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.
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How do I control my conformal coating thickness with my dip system?
PCBs being dipped on a DS101 System
The thickness of a conformal coating material applied during a dip process is dependent on several factors. However, the two critical points are:
- The viscosity of the conformal coating being applied
- the speed of withdrawal of the printed circuit boards coming out of the tank of the dip system
The viscosity of the conformal coating being applied
The viscosity of the conformal coating can be monitored by utilizing a flow cup. There are many designs but is essentially a cup with a hole in the base on a wire. You dip the cup into the liquid and lift it out of the conformal coating. you then time taken for the coating to empty from the cup.
Since the volume of the cup is known and fixed, you can relate the time to the viscosity of the conformal coating and you get a relatively accurate and simple method of measuring viscosity which is certainly suitable in 99% of cases.
The speed of withdrawal of the printed circuit boards coming out of the tank of the dip system
Using typical conformal coating dip systems like the DS101 dip system, the dip speed is controlled by air over oil hydraulics which can control the speed down to 2″ (50mm) per minute. This is very precise and more than adequate for conformal coating thickness control and repeatability. The key to dipping is to realise that the slower the withdrawal speed the thinner the conformal coating applied.
Control these two factors and you have a very repeatable conformal coating process.
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Design rules for using a solvent based conformal coating in a dip tank system
When buying a conformal coating dipping system it is worth considering the following:
- The exposed surface area of the dipping tank should be minimised to reduce evaporation of the solvents and limit exposure of air to moisture sensitive conformal coatings.
- A lid should be provided placed over the dip tank when not in use. This again limits evaporation of the solvents and limits exposure of air to moisture sensitive conformal coatings
- Ensure good material flow through the tanks and avoid dead areas of flow of the conformal coating. This avoids congealing coating and viscosity variations across the tanks
- Use a two-tank system with a recirculating pump. The dipping tank will stay level and gives an exact dipping depth for precision dipping.
- If using electronics in the dip system such as viscometers, heating systems and temperature control systems ensure they meet the correct HSE standards such as ATEX to avoid flammability and explosion problems.
- Avoid parts that are direct with the coating material if possible. This will avoid unnecessary maintenance.
- Ensure that there is enough volume of conformal coating in the tank versus the surface area of the tank that does not give you a rapid change in viscosity and an unstable dipping process
- Reduce the extraction airflow across the tank to the minimum allowed for Health and Safety needs. This minimises solvent evaporation and a significant change in viscosity.
- Use the correct type of pump for the process which is both solvent resistant and does not generate heat in the process
- Meet the fire regulations where required and supply in built fire suppression systems or have access to fire extinguishers
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How to verify the conformal coating thickness on a printed circuit board in production for a dip coating system
When using a conformal coating dipping system it is important to know that the dry film conformal coating thickness is correct on the circuit board. Ultimately, the conformal coating will only be protective if applied at the right thickness so control of the process is crucial.
First, when we are coating PCBs we must assume that the variables for the conformal coating dip coating process are set up correctly for the PCB. That is that
- The viscosity of the conformal coating is correct
- The withdrawal speed of the dip system is correct
- The temperature of the conformal coating is stable
These three parameters ultimately control the final thickness of the conformal coating on the circuit. Change one of the these and you can change significantly the conformal coating thickness.
Once this is set up and everything is in order we now want to monitor the coating thickness.
There are two options:
Option one: Measure the circuit board directly.
This can be done with a micrometer or a conformal coating eddy current system such as a Positector. However, this assumes that there is enough room for the probe or micrometer on the circuit board and (ii) there is metal in the PCB at the point of measurement for the Positector. Using this system after the coating is cured hard enough to test gives excellent readings
If this is not the case there is an alternative solution.
Option 2: Measure a test coupon
If the conformal coating thickness is correct on a circuit board when qualifying the process then it is possible to dip a test coupon to measure the equivalent coating thickness. This then allows you to use a test coupon at the start of the day’s production process to confirm everything is in order and no parameters have changed.
The process is the same as with measuring the circuit board. Dip the coupon. Dry it sufficient to measure the coating thickness and verify that the process is stable and there is no significant variation.
This is an easy method that is reliable. It also backs up your viscosity control measurements for your conformal coating and ensures your conformal coating dip process is in control.
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Can you use a moisture cure silicone conformal coating in a dipping machine?
Conformal Coating Dip System with PCBs hung ready to be coated
The answer is yes. It is done regularly and we have dip coating systems filled with moisture sensitive silicone materials that function perfectly.
The key is the way the conformal coating and the process are set up. Follow these steps to ensure your silicone dip conformal coating process is successful.
- The coating may skin on the surface. Remove this whenever it occurs.
- Use a catch tray in the weir of the dip tank. When the congealed coating drops into the catch tray the lumps will be caught.
- Apply a moisture-free gas across the surface of the tank. This inhibits the moisture in air prematurely curing the coating.
- Minimise the pumping of the coating. Turn the speed down to a minimum and only pump the coating when in use. turn off the pump there are long periods of no coating.
- Apply proprietary thinners over the top of the coating during long periods of shut down
Contact us now to discuss your conformal coating dipping process and how we can help you.
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Can I horizontally dip my printed circuit board in conformal coating and achieve a good finish?
Dipping PCBs in conformal coating
The answer is yes.
In fact we can dip your PCBs at any angle you choose. The key is control of the dipping depth and being able to hold the PCB. If we can achieve both successfully then it is perfectly possible to horizontally dip PCBs using automated batch dip coating machines such as the DS101 dip system.
There are many factors to consider such as the size of the board, the depth of dipping allowed, the type of conformal coating to be used, how to hold the PCB and the masking & components on the board that must be considered.
However, SCH regularly use this technique to minimise costs for customers. We can develop the fixtures to support the PCBs as well as design for multiple dipping of the boards.
Click conformal coating dip system FAQs for further questions
Try our different conformal coating dip system pages to see if they meet your needs:
- Bench top conformal coating dip system
- Floor standing conformal coating dip system
- Inline conformal coating dip system
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Questions to ask when considering a Conformal Coating Dipping Application
When selecting a conformal coating process it is important to ask the right questions.
With dip coating, the information required includes questions such as:
- What is the size of the Printed Circuit Board (PCB) you wish to coat?
- What is the typical volume of the PCBs you want to coat per day, week, month etc?
- Is there any masking required on the PCBs?
- Do you know how you would like to hold the PCBs or do you need help with fixture design etc?
- Is the PCB to be dipped vertically, horizontally or at another angle?
- What is the material you wish to use for coating the PCB?
- Is the material compatible with a dip coating process?
- Do you require a batch process (operator loads and unloads at same point) or an inline process (load one end and take off at another station)?
- Do you require any curing mechanism within the machine (heat cure, UV light)?
- Do you require any automated control processes such as viscosity material maintenance and automatic material top up?
Asking these questions ensures that a dip coating machine supplier can provide a detailed quotation on the exact machine you need for your project.
Dipping PCBs in conformal coating
Dip coating is the simplest and highest volume conformal coating process to be used. If printed circuit boards are designed for dip coating the huge savings in money, time and effort can be made. For help on design rules for dipping contact us direct.
For further information on Conformal Coating Dip Coating CLICK
- Conformal Coating Dip Systems (Inline)
- Conformal Coating Dip Systems (Batch)
- Conformal Coating Dip Systems (Bench)
- Conformal Coating Dip Systems FAQs
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Can the capacity of the DS101 conformal coating dip tank be reduced?
SCH can make the tank any size you want. However, there is a ratio of surface area of the tank to depth that is important. If you have too little volume of coating in relation to the surface area, the evaporation of the solvent will change the viscosity of the tank too quickly and you will constantly be monitoring it. We have no formula for this but making it too shallow could be a problem.
Click Conformal Coating Dipping FAQs to find out more about this and other issues relating to the process.
How is the height of the conformal coating material in the tank controlled on the DS101 dip coating system?
On the DS101 dip coating system there are two parts to the tank. These are the dipping area and the sump, which are separated by the weir edge. The material is pumped into the tank, over the weir into the sump. Therefore, the weir edge holds the height constant and the weir sump drops with material use.
Monitoring the weir sump depth is crucial again to learn how fast it is drained. We recommend a 25mm (1”) edge difference between the top of the weir and the sump material and keeping the material close to that avoids a wide evaporation area over the weir which means more solvent evaporation. This can also be critical with materials that do not re-dissolve into the material when dry like water based coatings. If they do dry /cure then these bits float around in the sump and then eventually could clog the pump. We would recommend using a stainless steel basket which we have designed to catch these bits like a sieve and any other bits floating (or even PCBs dropped!).
Click Conformal Coating Dipping FAQs to find out more about this and other issues relating to the process.
SCH have an option of automatic viscosity control and top up system for the DS101 dip coating system. Can you advise how this works?
Automated viscosity control is a sophisticated process reserved for companies who are going to process a lot of PCBs and change the viscosity of the tank a lot of times in a shift or for companies who want a totally closed loop process without manual adjustment.
The viscosity system is an inline viscometer with feedback monitoring the tank constantly. There is a dosing system that would adjust the coating as required, feeding back into the conformal coating tank either conformal coating material or conformal coating thinners.
Click Conformal Coating Dipping FAQs to find out more about this and other issues relating to the process.
Conformal Coating 