Conformal Coatings Vs Potting Compounds Notebook computer to guard my PCB, a coating or possibly a resin?
This can be a question which is often asked over the electronics industry and like any good engineering answer,?it depends– within the higher level of environmental protection required.? The first thing to consider is generally the style of any housing within that your PCB will be enclosed.? Somebody who is assembly is enclosed within a housing which can be designed to be the primary environmental protection, then this conformal coating is normally familiar with present you with a back-up towards primary protection made available from the housing.? Where the housing is just not suitable or competent at providing primary protection from the assembly looking at the operating environment, then this may a resin may well be a more sensible choice.?
The next question should then be “What is actually a coating as well as a resin?” After we take a look at what on earth is common forwards and backwards, they are generally organic polymers, that may cure to form an electrically insulating layer that shows some amount of chemical and thermal resistance. There exists a degree in commonality from the chemistry of your polymers used, with acrylic, epoxy, polyurethane and silicone to be the quite often encountered.
Conformal Coatings.
Generally,?conformal coatings?are thin films applied to the 25-100 micron dry film thickness range, triggering a minor weight increase of your assembly.? Often coatings are evident, therefore, the coated components are super easy to identify as well as the coating can be simply reworked and components replaced as required. Caffeine and thermal resistance of coatings is usually good for short exposures. A coating applies relatively little stress upon the ingredients, this is the particular advantage when a component has thin pins or legs.
The majority of coatings are 1K (single component) systems, that contain a protracted bath life, a small curing or drying temperature and short drying time. Like a single-part solution, they can be clearly simpler to process and apply; however, the vast majority of 1K coatings are solvent headquartered in order to modify their viscosity for application purposes. Newly released?two part?(2K) epoxy and polyurethane coatings, on the other hand, combine the safety and properties on the resin (see below), while using simplicity of application of a conformal coating but without solvents, it’ll a green advantage. These may provide excellent coverage and also their superior flexibility offers protection of delicate components. 2K coatings also deliver excellent mechanical properties and abrasion resistance but, being two-part, they’re more complicated to process in contrast to 1K coatings and maybe they are virtually impossible to remove, making board repair quite hard.? The coating can be applied manually by utilization of a paintbrush, spray gun or perhaps manually dipped.? However, increasingly, coatings are used by robotic selective coating systems to give a more controlled plus much more consistent process.
The wide usage of spray application for coatings has meant that the coating ought to have the lowest enough viscosity to hold the material to be atomised over the spray process. It can be traditionally meant that coatings have contained high amounts of solvents in order to reduce the viscosity from the base resin The solvent content of countless coatings means heat is commonly utilized to drive off the solvents to allow the resins with regard to, since if left for stopping at 70 degrees, solvent may remain input into the coating causing premature failure.
With increasing environmental awareness the sort of solvents used have changed to reduce the VOC (Volatile Organic Compound), in addition to the area of the solvent contained in the coating.? Modern coating materials in many cases are solvent-free, and called 100% solids because each of the material put on to the circuit board will cross-link to yield a dry-film of similar thickness to the wet-applied film.? These 100% solids coatings can cure by heat, moisture, or UV radiation based on the actual formulation.
Potting Compounds / Encapsulation Resins
Potting compounds and?encapsulants?is true from 0.5 millimetres thick, but are generally applied much thicker than this.? The raised thickness results in a significant improvement in weight and often results in a greater per unit price compared to a coating.? However, the improved thickness includes which the PCB is far better protected against chemical attack, specially in the installments of prolonged immersion. Also, a resin can supply superior protection against physical shock (based upon the formulation), considering that the almost all the resin will dissipate the forces all over the PCB, rather than allowing them to be concentrated. A layer of dark coloured resin can completely hide the PCB, that permits for some security in the design, and dependant on choosing the resin, removing of the resin can also result in the destruction of the PCB.
Potting compounds and Encapsulants are generally 2K (two component) systems, where a resin (Part A) is when combined the correct amount of Hardener (Part B), which starts a chemical reaction leading to a cross-linked polymer.? Resins usually have an extremely higher viscosity, and in most cases contain mineral fillers to help you their performance. Because there’s no need spray apply resins, a lot of resin formulations are VOC free, and the majority of resins were made to cure at 70 degrees, even so the cure time is often reduced via the application of heat, along with some resins, post cure may very well be required to allow resin to create its optimum properties Most resins starts off reacting when the 2 components are mixed together. The vast majority of curing reactions are exothermic as chemical bonds are broken and rearranged. It is the nature of exothermic reactions for getting hot, however heat are usually controlled from the careful judgement on the volume of material that ought to be cast as the single process. Excessive resin applied simultaneously, may lead to the components becoming over heated, or maybe in ab muscles worst, the casting catching fire.
Application of your resin is as simple as the using of a mix-pack, where the 2 components are given from a separated pack during the correct ratio. Anyone removed a divider, mixes both components thoroughly then poured to hide the necessary areas to your required depth (see our video?here). A lot like coatings, the application of automated 2K dispensing equipment is getting increasingly widespread to combine and dispense the resin as needed in the consistent and repeatable fashion.
It is interesting to make note of that, in a few applications, in which a 2K resin formulation could have been the first choice for circuit protection, a 2K conformal coating may turn in the market to become the better approach, as a consequence of its superior mechanical properties, balanced with 1K coatings.? Moreover, switching from your resin into a conformal coating will remove the weight penalties with the former, that may be essential to some applications.
So how to pick which is ideal for my application, will be middle ground?
The kind of the PCB, the housing and the anticipated end-use environment all play a major factor during the decision getting in touch with make use of a coating or simply a resin.
As previous, in the event the housing provides adequate best protection against environmental surroundings, then this usage of a coating provides for a back-up and can can protect you on the board should the primary protection be damaged or leak, and also can protect you against moist and condensation within the housing.
Often, potting compound resins are employed to form the main housing itself, and are thus portion of the primary protection from the system, and therefore are necessary to resist the many potential contaminants the housing might see during its end use environment.
Resins are often used in high profile electronics and electronics operating in explosive environments, use a total dielectric layer to avoid arcing.
A well-designed PCB and housing can make the utilization of either the coating or perhaps the resin a simple and efficient process, efficient within terms of the timeframe necessary to process plus the number of material required.
And merely to make things more complicated, Electrolube recently launched a variety of coating materials, in accordance with similar 2K chemistry to resins, but intended to be employed by selective coating equipment during the 200-400 micron range, thus combining numerous advantages of both technologies and minimising lots of the drawbacks of the.
Indeed, these new 2K conformal coatings have demonstrated excellent performance in?condensing?environments. In environmental chamber trials simulating highly condensing conditions, while a urethane resin potted assembly gave the top overall values in relation to circuit protection – and showed minimally change during condensing events – the very large improvement in thickness between it along with a 2K conformal coating didn’t show a considerable surge in performance. Indeed, the 2K coating achieved very similar results because potting compound at 1 / 10 the thickness. 2K conformal coatings does apply more thickly than previous coatings without chances of cracking. They’ll also be readily used by selective coating methods to offer a coating with better thickness, and sharp edge coverage that has performance somewhere in wherein a conventional conformal coating fails and potting is called for.
Authors: ?Phil Kinner, Alistair Little