A polyimide is typically a family of thermoplastic (and some thermoset) resins characterized by repeating imide linkages.

Most polyimides are thermoplastics, but can be end-capped with functional groups to make them thermosets

This charge transfer complex holds the chains together very tightly, limiting molecular movement.  This is why polyimides are so strong.

• Key properties
  : good reliability performance for film adhesives
  : excellent thermal stability
  : high Tg
  : good adhesion to metals
  : fast attach time for film adhesives
• Typical uses
  : thermoplastic resins are used for film applications that require <1 second attach times
  : die attach for memory chips
  : applications requiring high temperature resistance
• Limitations
  : high moisture absorption
  : high cure/process temperatures required
  : solvents used in paste products and residual solvents in film products may cause voiding in the bond line if not cured properly