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Laser Machining of Metallized PVDF Films

Polyvinylidene fluorine (PVDF) in a shape of semi crystalline films are widely used in the applications ranging from piezoelectric sensors [1], element of space telescopes [2] to pellicles for UV photolithography [3]

This article describes laser machining technique used by LLTI to pattern speaker electrode on a roll of PVDF film with copper- nickel coating on both sides of the film.

Measurement Specialties Inc. (Norristown, PA) was looking for efficient method of patterning speaker electrodes approximately 6X11” on a toll of PVDF film up to 600 feet long. Patterning electrodes includes removing copper –nickel coating .07” wide from both sides of the roll of 28um thick PVDF film with continuous metal coating on both sides. Laser machining has to be cost efficient method comparing to alternative chemical etching.

LLTI decided to use Excimer laser micromachining using KrF laser media (wavelength 248nm). In addition to removing metal coating on the border of 6X10” area, each speaker electrode has to have mark for the positive electrode and set of fiducials for skewing prior to automated cutting of electrodes from the roll. These unique requirements   required dedicated laser machining system, so LLTI laid out specification and integrated system for this application. Motion portion of the system included 6 axes controller for material handling stages with 16” of travel in X and Y. Reel to reel system was placed on a top of material handling stages and had close loop material feed and adjustable web tensioner. Motorized mask stage allowed switching between different masks required to machine complete electrode pattern. Also motorized Z stage for projection lens simplified system setup.

Combination of energy density and synchronization between material handling stages travel and repetition rate of the laser were the most important parameters and were optimized during R&D phase of the project. Applying too high energy density to PVDF film or overexposure caused deterioration of crystalline structure of the film and initiated optical absorption which resulted in increased surface and bulk conductivity. Further overexposure severely damaged chemical bonds in PVDF molecules and formation of burned intercrystallite areas visible with optical inspection. It was determined, that measuring electrical resistivity between machined electrode and the surrounding metal coating provide efficient method for monitoring quality of metal ablation.

  1. Piezo Film Sensors, Technical Manual, Measurement specialties Inc. Sensor Product Division
  2. Characterization, Performance and Optimization of PVDF as a Piezoelectric Film for Advanced Space Mirror Concepts, Sandia Report SAND2005-6846, Unlimited Release Printed November 2005
  3. A. Tregub, F. Eschbach, F. Lo Use of alternative polymer material for soft polymer pellicles, US Patent application Ser. No. 10/799,928, filed Mar.12, 2004