PCB绿油工艺简介

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.

4. lpi ink plug-f

plugging of via hole using lpi (liquid photo imagable) ink when thermal hysol ink is not possible (via to pad < 40 mils)

key control is maximum 2 print to have 90-100% till depend on customer requirement of either solder ball is allowed to have in via hole.

panel is loaded directly to s/m coating m/c without any pre-cure.

5. lpi ink plug-f cure

this process is to tack dry the lpi plug hole ink to avoid the ink adhere to any contacting surface, especially when the sub lpi pre-coat process is needed, otherwise, the plugged panels will be sent to the coating machine for coating directly, and then this process is combined with the final cure and located at the s/m last stage. but it must be emphasized that the curing time will change from 10mins to 90mins to achieve fully hardened plugging ink in the via holes.

6. lpi pre-coat

printing s/m lpi ink on definite panel surface is lpi pre-coat. depending on the different targets, the printing area can be copper traces or copper edges or some definite laminate area or the whole panel area.

it has the same process, as lpi printing only the aim is different.

usually, if the naked panels have very high copper traces or if the designer wants to reduce the impendence value, pre-coat on copper traces will be applied, this process can avoid the skip problem during the coating process and the impendence failure problem before the boards are shipped to customers.

if the ink coverage on copper edge is required, pre-coat on copper edge can be used. like the high base copper panels.

if the lpi ink is used to cover any press or inner layer defects, pre-coat on some definite areas is applied. and if the whole panel needs a more thicker s/m layer, do the pre-coat on the whole panel surface. at this point, it also can be regarded as lpi printing.

7. lpi pre-coat cure