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Before we look at conformal coating in the 21st Century, it is worth looking at how our industry has changed since the 20th Century and the effect these changes have had on reliability. 

30 years ago, we had:

• Through-hole PCAs with axial components and wide conductor spacing (see fig. 1)
• Round axial components that were easy to conformably coat
• Wide conductor spacing (causing a few problems with dendritic growth)
• Leaded solder
• The widely adopted practice of cleaning before conformal coating

Fig. 1

Now move forward 30 years. In that time, surface mount components have been developed that are predominantly square with sharp edges, conductor spacing has been reduced, and packing densities have increased to levels never dreamt of in the past (see fig. 2). 

When conventional coating methods such as hand spray, total dipping or robotic selective coating don’t provide the protection required, there is always selective dip coating.

What is selective dip conformal coating?

Selective dip coating is a process whereby the substrate rather than globally immerised in the coating, is discreetly coated in desired locales.  The technique in one form or another, has been around for over 25 years and is used with both classic solvent-based coatings and 100% UV cure conformal coatings.

It's no secret that conformal coatings increase the lifetime of electronic devices by providing a thin barrier that strengthens their ability to withstand harsh environmental conditions. That said, a lesser-known truth is adhesives and encapsulants provide a significantly higher level of protection on the entire assembly.

Why is that? Well, adhesives and encapsulants promote assembly protection by:

• creating environmental seals that protect against moisture and corrosion
• providing high-temperature resistance
• increasing shock and vibration-dampening
• generating strong bonds to a variety of substrates
• maintaining low shrinkage
• offering thermal conductivity

Bury it in

Counterfeit conformal coatings have infiltrated the electronics industry, posing a significant threat to device reliability. These counterfeit coatings may look like genuine products, but they lack the quality and protective properties required for electronic applications. Here are some reasons why counterfeit conformal coatings are causing failures:

Conformal coatings have a long and storied history with printed circuit boards. A good conformal coating protects PCB components from moisture, corrosion, contaminants, and additional PCB threats like vibration and thermal shock. Coatings are a complicated science, and there isn’t one best coating or application method for every job. These choices are dependent on the design, use case, and assembly of the PCB. For instance, manual brushing PCB coating material is a slow, tedious process; but for small batch applications, it’s quite cost-effective.

Regardless of the chosen method, there are fundamental application errors that can occur, leading to defects forming in the coating which ultimately limit the functional service life of the PCB.

Conformal coating technology is on a continuous path of improvement, and we're excited to say the latest step on that path just happened. UV550 is the most recent innovation from HumiSeal, continuing the trend of industry-defining capabilities in the conformal coating space. This is to be expected from the original inventors of conformal coating material. But what sets UV550 apart from the rest?

Let's discuss how the ever-changing requirements of the automotive and white market space fueled the thresholds this uv-curable material attains, especially with regard to its durability under the most extreme thermal and mechanical cycling conditions.  

HumiSeal development specialists have been designing high-performance, UV-curable conformal coatings for approximately three decades. Compared to legacy solvent-borne and silicone technologies, UV- curable coatings provide some unique properties that can be of great value such as- 

• Nearly instantaneous, consistent curing 
• Superb moisture and environmental protection
• Little or no VOC content

These coatings also lend themselves well to high-speed and high-volume applications due to manufacturing advantages such as- 

• Minimal WIP due to immediate cure capability 
• Low material cost due to 100% solids chemistry
• Smaller manufacturing footprint due to much smaller curing equipment

In the days before surface mount printed circuit assemblies, components (such as resistors, diodes, and capacitors) were axial, and printed circuit board components were installed with the “through-hole” method using large conductor spacing. With the advent of integrated circuits, these too were through-hole with good spacing between legs.

We at HumiSeal are no strangers to conformal coatings; and if you’re reading our blogs, it’s likely you’re familiar with these coatings as well. The word “conformal” is descriptive of the function of the coatings which are expected to spread and conform evenly across all surfaces that are to be protected. This uniform and even distribution is necessary to protect delicate electronic components from things such as humidity, water, vibrations, and thermal damage (to name a few).

We at HumiSeal would like to dedicate a bit of time and space to one of the most often ignored factors related to successful conformal coating processes: Clean Air.