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IPC announces a new standard, IPC-7621, Guideline for Design, Material Selection and General Application of Encapsulation of Electronic Circuit Assembly by Low Pressure Molding with Thermoplastics, a guidance document that offers instruction on using Low Pressure Molding (LPM) in place of potting for circuitry encapsulation.
Unlike potting, where the potting vessel becomes the outer “shell” of the encapsulated part, LPM utilizes mold tooling which is removable and re-useable. LPM also creates a physical layer, providing mechanical and environmental protection for handling and mounting the component device.
Typically, potting vessels are filled with potting compound which hardens in the vessel, causing the vessel to become part of the potted assembly. LPM requires no such vessel and can be molded into a desired form. LPM is commonly done with polyamide (PA) polymer, a thermoplastic, that is brought to liquid state, encapsulating electronic assemblies into a desired form or shape. After the material has cooled, a thick plastic layer remains, working as a protective, sealed barrier. This layer protects the board and components from the environment.
“LPM should be considered when you need to protect the fragile parts of the circuit assembly from shock, vibration, or corrosive or damp environments,” said Russell Steiner, chair of the 5-33g Low Pressure Molding Task Group that published the standard. “In high vibration environments, the mechanical adhesion and resonance dampening properties of LPM materials mitigate the force seen on component bodies and lead attachment. Because mold tooling is reusable, there is a significant cost savings when using LPM.”
IPC-7621 is intended to provide insight to the possible uses for LPM, covering terminology associated with the LPM process in relation to electronic board assembly.