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Transparent Flex Circuits

 DKN Research has been developing transparent & heat resistant flexible circuits. There are broad range choices for both of materials and manufacturing processes to build transparent circuits, therefore, the circuit designers can choose the best construction for the goal.

 

Substrate materials

Currently, there are three vendors for transparent polyimide films.

Electrical properties are equivalent as the traditional polyimide films. They are all heat resistant against soldering or wire bonding process. There are several differences with physical properties and surface properties.

 Standard thickness: 25 micron thick

  **Thicker and thinner films will be available by requests.

 Transparent PEEK film is under evaluation. It could have higher physical properties and stable chemical properties compared to the traditional polyimide films with wider thickness ranges.

 

Conductors

There are two kinds of choices for the conductors. They are transparent

and non-transparent materials. Generally, transparent conductors do not have high conductivities and high heat resistances. Appropriate combinations of different conductors could generate new advantages.

 

 *ITO sputtered (Transparent, <150 ohm sq.)

 *PEDOT ink screen-printable (Transparent, <150 ohm sq.)

 *Silver ink screen-printable  (<20 ohm sq.)

 *Graphite ink screen-printable  (>200 ohm sq.)

 *Ag nanowire ink screen-printable (Transparent, <80 ohm sq.)

 *Thin Ni/Cu/Au plated down to 0.2 micron thick (<10 ohm sq.)

 *Rolled annealed copper foils laminated with glue

  The transparency could be 20% lower than bare PI films.

  Thickness: 9, 12, 18 and 35 micron thick

 

3. Laminates

 Several combinations with transparent polyimide films are available for chemical etching and laser abrasion processes.

 *ITO coated films

 *Metal plated, double sided

  Electroless Nickel: < 0.1 micron thick

  Electro-plated copper: 0.1 to 5 micron thick

  Electro-plated gold: 0.05 to 0.5 micron thick

 *Metal foil laminated with glue

  Rolled annealed copper foils laminated:

   9, 12 and 18 micron thick

 

4. Cover layers

 There are two types of transparent cover layers.

 *Transparent films with glue

  Total thickness: 50 micron

  It reduces transparency 40%.

 *Transparent epoxy ink

  Thickness: down to 15 micron

  It reduces transparency 20%.

 

5. Circuit constructions

 There are many kinds of circuit constructions for the transparent flex circuits. The circuit designers should choose appropriate combinations based on the purpose.

 

 *Single side circuits with or without cover layer

  Conductors, transparent:

ITO,

PEDOT: Line width: <200 micron wide

Ag nano-wire: Line width: <100 micron wide

Thin copper grid etched:

 Line width: <500 micron wide

  Conductors, non-transparent:

   Thin copper plated:

    Line width: <50 micron wide

Copper foil laminated:

 Line width: <70 micron wide

Silver ink screen-printed

    Line width: <80 micron wide

Graphite ink screen-printed:

 Line width: <200 micron wide

Gold plating is available on the conductor traces.

 (Electroless and electro plating)

 *Double side with via or without cover layers

  Conductors: Same as single side circuits

  Via holes: Laser drilled down to 70 microns

    NC drilled down to 150 microns

    Nickel/Copper plated

    Silver ink filled

 

 

Etched Flexible Circuits

Laminate

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