1. Everyone in the PCB design industry understands that solder mask is a layer of ink applied to the surface of the PCB.

2. It serves not only as insulation but also protects the copper surface, while adding an aesthetically pleasing finish.

3. It acts like a layer of clothing on the PCB; therefore, any imperfections are easily noticeable.

4. As a result, solder mask issues are among the most frequent sources of customer complaints in the industry.

5. During the PCB solder mask process, even the most skilled and experienced professionals may encounter various quality issues.

6. Below, I summarize strategies for addressing some common problems, hoping to provide insights and assistance.

7. The common issues are as follows:

**Problem: Penetration, Blur**

8. **Reason 1:** Ink viscosity is too low.

**Improvement measures:** Increase the concentration without adding a diluent.

9. **Reason 2:** Screen printing pressure is excessive.

**Improvement measures:** Reduce the pressure applied.

10. **Reason 3:** Poor squeegee quality.

**Improvement measures:** Replace or adjust the angle of the squeegee.

11. **Reason 4:** The distance between the screen and the printing surface is either too great or too small.

**Improvement measures:** Adjust the spacing appropriately.

12. **Reason 5:** The tension of the silk screen has decreased.

**Improvement measures:** Create a new screen.

**Problem: Sticky Film**

13. **Reason 1:** The ink has not been properly baked.

**Improvement measures:** Verify the dryness of the ink.

14. **Reason 2:** The vacuum pressure is too strong.

**Improvement measures:** Check the vacuum system (do not introduce an air guide).

**Problem: Poor Exposure**

15. **Reason 1:** Insufficient vacuum.

**Improvement measures:** Inspect the vacuum system.

16. **Reason 2:** Incorrect exposure energy.

**Improvement measures:** Adjust to the appropriate exposure energy levels.

17. **Reason 3:** The exposure machine’s temperature is excessively high.

**Improvement measures:** Ensure the exposure machine temperature is below 26°C.

**Problem: Ink Won’t Dry**

18. **Reason 1:** Inadequate oven exhaust.

**Improvement measures:** Check the exhaust conditions of the oven.

19. **Reason 2:** The oven temperature is insufficient.

**Improvement measures:** Verify whether the actual oven temperature meets product requirements.

20. **Reason 3:** Insufficient thinner has been added.

**Improvement measures:** Increase the amount of diluent for full dilution.

21. **Reason 4:** The thinner dries too slowly.

**Improvement measures:** Use the recommended thinner [please use the company-approved thinner].

22. **Reason 5:** The ink is too thick.

**Improvement measures:** Adjust the ink thickness as needed.

**Problem: White Spots in Printing**

23. **Reason 1:** White spots appearing during printing.



**Improvement Measures: Mismatched Diluents**

Use compatible diluents [please utilize the company’s recommended diluents].

**Reason 2:** Sealing tape dissolution

**Improvement Measures:** Switch to white paper for net sealing.

**Problem:** Excessive Development (Corrosion Test)

**Reason 1:** High potion concentration and elevated temperature

**Improvement Measures:** Reduce both the concentration and temperature of the potion.

**Reason 2:** Development time is too lengthy

**Improvement Measures:** Shorten the development duration.

**Reason 3:** Insufficient exposure energy

**Improvement Measures:** Increase exposure energy.

**Reason 4:** Excessive developing water pressure

**Improvement Measures:** Decrease the developing water pressure.

**Reason 5:** Uneven ink mixing

**Improvement Measures:** Ensure the ink is stirred uniformly before printing.

**Reason 6:** Ink not dried

**Improvement Measures:** Adjust baking parameters; see the issue [The ink does not dry].

**Problem:** Green Oil Bridge Breakage

**Reason 1:** Insufficient exposure energy

**Improvement Measures:** Boost exposure energy.

**Reason 2:** Improper handling of the board

**Improvement Measures:** Review the treatment process.

**Reason 3:** Excessive pressure during developing and washing

**Improvement Measures:** Verify the developing and washing pressure.

**Problem:** Incomplete Development

**Reason 1:** Extended storage time after printing

**Improvement Measures:** Limit the placement time to within 24 hours.

**Reason 2:** Ink runs out prior to development

**Improvement Measures:** Operate in a darkroom before development (wrap fluorescent lamps in yellow paper).

**Reason 3:** Insufficient developing potion

**Improvement Measures:** Check the concentration and temperature of the potion.

**Reason 4:** Development time is too brief

**Improvement Measures:** Extend the development duration.

**Reason 5:** Exposure energy is excessive

**Improvement Measures:** Adjust exposure energy.

**Reason 6:** Over-baked ink

**Improvement Measures:** Modify baking parameters to prevent excessive burning.

**Reason 7:** Uneven ink mixing

**Improvement Measures:** Stir the ink uniformly prior to printing.

**Reason 8:** Mismatched thinner

**Improvement Measures:** Use compatible thinner [please utilize the company’s recommended thinner].

**Problem:** Poor Tin Coating

**Reason 1:** Incomplete development

**Improvement Measures:** Enhance various aspects contributing to poor development.

**Reason 2:** Contamination from post-baking solvents

**Improvement Measures:** Increase oven exhaust or clean the machine before applying tin.

**Problem:** Post-Bake Oil

**Reason 1:** Lack of segmented baking

**Improvement Measures:** Implement segmented baking.

**Reason 2:** Insufficient viscosity of plug hole ink

**Improvement Measures:** Adjust the viscosity of the plug hole ink.

**Problem:** Foaming on Tin

**Reason 1:** Over-development

**Improvement Measures:** Refine development parameters; see the issue [over development].

**Reason 2:** Poor pre-treatment of the board, leading to oily or dusty surfaces

**Improvement Measures:** Ensure thorough pre-treatment and maintain a clean surface.

**Reason 3:** Insufficient exposure energy

**Improvement Measures:** Verify exposure energy meets ink usage requirements.

**Reason 4:** Abnormal flux

**Improvement Measures:** Adjust flux as necessary.

**Reason 5:** Inadequate post-baking

**Improvement Measures:** Inspect the baking process after completion.

**Problem:** Ink Discoloration

**Reason 1:** Insufficient ink thickness

**Improvement Measures:** Increase the ink thickness.

**Reason 2:** Substrate oxidation

**Improvement Measures:** Check the pre-treatment process.

**Reason 3:** Excessive post-baking temperature

**Improvement Measures:** Re-evaluate baking parameters for prolonged duration.

**Problem:** Ink Matt Appearance

**Reason 1:** Mismatched thinner

**Improvement Measures:** Use compatible thinner [please utilize the company’s recommended thinner].

**Reason 2:** Low exposure energy

**Improvement Measures:** Increase exposure energy.

**Reason 3:** Over-development

**Improvement Measures:** Improve development parameters; see the issue [over development].

**Problem:** Internet Blockage

**Reason 1:** Rapid drying

**Improvement Measures:** Incorporate a slow-drying agent.

**Reason 2:** Slow printing speed

**Improvement Measures:** Increase speed while using slow-drying agents.

**Reason 3:** High ink viscosity

**Improvement Measures:** Add an ink lubricant or additional slow-drying agent.

**Reason 4:** Unsuitable thinner

**Improvement Measures:** Utilize designated thinners.

**Problem:** Weak Ink Adhesion

**Reason 1:** Incompatible ink formulation

**Improvement Measures:** Use appropriate ink formulations.

**Reason 2:** Inadequate drying time and temperature, along with insufficient exhaust air volume

**Improvement Measures:** Employ correct temperature and timing, and enhance exhaust air volume.

**Reason 3:** Incorrect or inappropriate additive amounts

**Improvement Measures:** Adjust dosages or switch to alternative additives.

**Reason 4:** High humidity levels

**Improvement Measures:** Improve air dryness.

The above outlines common quality issues and solutions in the PCB solder mask process, summarized for PCB designers.
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