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Adhesive vs Adhesiveless Flex Cores

Adhesive vs Adhesiveless Flex Cores


Adhesive Based flex cores utilize a layer of flexible adhesive which bond, under heat and pressure, each copper layer to the polyimide core. The adhesive is typically either epoxy or acrylic based.

  Adhesive Based Flex Cores


Adhesive Based Flex Core benefits:

  • higher copper peel strengths (dependent on adhesive type used)
  • reduced material cost


Adhesiveless flex cores have the copper directly attached to the polyimide core without the use of any adhesives. The absence of an adhesive results in a thinner, more flexible construction.

   Adhesiveless Flex Cores


Adhesiveless Flex Core benefits:

  1. Reduced flex thickness due to elimination of adhesive layers.
  2. Improved flexibility due to reduced finished flex thickness.
  3. Tighter possible minimum bend radius due to reduced finished flex thickness.
  4. Improved plated hole reliability in higher layer count flex designs
  • reduces number of layers of adhesive within the flex construction
  • high co-efficient of thermal expansion of flex adhesives can place plated holes under an excessive Z-axis stress during assembly which can lead to hole plating cracks
  1. Higher potential temperature ratings
  • flex adhesives have a substantially lower MOT (maximum operating temperature) than polyimide
  1. Improved controlled impedance signal characteristics
  • homogeneous construction of only polyimide between signal layers and reference planes
  1. Required to meet IPC 2223C rigid flex design guidelines
  • eliminates and/or reduces the use of flex adhesive within the rigid areas
  • improved plated hole reliability
  1. Better suited to hash environment applications



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