DESIGN AND PROCESS GUIDELINES FOR DM2700/2760PF SEALING GLASS PREFORMS

Preform Design Guidelines

Aim for 1 mm minimum of sealed length of fiber

  • End of tube sealing
  • Inside tube sealing

Select size of preform to generate the volume to accomplish the above

  • Combination of OD, ID, and length for correct volume
  • Preform will shrink ~ 15% during the melting process

Inside diameter of ferrule/tube depends on ferrule material

  • For low expansion metal such as Kovar (5.5 ppm/°C), recommended maximum ID is 0.025" (0.63 mm). Preferred is 0.010" (0.254 mm). Minimum is about 0.008" or 0.2 mm.
  • For high expansion metals such as stainless steel (18 ppm/C), there is only a practical maximum ID, unrelated to stress, of about 0.050" or 1.27 mm. Minimum is same as above.
  • For quartz ferrules, the maximum is 0.010" or 0.254 mm.

Preform Processing Guidelines

Heat ferrule by one of suggested processing methods

  • Heating ferrule is preferred to heating just the glass
    • Assures interface has reached temperature for good wetting
  • Heating rate must be at least 50 °C/minute
    • Too slow rate will retard the flow. Faster is better.

Temperature for optimum sealing is about 350 (400) °C for DM2700PF (DM2760PF)

  • Minimum sealing temperature is 320 (380) °C
  • Maximum temperature is about 450 (500) °C
    • Higher temperature will cause outgassing and crystallization

Time at temperature depends on maximum temperature

  • Use temperature/time combination that allows the glass to wet the inside of the ferrule to achieve a target of 1 mm of sealed length.

Common Methods for Heating Solder Glass to Form a Seal

  • RF Induction Heating
    • Localized and fast
    • RF absorbent (metal) ferrules only
  • Resistance heating
    • Very localized, fast -electrode dependent
    • Requires electrically conductive ferrule
  • Microflame generator
    • Hottest and fastest, very localized
    • All types of ferrules
  • Radiation
    • Resistance heated wire, good control of heat
    • Independent of ferrule type
  • Laser
    • Solder glass (DM2700) very absorbent of CO2 laser light
    • Ferrule type independent
  • Conduction
    • Heat source in contact with work piece
    • Heating rate depends on mass and thermal conductivity of ferrule

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