PCB Tech - Problems encountered in PCB solder mask process

Everyone in the PCB design industry knows that solder mask is a layer of ink printed on the surface of the PCB. It not only plays a role in insulation, but also protects the copper surface. It also plays a beautiful and beautiful role. It is like wearing on the outside of the PCB board. A piece of clothing, so any flaws in it are easy to be found, so solder mask is also the most prone to customer complaints of all processes. In the PCB solder mask process, you may also encounter a variety of quality problems as a clever and experienced person. The following summarizes the countermeasures for some common problems, hoping to inspire and help you. The common ones are as follows:

Problem: penetration, blur

Reason 1: The ink viscosity is too low.

Improvement measures: increase the concentration without adding diluent.

Reason 2: The screen printing pressure is too high.

Improvement measures: reduce pressure.

Reason 3: Bad squeegee.

Improvement measures: replace or change the angle of the squeegee screen.

Reason 4: The distance between the screen and the printing surface is too large or too small.

Improvement measures: adjust the spacing.

Reason 5: The tension of the silk screen becomes smaller.

Improvement measures: Re-make a new screen version.

Problem: sticky film

Reason 1: The ink is not baked dry

Improvement measures: check the ink dryness

Reason 2: The vacuum is too strong

Improvement measures: check the vacuum system (can not add air guide)

Problem: Poor exposure

Reason 1: Poor vacuum

Improvement measures: check the vacuum system

Reason 2: Improper exposure energy

Improvement measures: adjust the appropriate exposure energy

Reason 3: The temperature of the exposure machine is too high

Improvement measures: check the temperature of the exposure machine (below 26°C)

Problem: the ink won't dry

Reason 1: The oven exhaust is not good

Improvement measures: check the exhaust air condition of the oven

Reason 2: The oven temperature is not enough

Improvement measures: determine whether the actual temperature of the oven reaches the required temperature of the product

Reason 3: Put less thinner

Improvement measures: increase diluent, fully dilute

Reason 4: The thinner dries too slowly

Improvement measures: use matching thinner [please use the company's supporting thinner]

Reason 5: The ink is too thick

Improvement measures: appropriately adjust the ink thickness

Problem: White spots in printing

Reason 1: White spots in printing

Improvement measures: mismatched diluents, use matching diluents [please use the company's supporting diluents]

Reason 2: The sealing tape is dissolved

Improvement measures: switch to white paper to seal the net

Problem: Excessive development (corrosion test)

Reason 1: The concentration of the potion is too high and the temperature is too high

Improvement measures: reduce the concentration and temperature of the potion

Reason 2: Development time is too long

Improvement measures: shorten the development time

Reason 3: insufficient exposure energy

Improvement measures: increase exposure energy

Reason 4: The developing water pressure is too large

Improvement measures: lower the developing water pressure

Reason 5: Ink mixing is uneven

Improvement measures: stir the ink evenly before printing

Reason 6: The ink is not dried

Improvement measures: Adjust the baking parameters, see the question [The ink does not dry]

Problem: Green Oil Bridge Broken Bridge

Reason 1: Insufficient exposure energy

Improvement measures: increase exposure energy

Reason 2: The board is not handled properly

Improvement measures: check the treatment process

Reason 3: Too much pressure for developing and washing

Improvement measures: check the developing and washing pressure

Problem: The development is not clean

Reason 1: The storage time after printing is too long

Improvement measures: control the placement time within 24 hours

Reason 2: The ink runs out before development

Improvement measures: work in the darkroom before developing (the fluorescent lamp is wrapped in yellow paper)

Reason 3: Not enough developing potion

Improvement measures: the temperature is not enough, check the concentration and temperature of the medicine

Reason 4: Development time is too short

Improvement measures: extend the development time

Reason 5: Exposure energy is too high

Improvement measures: adjust the exposure energy

Reason 6: The ink is over-baked

Improvement measures: adjust the baking parameters, not to burn to death

Reason 7: Ink mixing is uneven

Improvement measures: stir the ink evenly before printing

Reason 8: The thinner does not match

Improvement measures: use matching thinner [please use the company's supporting thinner]

Problem: Poor upper tin

Reason 1: The development is not clean

Improvement measures: improve several factors of poor development

Reason 2: Post-baking solvent contamination

Improvement measures: increase oven exhaust or machine cleaning before spraying tin

Problem: post-bake oil

Reason 1: There is no segmented baking

Improvement measures: segmented baking

Reason 2: Insufficient viscosity of plug hole ink

Improvement measures: adjust the ink viscosity of the plug hole

Problem: Foaming on the tin

Reason 1: Excessive development

Improvement measures: improve the development parameters, see the problem [over development]

Reason 2: The pre-treatment of the board is not good, and the surface is oily. Dust

Improvement measures: do a good job of pre-treatment of the board and keep the surface clean

Reason 3: insufficient exposure energy

Improvement measures: check the exposure energy and meet the ink usage requirements

Reason 4: Abnormal flux

Improvement measures: adjust flux

Reason 5: Insufficient post-baking

Improvement measures: baking process after inspection

Problem: Ink discoloration

Reason 1: Insufficient ink thickness

Improvement measures: increase ink thickness

Reason 2: Oxidation of the substrate

Improvement measures: check the pre-treatment process

Reason 3: The post-baking temperature is too high

Improvement measures: too long time after checking the baking parameters

Problem: ink matt

Reason 1: The thinner does not match

Improvement measures: use matching thinner [please use the company's supporting thinner]

Reason 2: Low exposure energy

Improvement measures: increase exposure energy

Reason 3: Excessive development

Improvement measures: improve the development parameters, see the problem [over development]

Problem: Blocking the Internet

Reason 1: Drying is too fast.

Improvement measures: add slow drying agent.

Reason 2: The printing speed is too slow.

Improvement measures: increase the speed and slow down the drying agent.

Reason 3: The ink viscosity is too high.

Improvement measures: add ink lubricant or extra slow drying agent.

Reason 4: The thinner is not suitable.

Improvement measures: use designated thinners.

Problem: Ink adhesion is not strong

Reason 1: The ink model is not suitable.

Improvement measures: use appropriate inks.

Reason 2: The ink model is not suitable.

Improvement measures: use appropriate inks.

Reason 3: The drying time and temperature are incorrect and the exhaust air volume during drying is too small.

Improvement measures: use the correct temperature and time, and increase the exhaust air volume.

Reason 4: The amount of additives is inappropriate or incorrect.

Improvement measures: adjust the dosage or switch to other additives.

Reason 5: The humidity is too high.

Improvement measures: improve air dryness.

The above are the common quality problems and solutions in the PCB solder mask process summarized for the majority of PCB designers.