In applications such as hot pressing, electronic thermal insulation, and circuit board cushioning, the flame retardancy, high-temperature resistance, and combustion safety of foam materials directly determine workshop fire risks and product yield. The three mainstream materials available on the market-EVA foam, EPDM foam, and flame-retardant silicone foam-differ significantly in their flame resistance performance. Below is a comprehensive comparison covering combustion rating, high-temperature behavior, smoke toxicity, and applicable operating conditions.
一. EVA foam (standard affordable foam material)
Native EVA is a highly flammable material with an extreme oxygen index of only 17–19; unmodified specimens meet the UL94 HB combustible rating. It burns continuously upon exposure to open flames and melts into droplets that can ignite surrounding panels and equipment, releasing large amounts of pungent smoke and toxic volatile compounds during combustion.
Even when flame retardants are added to produce modified fire-resistant EVA, it only achieves V-1/V-0 rating temporarily and has significant drawbacks: under prolonged exposure to temperatures above 80°C, the internal flame-retardant filler gradually leaches out, causing rapid deterioration of flame resistance after repeated heating; at temperatures exceeding 120°C, the material softens and shrinks, making it entirely unsuitable for the continuous high-temperature operating conditions of PCB hot presses (over 200°C).
The sole advantage is its low cost; it is only suitable for ambient-temperature packaging and low-temperature storage, and strictly prohibited for use in high-temperature production lines.
二. EPDM (Ethylene Propylene Diene Monomer) foam (general-purpose foam for HVAC sealing)
The EPDM features a molecularly saturated structure with exceptional weather resistance and ozone resistance. Its modified version meets UL94 V-0 flame retardancy standards, forming a carbonized layer that inhibits fire spread during combustion while producing minimal melt droplets and exhibiting significantly lower smoke density than EVA.
However, there is a clear upper limit to its high-temperature resistance: the long-term stable operating temperature ranges only from-40°C to 120°C, with short-term peak temperatures not exceeding 175°C. Continuous exposure to temperatures above 180°C will gradually cause softening and loss of elasticity; the flame-retardant carbon layer may deteriorate and detach at temperatures exceeding 200°C, thereby losing its fire-resistant protection capability.
Primarily used for air conditioning systems, pipeline insulation and sealing, as well as short-term low-temperature thermal insulation applications; however, it is not suitable for use with PCB multilayer boards or HDI high-temperature bonding processes.
EPDM foam with bubbles
三. Flame-retardant foam silicone (the recommended material for PCB press sponge pads)
Specifically developed for high-temperature industrial applications, this foam material features a standardized formulation that consistently meets the highest flame retardancy rating of UL94 V-0, making it the most comprehensive fire-resistant option among the three available options.
Combustion characteristics: It self-extinguishes rapidly upon contact with an open flame within 10 seconds, exhibiting only slight surface carbonization without molten combustible droplets; produces low smoke, is halogen-free and non-toxic, and does not release corrosive gases that could contaminate copper foil or circuit boards.
High-temperature flame-retardant stability: It withstands prolonged exposure to temperatures ranging from 200–230°C, and even short-term localized overheating up to 250°C in a press does not cause softening or collapse. Its closed-cell structure provides sustained thermal insulation; the flame-retardant filler neither leaches out nor degrades at high temperatures, with no significant decline in fire resistance after over a thousand thermal compression cycles.
Key advantages: sulfur-free and free from precipitates, featuring high resilience for repeated use while meeting three core requirements-flame retardancy safety, balanced pressure buffering, and high-temperature resistance-making it perfectly suited for high-safety production lines such as PCB thermal pressing and new energy high-temperature insulation applications.