Edge-coupled coated microstrip with single dielectric below the trace
As in the case of the Surface Microstrip this construction is simple to fabricate, but the extra process of adding solder mask coating can cause impedance variations. The Si9000 enables the operator to specify the thickness of the coating outside, above and between the traces to allow for variations in the board fabricating process.
This construction is particularly sensitive to solder mask flooding with LPI (Liquid Photo Imagable) solder mask. This causes the dielectric constant in the edge coupling region to vary, depending on flood depth.