Hermetic Welds for Microwave Packages, Sensors and Relays
Lasers produce hermetic seals, preventing contaminants reaching sensitive circuits and trapping high quality inert atmosphere inside the package.
Delivering very low heat, Laser welds can be located close to polymer seals, glass-to-metal seals, soldered components and electronic circuits.
In many applications the alloy of choice for microwave packages is aluminum. It is easy to machine, lightweight and possesses the necessary electrical and thermal properties.
A 4047 alloy lid is Laser welded to a 6061-T6 alloy base with a butt, lap or fillet joint. The 12% silicon-aluminum alloy 4047 can be fusion welded to the 6061 without cracking for a strong hermetic seal.
Unlike other electronic devices, the package around the active elements form part of the microwave circuit. As most microwave circuits involve expensive radar or communication systems, very reliable hermetic seals and high yields are needed.
The packaging must also be robust and capable of being opened and reworked when needed. For rework, an end mill can machine through the Laser weld. Once repaired, another lid can be welded onto it. The number of repairs is virtually unlimited.
In some instances Laser welding is required through the lid into the dividing labyrinth walls to isolate certain parts of the circuit.
redPOWER CW Lasers are the best choice for microwave package sealing. Their high peak powers and low heat input can handle all the different alloys and create a very stable process while maintaining deep penetrations.
Fiber optic beam delivery is most common for these parts because of the consistent focus spot size and top-hat energy distribution which helps with fillet and butt joints to fill any gaps. It also achieves a good metallurgical mixing of alloys.
Welding speeds are generally 150-300mm/min for aluminum alloys and up to five times faster than those rates for iron alloys. If needed, weld penetrations of over 1.5mm are possible.
The mechanical contact connections used in relay units can be fouled by debris or create potentially explosive sparks. To protect against this, hermetic seals are used in their production.
These units use glass-to-metal seals as feed-throughs that are very close to the seam. Too much heat and the glass will crack. With low heat input, Lasers successfully assemble the relay contacts using spot welds, before hermetically sealing the header onto the can with a seam weld.
Stainless steels are typically used for the can, but other iron alloys can be used depending on their magnetic properties. The header is often manufactured out of a cupro-nickel or Kovar material to match the glass-to-metal seals.
The relay contact components can vary a great deal, depending on their electronic and wear properties. Weld penetrations tend to be low (around 100μm – 250μm) to ensure minimal heat input.
redPOWER CW Lasers produce the necessary pulse energy and discrete pulses for spot welding relay components. They can also produce the seam weld around the header. For small packages a galvo mirror system can be used to move the beam around the part.
Sensors incorporate sensitive electrical and mechanical transducers that must be protected with hermetic seals.
Integration of a Laser into a sensor welding line is simple, with minimal control requirements, a robust process window and virtually no consumables or adjustments required compared to micro-tig, resistance welding or brazing.
Time-share multiplexing can direct the output from one Laser to multiple workstations to make best use of the Laser system. The welding parameters can be changed faster than the 50msec switching time between fibers. CCTV through-the-lens viewing can also be used to align and monitor the Laser beam.
For very high throughput and low heat input redPOWER CW Lasers produce the highest welding rates at the lowest cost.
They can also be very effective for small devices where heat input is critical or where the alloys are more reflective (like aluminium or gold plated parts). It possesses the peak power to process reflective materials and can weld to deep penetrations at low average power.
If you enjoyed reading this article, why not register for future articles?