Automatic Line Screen Printers
Screen printing process visualization:
Screen printing of solder pastes is the most effective and fast process of applying material to the pads of the PCB.
In this process, in comparison with the paste dosing technology, the following features can be distinguished:
+ high performance
+ high repeatability
- high stencil cleanliness requirements
- the need to control the quality of the application
Applied solder paste at the contact area (result):
Modern automatic line printers are equipped with an automatic stencil cleaning system.
These systems, to achieve the greatest effect, clean the stencil from the paste in 3 stages:
- wet cleaning (lint-free paper moistened with solvent) - elimination of paste residues and dirt from the underside of the stencil
- dry cleaning (without solvent) - removal of residual solvent, paste and flux
- vacuum cleaning (absorption of dirt from the bottom of the stencil)
Thanks to the use of these cycles, it is possible to guarantee the stencil purity throughout the entire printing process with virtually no operator
The most important technological parameters of screen printing process:
1. The diameter of the roller paste: 12.5-25 mm
2. The speed of the squeegee: 15-250 mm / sec
3. Angle of squeegee: 12-60 °
4. Pressure squeegee: 1-6 kg / 100mm squeegee length
5. Stencil thickness: 75-300 microns
6.Speed of separating the board from the stencil: 0.3-12mm/s
Equipment options and features of their use in production:
1.Manual screen printer (single and small-scale production):
- Combination of a board and stencil: manual, micrometric screws
- Board clamp to the stencil: manually, mechanical lever lifting
- Print speed: manually squeegee or squeegees mounted on guides
- Stencil pressure on stencil and inclination angle: completely dependent on the operator
- Separation of the board from the stencil (separation): manually at an arbitrary speed
- Print clearance: operator dependent
- Conveyor: absent; the board is manually transferred from the printer to the installation
- Application Inspection: Visual
- Cleaning the stencil: manually
2.Semiautomatic screen printers (small and medium production):
- The combination of the board and stencil: manual, micrometric screws, ease of setup through the use of video cameras
- Board clamp to the stencil: pneumatic / servo
- Print speed: stepper motor / servo
- Stencil pressure on stencil: pneumatic cylinders with adjustable pressure
- Separation of the board from the stencil (separation): automatic
- Print clearance: mechanical adjustment
- Conveyor: absent; the board is manually transferred from the printer to the installation
- Application Inspection: Visual
- Cleaning the stencil: manually
3.Automatic Line Screen Printers
- Board and Stencil Combination: Servo
- Stencil board clamp: servo drive
- Print Movement (Print Speed): Servo
- Squeegee pressure on stencil: stepper drive with calibrated height-pressure scale, or with feedback and pressure sensor
- Separation of the board from the stencil (separation): servo drive
- Print gap: servo drive
- Conveyor: moving the board throughout all stages of the process
- Application Inspection: Usually by means of a video camera for the recognition of reference points
- Stencil cleaning: automatic (wet, dry, vacuum)
