Borey Advanced — Challenges Encountered During SMT Pick-and-Place Machine Processing

1. Bridging: Bridging occurs when solder paste is printed onto adjacent pads. Possible causes include misalignment of the stencil and PCB, excessive printing pressure, large printing gaps, or a dirty or damaged stencil. To address this, adjust printing parameters appropriately and ensure the stencil is cleaned promptly.

2. Reasons for depressions in solder paste patterns: excessive squeegee pressure; inappropriate hardness of the rubber squeegee; and overly large stencil apertures.

Impact: Incorrect solder volume can lead to cold solder joints and compromised joint strength.

Solution: Adjust printing pressure; replace with a metal squeegee; refine the stencil window design.

3. Causes of excessive solder paste: The stencil aperture is too large; there’s excessive clearance between the stencil and the PCB.

Impact: Easily leads to bridging.

Solution: Check the template window specifications; adjust printing parameters, especially the clearances on the PCB template.

4. Reasons for misaligned patch printing orientation: Misalignment between the stencil and PCB is the primary factor we need to consider. Additionally, there may be issues with poor stencil manufacturing quality, or in some cases, the printing machine simply lacks sufficient precision.

Impact: Easily causes bridging.

Solution: Adjust the template orientation; calibrate the printing machine.

5. Insufficient solder paste volume refers to a situation where there isn’t enough solder paste applied to the PCB pads. Issues such as no paste, incomplete solder joints, insufficient soldering, and even depressions all fall under the category of inadequate paste coverage. Since insufficient paste volume is influenced by various factors—including printing pressure, squeegee speed, lift-off conditions, solder paste performance and condition, stencil fabrication methods, and poor stencil cleaning—it’s crucial to optimize printing parameters for maximum efficiency.

6. Bridging phenomenon on the solder paste—bridging refers to the solder paste spreading into the areas surrounding the pads that are meant to be filled. This issue typically occurs due to excessive printing squeegee pressure or oversized apertures in the stencil and PCB. To address this, adjustments to printing parameters should be made, and the stencil should be cleaned promptly as needed.