IC Explained

Ion Chromatography is a test that can identify specific anions and cations, and knowing the area of the circuit assembly, the loading in µg/cm² can be calculated for each species. For the IC technique to measure the different types of ions, different columns are required, hence halides, cations, weak organic acids, etc. need different columns.

Challenges with IC

This data, while very useful in identifying material and process issues, does not directly provide evidence either way in regard to OE. The SIR test provides a resistance value which can be readily interpreted in the context of circuit performance, while the IC test provides a quantity of an ionic species, e.g., 1µg/cm² of Chloride. This has no context in terms of circuit performance. Another factor is that if simultaneous measurements are required, more than one IC tester will be required.

The weight of an anion can only be interpreted in terms of a library value, that has been previously established by testing golden (known good) assemblies or from SIR tests. The IC route can become extremely complicated as the IC test can reveal many anions and cations, and the interactions of these ions can be complicated.

We cannot just add up the total number of ions as there can be synergistic effects, and specific material reactions on the circuit assembly. Hence comparing ion counts with library values may not provide an accurate prediction on circuit reliability from a corrosion perspective.

The IC test is therefore a qualitative test and does not meet the requirements for OE on it’s own. Furthermore, the IC test does not provide any specific location, or component type information. The extraction of the solution is a result of immersing a circuit assembly into an alcohol water solution in a bag and holding that bag in a water bath at 80°C for 1 hour. Any ions released and subsequently measured cannot be traced to any component, or component type.

SEC/ROSE Technique

What is of interest in the context of SIR and IC testing, is the Solvent Extraction Conductivity (SEC) technique. This technique was utilised in the Resistivity of Solvent Extract (ROSE) test and had a pass/fail level of 1.56µg/cm² of NaCl.
With the advent OE the ROSE test has been removed and can no longer be used as a go/no go test.

The SEC technique has been incorporated into the new Process Ionic Contamination Test (PICT), and here the measured contamination is compared to a library value for a golden and known good board. Similarly, to the IC technique the PICT test measures the total dissolved ion content, anions and cations, and can be made in as little as 3 minutes whilst being run at ambient temperature. The PICT test is, importantly, as sensitive as the IC technique. On top of this, the equipment is robust and can be used in a production environment, whereas SIR and IC are laboratory equipment.