Our newsletter contains valuable information on a wide spectrum of electronic engineering subjects; from Pb-free and RoHS, design for reliability, and more! Subscribe to Newsletter

History of Ion Chromatography

Chromatography is a method for separating mixtures of substances using two phases, one of which is stationary and the other mobile moving in a particular direction. Chromatography techniques are divided up according to the physical states of the two participating phases. The term Ion Exchange Chromatography or Ion Chromatography (IC) is a subdivision of High Performance Liquid Chromatography (HPLC).

Definition of Ion Chromatography

A general definition of ion chromatography can be applied as follows: “ion chromatography includes all rapid liquid chromatography separations of ions in columns coupled online with detection and quantification in a flow-through detector.”

How Ion Chromatography Works

A stoichiometric chemical reaction occurs between ions in a solution and a solid substance carrying functional groups that can fix ions as a result of electrostatic forces. In anion chromatography these are quaternary ammonium groups. In theory, ions with the same charge can be exchanged completely reversibly between the two phases. The process of ion exchange leads to a condition of equilibrium; the side to which the equilibrium lies depends on the affinity of the participating ions to the functional groups of the stationary phases.

DfR Solutions uses the Advanced Modular IC System manufactured by Metrohm Peak (see image at right).

DfR Solutions provides guidelines for board cleanliness and contamination.

DfR Solutions subjects boards to ion chromatography in determining the root-cause of dendritic growth.

Various steps of the board manufacturing process

• Process Step 1 — Bare printed circuit board (PCB)
• Process Step 2 — After through hole insertion/before SMT
• Process Step 3 — After SMT
• Process Step 4 — After hand insertion and wave
• Process Step 5 — Before conformal coating
• Process Step 6 — After conformal coating/before stud insertion
• Process Step 7 — After final inspection

Our procedure for measuring ionic residues is based upon IPC-TM-650 method 2.3.28 and is as follows:

1. Wear clean room vinyl gloves with less than 3 ppm of chloride.
2. Record area of PCB, which is equal to (length x width x 2) + 10% for populated boards.
3. Place the PCB into a clean KAPAK brand heat-sealable polyester film bag.
4. Add a mixture of semiconductor grade isopropanol (75% by volume) and high-purity deionized water (18.2 MΩ-cm grade, 25% by volume) into the bag, until PCB is submerged.
5. Heat seal the bag and place in an 80°C water bath for one hour.
6. Remove the bag from the water bath; pour out, measure, and record the final volume of the sample solution.
7. Remove the test PCB from the bag.
8. Place the test PCB on a clean holding rack for air-drying at room temperature.
9. Prepare standard solutions of anions, cations, or weak organic acids for system calibration.
10. Run the queue of blank, standard, and sample solutions on Metrohm-Peak ion chromatography system.
11. Record the measured ion concentrations (in ppm) from the ion chromatography.
12. Calculate μg/in2 value for each standard ion from the formula given.