How much of the actual conformal coating can be used and how much is wasted is a fundamental point that many engineers can miss.
This amount that is useful to the coating process is described as the amount of solids content in a conformal coating. It is the amount of actual conformal coating material that can be deposited on the circuit board to protect it. The remaining percent is volatile and evaporates away.
Therefore, the more solid content in your conformal coating you have the more circuit boards you can coat. Conversely, a low solids content in a conformal coating means less boards can be coated and lots of excess waste.
So, you want to have as much solids content as possible per liter when you buy the conformal coating material.
Check the technical data sheet
All reputable conformal coating companies have datasheets on the individual materials. They should be able to tell you the solids content of the coating.
Once you have these values you can see the differences in the solids content. These differences can be striking and you can be wasting a lot of money on solvents that literally evaporate away.
Further, it is important to determine the final solids content of the material that you will use in production. That is the correctly blended coating ready for application at the right viscosity.
Take the following example that is typical of conformal coatings sold commercially around the world.
Conformal coating X has a 35% solids content.
Its viscosity is 190 cps at this solids content.
However, to spray the coating X in a spray gun it must be reduced in viscosity. So, the coating must be diluted by approx. 50% with thinners to reach this viscosity.
This means material X is now 18% solids. This also means there is >80% of the material that evaporates away!
So, making sure you have the right solids content for the production process is important.
Making sure you have the right solids content of your conformal coating for the production process is important so that you can calculate the true cost of your process.
Check the market!
You cannot assume that all conformal coating materials are similar.
For example, SCH India has a UL approved acrylic conformal coating (Protective Coating 101) that is 44% solids at 24 cps and ready to spray.
However, nearly all of the leading brands are similar to Material X and this means that the Protective Coating 101 coating has more than twice as much coverage power for the same liter of material compared to nearly all competitive materials.
If the coatings are similar in price at this viscosity then you need to buy at least 2x more of material X than the higher solids product to get the same coverage.
Quite a saving can be made if care is taken!
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