Lasers solder telecoms fibers

17 Jun 2002

A fiber-coupled array of diode lasers can produce a high-quality gold-tin solder joint in just two seconds.

Laser manufacturer Coherent, US, has developed a fiber-coupled, high-power diode laser system that solders high-quality gold-tin joints. This technique could replace current methods that use solid-state lasers, making soldering of gold-metallized telecommunications fibers to gold-plated substrates faster and easier.

Coherent's applications manager Tony Hoult said: "We believe the high-power diode laser soldering technique will help a number of telecom component developers through a manufacturing barrier that they have been up against for some time."

Two issues influenced the development of the system. First, typical telecommunications fibers are 125 µm in diameter, placing demands on the accuracy of the soldering system. Second, the gold-tin solder has both a high thermal conductivity and melting point (280°C). A balance between the laser's power density and the exposure time is needed to prevent heat damage.

To overcome these difficulties, the Coherent researchers have developed a 40 W fiber-coupled high-power diode laser array unit. It delivers 800 nm light via a 800 µm diameter fiber to the surface requiring soldering.

By controlling the beam's timing and positioning, the researchers use a beam spot of 800 µm, corresponding to a power density of 6 kW/cm², to adequately cover the 500 µm gold-tin solder joint. This produces defect-free joints with no associated damage to the fiber in two seconds.

The system offers an alternative to the more complex solid-state laser techniques that are currently used to weld telecom fibers onto substrates.

"Using solid-state lasers is a hard process to control," said Hoult. "You need precise beam placement as three spots are used in the welding process. Accurate fiber alignment is also required and this is hard to achieve so people started looking at laser soldering."

Author
Jacqueline Hewett is news reporter on Optics.org and Opto & Laser Europe magazine.