scope:

Statement of Scope

This handbook addresses understencil cleanliness during stencil printing, removal of solder paste from stencils following the cleaning process and misprint PCB board cleaning considerations.

Purpose

The goal in stencil printing is to place an exact amount of material in a precise location on the PCB. The print medium might be solder paste, adhesive/glue, flux, or thick film materials. The squeegee speed or pressure can affect the quality of the material deposition, the stencil is the primary control mechanism for material deposition. The purpose of this handbook is to provide the assembler best practice guidelines for understencil cleanliness during the stencil printing process, and stencil cleaning once the stencil is removed from the stencil printer. The document also addresses best practices for cleaning a PCB that was misprinted.

Problem Statement:

The stencil and PCB must be well aligned and in very tight contact (gasketing) to achieve an acceptable print. The problem is that poor contact between the stencil and the board can cause poor quality prints resulting in soldering defects. A common root cause of gasketing issues is solder paste on the stencil's contact side. The cleanliness of the stencil is critical to the success of the stencil printing process. Insufficient solder is the primary cause of defects originating from the stencil printing process; therefore, stencil cleanliness is an essential process step for delivering the proper amount of solder paste to the PCB pads.