aiding inspection and detection in the quality control process. Although used in this trial for experimentation purposes, at 10% solids content, Novec 1710 coating is recommended to be used as a concentrate to replenish coating solids in application baths or as a component with other materials to create unique liquid solutions, rather than as a final coating.

In this testing, both of the Novec coatings added considerable protection to the components to which they were applied. The protection they provided substantially reduced the effect of water, corrosion and other contaminants that could electrically shorten the lifetime and performance of the electronic device.

Experiment OverviewTesting began by applying the coating over rigid printed circuit boards with electrical test patterns. The circuit boards were then connected to an external power supply that maintained a constant voltage. Based on a modification of the IPX71, 2 testing standard (see IPX7 Test Method and 3M Modifications plus Test Results), powered test boards were immersed in water or salt water for an extended time period. The resistance of the circuit was then measured over time and charted to determine the effect of the water on the circuitry.

Test BoardsFor this study, IPC-Association Connecting Electronics Industries approved printed test boards IPC-B-25A3 were used. The IPC-B-25A test board meets guidelines for testing solder masks (IPC-SM-804C) and conformal coatings (IPC-CC-830B) and is shown in Figure 1.

Figure 1. The IPC-B-25A printed test board

Board Preparation and Coating ApplicationThe boards were cut vertically to isolate the test pattern D from patterns E and F. Test patterns D, E and F were then used separately in the water immersion test.

Prior to coating, the boards were cleaned with 3M™ Novec™ 72DA Engineered Fluid in a vapor degreaser. Novec 72DA fluid is effective at removing surface contaminants and particulates that, if left on the circuit board, might impact coating performance.

3M™ Novec™ Electronic Grade Coatings

Technical Paper

Protection of Printed Circuit Boards and Electronic Components from Water and Salt Water by Using 3M™ Novec™ Electronic Grade Coatings


3M recommends either spray coating (in a controlled environment) or dip coating as application methods. For this study, both methods were used to demonstrate the flexibility of application options and to measure any differences resulting from the application methods. For testing, boards with different targeted thicknesses of the coatings were generated by spraying, dipping or a combination of these processes.

For dip coating, the process began with a chamber filled with 3M™ Novec™ Electronic Grade Coating. The chamber was on a table which moved up and down at a controlled rate. The removal rate of the boards controlled the thickness of the coating. In general, the faster the board is removed, the thicker the coating. To coat the boards, they were dipped, held in solution for 30 seconds and removed from the coating solution at a rate of 12 inches per minute. The boards were allowed to dry and then wire leads were soldered to the board’s contacts. These contacts and the lead connected to the open structure comb pattern were insulated by covering with 100% silicone, leaving just the comb structure test pattern exposed. The board was then placed in the immersion test chamber.

Spray coating can be done manually or by automated spray equipment (3M does not recommend manual spray application without worker exposure control).* For this study, boards were coated using a hand operated air driven sprayer. The volume of coating applied was varied so a thickness of 2µm (2 microns) or less was achieved. Wire leads were then soldered to the boards and insulated with silicone as described above.

IPX7 Test Method and 3M ModificationsThe water immersion test was based on a modification of the IPX7 test standard that has been established by the International Electrotechnical Commission (IEC).4, 5 The IP Code, sometimes referred to as the Ingress Protection Rating,6, 7 classifies the degree of protection against intrusion into the interior of a device. The IPX standard and tests have been used by the electronics industry for evaluating the ability of water, dirt, dust and other contaminants to ingress into an enclosure. Protection from these contaminants is critical as they have the potential to create conditions that could shorten the service life of an electronic device.

Although there are multiple levels of IPX protection classifications, IPX7 is often referenced for water immersion testing. It provides an indication as to how well an electronic device would survive if immersed in water. This test calls for an unpowered electronic device to be immersed in 1 meter of water for 30 minutes. After the 30 minutes, the device is removed and the power turned on. If it operates as it was designed, the device is considered to meet the IPX7 classification.

While the IPX7 test method uses actual commercial devices, device enclosures can vary in their design and ingress capability. For this reason, this study eliminated the enclosure and evaluated the performance of coatings applied directly on exposed test boards.

To test at a rigorous level (beyond the IPX7 test protocol), testing in salt water was also carried out. To ensure that a device’s electronics would survive these conditions, plus add another level of performance requirements, the sample boards were tested under power. A comparison of these test methods are described in Table 1.

* Before using this product, please read the current product Material Safety Data Sheet (available through your 3M sales or technical service representative or at www.3M.com/Novec) and the precautionary statement on the product package. Follow all applicable precautions and directions. Always practice smart and safe industrial hygiene practices.

Test Method

Immersion Depth Liquid Media Time

(Min) Powered

IPX7 1 Meter Water 30 NoA 1 Meter Water 60 3 VoltsB 1 Meter 5% aqueous NaCl 60 3 Volts

Table 1: IPX7 and 3M test conditions A and B

Using a Solartron™ model 1287 potentiostat8 in conjunction with a Solartron™ model 1260 impedance analyzer, a constant current of 3 volts was applied to the test pattern. Current leakage across the open comb structure test pattern (D, E or F from Figure 1) during the 60 minute immersion test was then measured. After 60 minutes, the board was removed, rinsed with water and evaluated. The 3M system for Test Methods A and B is depicted in Figure 2.

V

AAmmeter

Power Supply3 V Voltmeter

Comb Structure

Figure 2. Electrical wiring for Test Methods A and B

Test ResultsWhile the IPX7 is a test to show water ingress, our testing eliminated the enclosure, ensuring that test boards were completely exposed to the aqueous solutions.

To make the testing more aggressive, modifications were made beyond the IPX7 protocol: 1) immersing in both water and salt water, 2) powering the electronics during testing and 3) extending the immersion time to 60 minutes. In all of these cases, the coated sample boards did not demonstrate the corrosion and degradation of the metal traces to the extent that the uncoated samples boards showed.

Test Method A was used to test IPC-B-25A printed test board patterns D, E and F coated with Novec 1710 or 2708 coating. There was no corrosion, dendritic growth, copper loss or line thinning observed (Figure 3). When Test Method A was used on uncoated test patterns, there was significant corrosion and line thinning (Figure 4).

No corrosion or copper loss on the “+” lead

Figure 3. Example: Test patterns coated with Novec 1710 coating and Novec 2708 coating performed similarly after Test Method A.

2

Test Method B replaced the water with a 5% aqueous sodium chloride solution. This method made for an extremely aggressive test, as exemplified by the striping of the copper trace lines from the test boards during the immersion time. Even within this environment, the Novec coatings protected the surfaces. When Test Method B was used to test boards coated with 3M™ Novec™ 1710 or 2708 Electronic Grade Coating, there was minimal corrosion in spots along the edge of copper traces. Uncoated test patterns, when tested with Test Method B, were completely corroded and much of the copper tracings were removed from the board, thus creating electrical connection opens (Figure 4).

Figure 4: Summary of Novec 1710 and Novec 2708-coated test patterns after Test Method A and Test method B. Note that the uncoated lines show signs of loss of the copper traces.

For the coated boards, current leakage (as measured by the potentiostat) across the test circuit was negligible at less than 0.01 amps. In contrast, for the uncoated boards, current leakage across the test circuit was immediate and significant (exceeding 2 amps) when using either Test Method A and B. The uncoated test pattern under these conditions typically failed within 60 minutes as shown by complete copper loss on the positively charged side of the pattern. Boards coated with Novec 1710 or 2708 coatings did not fail (Figure 5).

Test Method A

0.50

0.40

0.30

0.20

0.10

0.000 10 20 30

Time (Min)

Curr

ent (

Amps

)

40 50 60

Uncoated

Novec 1710 or 2708 Coated

Test Method B0.30

0.25

0.20

0.15

0.10

0.05

0.000 10 20 30

Time (Min)

Curr

ent (

Amps

)

40 50 60

UncoatedFailed

Novec 1710 Coated Novec 2708 Coated

Figure 5: Solartron™ potentiostat data showing current flow

Uncoated test boards had extensive corrosion when immersed in both water and salt water. This was evident by observing current flow immediately across the test pattern when exposed to the test fluid. In contrast, test boards coated with Novec 1710 coating or Novec 2708 coating showed no current flow even after 60 minutes.

Summary and Conclusions3M™ Novec™ Electronic Grade Coatings provide an effective barrier for metals and surfaces including electronic circuit boards, helping to protect them from moisture, liquids, corrosion, line thinning and dendritic growth. This protection adds to the performance and longevity of the surfaces, metal connections and an electronic device’s service life.

References1 The IP Code is a test standard published by International Electrotechnical Commission (IEC) and describes the level of protection provided by an enclosure. For an explanation of the IP code see: http://www.ce-mag.com/archive/06/ARG/bisenius.htm

2 IP Code Defined: http://www.osram.com/media/resource/hires/342330/technical-application-guide---ip-codes-in-accordance-with-iec-60529-gb.pdf

3 IPC-Association Connecting Electronics Industries is an organization that sets standards used by the electronics manufacturing industry: https://www.ipc.org/default.aspx

4 IEC 60529: Degrees of protection provided by enclosures (IP Code). International Electrotechnical Commission, Geneva: http://www.iec.ch/

5 IP Ratings vs. NEMA Ratings: http://www.bisonprofab.com/ip-ratings-explained.htm

6 Understanding the IP (Ingress Protection) Ratings: http://www.maximintegrated.com/app-notes/index.mvp/id/4126

7 Interpreting the acronym officially in the standard text: http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=39578

8 Solartron Analytical is a manufacturer of electronic instruments: http://solartronanalytical.com/

3


Not Tested Uncoated Novec 2708 Novec 1710

Not Tested Uncoated Novec 2708 Novec 1710

Test Method B

Test Method A

Electronics Materials Solutions Division 3M Center, Building 224-3N-11St. Paul, MN 55144-1000www.3M.com/novec1-800-810-8513

Solartron is a trademark of Lloyd Instruments Limited.

3M and Novec are trademarks of 3M Company. Used under license by 3M subsidiaries and affiliates.

Please recycle. Printed in USA. © 3M 2014. All rights reserved. Issued: 7/14 9851HB 60-5002-0725-7

3

The Novec brand is the hallmark for a variety of patented 3M compounds. Although each has its own unique formula and performance properties, all Novec products are designed in common to address the need for safe, effective, sustainable solutions in industry-specific applications. These include precision and electronics cleaning, heat transfer, protective coatings and surface modifiers, fire protection, lubricant deposition and several specialty chemical applications.

The 3M™ Novec™ Brand Family

3M™ Novec™ Engineered Fluids ■ 3M™ Novec™ Aerosol Cleaners ■ 3M™ Novec™ 1230 Fire Protection Fluid ■ 3M™ Novec™ Electronic Grade Coatings ■ 3M™ Novec™ Electronic Surfactants

United States 3M Electronics Materials Solutions Division 800 810 8513

China 3M China Ltd. 86 21 6275 3535

Europe 3M Belgium N.V. 32 3 250 7521

Japan Sumitomo 3M Limited 813 3709 8250

Korea 3M Korea Limited 82 2 3771 4114

Singapore 3M Singapore Pte. Ltd. 65 64508888

Taiwan 3M Taiwan Limited 886 2 2704 9011


For Additional InformationTo request additional product information or sales assistance, contact 3M Customer Service at one of the numbers below or visit 3M.com/Novec.

For other 3M global offices or information on other 3M products for electronics, visit our website at 3M.com/electronics.

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.

Product Comparison SummaryProperty 3M™ Novec™ 1710 Electronic Grade Coating 3M™ Novec™ 2708 Electronic Grade Coating

Solids 10 wt% fluoropolymer 8 wt% fluorinated polymerSolvent 3M™ Novec™ 7100DL Engineered Fluid 3M™ Novec™ 7200 Engineered FluidShelf Life 4 years from date of manufacture in unopened container 1 year from date of manufacture in unopened container

Coating Solution

Appearance Clear, colorless to light-colored liquid solution Transparent, orange, liquid solutionSpecific Gravity 1.5 g/mL 1.4 g/mLBoiling Point of Solvent 61°C (142°F) 79°C (174°F)Flash Point None (per closed cup method) None (per closed cup method)

Environmental Low in toxicity, non-ozone depleting, nonflammable, VOC exempt (U.S. EPA), RoHS compliant, contains no chlorine or bromine

Low in toxicity, non-ozone depleting, nonflammable, low-VOC, RoHS compliant, contains no chlorine or bromine

System One Part One Part

Dry Fluoropolymer Coating

Appearance Transparent, colorless Transparent, light yellow to orange (depending on thickness)

Coating Thickness Typically 1 to 10 microns (depending on application method) Typically 0.5 to 25 microns (depending on application method)Solvent & Chemical Resistance Yes Yes Tg (glass transition temperature) 44.5°C (112°F) 53°C (127°F)Thermal Stability of Dry Film Can withstand 175°C for 24 hours and maintain repellency Can withstand 175°C for 24 hours and maintain repellency

Contact Angles (static, dip coated/dried on glass substrate) 105° (water), 65° (hexadecane) 105° (water), 65° (hexadecane)

Solder-Through Repairability Yes Yes

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IntroductionA study was conducted to show the capability of 3M™ Novec™ 2701, 2704 and 2708 Electronic Grade Coatings to mitigate corrosion of exposed metal on printed circuit boards and electronic components under harsh environmental conditions.

Novec 2701, 2704 and 2708 electronic grade coatings are fluorinated polymers carried in segregated-hydrofluoroether fluids sold by 3M under the Novec trade name. These polymer coatings are designed for protection of printed circuit boards, components and a variety of surfaces from moisture and corrosion.

Novec 2701, 2704 and 2708 electronic grade coatings dry to a thin, transparent film with excellent hydrophobic and oleophobic properties. They do not require thermal curing and are easy to apply – whether by liquid dipping, spraying (controlled) or brush applying. The solution and polymer are both low in toxicity, non-ozone depleting and RoHS compliant. These coatings incorporate a yellow-orange dye into the polymer backbone that is designed to fluoresce under UV light to aid inspection and the quality control of the coating process.

BackgroundDuring the transition away from printed circuit board finishes that contain lead, many industries have reported corrosion when using circuitry plated with metals such as silver and tin.1,2,3

Industries that have cited these issues include petrochemical, water treatment, and rubber manufacturing.3 Circuitry subjected to the harsh environments associated with these and other industries is susceptible to corroding relatively quickly.1,2,3 In addition, geographic location can contribute heavily to this problem.3 The creep corrosion from exposure to these harsh environments often leads to electrical shorts and failures quickly because the characteristic dendritic growth can cause bridging.1,2,3 For industries that rely heavily on the use of electronics to function, creep corrosion needs to be mitigated, especially in cases where electronics must meet high minimum requirements.

ExperimentTest BoardsStandard IPC-B-25A test boards are commonly available and were used in the study. These printed circuit boards (PCBs) meet guidelines for the testing of solder masks (IPC-SM-804C) and conformal coatings (IPC-CC-830A).

Immersion silver (ImAg) finish is used in electronics as an alternative to lead-tin finishes.1 Therefore, IPC-B-25A test

boards with ImAg and bare copper (Cu) finishes were both treated with Novec electronic grade coatings and tested. Additionally, some with ImSnPb finish, vias and solder mask were also tested. Boards of each surface finish that were not treated with Novec electronic grade coatings were used as control samples and tested under the same conditions as the boards which were treated.

It has been stated by some groups that flux residues, which result from the board construction process, may be necessary to simulate the dendritic growth involved in creep corrosion in the laboratory.1 Because of this, in our study some boards were treated with flux and reflowed before being coated and tested. It was found that boards with no flux residues were just as susceptible to creeping corrosion as boards with flux residues. Therefore, the focus remained on the clean IPC-B-25A test vehicles, shown in Figure 1 below.

Figure 1. The IPC-B-25A test vehicle.

Coating ProcessThe IPC-B-25A test boards were cut in half vertically in order to accommodate the ASTM test conditions and the limited space in the test chamber. The cut boards were then cleaned with 3M™ Novec™ 72DA Engineered Fluid in a vapor degreaser. Novec 72DA fluid is effective at removing surface contaminants and particulate that, if left on the board, may have an impact on metal corrosion rates.


Technical Paper

Corrosion Protection of Metal Surfaces from Sulfur by Using 3M™ Novec™ Electronic Grade Coatings


Each board was coated by a dip coating process. The process began with a chamber filled with one of the 3M™ Novec™ 2701, 2704 or 2708 Electronic Grade Coatings. The chamber sat on a table which moved up and down at a controlled rate. The rate at which the boards were removed controlled the thickness of the coating. In general, the faster the board is removed, the thicker the coating. The boards were dipped, held in solution for 30 seconds and removed from the coating solution at a rate of 12 inches per minute. The boards were allowed to dry and then placed into a flowers-of-sulfur test chamber as described below.

To simulate the type of conditions that might occur in the field, some boards were treated with flux prior to being tested. To do this, the coating process was modified slightly for boards that would be treated with flux. These test vehicles were first cleaned as stated above, the chosen flux was applied and the boards were then reflowed. The boards were allowed to cool to room temperature and then coated by the dip coating process as described above.

High Humidity - High Sulfur Test “Flowers-of-Sulfur” (FoS)A variety of methods can be used to test the porosity of coatings and protective finishes. The ASTM B809 method provides a standard method by which to induce the corrosion of various metal finishes.4 The test is designed to recreate the problematic high hydrogen sulfide gas and high humidity environment found in many industries.

The testing setup is shown in Figure 2. A 10 L glass desiccator was used as the test vessel. Grease was never used to seal the lid to the chamber and there was a vented stopper which allowed for equilibration of the system without pressure buildup. The test vessel contained a potassium nitrate solution in which there was a Petri dish containing elemental sulfur floats. The samples were suspended at least 75 mm above the sulfur powder. The samples were held in place above the sulfur source by an apparatus and the clips were not affected by the sulfur.

Figure 2. Samples in the flowers of sulfur chamber setup as described in the ASTM B809 test method.

Data“Flowers-of-Sulfur” (FoS)The FoS test method was used to study how the finish of a circuit board behaves in a corrosive, sulfur-containing environment. The method was designed to show whether attempts to mitigate corrosion, specifically creep corrosion, with a protective coating were successful.

Treated and untreated Cu finish test vehicles were exposed to the corrosive high sulfur environment in this study. After 10 days of exposure to the FoS test, untreated Cu finish boards were found to have succumbed to severe tarnish and creeping corrosion.

Cu finish boards that were treated with Novec 2708 coating, however, had minimal tarnish and no creep corrosion after 10 days of exposure. There was also substantially less tarnish and corrosion on Cu finish boards which were treated with Novec 2704 and 2701

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Cu/uncoated = 10 days Cu w/Novec 2701 = 10 days

Vented Stopper

PCB Samples

Elemental Sulfur

Saturated KNO3 solution

Cu w/Novec 2704 = 10 days Cu w/Novec 2708 = 10 daysFigure 3. The pictures on the top and bottom left show uncoated Cu finish B-25A test vehicles before and after 10 days exposure in the FoS chamber. The three larger pictures on the right show Cu finish B-25A test vehicles which were coated with 3M™ Novec™ 2701, 2704 and 2708 Electronic Grade Coatings after 10 days exposure in the FoS chamber.

“Flowers-of-Sulfur” (FoS) Chamber Test Results (60°C, >90% RH)

Cu - Time = 0

coatings after 10 days than on untreated boards. The testing showed that the characteristic dendritic growth of creep corrosion was drastically reduced by the presence of 3M™ Novec™ 2701, 2704 and 2708 Electronic Grade Coatings.

The conclusion was that treatment of circuitry with Novec coatings mitigated damages caused by exposure to the corrosive environment inside the FoS chamber. This difference in corrosion growth is shown in Figures 3 and 4.

Flowers-of-Sulfur (FoS) Chamber Test Results (60°C, >90% RH) 10 Days

Figure 4. The pictures on the top and bottom right show uncoated Cu finish IPC-B-25A test vehicles before and after 10 days exposure in the FoS chamber, respectively. The bottom left picture shows a Cu finish IPC-B-25A test vehicle which was coated with 3M™ Novec™ 2708 Electronic Grade Coating after 10 days exposure in the FoS chamber.

Since ImAg and other finishes are often used to protect Cu circuitry, alternate finishes were also included in the study. Figure 5 shows results of coated and uncoated boards with these alternate finishes.

The IPC-B-25A design was used for the ImAg finish boards and a 3M-designed test board was used for the ImSnPb finished boards. The latter was done in addition to the IPC-B-25A boards to determine whether the creep corrosion phenomena could be mitigated on a typical solder mask, which is present on circuit boards in most cases. The coatings did mitigate corrosion on both alternate finishes tested.

Flowers-of-Sulfur (FoS) Chamber Test Results (60°C, >90% RH) Alternate Finishes After 34 days

ImSnPb No Flux

ImAg Treated with Kester® 984 Flux

Figure 5. The pictures on the top left and right pictures show coated and uncoated ImSnPb finish test vehicles after 34 days exposure in the FoS chamber, respectively. The bottom left and right pictures show ImAg finish B-25A test vehicles coated and uncoated after 10 days exposure in the FoS chamber, respectively.

Summary and ConclusionsCreep corrosion can be driven by many factors and is an increasing concern for many industries, end customers and the circuit board industry. Tests were completed to demonstrate whether coating printed circuit board circuitry would help to reduce the progress of creeping corrosion caused by sulfur in the environment.

In this study, 3M™ Novec™ 2701, 2704 and 2708 Electronic Grade Coatings were applied over a variety of metal and metal finished electronic circuitry surfaces. Uncoated versions were used as a control and compared over time to the coated versions.

A FoS chamber was chosen as the test method for inducing creep corrosion. It simulated the high hydrogen sulfide gas and high humidity environments in which circuitry is increasingly being used.

This testing procedure resulted in a dramatic difference with the coated versions showing significantly less corrosion development. The conclusion was that Novec 2701, 2704 and 2708 electronic grade coatings help mitigate the formation of creeping corrosion of exposed metal on circuit boards caused by exposure to high levels of sulfur and humidity. 1 Xu, C., Smetana J. Franey, G. Guerra, D. Flemming, W. Reents, Dennis Willie, Alfredo Garcia, Guadalupe Encinas, and Jiang Xiaodong. “Creep Corrosion of PWB Final Finishes: Its Cause and Prevention.” IPC APEX EXPO Proceedings (n.d.): n. pag. Web.

2 Kenny, Jim, Karl Wengenroth, Ted Antonellis, ShenLian Sun, Cai Wang, PhD, Edward Kudrak, and Joseph Abys, PhD. “PWB Creeping Corrosion Mechanism and Mitigation Strategy.” Enthone Inc., Crookstone Electronics, n.d. Web.

3 Schueller, Randy, PhD. “Creep Corrosion on Lead-Free Printed Circuit Boards in High.” Dfrsolutions.com. SMTA International Proceedings, Oct. 2007. Web. 19 Aug. 2013.

4 “ASTM B809 - 95(2008).” Standard Test Method for Porosity in Metallic Coatings by Humid Sulfur Vapor (“Flowers of Sulfur”). N.p., n.d. Web. 15 Aug. 2013.

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Coated with Novec 2704

Coated with Novec 2704

Uncoated

Uncoated

Cu – Novec 2708 at 10 days Cu – Uncoated at 10 days

Cu - Time = 0

Electronics Markets Materials Division 3M Center, Building 224-3N-11St. Paul, MN 55144-1000www.3M.com/novec1-800-810-8513

Kester is a registered trademark of ITW Kester.

3M and Novec are trademarks of 3M Company. Used under license by 3M subsidiaries and affiliates.

Please recycle. Printed in USA. © 3M 2014. All rights reserved. Issued: 4/14 9728HB 60-5002-0724-0

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The Novec brand is the hallmark for a variety of patented 3M compounds. Although each has its own unique formula and performance properties, all Novec products are designed in common to address the need for safe, effective, sustainable solutions in industry-specific applications. These include precision and electronics cleaning, heat transfer, protective coatings and surface modifiers, fire protection, lubricant deposition and several specialty chemical applications.

The 3M™ Novec™ Brand Family

3M™ Novec™ Engineered Fluids ■ 3M™ Novec™ Aerosol Cleaners ■ 3M™ Novec™ 1230 Fire Protection Fluid ■ 3M™ Novec™ Electronic Coatings ■ 3M™ Novec™ Electronic Surfactants

United States 3M Electronics Markets Materials Division 800 810 8513

China 3M China Ltd. 86 21 6275 3535

Europe 3M Belgium N.V. 32 3 250 7521

Japan Sumitomo 3M Limited 813 3709 8250

Korea 3M Korea Limited 82 2 3771 4114

Singapore 3M Singapore Pte. Ltd. 65 64508888

Taiwan 3M Taiwan Limited 886 2 2704 9011


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.

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