Changes in PCB assembly design, including lower component stand-off heights and denser component placement, coupled with new generation soldering materials are posing considerable new challenges for PCB cleaning process. Common problems encountered are highlighted here, and effective cleaning can help resolve them:
- flux residue can underfill low stand-off components
- electrochemical migration between narrow interconnects
- solder mask defined pads decrease z-axis, and can hinder cleaning
- shadowing effects caused by dense component placement
- high reflow temperatures and overheating can cause oxidised residue, hard to remove
- trapped cleaning chemicals on low stand-off components can cause rinsing problems, and lead to assembly defects
Stencil printing problems occur in 70% of surface mount printing issues, and effective stencil cleaning is vital to improving process yields. However, careful matching of chemistries to equipment is essential for a reliable, repeatable and cost-effective process.
- solder paste build up in stencil apertures
- smaller stencil apertures are particularly prone to clogging
- bridging or insufficient solder paste on PCB due to stencil contamination
- solder balling, tombstoning and poor board release following solder reflow
- cleaning chemistry mismatch with stencil nano coating can damage the nano coating, reducing stencil life and printing performance
Fraser Technologies can help customers undertake tests on existing cleaning chemistries to ensure optimum compatibility with processes and equipment, and therefore best results.