Ultrasonic Welding Handles Thin, Delicate Materials for PV Solar Cell Assembly

Process is also Reported to Create Stronger Welds in Assembly of Lithium-ion Batteries

WEST CHESTER, Pa.—As markets for renewable energy heat up, ultrasonic welding is one manufacturing method that's meeting a need created by the increased production of photovoltaic solar cells, according to Janet Devine, president, Sonobond Ultrasonics, West Chester, Pennsylvania. The ability of the process to weld thin, delicate materials without damaging the weld zone is an advantage in PV cell manufacturing, where ultrasonic welding is used to weld thin strips of conductive aluminum foil to a metallized layer that is deposited onto glass. The aluminum conductors serve as electrical interconnects between the photovoltaic cells, which are connected together and mounted to form a photovoltaic module. And as multiple modules are wired together, they begin to form an expanding array that will eventually provide enough voltage and current to serve as a source of electrical power.

"Ultrasonic welding produces a low-resistance joint and minimizes the loss of electrical energy when modules are connected," wrote Devine in her article, "Ultrasonic Welding Plays Key Role in Photovoltaic Cell Assembly," published by Welding Journal.

Ultrasonic welding of metals combines high-frequency mechanical vibrations with the application of pressure to produce a bond between two materials, even if they're dissimilar. The process directs high-frequency ultrasonic energy via a welding tip to the surfaces of the metals to be welded. Energy disperses the oxides and surface films between the workpieces to create a strong metallurgical bond without the use of excessive heat and solder materials.

"There are no other foreign substances introduced," Devine said in a recent phone interview. "And, unlike fusion welding, the heat level is not to the point that it melts [metal] materials, so the damage from heat is minimal."

When used on thermoplastics, ultrasonic welding produces enough frictional heat to cause local melting on parts to be welded. This isn't the case with metals, which never reach the melting point during the process.

Another application for ultrasonic welding is the assembly of lithium-ion batteries, which are being used increasingly in hybrid electric cars, as well as laptops, cell phones, and power tools. Capable of being formed into various shapes to fit the devices they power, lithium-ion batteries are lightweight, rechargeable, and can store nearly 500 per cent more watt hours per weight than lead-acid batteries. In cases where welding of multiple layers or delicate foils is required, ultrasonic welding produces "better weld strength and electrical conductivity" than conductive adhesives, according to Devine.

For more on Sonobond Ultrasonics, visit www.SonobondUltrasonics.com.