CLEANING OF CIRCUIT CARD ASSEMBLIES OF RESIDUAL RMA FLUX
Author: Govind Vazirani Company: Kaiser Electronics Date Published: 9/10/1996
Surface Mount International
Abstract: Kaiser Electronics (I@ is using a RMA flux for Wave-soldering and a solder paste containing RMA flux for reflow solder joints on circuit card assemblies. Freon 113 had been used to clean the soldered boards. The company had set a goal of being substantially CFC free by the end of July 1995 and has accomplished the established goal. The objective of this work was to find an effective way of cleaning residual RMA flux products from under the surface mount devices (SMDS). Even if Freon 113 were available in the future, an alternative chemistry had to found because CFCS are not very effective in removing RMA from under the SMDS. An alternative, water soluble organic acids flux chemistry (WS), was also evaluated. Results of water soluble flux cleaning will also be outlined. How the use of water soluble flux will affect the choice of the cleaning chemistry and equipment will be presented. Discussed will be types of chemistries evaluated i.e. Aqueous, semi-aqueous and organic solvents. Aqueous chemistry, basically saponifiers (organic and inorganic), will be discussed in fill detail. Taguchi type of design of experiments (DOE) were carried out, using test boards with SMDS to optimize chemistry, concentration of chemistry, wash temperature and wash time. SMDS were removed from the cleaned boards and visually examined under the microscope for residual flux, Complete removal of flux under the SMDS was used as the only criteria for effective cleaning. Presented will be rationale for using the above criteria. Also presented will be types of equipment viz. In-line or batch, cost, throughput and effectiveness of each option.