The answer depends on a few factors so the cost/volume should not be the sole metric. Instead, we need to consider the surface area of the part, method of application and likely dry film thickness of coating we end up with. For example, if your part measures 380 cm2, you can estimate the amount of parts you can coat with a finite volume of coating using the theoretical coverage value found in the TDS. This value assumes a dry film thickness (defined in the calculation) and 100% transfer efficiency which is also variable. For example, using the 842UR, the theoretical coverage based on 2 mil dry film thickness and 100% transfer efficiency is 26,570 cm2/L, so 1 L of material should coat
=26,570 cm2/L ÷ 380 cm2 or 70 parts.
In reality, your transfer efficiency will depend on method and operator but a good guide is 80% for spray application and 90-95% for manual brush so the coverage can be adjusted accordingly
=26,570 cm2/L x 80% or 21,256 cm2/L
Dry film thickness is another variable which can only be determined experimentally and may differ between operators. Coatings for board level shielding can typically be applied quite thin to realize cost savings so assuming an operator can achieve 10 microns (0.4 mils) consistently, coverage is
=26,570 cm2/L x (2 mil/0.4 mil) = 132,850 cm2/L
Once you have a reasonable idea of how many parts of a given surface area you can coat per unit volume, you can take the cost of that volume, divide by the number of parts to get an estimate of the cost per part, which is a better reflection of project costs.
