ProCoat  
 
 
ipc logo
 
     
     
 

ProCOAT Frequently Asked Questions

Conformal coatings are specially formulated lacquers designed to protect PCBs and related equipment from the environment. This improves and extends the working life and ensures security and reliability of performance. These coatings “conform” to the contours of the boards and it’s components, creating a thing (25-50 microns) layer which is both lightweight and flexible. This protects circuitry from hazards such as chemicals, vibration, moisture, humidity and high temperatures. For circuit boards that are not conformally coated, these conditions can cause corrosion, mold growth and current leakage, resulting in board failure.

Below is a list of the most common questions we have been asked over the years. If you don’t find an answer to your questions below, do not hesitate to give us a call at 760-510-9003 x121.

- What standard should I be using for application and inspection of conformal coating?
- Are 'harmful gasses' created when reworking coated components?
- Are there any specifications available that can prove everything is safe reworking?
- What type of conformal coating should be used if the board has "press fit" connectors to be pushed through the conformal coating?
- Conformal Coatings protect against moisture. If I use a Conformal Coating is my assembly waterproof?
- Why use a Conformal Coating?
- Is Pot and Shelf Life critical on conformal coatings?
- Is Out-Gassing an issue with Conformal Coatings?
- How important is it to use the Correct Conformal Coating?
- How do you control the coating thickness in the dipping process and what is the tolerance of the coating thickness?
- How do I monitor the viscosity?
- What is the loading mechanism for the PC 101 Precision Dip Coating System?
- Is the argon blanket an important option for the PC 101?
- Technical Support

What standard should I be using for application and inspection of conformal coating?

First, you need to distinguish between application and selection of coating, and qualification and manufacture of coating. As a rule the first is for the user of the end coating product and the second is for the manufacturer of the coating.

The Interconnections & Packaging Conference (IPC) standards are very good for both these areas and their details can be found on www.ipc.org.

For manufacturing you need IPC-CC-830B which details all the hoops a manufacturer has to jump through to self-certify the quality of their product.

In your case, for production purposes you would need either the IPC A -610 standards or the IPC –HDBK-830. The first gives some minor references which are of limited help except for specifying acceptance criteria. However, the handbook is a compilation of the conformal coating industry’s practical knowledge and will help designers & users of conformal coatings to understand the practical implications of selection, application and inspection, explaining in detail how to achieve the best results.

Are 'harmful gasses' created when reworking coated components? Are there any specifications available that can prove everything is safe reworking?

As far as dangerous chemicals being evolved during rework is concerned, you need to check the MSDS sheets and refer to us but most coatings are relatively benign.

What type of conformal coating should be used if the board has "press fit" connectors to be pushed through the conformal coating?

The key is to choose a soft coating to enable ease of push-fit and avoid risk of damaging the connector. Acrylic materials are generally used by most people doing this kind of assembly, although some softer urethane coatings can work with a bit more effort, especially if the connector is fitted as soon as the material is touch dry. UV cure materials are generally pretty tough after UV curing and so are less suitable (in general) for this kind of assembly.

Conformal Coatings protect against moisture. If I use a Conformal Coating is my assembly waterproof?

All Conformal Coatings can be described as semi permeable membranes. Although they protect the assembly from the negative effects of high humidity environments and water vapor, Conformal Coatings DO NOT render electronic or printed circuit assemblies waterproof against standing water. With a properly applied Conformal Coating an electronic assembly MAY be able to withstand full contact with water for a short time. However this is NOT RECOMMENDED.

Why use a Conformal Coating?

Due to the decrease in size of PCBs and the increased packing density, there is increase in the chance of shorts, corrosion, dendrite growth and electro migration. Conformal coating a PCB can improve the long term reliability of an assembly through careful application.

Conformal coatings are defined as thin polymeric films which “conform” to the surface of the printed circuit board (PCB) and components. The conformal coating acts as an insulator. It protects the electronic circuits from the environment including moisture ingress and contaminants such as airborne dust which could lead to corrosive effects and shorts, as well as providing mechanical strength for vibration and shock.

Is Pot and Shelf Life critical on conformal coatings?

It depends on the conformal coating material type as to how important shelf and pot life need to be monitored. The most critical type of conformal coating which is affected by pot life is moisture cure materials such as conformal coating silicones. Any premature curing of the moisture cure product can cause production problems and the silicone coatings must be monitored carefully. Other conformal coatings that may have pot life issues are two part products, which when mixed, will begin to cure within the allotted time period and cannot be reversed. The manufacturer’s recommended shelf life and pot life should be reviewed and tracked closely.

Is Out-Gassing an issue with Conformal Coatings?

Some conformal coating materials out-gas and can cause conformal coating failures. The effect can occur in a vacuum or when the conformal coating is heated, which can result in conformal coating material volatizing and re-depositing on sensitive components. The following conformal coating materials meet and or exceed NASA specifications for out-gassing:

Arathane 5750 by Huntsman

Aptek 2503 by Aptek Labs

Solithane 113 by Crompton-Uniroyal Chemical

CE-1155 by Cytec Industries

How important is it to use the Correct Conformal Coating?

Choosing the right conformal coating material means selection of the right conformal coating for (i) the printed circuit board (PCB) in the field for its long term reliability and (ii) the correct conformal coating application method giving a cost effective method without affecting the performance of the conformal coating to protect the PCB. The environment where the PCB is going to be used is also very important.

For example, application of a UV cure conformal coating like Humiseal UV40, Dymax 984LVUF or 987 gives an instantaneous cure and offers fantastic moisture and chemical protection. This would require a specialist UV conveyor and UV lamps for curing the UV conformal coatings.

How do you control the coating thickness in the dipping process and what is the tolerance of the coating thickness?

The dip speed is controlled by air over oil hydraulics which can control the speed down to 2" per minute which is very slow and more than adequate for conformal coating. Repeatability is about getting accurate viscosity control since the withdrawal rates and viscosity control the coating thickness.

Typical speeds for conformal coatings at viscosity of 200 cps are 6" withdrawal speed giving a 25-50um coating for an acrylic coating. This does vary from coating material to material so control measures should be put in place if accurate thickness is required. Manufacturing specifications or customer requirements are crucial in adhering to viscosity.

The typical coating tolerance is depending on what you measuring on? If it is a flat coupon, then with a known viscosity of product you should be able to achieve +/- 5um.

How do I monitor the viscosity?

The viscosity is monitored by utilizing a zahn type measuring cup. This is essentially an egg cup with a hole in the base on a wire. You dip the cup into the liquid and lift it out of the coating. Since the volume of the cup is known and fixed, if you time the flow of the coating out of the cup you get a relatively accurate and simple method of measuring viscosity which is certainly suitable in 99% of cases.

What is the loading mechanism for the PC 101 Precision Dip Coating System?

The PCBs are hung on the cross rods by hooks or any other form of jigging ( we can custom build). The immersion and withdrawal of the cross rods is carried out by a custom piston which moves up and down at a controlled rate down to 1-2”/min since we use an air over oil system.

Is the argon blanket an important option for the PC 101?

The argon blanket is a useful accessory for overlaying conformal coatings that are sensitive to moisture such as moisture cure silicones like Dow Corning 2577. The principle is the argon gas is heavier than air and using a series of valves a blanket of argon gas is bled over the conformal coating tank, effectively trapping the solvents under the argon. This is also effective in regions of high humidity and can help prevent moisture ingress.

Technical Support

If your company requires any information involving conformal coating, potting, or encapsulating, we can help save you time, money, and pain.

We are here to help and provide excellent service. Pick our brains! Call our Technical help line at 760-510-9003 ext. 121 for impartial expert advice on all aspects of conformal coating, potting, Underfill and encapsulation, including Health & Safety risks, guidance on the selection of conformal coatings solutions, removal of coatings and general applications, and trouble shooting. Call us now! We are eager and happy to assist you.

 
     
 
© 2015 ProCOAT Inc.