Five Reasons Why Conformal Coating Dipping can be One of the Most Effective Production Processes
Dipping a circuit board in coating can be highly effective. Here are five reasons why:
- You can dip many boards at once. It can be the fastest conformal coating process of all the methods.
- It is an extremely simple process. Hang the circuits, press a button and the boards are coated.
- The process is very repeatable. Once set up the conformal coating thickness will be constant with very few process controls.
- The conformal coating penetrates underneath components. This gives complete coverage.
- The boards are coated both sides simultaneously. This halves the process time.
For further information click conformal coating dipping
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How to Select a Conformal Coating Process – The Holistic Approach
Choosing a conformal coating process is a complicated and involved process usually balancing a number of trade-offs and compromises.
This is because of three major parts of the complete process that can offer different options and create difficult choices.
These parts are:
- The Conformal Coating Material Requirements
- The Application Method Selected
- The Circuit Board Design
When you consider these three points you have to balance them to create the best compromise solution that suits your requirements.
This is the Holistic Approach to conformal coating.
What is capillary flow in conformal coating and why does it occur?
Capillary / Scavenging on a printed circuit board where the coating has run away from an area around a component.
Capillary flow (also known as scavenging) in conformal coating is where the conformal coating pulls or runs away from certain areas of a PCB to more favourable sectors due to a combination of effects. This can leave a patchy finish on the surface of the board.
Factors that influence the capillary effect during processing include:
- low viscosity of the conformal coating
- an abnormally high amount of coating applied
- a low surface energy of substrate
- the high surface tension of the conformal coating.
For further information Click capillary conformal coating failure mechanism technical bulletin
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What standards can the SCH Technologies Conformal Coating AOI systems inspect to?
The systems have a variety of software options right up to inspecting TRUE IPC Class III standards. The reason we state true standards is that most people are not inspecting to this level even though they think they are. This is due to two reasons:
- It is very difficult to inspect to IPC Class III standards as it is under magnification, is time-consuming and challenging for operators.
- Also, it is very difficult generally for customers to produce conformal coating finish to this level without creating lots of defects.
The key to all inspection, manual or automatic, is to decide what you are looking for.
The surface energy of the substrate is lower than the conformal coating
So, what type of conformal coating defects are you looking for? Are you looking for bubbles?Are you looking for foreign bodies? Or is it just coating in the right place and coating not in connectors? These questions are related to the inspection criteria you desire and it is very important to define exactly what are you actually looking for.
The software we use can measure all of these factors. The key is to understand whether your production process can stand up to the level of inspection/interrogation that the machine will provide?
Click For further information on Conformal Coating AOI Systems from SCH Technologies.
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How do you apply parylene to a printed circuit board?
Parylene is applied through a specialised vapour deposition process at ambient temperature. Parylene polymer deposition occurs at a molecular level, where the coating literally grows one molecule at a time on the substrate surface, assuring entirely conformal and uniform layers of parylene conformal coating are applied.
The process begins with the raw, granular material called the dimer which is heated under vacuum. The dimer is then reduced to a gaseous state in the vaporising chamber. The vapour is next drawn into the furnace and heated to very high temperatures (pyrolised) to allow for sublimation and the splitting of the molecule to a monomer. The gas is finally drawn into the room temperature deposition chamber, where the monomer gas deposits on all surfaces as a thin, transparent polymer film and the result is a parylene conformal coating uniformly deposited on the product.
Because the Parylene is applied as a gas, the conformal coating easily penetrates everywhere on components, providing complete and uniform coverage. Literally a conformal coating. . While Parylene coatings can range in thickness from hundreds of angstroms to several mils, a typical thickness is in the microns range.
If you would like to know more about parylene and coating services or other products offered and supported by SCH Technologies, please do not hesitate to contact us
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Is it advisable to clean my boards before your conformal coating application process?
Whether to clean a PCB before coating is a difficult question to answer simply. However, the best advice is if the product is safety critical and you have not tested the product for long term reliability it may be worth cleaning!
The problem lies in not knowing what contaminants are on the surface of the board before coating. These contaminants could be from a variety of sources including the bare board manufacture, the solder resist used and whether it is compatible with the coating, the assembly processes including fluxing and the handling process.
Determining if the board contaminants are relatively benign is possible using techniques like Surface Insulation Resistance (SIR) testing? However, it can be complex and could be quite costly depending on the level of investigation. This cost however needs to weighed against the potential costs of returns, reputation and consequential losses if it
If you would like to know more about cleaning before coating or other products and services offered and supported by SCH Technologies, please do not hesitate to contact us
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Why are there so many different conformal coating application methods?
Coating a printed circuit board initially seems to be a straightforward process. After all how difficult can it be to apply a “varnish” to a pcb? The problem is there are so many variables to consider.
First, there is the PCB itself. you must consider its size, the components on the PCB and whether they need to be coated or must not have coating on them, what you are protecting from (moisture, water, chemicals, heat etc) and the volume to be processed?
Once these details are understood then you have to select a conformal coating material. But, selecting a coating influences the application process. For example, choosing a UV cure coating obviously means a UV cure conveyor is required. But, it also means certain robotic valves cannot function in general with these materials. So, coating selection automatically influences the application method.
In fact, the material, the PCB and the application method must be considered as a whole to give you the best chance of developing the optimum process for costs, time and protection.
Click Which conformal coating application method should I choose? Do I dip, spray or brush? to find out more.
Designing for Selective Robotic Conformal Coating Processing: Rule 1
When you are considering the board design for applying the conformal coating using a robot system then consider how you want the board to be coated? Must all of the PCB be coated? What areas are critical and what must not be coated? Are there areas where it doesn’t matter if coating is there or not?
Rule 1
Designate three areas on a conformal coating diagram. These are:
- Areas that MUST be coated
- Areas that MUST NOT be coated
- Areas where it doesn’t matter (coating is optional).
Breaking the PCB into these three areas allows application engineers to understand the priorities of the protection required for the coating, especially where coating doesn’t. Removing the ambiguity from the process creates focus on what really matters.
The Rules
The Rules for Selective Conformal Coating are straightforward. Follow them and you can save money and time in your application process. However, if the Rules are not followed, the resultant circuit board design can challenge even the most sophisticated conformal coating system and its operator to achieve the finish desired.
Click Designing Circuit Boards for Selective Robotic Conformal Coating for further Rules.
How do you control the conformal coating thickness in the dipping process and what is the tolerance of the coating thickness?
Controlling the thickness of a conformal coating applied to a printed circuit board using an automated dip coating process is straightforward.
Click Conformal Coating Dipping FAQs to find out more about this and other issues relating to the process.
How do I spray the EMI / RFI Shielding Coating?
Follow proper techniques as outlined by the gun manufacture. For best results, keep the gun-to-surface distance constant. Move the gun in a straight line along the surface, avoiding arcing motions. Use spray-and-release strokes to avoid excess paint in one spot. If possible, start and end each stroke off the surface.
To apply the required thickness
1. At the recommended distance, spray a thin and even coat onto the surface. Overlap the previous stroke by 50% to avoid gaps in coverage.
2. Before spraying another coat, wait 2 to 5 minutes (depending on the product specifications). The delay avoids trapping solvent between coats.
3. Apply additional coats until the desired thickness is achieved.
4. Let dry for 5 minutes (flash off time) at room temperature.
If you would like to know more about RFI Shielding Paints or other products and services offered and supported by SCH Technologies, please do not hesitate to contact us
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Website: Click
RFI EMI Shielding Coating Fundamental FAQ’s for the full range of information
EMI / RFI Shielding Coating Application Guide for information on application
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Conformal Coating 