How to Eliminate PCB Static in Medical Electronics
Medical device technology is continually advancing and helping shape the future of healthcare. It is used in every area of the industry, from simple remote patient monitoring like smart watches to sophisticated implantable equipment like pacemakers and cochlear hearing devices. Its importance is evident with the global medical electronics market size evaluated at USD $101.06 billion in 2022 with growth projections anticipating $248.43 billion by 2032.1
This growing technological demand calls for extremely complex miniaturized electronics. Printed circuit boards (PCBs) must be smaller and lighter but still contain the complex circuitry required to power these highly technical medical devices. Medical electronics must, without fail, be reliable with longterm functionality. However, these small, densely packed PCBs make managing faults problematic and challenging.
Electrostatic discharge (ESD) is one problem that can severely affect electronic medical devices causing malfunctions and damage to the microelectronic components. An estimated one-third of PCB failures are attributed to ESD. Without controls and effective processes to eliminate electrostatic discharge in medical devices, it can cause serious hazards to human safety.
WHAT IS ESD?
ESD is the rapid release of built-up charge between objects, causing electricity to flow between them. When one object is positively charged and the other negatively charged, the protons and electrons that carry these charges try to balance each other out by quickly exchanging at the point of contact. The sudden release of the built-up charge results in an ESD spike. Although it can’t be seen, the spike can damage both the PCB and electronic components, particularly sensitive parts like resistors, capacitors, diodes, integrated circuits, transformers, and transistors.
There are two forms of ESD damage: catastrophic and latent failure. When an electronic device suffers latent damage, it may be partially degraded but continues functioning. However, the device becomes unreliable as its lifetime reduces, affecting its operational behavior.
Latent damage is nearly impossible to detect with damaged PCBs passing initial inspection during manufacturing. Catastrophic damage, however, is more obvious and can usually be found through performance tests during quality control inspections. It causes permanent damage to the PCB, leaving the electronic component unusable.
ESD is so detrimental to electronic devices that governing bodies like the International Electrotechnical Commission (IEC) and American National Standards Institute (ANSI) include the phenomenon in their standards IEC 61340 and ANSI/ESD S20.
ESD can occur at any stage of the manufacturing and assembly process; however, the most common route is through touch. The human body and certain clothing can store 500-2,500 V of static electricity during a typical workday.
ESD can be found in every corner of a production facility; however, manufacturing areas with more hands-on processes are at higher risk. For example, receiving, assembly, repair, cleaning, inspection, and packaging are the most ESD-vulnerable production spaces. Other common sources of ESD include using ungrounded electrical equipment such as an oscilloscope when troubleshooting electronic circuitry.
Production equipment like carts, conveyors, and machinery or materials rubbing together can also build up friction and create ESD. Another instigator is rapid air movement, such as using compressed air or a fan to dry a PCB assembly.
HOW TO MANAGE ESD
Although it is impossible to eliminate 100 percent of ESD, effective measures can be taken to reduce ESD during surface mount technology (SMT) production. Here are some recommended methods.
Environmental Control. Certain areas of a manufacturing facility are more at risk of electrostatic charge than others, but by combining these protective measures, electrostatic charge can be reduced.
- Wear antistatic wrist straps or heel straps connected to a grounded line to dissipate static from workers when working on sensitive PCBs.
- Use conductive floor mats to discharge static buildup from shoes.
- Wear antistatic clothing and shoe coverings.
- Ensure that all work tables, floor mats, and wrist straps are grounded.
- Keep air humidity in the production area between 40 and 70 percent to help prevent static buildup.
- Never use compressed air when drying PCBs.
- Remove all unnecessary items from the work area that have the potential to create ESD.
- Ensure that the PCBs are shipped in static-controlled containers.
Cleaning is an effective way to reduce ESD. Work surfaces and tools used to assemble, clean, and test PCBs hold static charges, so it is important to dissipate the charges and contamination by wiping them down with presaturated, ESD-reducing cleaning wipes. High-quality ESD cleaning wipes are also effective at removing grime, grease, oil, and fingerprint contamination, which can also be problematic to PCB reliability.
Aerosol flux removers and cleaners are one of the most common PCB cleaning tools. However, some aerosol-style cleaning fluids can generate up to 12,000 V of ESD, which is created by the friction of the molecules as they move down the plastic spray tube. Instead, consider using dispensing tools made from durable aluminum and stainless steel.
In addition, installing a stat-zapping tool to the aerosol can helps make the cleaning technician part of the grounding circuit by maintaining contact with the static zapping tool itself. The charge is carried to the ground, reducing ESD to just 50 V.
ESD-safe controlled flux remover fluid dispensing systems can also help to control static. A flux remover dispensing tool uses grounding measures to reduce the static going to sensitive electronic components. It is also a very effective way to clean dense miniaturized PCBs. The fluid can reach under the low surface-mounted components to loosen and rinse away contaminants for more thorough cleaning and static dispersal.
STAY IN CONTROL
For medical devices with critical electronic components, damage from ESD during manufacturing can introduce defects, with devices failing once the product is in use, endangering the patient’s safety.
ESD can affect the functionality and reliability of medical equipment, so implementing control through strategies, processes, and effective ESD-safe cleaning fluids and tools is essential when manufacturing sensitive medical electronics.
Article Source：Medical Design Briefs