In our daily operations and customer inquiries, we have found that there are many questions about the anti-static standards of "anti-static silicone foam board" among people. Just how "anti-static" is it? What are the authoritative testing standards? What are the different requirements for different application scenarios? Today, let's make it clear thoroughly.
一, Core Indicators: Resistivity is the key
The core indicator for measuring anti-static performance is resistivity. According to the path through which the current passes, we mainly focus on two parameters:
1.Surface Resistivity (surface Resistivity) : the resistance of a material when current flows along its surface. Unit: Ohm (Ω)
2. Volume Resistivity (volume Resistivity) : the resistance of a material when current passes through it. Unit: Ohm ·cm (Ω·cm).
For porous materials like foamed silicone rubber, volume resistivity is usually a more crucial indicator as it can comprehensively reflect the overall electrical conductivity of the material.
二, Mainstream Standards and Grade Classification Currently.
There is no absolutely unified single standard for the grade classification of anti-static materials internationally. However, the following mainstream systems and standards are widely cited and adopted:
1. ESD Association (ESDA) Standards - The most authoritative Electrostatic Protection System The standards formulated by the Electrostatic Discharge Association of the United States are the most authoritative references in the electronics industry. Its standard ANSI/ESD S20.20 classifies materials into three categories, which is crucial for our understanding of the anti-static grade:
1)Conductive materials (Conductive) : surface resistivity: less than 1 x 10⁴ Ω (i.e., <10,000 Ω) volume resistivity: Less than 1 x 10⁴ Ω·cm. Characteristics: The charge dissipates extremely fast, which may cause rapid discharge of electrostatic sensitive components (CDM damage). It is often used in situations where grounding is required and charges need to be discharged quickly, such as anti-static floors and table MATS.
2)Static dissipation material (static Dissipative) : surface resistivity: 1 x 10⁴ Ω to 1 x 10¹¹ Ω volume resistivity: 1 x 10⁴ Ω·cm to 1 x 10¹¹ Ω·cm features: this is the most common grade of anti-static silicone foam board! It can discharge static charges to the ground at a controllable and relatively slow speed, avoiding the generation of instantaneous large currents, and thus safely protecting most electronic components.
3)Insulating material: Surface resistivity: greater than or equal to 1 x 10¹² Ω (i.e., ≥1,000,000,000,000 Ω) Volume resistivity: greater than or equal to 1 x 10¹² Ω·cm Characteristics: Electric charge cannot flow and static electricity is prone to accumulate. Ordinary silicone rubber falls into this category.
2. Other common standards
ASTM D257: American Society for Testing and Materials standard, which is the standard test method for measuring the direct current resistance or conductance of insulating materials.
IEC 61340: An International Electrotechnical Commission standard, similar to the ESDA standard, is also a globally recognized standard system for electrostatic protection.
Military standards such as MIL-PRF-87893: They have more stringent and specific requirements for the performance of anti-static materials.
The anti-static standard for anti-static silicone foam boards mainly depends on whether its volume/surface resistivity falls within the "static dissipation" range of 10⁴ to 10¹¹ Ω·cm. Which specific sub-range you choose depends on the electrostatic sensitivity of the product you want to protect and industry standards.