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