Background

In the past, we have had issues with debris on our boards causing inaccurate measurements, particularly on the AFEs. This caused battery faults when in fact the battery was completely fine. We want to avoid these false positives to increase the reliability of the car. During regular car operation, filtering out these particles would mean decreasing the airflow through the electrical enclosures, thus diminishing our cooling ability - this may be fine. However, the electrical enclosures are open very often for debugging/replacing/upgrading boards, so we would like the protection to be part of the board itself.

We are not necessarily expecting liquid to spill on the boards, but it can (and has - FSGP 2019, and I’m sure earlier as well) happen since we do clean our solar array by spraying water on it and potentially have to drive in the rain during competition.

What is 'conformal coating'

Conformal coating is the process of spraying a special polymeric film on the PCBs to protect them from the conditions. This coating is able to ‘conform’ easily to the irregular shapes of the board to protect all the components. The application coatings have a resin base so when the spray dries it will solidify onto the board. There are several different resin bases that each provides their unique advantages.

Types of ‘conformal coating’ / potting

Types of board coatings - list descriptions, advantages, disadvantages, purchase links

Type	Description	Advantages	Disadvantages	Price / Purchase links

Type

Description

Advantages

Disadvantages

Price / Purchase links

Silicone Resin (SR)

Confromational Coating using a Silicon Resin Base

Higher working temperature (-40C to 200C)
High chemical and general resistance protection

Challenging removal (need special solvents, long soaking periods and even brushes)
Expensive

$37CAD - https://uk.farnell.com/electrolube/fsc400/coating-silicone-flexible/dp/1616570 ($37)

Acrylic Resin (AR)

Confromational Coating using a Silicon Resin Base

Most Affordable
High Dielectric Strength
Very easy to remove (using a variety of solvents)
- Good for reworking and debugging
Simple drying process (<20 minutes)
Working temperature range: -40C to 60C (short term protection to 100C)

Not the best in class at protection but still sufficient

https://www.mouser.ca/ProductDetail/MG-Chemicals/844AR-340G?qs=T3oQrply3y9urZcHv3hIkA%3D%3D

$28 but free shipping to Canada https://www.amazon.ca/MG-Chemicals-Acrylic-Lacquer-Conformal/dp/B008OA7178/

Potting Materials

Potting uses a "pot" in the form of a case, shell or similar enclosure, to completely cover the board, protecting it from the surrounding environment - a tough form-fitted shell around the board.

potting cases are secure
offer dielectric protection
safeguard the PCB from the polluting effects of acids, bases, corrosion, salt and most solvents

Very challenging to remove for reworking/debugging
No ventilation

Due to these downsides of potting, it would not be feasible for our purposes.

Recommendation

From the research and suggestions from professionals, a conformational coating using acrylic resins is the best option for protecting our PCBs. This option is recommended for projects that are lower budget, require debugging or reworking and small scale. Although it does not provide the best in class protection I believe it will be sufficient for our needs.

Application

Clean Board
Spray at 45 Degree angle to the board from all 4 sides
Let dry for 30minutes

Removal

https://www.walmart.ca/en/ip/equate-beauty-100-acetone-nail-polish-remover-pump/6000200715614
1. Nail polish remover with acetone can be used to remove areas of the coating that need reworking or to uncover leads
Just apply the Nail Polish Remover

Customer Research

r/solarracing

Other teams have resorted to just applying a silicon coating after all the debugging is done or using a full 3d printed enclosure. I would hesitate to take these routes because of my understanding of our project constraints. We are heavily dependant on passive air cooling so fully enclosing the board may not be feasible. Also, from what I understand we had the dust issues before the competition and need a solution during the testing phases too.

IPC Standards

IPC-CC-830C: This is the main standard for conformal coating. It is used to qualify different conformal coating products, and contains sections on materials, shelf life, curing, chemical, viscosity, and appearance requirements. It also contains standards on fungus, moisture, and flammability resistance as well as dielectric withstanding voltage and other electrical specifications.
IPC-A-610G: This standard covers the acceptability of electronics assemblies, and as such has a section on the requirements for conformal coating coverage and thickness.
IPC J-STD-001F: This standard covers the requirements for soldered electrical and electronic assemblies, and has a section dealing with materials and application of conformal coatings