Xylene and Toluene. Two words that can evoke concern and add to paperwork for environmental health and safety departments and manufacturing professionals. Aromatic solvents have been safely used for decades by employing basic safety equipment including gloves, masks, and proper workplace ventilation. Nevertheless, concerns for maximizing employee safety and minimizing effects on the environment have led electronics manufacturers to seek out alternatives. For over 20 years, HumiSeal® has supplied a wide-ranging group of aromatic-free products across all traditional chemistries to manufacturers for whom these concerns are critical.
The evolution of conformal coatings for protection of PCBs and electronics has accelerated over the past few years. One development in particular has increased in popularity due to a promising array of advantages over its predecessors. These are LED Curable Coatings.
A partial list of existing technologies for conformal coatings would include:
- acrylics (both solvent and water-borne)
- solvent-borne polyurethanes
- silicone-based polymers
- synthetic rubber (solvent-borne)
- Parylene technology
- UV-curable acrylated urethanes (arc and microwave bulb source)
and most recently . . .
Picking a Conformal Coating
You and your organization have spent weeks or months researching conformal coatings to meet the demanding specifications of your customers. These can include factors such as dielectric strength, thermal and mechanical shock properties, processing considerations, and so on. At some point, the critical consideration of price and cost must be added to the equation. The amalgamation of cost and performance could be considered a measure of the true value of any specific coating.
Conformal coating thickness is one of the most important characteristics to ensure long-term reliability of your electronics. A minimum coating thickness is essential to provide the required function of the conformal coating, but if a conformal coating application is too thick, it can actually have negative effects on your level of protection.
Which conformal coating thickness should be applied to reach optimal protection?
For decades, HumiSeal products have been considered the “gold standard” in electronics protection. As a result, it is no surprise that unscrupulous chemical manufacturers have been continuously trying to profit from this reputation through the production of copycat or counterfeit products. While imitation is considered the sincerest form of flattery, the use of counterfeit materials is a serious danger to the integrity of your electronics production.
For many electronics manufacturers, the original justification for specifying a silicone coating is lost deep within the mists of time and it may be time for a re-evaluation and consideration of the question,
“Do we really need a silicone conformal coating?”
Humiseal® remains in a uniquely qualified position to help you answer this question. Unlike many coatings sources, Humiseal offers a full line of all the major conformal coating technologies including acrylics, urethanes, synthetic rubbers, water-borne, and yes; silicones. As a result, you can be certain of an unbiased approach to product evaluation that will result in the most cost-efficient material to meet your needs.
There are a number of factors to consider when evaluating your application to answer whether there is really a need for silicone technology:
IPC CC-830 revision B is a conformal coating qualification standard mostly used by board fabricators, OEM design engineers, and coatings suppliers.
There are two fundamental uses of this IPC standard:
- Coatings’ performance capabilities
- Quality consistency
In this blog, we will go over some of the specifications along with tests requirements, passing criteria, and quality characteristics.
The conformal coating process, like any other processes, has different variables, inputs, and outputs. In order to be able to control the results of your application (outputs), we need to fully understand how each variable affects the process.
The importance of the variables
To get the right amount of liquid, thickness, right coverage, no contamination on keep out areas, etc., you need to identify and understand the variables of the process.
The most important variables:
- Machine parameters (speed and Height)
- Curing method
In this blog, we will concentrate on reviewing the first variable: Viscosity
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.
The application of the conformal coating in a uniform and consistent coverage is a key challenge that defines the reliability of the finished product.
A thin coating will provide inadequate protection against corrosion or insulation between conductors. Conversely, if the conformal coating is too thick, it will increase the risk of forming other types of coating defects such as bubbles, insufficient curing, and potential cracking during thermal shock cycles.
Besides the verification of the process parameters such as coating viscosity and the application method is correctly setup, the amount of conformal coating material applied on the printed circuit boards can be measured before curing. For this, wet film conformal coating thickness gauges are used. This method ensures quality control while the coating material is still wet.