Technical note: common quality problems in PCB solder mask process and improvement measures.

Solder mask is a layer of inl printed on the surface of PCB, which not only plays the role of insulation, but also plays the role or protecting the copper surface, and also plays the role of beautiful appearance. It is just like a piece of colthing on the outside of PCB, so any defect of it is easy to be found. Therefore, solder mask is also the procss that is most likely to incur customer complaints among all processes

 

The following is a summary of the common quality problems and improvement measures of solder mask process, hope it can give you inspiration and help.

 

A little white print?

Reason 1: there are white spots in printing process

Improvement; Diluent mismatch

Reason 2: The sealing tape for sealing the net is dissolved

Improvement measures: use white paper to seal the net

 

Adhesive film?

Reason 1: ink is not baked dry

Improvement: check the drying degree of ink    

Reason 2: Too much vacuum

Improvement: check the vacuum pumping system ( could without adding air guide strip )

 

Under exposure

Reason 1: bad vacuum pumping

Improvement: Check the vacuum system

Reason 2: Inappropriate exposure energy

Improvement: Adjust the right exposure energy

Reason 3: Exposure machine temperature is too high

Improvement: check the temperature of the exposure machine (below 26℃）26℃）

 

The ink did not dry?

Reason 1: The oven doesn't exhaust well

Improvement: Check the oven exhaust condition

Reason 2: The oven is not hot enough

Improvement: Determine whether the actual temperature of the oven reaches the required temperature

Reason 3: Less diluent

Improvement: increase the thinner, fully dilute

Reason 4: Thinners dry too slowly

Improvement: Use a matching diluent

Reason 5: ink is too thick

Improvement: appropriate adjustment of ink thickness

 

Under developing

Reason 1: the printing time is too long

Improvement: control the placement time within 24 hours

Reason 2: before developing ink light

Improvement: work in darkroom before development (fluorescent lamps are wrapped in yellow paper)

Reason 3: Not enough developing liquid

Improvement: temperature is not enough to check the concentration of the potion, temperature

Reason 4: Development time is too short

Improvement: to extend the development time

Reason 5: High exposure power

Improvment: Adjust the exposure energy

Reason 6: ink backing excessive

Improvement: adjust the baking parameters, can not be baked dead

Reason 7: ink mixing uneven

Improvement: before printing ink stir evenly

Reason 8: Diluent don't match

Improvement: Use a matching diluent

 

Overdevelopment

Reason 1: the potion concentration is too high, the temperature is too high

Improvement: Reduce potion concentration and temperature

Reason 2: The development time is too long

Improvement: shorten development time

Reason 3: Insufficient exposure power

Improvement: Improve the exposure energy

Reason 4: development water pressure is too large

Improvement: lower development water pressure

Reason 5: ink mixing uneven

Improvement measures: before printing ink stir evenly

Reason 6: ink is not drying

Improvement: adjust the baking parameters, see the problem [the ink did not dry]

 

Green oil bridge broken?

Reason 1: Insufficient exposure power

Improvement: Improve the exposure energy

Reason 2: plank did not handle

Improvement: check the processing process

Reason 3: developing and washing pressure is too high

Improvement: adjust developing and washing pressure 

 

Blister on tin:

Reason 1: Overdevelopment

Improvement: to improve the development paramerters, see the problem[overdevelopment]

Reason 2: plate before processing is bad, the surface had smeary. Dust class

Improvement: do a good job of plate treatment, keep the surface clean

Reason 3: Insufficient exposure power

Improvement: check the exposure energy, in line with the requirements of ink use.

Reason 4: abnormal soldering flux

Improvement: Adjust soldering flux

Reason 5: Insufficient post- baking

Improvement: check the post-baking process 

 

Dewetting

Reason 1: the development is not clean

Improvement: to improve several factors of "under developing"

Reason 2: after baking solvent pollution

Improvement: Increase oven exhaust or clean the oven before tin spraying 

 

After drying and blasting oil?

Reason 1: did not segment baking

Improvement: segment baking

Reason 2: plug hole ink viscosity is not enough

Improvement: adjust the plug hole ink viscosity

 

Ink matte

Reason 1: Diluent mismatch

Improvement: Use a matching diluent

Reason 2: Low exposure power

Improvement: Increase exposure energy

Reason 3: Over development

Improvement: to improve the development parameters, see the problem [Over Development]

 

Solder mask Discoloration

Reason 1: ink thickness is not enough

Improvement: increase the thickness of ink

Reason 2: substrate oxidation

Improvement: Check the pre-treatment process

Reason 3: the post-baking temperature is too high

Improvement: check the baking parameters after too long

 

Ink adhesion is not strong

Reason 1: ink model selection is not appropriate

Improvement: change the appropriate ink

Reason 2: the drying time, temperature is not correct and the exhaust air volume is too small during drying

Improvement: use the right temperature and time, increase the exhaust air

Reason 3: the dosage of additives is not appropriate or correct

Improvement: adjust the dosage or use other additives

Reason 4: Too much humidity

Improvement: improve air dryness

 

mesh clogging

 

Reason 1: Too fast drying

Improvement: add slow drying agent

Reason 2: printing speed is too slow

Improvement: increase the speed and slow drying agent

Reason 3: ink viscosity is too high

Improvement: add ink lubricant or special slow - drying agent

Reason 4: diluent don't work

Improvement: use specified diluent

 

 

Infiltration, blurring

Reason 1: ink viscosity is too low

Improvement: increase the concentration, do not add diluent

Reason 2: screensilk pressure is too large

Improvement: Reduce stress

Reason 3: glue scraping bad

Improvement: replace or change the Angle of rubber scraping screen printing

Reason 4: screen and printing surface distance is too large or too small

Improvement: Adjust the spacing

Reason 5: screen tension is smaller

Improvement: remake a new screen version

 

Solder mask Crinkled

Reason 1: Solder mask ink is too thick

Improvement: reduce viscosity

Reason 2: ink drying is too slow

Improvement: Add a quick-drying agent

Reason 3: Insufficient drying

Improvement: raise the drying temperature or extend the drying time

Reason 5: Poor environment after silk screen process

Improvement: reduce temperature and humidity, strengthen ventilation

 

Blisters and pinholes 

osity is too high

Improvement: reduce viscosity

Reason 2: printing screen is too fast from the plate

Improvement: Reduce the speed off the plate

Reason 3: table top is not level off

Improvement: Adjust or replace the table top

Reason 4: The ink itself is wrong

Improvement: add defoaming agent or replace the ink

Reason 5: ink stirring did not stand for a period of time

Improvement: ink stirring need to stand for a period of time

Reason 6: it was direct drying board after silkscreen printing

Improvement: after silkscreen printing need to stand for a period of time before drying board

 

After curing the ink white

Reason 1: diluent don't work

Improvement: use specified diluent

Reason 2: ink contains moisture

Improvement: replace with new ink

Reason 3: high humidity in the air

Improvement: reduce air humidity