Improved determinations of residual anions and organic acids to evaluate printed circuit board cleanliness

Importance of the topic

Monitoring residual inorganic anions and organic acids on printed circuit boards is essential to maintain reliability and avoid failures in electronic devices. Ionic and acidic residues from flux and manufacturing steps can lead to corrosion, soft shorts, or performance degradation over time.

Study objectives and overview

This application brief presents two improved ion chromatography approaches to evaluate PCB cleanliness according to the IPC-TM-650 test method:

• Method A: Temperature‐modified hydroxide gradient separation at 20 °C for a rapid 38 min analysis.
• Method B: Methanol‐enhanced gradient based on AN1163 for extended 60 min separation.

Methodology and Instrumentation

Both methods were implemented on a Thermo Scientific Dionex ICS-6000 HPIC system with:

• Dual Pump DP for eluent generation and suppressor regeneration.
• Eluent Generator EG and HP EG degasser.
• CD Conductivity Detector with external water mode suppressor (ADRS 600).
• Dionex IonPac AG11-HC guard and AS11-HC analytical columns (2 mm i.d.).
• Autosampler with 100 μL syringe and 10 mL vial trays.

Reagents included methanesulfonic acid, organic acid standards (adipate, phthalate, malate, succinate, glutamate), and a combined seven-anion standard. All standards were prepared in ASTM Type I ultra-pure water.

Method A employed a stepped KOH gradient (1–85 mM) without organic modifier, at 20 °C column temperature.
Method B used a similar KOH gradient with a 2–15 % methanol gradient and 30 °C column temperature to enhance selectivity.

Main results and discussion

Method A separated nine organic acids and seven anions within 38 min with clear resolution except partial overlap of succinate and malate. System backpressure was ~2 600 psi.
Method B achieved improved partial resolution of succinate and malate over 60 min using methanol, with backpressure between 2 400 and 3 000 psi. Both methods lowered system pressure compared to AN1163.

Benefits and practical applications

These alternative protocols offer practical advantages for PCB quality control:

• Reduced system backpressure extends column and suppressor lifetime.
• Flexibility to choose faster or higher-resolution analysis based on laboratory needs.
• Compliance with IPC-TM-650 enables consistent cleanliness monitoring.

Future trends and potential applications

Further improvements may include higher-capacity columns, coupling with mass spectrometry for structural confirmation, and adaptation to broader electronic or semiconductor contamination assays. Automated workflows and advanced data processing will enhance throughput and data integrity.

Conclusion

Two modified high-pressure ion chromatography methods were demonstrated for reliable determination of residual anions and organic acids on PCBs. Each offers a balance of resolution, speed, and reduced backpressure to support industrial cleanliness testing.

Reference

• Huang B, Rohrer J. Determination of anions on the surface of printed circuit boards by IPC-TM-650 Method 2.3.28 using HPIC (Thermo Scientific Application Note AN1163), 2016.
• IPC TM 650 Test Methods, IPC International, Inc., Bannockburn, IL, USA.
• ASTM D1193-99e1 Standard Specification for Reagent Water, ASTM International.