Just because you’ve run some tests with positive results doesn’t mean your components will be reliable. Your product might still fail. Corrosive residues on even small areas of an electronics assembly can easily cause failures. These localized corrosive residues can originate from any number of steps in an electronics assembly process – even, in the following case, in a component plating process upstream in the supply chain.

What Causes Product Failure

The cause of product failure can be difficult to track down, but it is frequently basic. Ionic residues that reside on assemblies can, over time, manifest into an electrochemical reaction, which results in dendritic growth. Dendritic growth is a phenomenon where ions move from one surface toward another. This movement is stimulated by moisture, electrical bias and, frequently, corrosion. The dendrite can grow from one conductor toward another until it results in a current leakage path between isolated circuits, causing a circuit malfunction or failure.

How Product Failures Occur

A client was experiencing discharged batteries on approximately 10% of the inventory of an electronics assembly within two weeks of warehouse storage, with the product switched “off.” Cleanliness testing with bulk extraction (ROSE testing), and even with bag extraction and ion chromatography analysis, revealed no problem – a clean assembly. The detrimental residue was in a small, concentrated amount – such that the average cleanliness of the assembly was not measurably affected.

Localized testing with the Foresite C3 indicated residual MSA (methane sulfonic acid) at a capacitor in the battery circuit, from the capacitor plating process that had not been sufficiently rinsed. The capacitor cleaning process was corrected and the assembly failures were eliminated. In this case, the client’s processes produced product that was free of residue and passed testing, but failed.

Testing Is Still Worth It

Various test methods are critical in vendor evaluation, materials selection, process control, and product qualification. Two important test protocols for evaluating residue impact on performance are:

• ESS testing (Electrical Stress Screening) where the product is thermal cycled and tested under bias and in humidity;

• SIR testing.

Keep in mind that not all testing and cleaning processes are the same. It is important to know the capabilities and limitations of each of your methods.

An Effective Tool for Detecting Ionic Residues

The C3 is an effective tool for detecting ionic residues that can manifest as an electrochemical reaction, resulting in dendritic growth. Rather than producing an average cleanliness value for an entire assembly, the C3 allows close scrutiny of selected, critical areas in order to understand the corrosive nature and reliability impact of any residues. 

Localized cleanliness testing, AKA the C3, is one more testing tool to be added to a testing regiment to supplement, not replace, other test methods.