● LPI Soldermask
● Curtain Coating
The LPI, also called as LIPSM technology, was developed in the 1980’s to meet the new application demands placed upon solder masks by the rise in surface mount technology. Now it is almost the most common used soldermask. There are a variety of methods to apply LPI solder resist to printed circuit boards, eg, silk screen printing, curtain coating, electrostatic spray, air spray. This article will introduce the LPI Curtain Coating.
Curtain coating has become more widely used in the circuits industry as PCBs have become more complex, with higher track densities and narrower track widths. With the curtain-coat technique LPI is applied as the printed circuit board passes through a sheet, or curtain, of low viscosity ink falling through a narrow slot. The curtain coating can apply liquid material at very high speed with low material loss.
Curtain coating appears a coating variation phenomenon - "shadowing". Shadowing results from reduced solder mask on the trailing edge of traces parallel to the curtain compared with the leading edge of those traces.