Generally, boards are made from waterproof fiberglass materials that can withstand high temperatures and provide insulation between the copper layers, as well as minimize interference and promote good signal integrity.

These properties make fiberglass an ideal material for universal printed circuit boards. And that is why they are widely used in most consumer electronics products.

What do you mean by extreme conditions?

It does not necessarily have to be a space environment, even in our environment there are many environments that can be considered extreme in relation to the operation of electrical equipment.

• Environments with extreme temperatures, both hot and cold.
• Environments where there are fluctuations in temperature or humidity
• Generally rainy/humid environments
• Industrial dusty environments where dust or other contaminants are present.
• Surges, either natural (e.g. lightning) or man-made.
• Locations where electrostatic or electromagnetic interference occurs.

Designing circuit boards to withstand harsh conditions requires special skills and knowledge to ensure that the final product will last as long as possible in extreme conditions.

Let's take a look at the challenges faced when manufacturing circuit boards for extreme environments.

Temperature

Every electronic device generates a certain amount of heat during operation. For standard circuits, this amount of heat is not enough to damage the entire circuit board. However, in an environment with extremely high temperature, the board would already be problematic.

A way to dissipate the heat from the circuit board is to add a copper surface layer in the non-conductive part of the circuit. For example, FR-4 fiberglass material is not an excellent conductor of heat, and pouring copper in areas outside the circuit helps cool the circuit.

But beware, this technique only works up to a point. If the heat produced is too great, use metal-clad printed circuit boards. These are boards that have an electrically insulated aluminum sheet as a base plate. Aluminum absorbs heat much faster than FR-4 material, protecting the circuit board components from overheating and extending their life. Aluminum circuit boards are generally used, for example, in the manufacture of LED luminaires, especially in flat panel lighting.

And if even the integration of aluminum boards is not enough, a ceramic circuit board is a suitable choice. The basis of a ceramic printed circuit board is extremely thermally conductive elements and compounds such as aluminium oxide, aluminium nitride and beryllium oxide (which are often coated with gold). This coating will help remove heat from hot spots faster and dissipate it over the surface of the board and into the surrounding area.

Ceramics offer a significant advantage over traditional materials such as FR-4 and metal-clad plates when it comes to heat dissipation.

• Heat transfer through the plate is significantly more efficient because the components are directly on the plates without an insulating layer.
• Ceramic has a very low coefficient of thermal expansion (CTE), which allows for additional compatibility options in PCB design.

Generally, it is not necessary to deal with the manufacture of PCBs when they are used in temperature extreme environments, but with the placement of external cooling means. The same then applies to assembly.

Moisture and dust

If the circuit board will be placed outdoors or exposed to a natural environment, it must be protected from the weather, including water, dirt and dust. Without proper surface treatment, damage to the circuit or equipment will occur. To prevent this, the circuit board must be coated with a surface varnish to keep the circuitry dry and dust free.

There are basic types of lacquers, each with their own advantages and disadvantages.

• Acrylic resin
• Urethanes
• Epoxy resin
• Silicone resin
• Parylene

Acrylic resins: popular for simple application technology, minimal thermal effects on drying and easily adjustable viscosity. In addition, they do not shrink further after evaporation of the solvent and cover the same surface as after application. If a solder joint needs to be repaired or a component needs to be replaced, the solvents can be easily removed after curing. Unfortunately, this is due to the low chemical resistance of the coating. And also with this type of coating, what form of curing occurs, if by elevated temperature, then it must be taken into account that acrylic coatings have a low glass transition temperature Tg. If this temperature is exceeded, the coating may stretch. Conversely, if UV is used to cure, imperfect curing may occur in shaded areas. This treatment produces a pungent odour with the side effect of skin irritation.

Urethanes: Coatings are heat curable within three hours but have a shorter life. When curing by evaporation of the solvent, increased humidity, which adversely affects the speed of the process and the desired properties, must be avoided. After curing, they retain their dielectric properties best when loaded in the ambient environment.

Epoxies: can withstand higher glass transition temperatures. They also provide good resistance to mechanical damage. They are resistant to moisture and chemical environmental influences, which means they are almost chemically non-removable for possible repairs.

Silicones: silicone coatings find use in applications where electronic assemblies must withstand extreme temperatures and high dielectric strength is required. Silicone resins are flexible, resistant to moisture and solar UV radiation. They are most commonly used in the automotive industry. Their disadvantage is their reduced handling time before curing and against mechanical stress in the form of abrasion.

Parylene: It works best against environmental chemicals and moisture. It has excellent dielectric properties, mechanical resistance and a low coefficient of thermal expansion. The disadvantages of parylene are the need for vacuum masking of unpainted areas, more technologically demanding repairs and lower UV resistance.

The choice of paint is based on the application and the functional requirements within the application. Some components on the circuit board cannot be covered with a protective varnish. These include, for example, contact systems, trimmers and similar components.

These components should be covered or painted with a removable varnish before application to prevent a protective coating from forming.

High performance printed circuit boards

Circuit board circuits are made of thin copper traces. These copper traces are sized for low power applications because the current flowing through the conductive material is directly proportional to the width and thickness of the trace cross section. For universal circuit boards, the layer thickness is 1oz =35 micrometers. Therefore, if we need a higher current load, we can increase the width of the trace or make the trace multi-layered to increase the cross-sectional area to conduct more current.

Other problems that need to be addressed are interference in the form of electrostatic discharges or electromagnetic waves. However, these will be dealt with separately in the next section. Designing printed circuit boards that can withstand all challenging conditions is by no means a simple task and encounters many constraints.