scope:

INTRODUCTION

Many printed wiring assembly (PWA) failures that occur in the field can be attributed to manufacturing residue that were not properly removed. It is essential that the cleaning process be monitored to ensure proper removal of contaminants that may, when exposed to time, temperature, and humidity, lead to high defect rates.

The most common method for evaluating the cleanliness level of a PWA is a method called the Resistivity Of Solvent Extract (ROSE) test. The original procedure, developed in the early 1970s, used a laboratory squeeze bottle filled with a 75% isopropanol (IPA) and 25% deionized water solution to dissolve ionic contamination from the PWA into a beaker. The resistivity of the extract solution was then measured and assigned a value based on a sodium chloride (NaCI) standard. In the last 20 years, several manufacturers have developed and marketed equipment to perform this type of testing. During that time, radical changes have been made to the systems, such as the addition of solvent heaters, sprays and microprocessors. Recent studies have shown discrepancies among not only the different manufacturers, but also among different parameters such as solvent temperature and volume. To continue using this test to manage a process or to make decisions on what cleaning alternative works best, it became necessary to investigate what variables influence final results and standardize a test procedure.

The goal of this project is to give users of cleanliness test equipment a better understanding of ionic cleanliness testing. How much does solvent temperature influence the final cleanliness results? How critical is the 75% isopropanol to 25% water ratio? Is spraying the solvent important? Will today's systems remove contamination from under a component with a .005" standoff heights? Is static or dynamic the more efficient or effective process? This project has explored these questions and has determined what variables most influence ionic cleanliness test results.