During production stencil printing, circuit boards are periodically misprinted due to clogged apertures, stencil out of alignment, solder paste rheology shifts and other issues. Stencil misprints are defined as:
- A-Side Misprint: Initial print out of alignment with no components previously placed
- B-Side Misprint: A-Side was successfully printed and components placed and soldered. The subsequent process of printing the B-Side results in the solder paste being out of alignment resulting in a B-Side misprint
Assemblers commonly address the misprint cleaning need by either hand wiping* the misprinted side of the circuit card and/or clean the misprint in a stencil cleaning machine. Both methods create the potential for quality issues. First, when wiping solder paste from the misprinted side of the board, solder paste can be trapped in solder mask defined channels, through-hole vias, and other board geometries (Figure 1). Numerous quality problems can result due to lack of control and definition.
*Hand Wiping before Cleaning is not Recommended
Hand wiping before cleaning is not recommended: solder paste trapped in vias.
Best practice is to clean the misprinted circuit board using an aqueous cleaning solution within an electronic assembly production aqueous cleaning process. Production cleaning systems remove both wet solder paste and reflowed flux residues while meeting quality and yield objectives. To capture the wet solder paste, innovative collection and filtration systems safely capture and contain solder spheres from being sprayed onto production assemblies. Additionally, the containment and filtration systems prevent raw solder paste from entering the rinse water streams.
Filtration System Designed to Capture Wet Solder Paste
Using a production cleaning machine provides numerous benefits to the assembler.
- Recovery and rework of expensive hardware
- Removal of wet solder paste
- Containment of solder spheres
- Removal of reflowed flux residues
- Exceptional rinsing
- Ionically clean assemblies
- Aquanox A4241
- Ideally suited for batch spray-in-air cabinet style cleaning machines
- Strong match to water soluble and rosin flux types
- Cleans many low residue flux types dependent on wash concentration levels
- Best in Class compatibility with aluminum, copper, tin and lead
- Excellent choice for cleaning B-Side Misprints
- Aquanox A4625B
- Ideally suited for batch spray-in-air cabinet and planar cleaning machines
- Strong match to low residue no clean flux types
- Best in Class for lead-free no clean flux residues
- Aquanox A4639
- Ideally suited for batch spray-in-air and cabinet and planar cleaning machines
- Excellent compatibility with aluminum, copper, tin and lead
Designed to clean all flux types