soldermask process is an important process in printed circuit board (pcb) industry. the main purpose of this process is to apply a non-conductive coating on the surface of the pcb, which is used to protect the circuitry on the board from damage in later stages of processing. usually, it is responsible for the board green appearance.

normally, the soldermask process includes the following process stages:

stage remarks
surface clean i/s,jet-scrubber
hysol plug-f* thermal cure ink
hysol ink cure* 
surface clean i/s, jet-scrubber
lpi ink plug-f* 
lpi plug-f cure*
lpi pre-coat*
lpi pre-coat cure* 
s/m coating
exposure diazo, silver halide film
developer
carbon ink print*
carbon ink pre-cure*
legend print*
plug-f cure, final cure*
peelable *
peelable cure*
hal,gold,silver
stamp,route
e.t.
peelable*
peelable cure*
visual
packing

* skip stages when they are not required.

s/m process definition

1. surface clean
cleaning of copper surface by means of micro-etch and roughening by abrasion of brushing with aluminum oxide powder or high-pressure jet spraying.
panel is then d.i. rinsed and heated air dried for s/m plugging or coating on surface.
this is the most important foundation for s/m adhesion. anything less done on this operation will result in s/m peeling after thermal shock at metal deposition process of hal, or even gold plating.

2. hysol plug-f
plugging of via hole using hysol ink as per customer requirement using horizontal mesh printing table with doted screen.
key control of this stage is to have maximum 2 print with 80-100% wet volume fill.
this is to minimize solder ball entrapment in via-f at hal process.

3. hysol ink cure
a 2 stage curing process is used to fully cure hysol ink being plugged in via hole.
1st stage of lower temperature (210f, 90min) is to allow air entrapped in via hole and solvent in ink system to escape before a 2-stage hardening on surface has taken place.
without a 1st stage cure, ink in hole will flow out at the 2nd stage cure and cover any pad around via hole.