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ProCOAT Services

ProCOAT provides conformal coating services, using a variety of different types of coatings. Understanding the general characteristics of these common types of coatings used in the industry will allow you to make the best choice for your particular application. Our processes conform to IPC-CC-830, MIL-I-46058C, MIL-P-28809, NASA-STD-8739-1 and UL746C

ProCOAT regularly provides expediting or fast track services of 1, 2, 3 days and same day turnaround times without compromise to the quality of conformal coating at highly competitive prices. This is unprecedented in the conformal coating industry.

Our Process Engineers are expert in cleaning, masking, repair, complete removal of all types of conformal coating and conformal coating application. We have the skills, experience and capability to provide you with excellent service from one board to 2000 boards at a time.

ProCOAT has served and continues to serve Military, Aerospace, Medical, Industrial and commercial companies to protect their printed circuit boards. Our attention to detail, expertise and excellent customer services are widely recognized to be the best in our field and beyond your expectations.

ProCOAT understands the importance of efficiency and reliability in conformal coating services. Our customers choose us because they understand our workmanship is of an exceptional standard and we keep our promises. ProCOAT is proud to use Humiseal, Dexter Hysol, Dymax, Miller-Stephenson, Cytec, 3M, Chemtronics, Dow Corning, Huntsman, Aptek Laboratories, MG Chemicals, and Specialty Polymers & Services, Inc.

TYPICAL CHARACTERISTICS OF VARIOUS CURED COATING MATERIALS

Properties Acrylics Urethane Epoxy Silicone
Volume resistivity, ohm/cm (50% RH, 23°C) - 2 x 1015 - -
Volume resistivity, ohm/cm (50% RH, 23°C) 1015 11 x 1014 1012 - 1012 2 - 1015
Dielectric constant, 60 cycles 3 - 4 5.4 - 7.6 3.5 - 5.0 2.7 - 3.1
Dielectric constant, 103 cycles 2.5 - 3.5 5.5 - 7.6 3.5 - 4.5 -
Dielectric constant, 106 cycles 2.2 - 3.2 4.2 - 5.1 3.3 - 4.0 2.6 - 2.7
Dissipation (power) factor, 60 cycles .02 - .04 .015 - .048 .002 - 2.7 .001 - .007
Dissipation (power) factor, 103 cycles .02 - .04 .043 - .060 .002 - .02 -
Dissipation (power) factor, 106 cycles 2.5 - 3.5 .05 - .07 .03 - .05 .001 - .002
Thermal conductivity, 10.4 cal/sec/dq.cm/1°C/CM 3 - 6 1.7 - 7.4 4 - 5 3.5 - 7.5
Thermal expansion 10.5/°C 5 - 9 10 - 20 4.5 - 6.5 > 25
Resistance to heat (°F) continuous 250 250 250 400
Effect of weak acids None Slight dissolve None Little to None
Effect of weak alkalis None Slight dissolve None Little to None
Effect of organic solvents Attached by ketones, armoatics, & chlorinated solvents Resists most Generally resistant Attacked by some


COATING SELECTION CHART

(Ratings in descending order - "A" being optimum)

  Acrylic Urethane Epoxy Silicone
Ease of application A A / B C C
Ease of rework/removal (chemically) A B / C - C
Ease of rework/removal (burn through with soldering iron for spot rework) A A / B C -
Abrasion resistance (rubbing) C B A C
Mechanical strength C B A B
Temperature resistance A B D A
Humidity resistance (moisture) A A B C / D
Humidity resistance (extended periods) A A C C / D
Pot life A B D D
Optimum cure A B B C
Room-temperature cure time A B B C
Elevated-temperature cure time A B B C
Cost A A /B A D


SELECTING THE PROPER COATING

There are several parameters to keep in mind when selecting the right conformal coating. The product’s application environment is obviously one of the keys, but so are the physical characteristics of component assembly.

To what types of contaminants will the assembly be subjected? What is the severity and duration of contact? Is mechanical stress or heat a factor? How delicate are the mounted component leads and connections on a PCB?

Selecting conformal coatings requires an analysis of physical, mechanical, thermal, electrical and optical properties. Physical properties include viscosity and gap fill, the space between the material and the substrate. Mechanical properties include tensile strength, tensile modulus and elongation. Thermal properties such as temperature range, thermal conductivity and coefficient of thermal expansion (CTE) are important considerations also. Electrical properties for conformal coatings include electrical resistivity, dielectric strength and dielectric constant.

Conformal coatings are not restricted to the environments described here. Many special purpose applications make use of conformal coatings, such as electrical power and high voltage products including generators, transformers, circuit breakers and motor assemblies. Specialized conformal coatings meet military specifications (MIL-SPEC) MIL-I-46058, IPC-CC-830, IPC-4101, MIL-STD-1188 and are suitable for many applications. Flame retardant materials resist ignition or reduce the spread of flames when exposed to high temperatures. Flexible or dampening materials form layers that can bend without cracking or de-laminating.

In fact, flexibility is of primary concern where PCBs are concerned and where PCB real estate is critical. The differences in coefficient of thermal expansion (CTE) between a non-flexible conformal coating and the PC board and its mounted components may lead to damage of light-gauge leads and connections. This effect is particularly a problem on boards that experience repeated temperature cycling.

In these applications, a rigid coating may cause damage to the substrates it was originally designed to protect. This reason, along with the ongoing miniaturization of electronics, supports the need for more flexible conformal coating materials to prevent stress on fine-pitch leads and very small components.

CONFORMAL COATING TYPES

The choice of the right coating requires knowing what threats the assembly will be subjected to and its vulnerability to the coating characteristics. As mentioned above, an inflexible coating can stress mounted components to the point of failure. The ease of application and its removal when components fail, are of prime importance.

IPC/MIL specifications classify conformal coatings into types by the cured chemistry of the coating. The types and associated acronyms are shown below:

Type AR - Acrylic
Type ER - Epoxy
Type SR - Silicone
Type UR - Polyurethane or Urethane

These are listed below with their primary characteristics and considerations.

Acrylic:

Generally the easiest of the conformal coatings to handle. The thermoplastic lacquer base means the coating is easy to apply and easy to remove and repair. Moisture resistance is comparable to urethane and silicone, but it has poor resistance to petroleum solvents and alcohol. Dielectric withstand >1500 volts. Temperature range -59°C to 132°C.

Silicone:

Good thermal shock resistance due to flexibility. Also easy to apply and repair, although overall removal may be challenging. Moisture resistance is similar to urethane and acrylic. Dielectric withstand may be somewhat lower than for the other coatings (1100 volts/mil), but flexibility of silicone coating allows for much thicker film build than comparable acrylic or urethane coating. Temperature range -65°C to 200°C.

Urethane:

Hard, durable coating that offers excellent abrasion and solvent resistance. Similar moisture resistance to acrylic and silicone, but significant shrinkage during curing and extremely hard film may stress components. Urethane is a difficult coating to apply and nearly impossible to remove. Rework may be accomplished by burning through coating with soldering iron (using appropriate safety precautions due to isocyanates in the cured film) on local areas, but stripping of large areas or whole boards is nearly impossible. Temperature range -59°C to 132°C.

Epoxies:

Excellent resistance to moisture and solvents, usually a two-part thermosetting coating. Coating shrinks during curing, leaving hard, difficult-to-repair film, which may stress components. Due to the extreme solvent resistance of the film, coating is virtually impossible to strip.

UV LIGHT CURE COATING

UV light curing conformal coatings cure tack free in seconds upon exposure to ultraviolet and/or visible light. Each conformal coating is solvent-free and does not contain VOCs, eliminating the need for solvent handling while enhancing worker safety.

The hybrid acrylated-urethanes (AR/UR) form the backbone of most of today’s UV curable coatings. These coatings contain photoinitiators which, when irradiated by UV exposure, cause the monomers to produce free-radicals that cross-link the polymer chains. This causes the coating to cure instantly.

COATING THICKNESS

Under the IPC–CC-830, MIL-I-46058 and IPC-A-610 guidelines, recommended conformal coating thickness has been defined as follows:

Type of Coating Thickness in inches Thickness in mm
Acrylic 0.00118 - 0.00512 0.03 - 0.13
Polyurethane or Urethane 0.00118 - 0.00512 0.03 - 0.13
Silicone 0.00197 - 0.00827 0.05 - 0.21
Epoxy 0.00118 - 0.00512 0.03 - 0.13
 
     
 
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