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.
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On the DS101 dip conformal 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!).
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Automated viscosity control on a conformal coating dipping system such as the DS101 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 for further information on the DS101 conformal coating dip machine.
Checking the viscosity on the DS101 Conformal coating dip system is down to the time the tank lid is off. If it is off all day I would suggest twice a day check to ensure control. If it is a few hours then each time you start. The main issue is building a pattern of use. As you use the dip coating system, record the hours, volume of boards and the conformal coating thinners used, and chart this. Then, you will be able to anticipate when it needs checking and when it doesn’t. Also, contributes to the lean manufacture processing.
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The argon blanket is a useful accessory for overlaying conformal coatings that are sensitive to moisture such as moisture cure silicones like Dow Corning 2577. The principle is the argon gas is heavier than air and using a series of valves a blanket of argon gas is bled over the conformal coating dippin tank, effectively trapping the solvents under the argon. This is also effective in regions of high humidity and can help prevent moisture ingress.
Click for further information on the DS101 dip coating system.
