Ensuring Quality Welds in Medical Devices

Many customers involved with laser welding measure the pulse energy output of their lasers, but is this all the data required needed to ensure quality welds? Steve Schellenberg at Spinal Modulation had his doubts. While he found pulse energy measurement using his Ophir equipment useful in qualifying his laser welding process, two of his laser welding stations were producing different quality welds despite producing identical laser pulse energies. One laser welder seemed to be doing an OK job, while the other welder produced significantly lower quality welds. Steve suspected differing laser profiles might be the culprit and invited an Ophir representative in to characterize the profiles of each welding laser.

An SP503 CCD Beam Profiler with a LBS-300-NIR beam attenuator was used to characterize the beam profile in each laser welder. As expected, the “bad” laser welder had a very jagged and non-uniform profile, as seen below.

Figure 1. “Bad” laser welder shows irregular profile.

To Steve’s surprise, the “good” laser welder also had a non-optimal irregular profile as well, as shown below.

Figure 2. “Good” laser welder also shows irregular profile.

Realizing an opportunity to improve manufacturing yields in the production of a medical implant, Spinal Modulation invested in an SP503 and LBS-300-NIR beam attenuator as part of a project to improve yields and overall product quality. Working with their laser welding vendor, they replaced a laser pumping chamber in their system with one designed to produce a more uniform flat top beam. They obtained the following profile:

Figure 3. After replacing a laser pumping chamber.

While this significantly improved the uniformity, Steve still noticed a slope to the profile. Hoping to improve the profile uniformity further, he ended up speaking with an engineer at his laser welder vendor who suggested rotating the laser crystal in the welder. That was the final piece of the puzzle, resulting in a uniform flattop beam.

Figure 4. After rotating the laser crystal in the welder.

According to Steve, the new welds are “like butter” and Spinal Modulation greatly increased their yields in this critical welding production step.

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