Also available are screen defined coverlays (thermal & UV) for flexible applications, the UV coverlay does not offer resistance to HASL, ENIG or other aggressive process. The peelable product is also suitable for use on most flexible PCBs.
All these products are applied by screen printing a pattern onto the board. This type of product has dominated the PCB industry for decades although their use is now largely being superseded by photoimageable products. The major disadvantage is that track coverage and image definition are mutually opposing goals in screenable solder mask application- Their weakness is that they suffer from an inability to hold increasing tight tolerances whilst maintaining track coverage. They may be unsuitable for today's high technology HDI requirements. The cost of these conventional products and by elimination of process steps involved in photo imageable process, screen defined resists can be a cheaper option for some types of PCB. Removal of UV exposure & associated photo tools and elimination of developer stage also allow faster and simpler PCB production.
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