Where Should I Test for Residues?
If you don’t know where to test, you’re going to miss things. In today’s electronics manufacturing environment, assemblers continue to overlook critical areas that are at risk of becoming contaminated. These areas could have corrosive residues present, which could cause product failure.
So, how do you know where to test? It can be difficult. Many times, the residues that cause problems are not visible. To deal with this, it is important to bring in someone who knows what to look for.
Know What to Look For
At Foresite, we know testing the entire assembly isn’t always possible. There may be small, localized areas of residues that will be diluted and potentially undetectable if the entire assembly is tested. We’ve run into this scenario time and again.
An Example
An assembly from a plant in Malaysia was sent to our laboratory for analysis. For this project we utilized FTIR, SEM/EDX and ion chromatography analysis using localized extraction techniques with the C3 Cleanliness Tester. We found flux residues in addition to a concentration of tin and lead, which indicates that electromigration was occurring in this area. Visible white residue and dendritic growth were present. Based on those findings we decided to go further and analyze the white residue to better understand the reason for the dendritic growth. We found high levels of chloride, sulfate, and weak organic acid (WOA) in the visible white residue present on the connector and housing. Low, acceptable levels of ionic residues were found on two reference areas. These results indicated that an external fluid contaminant had been introduced at some point and caused the visible white residues and dendritic growth. We recommended the necessary steps to the customer and proceeded from there.
Why Traditional Testing Methods Don’t Work
If we’d used traditional testing methods, such as ROSE testing, we may have missed the localized areas of residue and dendritic growth. Traditional test methods extract the whole board, whereas our testing methods looked at localized areas of the board. With the knowledge, methods and techniques available to us, we are capable of finding corrosive residues that others miss.