ESD (electrostatic discharge)

Electrostatic charge is caused by friction, contact and routing processes. Materials such as plastics, textiles or metals store electrical charges that discharge suddenly when touched or approached. This process is particularly critical in the electronics industry, as even the smallest voltages can destroy sensitive components.

The consequences are often irreversible damage to electrical, electronic and optoelectronic components. Printed-circuit boards (PCBs) fitted with components such as metal-oxide-semiconductor field-effect transistors (MOSFETs) or insulated-gate bipolar transistors (IGBTs) are particularly susceptible. IC chips (integrated circuits) and substrates used in the semiconductor industry and electronics manufacturing are also at risk. Rapid equalization of the potentials causes high electrical voltages, which can lead to irreparable faults in assembled circuit boards and their sensitive individual components.

Electrical conductivity of materials

In order to effectively protect electronic components from ESD damage, for example during handling, the electrical conductivity of the materials used plays a central role. As these materials are in direct contact with the workpiece, they must ensure that electrostatic charges can be discharged in a controlled and damage-free way.

Electrical conductivity describes the ability of a material to safely discharge charges via its specific resistance. Depending on the resistance value, this happens either very quickly – as is the case with conductive materials – or in a delayed and controlled manner, as is typical for dissipative materials. The decisive factor here is always the specific resistance, which determines at what speed and in what way charges are safely discharged.

Resistance ranges in ESD protection

Depending on the material class, there are different specific resistance ranges:

• Conductive plastics are typically between 10³ and 10⁵ Ω and allow charges to be discharged very quickly.
• Dissipative materials are in the range of 10⁶ to 10⁹ Ω and ensure a controlled, damage-free discharge. The materials NBR-ESD ans HT1-ESD used by Schmalz falls precisely within this range and thus ensures safe voltage dissipation on the workpiece.
• Antistatic materials show significantly higher values between 10¹⁰ and 10¹² Ω and work primarily against charge accumulation without strongly dissipating the charge themselves.

Test method for conductivity

The “point-to-ground” measurement is one particular means of verifying discharge capacity while taking the specific resistance into account. Based on this measurement, it is possible to identify the range in which the resistance of the overall system lies. With the aid of special resistance meters, the discharge resistance between a measuring point (1) and a grounding point of the system (ground potential) (2) can be established.

Suitable materials are often marked with the ESD protection symbol for better orientation. This symbol indicates that a product is suitable for ESD protection and reliably protects other components from electrostatic discharge.

To ensure that ESD protection is not only ensured at material level and in test procedures, but is also consistently implemented in the practical working environment, clearly defined areas with coordinated measures are required.

An ESD protection zone, or "EPA" for short (Electrostatic Protected Area), is a special working area in which all materials, tools and work equipment are designed to be electrically dissipative. This includes dissipative floors, earthing systems, ESD-compliant clothing and packaging. The aim is to prevent and discharge electrostatic charges in a controlled manner so that sensitive components such as printed-circuit boards, semiconductors or optoelectronic components are reliably protected.

ESD protection is essential in the electronics industry. Sensitive PCBs containing components like MOSFETs and IGBTs are highly vulnerable to electrostatic discharge and require reliable protection throughout all handling procedures.