In simple terms, the effects of the stencil on SMT printing defects mainly come from seven aspects: stencil thickness, number of apertures (either too many or too few), aperture position, aperture size, aperture shape, roughness of the aperture walls, and cleanliness of the apertures after stencil use. Let’s elaborate on each of these:
- Stencil Thickness: It affects the presence of solder balls, solder bridges, shorts, excessive or insufficient solder.
- Number of Apertures: It influences the presence of tombstoning or misplacement of components.
- Aperture Position: It affects the occurrence of solder balls, solder bridges, shorts, component misalignment, and tombstoning.
- Aperture Size: It influences the presence of excessive solder, insufficient solder strength, solder bridges, shorts, component displacement, and tombstoning.
- Aperture Size: It affects the occurrence of shorts, excessive or insufficient solder, solder balls, and other quality issues.
- Aperture Shape: It influences the occurrence of solder balls, shorts, solder bridges, insufficient solder strength, and tombstoning.
- Cleanliness of Apertures after Stencil Use: It is recommended to use a professional stencil cleaning machine, such as the Silman Tech Stencil Cleaning Machine DEZ-C730.
To control the first-pass yield of solder paste printing quality, it is necessary to choose the appropriate solder paste and ensure the storage environment and method of the solder paste. Strictly follow the solder paste usage process, design the component distribution ratio and position according to different products, and select the appropriate stencil aperture shape, aperture size, and stencil thickness for different components. Solder paste printing machines vary in quality, with various brands and types available for different applications. Especially for 03015, 01005 components, and fine pitch BGA with small ball diameters, the requirements for repeatability and precision of solder paste printing are increasingly high. When selecting a printing machine, it is best to test its CMK and CPK values to avoid production efficiency constraints due to the performance of the printing machine.
These are the effects of stencil on SMT printing defects. We hope this information is helpful.
