IMPACT OF MULTIPLE THERMAL CYCLES ON THE CLEANING PROCESS

摘要

Printed circuit board manufacturing is a highly complex process and incorporates numerous steps. The soldering process is critical and may include reflow oven and/or wave solder equipment as well as a baking process. Also, PCBs may be single or double-sided thereby necessitating multiple thermal cycles. Following the soldering process, ICT (In-Circuit Testing) may be required. If the boards are reflowed with RMA or water soluble pastes, the boards are cleaned and the test points are free of residues. If No Clean solder paste is used, the flux residues can typically be penetrated by the pin probes. However, for substrates with No Clean solder paste exposed to multiple reflow cycles, pin probing is problematic and the flux residues must be removed for accurate testing. There are many opportunities to clean PCBs following a soldering process. This study was conducted to assess the effects of numerous thermal heat cycles on the PCB cleaning process or flux removal. Thermal cycles considered included single reflow, dual reflow and dual reflow plus bake. Solder pastes considered included RMA, No Clean and water soluble (OA), both leaded and lead-free. Two micro phase cleaning agents were considered for cleaning all solder pastes as well as Dl-water for cleaning the water soluble pastes. The cleaning process employed included spray-in-air inline equipment. The substrates were not cleaned between the thermal cycles. Populated test vehicles were used and cleanliness assessment was determined through visual analysis on the surface and under component as well as IC (Ion Chromatography) analysis. Cleaning process parameters were established for the single reflow process and maintained for all thermal cycle variations for comparative purposes.