Printing
Printing is a crucial aspect of PCB manufacturing process.
(1) Type of squeegee: There are two types of squeegees: plastic and steel. For IC printing with PTTCH less than or equal to 0.5, steel squeegee is recommended to ensure proper formation of solder paste after printing.
(2) Adjustment of the squeegee: The squeegee should be set at an operating angle of 45 degrees, which can help improve the alignment of stencil openings and reduce damage to fine-spaced openings. The pressure of the squeegee is typically set at 30N/mm2.
(3) Printing speed: The speed at which the solder paste is pushed through the template by the squeegee is crucial. A fast printing speed aids in template rebound, but can also prevent paste leakage. A slow speed may lead to poor resolution of solder paste on the pads. The recommended printing speed range for fine pitch is 10-20mm/s.
(4) Printing methods: There are two common printing methods – “contact printing” and “non-contact printing”. The former involves a gap between the template and PCB, typically 0.5-1.0mm, allowing for different viscosity solder pastes to be used. The latter involves no gap between the template and PCB, ensuring high printing accuracy, especially for fine pitch and ultra-fine pitch applications.
Mounting height
For ICs with PTTCH of 0.55mm or less, a mounting height of 0 or 0-0.1mm is recommended to prevent solder paste collapse and potential short circuits during reflow.
Backflow
Backflow during reflow can be caused by various factors, including excessive heating rate, high temperature, solder paste heating faster than the circuit board, and fast flux wetting speed.
Printing is a crucial aspect of PCB manufacturing process.
(1) Type of squeegee: There are two types of squeegees: plastic and steel. For IC printing with PTTCH less than or equal to 0.5, steel squeegee is recommended to ensure proper formation of solder paste after printing.
(2) Adjustment of the squeegee: The squeegee should be set at an operating angle of 45 degrees, which can help improve the alignment of stencil openings and reduce damage to fine-spaced openings. The pressure of the squeegee is typically set at 30N/mm2.
(3) Printing speed: The speed at which the solder paste is pushed through the template by the squeegee is crucial. A fast printing speed aids in template rebound, but can also prevent paste leakage. A slow speed may lead to poor resolution of solder paste on the pads. The recommended printing speed range for fine pitch is 10-20mm/s.
(4) Printing methods: There are two common printing methods – “contact printing” and “non-contact printing”. The former involves a gap between the template and PCB, typically 0.5-1.0mm, allowing for different viscosity solder pastes to be used. The latter involves no gap between the template and PCB, ensuring high printing accuracy, especially for fine pitch and ultra-fine pitch applications.
Mounting height
For ICs with PTTCH of 0.55mm or less, a mounting height of 0 or 0-0.1mm is recommended to prevent solder paste collapse and potential short circuits during reflow.
Backflow
Backflow during reflow can be caused by various factors, including excessive heating rate, high temperature, solder paste heating faster than the circuit board, and fast flux wetting speed.
