Tips for Testing PCB Cleanliness

Author: Elizabeth Norwood

Effective PCB design involves meticulous consideration of various factors, including component orientation, signal trace routing, and flux/paste mixture. Yet, one aspect often overlooked by PCB designers is the early selection of cleaning methods and fluids. Typically, cleaning choices are deferred until the latter stages of production, after finalizing decisions on solder pastes and conformal coatings. However, this delay can result in manufacturing contaminants such as flux residue, dust, and moisture becoming trapped on the board, leading to performance and reliability issues like dendrite growth, oxidation, noise, shorting, electrochemical migration, and intermittent operation.

Plan to Test

To circumvent production delays, recalls, and costly returns, designers must proactively plan and specify an appropriate flux remover compatible with their chosen solder paste, flux, and PCB substrate during the initial design phase. This preemptive approach mitigates cleaning complications during production and ensures long-term PCB performance and reliability. Fundamental to PCB design is pre-testing, where understanding how to clean all PCB elements early in the process is crucial. By conducting test cleaning during the conceptual stage, designers gain insights into how their choices impact board performance.

Small-Scale Testing

Conducting test cleaning on a limited run of PCBs before full-scale manufacturing proves beneficial in achieving functional parts. Once the cleaning fluid and process have been validated on a smaller scale, production can be scaled up to meet higher volume demands. Small-batch preemptive testing helps eliminate surprises, ensuring enhanced board reliability.

Pre-testing can occur in-house if the facility possesses appropriate capabilities. Alternatively, outsourcing is a popular choice for PCB cleanliness assurance. MicroCare can conduct comprehensive testing and cleaning trials in accordance with standards specified by the PCB designer, ranging from visual inspections to strict IPC-610 requirement testing.

Testing Methods

Various methods and techniques are employed in PCB testing to detect and measure contamination levels on the board's surface. The choice of testing method depends on the type of contamination and desired precision.

Surface Insulation Resistance (SIR) testing is a highly precise method that assesses the reliability of electrical components post-cleaning based on signal strength and quality. Ionograph or Resistivity of Solvent Extract (ROSE) testing, while less precise than SIR testing, offers faster and user-friendly evaluation of ionic contamination by immersing the PCB in deionized water. Ion Chromatography (IC) testing, the most precise and reliable method, quantifies weak organic acids and individual ions to assess cleanliness.

Work with a Testing Partner

For cleaning assistance, PCB designers should collaborate with PCB cleaning fluid partners well-versed in cleaning dynamics, methods, and pre-planning. Engaging our cleaning experts early in the design process helps avoid unexpected issues, reduces costs, ensures PCB reliability, and expedites product delivery.