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Welding Aluminum? Use Lasers for Best Results.

Aluminum: it is relatively inexpensive, offers excellent thermal and electrical conductivity, possesses an attractive finish, and has limited susceptibility to corrosion. It’s no wonder manufacturers turn to it – especially those making packages for sensitive electronics. But the qualities that make aluminum so attractive, also make it notoriously difficult to weld. In today’s post, we are going to discuss how to achieve strong welds with excellent hermeticity using aluminum. Spoiler alert: we recommend laser welding in a butt weld configuration.

How the different technologies stack up when welding aluminum

There are several welding technologies to choose from and each one comes with its own set of challenges when joining aluminum. Here is a comparison of the three most commonly used methods:

While all three technologies present challenges, laser welding offers the most stable and reliable solution. It generates the smallest heat affected zone, protecting the sensitive contents of the package.

Choosing the right laser

A number of laser sources can weld aluminum.  Available options include pulsed Nd:YAG, continuous wave (CW) fiber, or quasi continuous wave (QCW) fiber, each paired with a focus head to deliver the energy to the part. The best laser solution for your application depends on part design, factory floor space, budget and more. Here are a few considerations:

  • Pulsed Nd:YAG, usually configured with a fixed focus head, is a commonly selected laser source for aluminum welding. It is still the laser of choice for complex geometrical welds where stage motion limits speed in corner areas. Its larger spot sizes help accommodate for fit-up tolerances, providing a fairly robust weld for production.
  • CW fiber lasers are also popular due to their low consumable nature and faster weld speeds. Challenges exit, however, with the small beam diameter which makes it difficult to overcome manufacturing tolerances. CW fiber lasers are best for welding from the top of the package where the weld path geometry is “1D” or “2D”.
  • QCW fiber lasers land somewhere between pulsed Nd:YAG and CW fiber lasers. In pulsed mode, they behave similarly to pulsed Nd:YAG lasers. Pulsing can be controlled to limit heat input to the part. However, these lasers typically have small spot sizes which can make it difficult to bridge gaps between parts, so component manufacturing tolerances must be tighter.

Package design plays an important part in success

The three basic joint types commonly used for laser welding are butt, fillet, and lap. In our experience, butt welding achieves the very best hermeticity, and the greatest strength per watt of laser power as the laser penetrates directly down the interface line between the two parts. The figure below shows weld penetration for the three basic weld geometries in red. The strength of the weld is found along the yellow line.

The following table outlines the four most common package design geometries. We have found that a recessed butt joint weld is best because it allows for easy, repeatable positioning of the lid, provides beam access from the top, and limits the number of degrees of motion. It is also easier to automate, with potential for multiple up configuration.

A side butt weld would be the next best choice. This option allows the use of a simple, flat lid of any thickness. Creating a strong joint requires at least 3-axes of motion and good joint line positioning.

Tips and tricks for successfully laser welding aluminum:

After evaluating the considerations shown above, we recommend the following when welding aluminum:

  • Since aluminum is more prone to impurities that can lead to weak, porous welds, be sure to thoroughly clean the package to remove oil, grease, fingerprints, and other surface contaminants.
    • Remove surface oxides using a brush, acid, or laser.
    • Assemble parts quickly to avoid further contamination.
    • Keep parts dry and at room temperature. If not welded within a few days, repeat cleaning process.
  • Select aluminum alloys that are known weldable combinations.
    • AL 1000 series
    • AL 3000 series
    • AL 6061 cannot be welded to itself without micro-cracking, but using an alloy of Al 4047 or 4043 for the lid can be welded
  • For butt welds where manufacturing tolerances sometimes lead to a wide gap, the small beam from a CW can be problematic. However, it is possible to oscillate the beam either with a “wobble head” or a galvo scanning solution to increase the size of the melt pool and bridge the gap.
Category: Laser Welding