Contents

• 1. Why is Pre-treatment Necessary?
• 2. What is Resolution?
• 3. Why is Solder Mask Plugging Needed for BGA?
• 4. Impact of Poor Solder Mask Exposure
• 5. Why Does the Solder Mask Develop Air Bubbles?
• 6. Functions of Solder Mask Ink on PCB
• 7. Why is Pre-baking Required Before Legend Printing?
• 8. Role of the Squeegee in Printing
• 9. What is Off Contact (Screen Distance)?
• 10. What is Mesh Count?

Common PCB Issues

1. Why is Pre-treatment Necessary?

   • Removes oxidation, grease, and fingerprints from the board surface to ensure proper adhesion of the dry film to the substrate.
   • Increases surface roughness to enhance the adhesion of ink or film.

2. What is Resolution?

   • Refers to the minimum line width or spacing that can be formed within a 1mm range.
   • Affected by the thickness of the resist and light scattering—thicker films result in lower resolution.

3. Why is Solder Mask Plugging Needed for BGA?

   • Prevents foreign contaminants from remaining in the holes, which could flow out due to heat during soldering and affect component performance.
   • Standards:
     • Holes must be fully plugged without any exposed copper.
     • Should not be overfilled to avoid affecting soldering.

4. Impact of Poor Solder Mask Exposure

   • Incomplete solder mask development may cause ink to cover the pads, affecting soldering.
   • In severe cases, it can lead to short circuits.

5. Why Does the Solder Mask Develop Air Bubbles?

   Main Causes:
   • Residual air in the ink expands when heated, forming bubbles.
   • Narrow line spacing prevents complete ink filling.
   • The contact angle between the squeegee and mesh affects ink penetration into fine traces.
   Prevention Methods:
   • a. Let the ink settle after stirring to reduce internal bubbles.
   • b. Allow the board to rest before baking to release trapped gas slowly.

6. Functions of Solder Mask Ink on PCB

   • Protects circuits and prevents solder bridging during assembly.
   • Provides electrical insulation, chemical resistance, and heat resistance.
   • Enhances the overall appearance of the PCB.

7. Why is Pre-baking Required Before Legend Printing?

   • Enhances the adhesion of legends to the board surface, preventing them from peeling off during further processing.
   • Improves the hardness of the solder mask ink, reducing the risk of scratches.

8. Role of the Squeegee in Printing

   • Controls the amount of ink deposited, affecting printing quality.
   • The angle of the squeegee influences printing precision and uniformity.

9. What is Off Contact (Screen Distance)?

   • The distance between the screen and the PCB surface, typically set between 3–5mm.
   • Proper off contact prevents ink smudging and improves print accuracy.

10. What is Mesh Count?

• Indicates the density of mesh openings, usually measured as the number of threads per inch, such as 150T, 180T.