Protecting medical device PCBs from electrostatic discharge

Elizabeth Norwood, senior chemist at MicroCare, outlines ways that medical device manufacturers can prevent electrostatic discharge with printed circuit boards.

Electrostatic discharge (ESD) poses a serious yet invisible threat to the printed circuit boards (PCBs) powering critical medical devices like patient monitors, infusion pumps, and pacemakers. According to a study in Semiconductor Reliability News, an estimated 60% of device failures are caused by ESD and electrical overstress (EOS), costing the electronics industry millions annually in damaged and degraded parts. As electronic devices become faster and the circuitry gets smaller, sensitivity to ESD is increasing. 

By proactively addressing vulnerabilities through cleaning and grounding protocols, medical device manufacturers can enhance reliability and achieve efficiencies by preventing device failure related to ESD. This ensures dependable performance throughout its targeted product lifecycles, reinforcing the importance of patient safety.

ESD risks in medical electronics 

ESD is the sudden flow of electricity between two electrically charged objects caused by contact, an electrical short, or dielectric breakdown. In PCBs, ESD can be detrimental and cause, what is known as, ‘catastrophic’ failure, immediately damaging the electronic components. However, catastrophic failure is often detected through performance testing. The PCB ceases to function entirely, and the damage is apparent, often necessitating replacement or extensive repair.

The problematic form of ESD is ‘latent’ failure, which is less obvious and manifests over time. Latent damage occurs during an electrostatic discharge, but its effects may not be immediately apparent during initial inspections or testing. The damaged PCB may pass the initial checks and seem functional, but it is prone to malfunction or failure later in its lifespan.

In medical device production, the primary driver of ESD events stems from technicians performing standard assembly and test procedures. Walking between rooms or workstations can generate up to 35,000 volts of static electricity. Any employee movement ranging from garment adjustments to reaching for tools produces further static build-up. Without mitigations in place, inadvertently touching a medical device PCB can transmit enough voltage to damage sensitive components. Compounding trouble spots in production include non-grounded machinery, synthetic surfaces, clothing, and compressed air discharges during cleaning routines.

Control ESD Risks  

While complete electrostatic discharge elimination is impossible within manufacturing environments, actions to reduce risks are achievable through ESD control protocols, for example:

1. Mandate technicians to wear anti-static wrist or heel straps connected to a grounded line while handling sensitive PCBs.

2. Use conductive floor mats to discharge static build-up from technicians' shoes.

3. Enforce the use of anti-static clothing and shoes, reducing the likelihood of static charges accumulating during the manufacturing process.

4. Ensure the grounding of all worktables, floor mats, and wrist straps, creating an interconnected grounded environment to mitigate static risks.

5. Maintain humidity levels between 40-70% in the production area, an effective preventive measure against static build-up in the air.

6. Remove unnecessary items, such as notepads and pens from the work area.

7. Package electronic devices in static-controlled containers.

Addressing ESD risk through cleaning 

Work surfaces and tools integral to PCB assembly and testing often carry static charges, posing an ESD threat. Wooden workbenches, metal racks, synthetic floor mats, and even seemingly innocuous tools like soldering irons can all contribute to ESD.

Mitigate these risks by systematically wiping tools and surfaces with pre-saturated ESD-reducing cleaning wipes. Specifically formulated to remove dirt, grease, and fingerprints, these wipes maintain cleanliness without introducing lint or static charges. 

Opt for static dissipating PCB cleaning tools to counter the hazards associated with some metal flux removers and cleaning fluid cans, which can generate up to 12,000 volts of ESD. Using a static-zapping dispensing tool that replaces the plastic straw will further reduce any ESD, minimising it to a harmless fifty volts. 

Enhance safety measures by considering the use of a controlled static-safe flux remover dispenser. This system offers precise control over the application of flux remover, reducing wastage. Both the dispensing tool and brushes carry ESD charges to the ground, significantly minimising the threat to PCBs and sensitive components.

Addressing ESD at its source is crucial in PCB manufacturing to prevent potential compromises in production output, PCB quality, and overall device reliability. PCB fabricators should develop robust strategies, focusing on controlling the work environment and implementing effective cleaning tools.

Reduce the threat of ESD

While eliminating electrostatic discharge in production environments is impossible, medical device manufacturers can significantly mitigate its risks through ESD control protocols and cleaning practices.