Solder paste is most commonly applied to a Printed Circuit Board (PCB) through a process involving a stencil printer. This technique ensures accurate placement of the paste onto the specific pads where components will be soldered.
The primary method used for applying solder paste utilizes squeegee blade printing.
Squeegee Blade Printing Explained
This is the most prevalent technique in PCB assembly lines due to its efficiency and precision when used with a properly designed stencil. The process typically involves the following steps:
- PCB Placement: The bare PCB is securely positioned within a stencil printer.
- Stencil Alignment: A metal or plastic stencil, which has precise openings corresponding to the solder pads on the PCB, is aligned directly over the board.
- Paste Application: A roll or bead of solder paste is deposited onto the stencil surface.
- Squeegee Action: According to the reference, the most common method of applying solder paste to a PCB using a stencil printer is squeegee blade printing. The squeegees are the tools used to apply the necessary force required to move the solder paste across the stencil and on to the PCB. The squeegee blades traverse the stencil, pushing the solder paste through the openings and onto the corresponding pads below. The force and angle of the squeegees are crucial for achieving the correct amount of paste deposition.
- Stencil Separation: Once the paste is applied, the stencil is carefully lifted away from the PCB, leaving behind precise deposits of solder paste on the component pads.
- Inspection: The solder paste deposits are typically inspected using automated systems (Automated Solder Paste Inspection - API) to ensure proper volume and shape before components are placed.
Key Components in Squeegee Printing
- Solder Paste: A viscous mixture of solder alloy particles, flux, and a binding agent.
- Stencil: A thin sheet with apertures (holes) cut out to match the solder pads on the PCB. It acts as a template for paste deposition.
- Squeegee Blades: Tools (usually metal or polyurethane) that push the solder paste across the stencil and through its apertures.
While squeegee printing with a stencil is the industry standard, other methods like jet printing exist. However, squeegee blade printing remains the most common method as highlighted by the reference.
