// Showcase
The laser is the easy part. The real work is in the surface and the temperature profile before and after.
A manufacturer of vacuum measurement technology needed a ceramic pressure sensor joined whose reference chamber has to stay sealed at 10⁻⁷ mbar forever, with no flux, no tool contact and no damage to the ceramic from thermal stress. Four things had to line up at once: shorter cycle time, less scrap from bad solder joints, less scrap from thermal stress, and the sensitive surface was only allowed to change minimally.
With a fibre source at 150 W and 940 nm through a 400 µm fibre and a 300 mm working distance, contactless, in vacuum, preheated to 150 °C. Six phases per solder joint: loading with cleaning and solder application, preheating, soldering, stress-relief post-heating, controlled cooling, unloading. Before we locked in the design, we measured the reflectivity of the real component surfaces and found a catch: plasma cleaning raises it from around 37 to 53 percent at the process wavelength, so a third less power couples in. Cleaning turns out to be a process parameter, not just a hygiene step.
A joining process designed around the ceramic rather than the laser, validated with a thermal simulation that we checked against real temperature measurements at four measuring points and three power levels, instead of just trusting the maths. The result is a temperature profile that seals the solder joint reliably without putting the reference chamber or the ceramic at risk, at a cycle time that makes series production pay off in the first place.
A six-phase, contactless laser soldering process for series production in high vacuum: 33 sensors per chamber run, 16 seconds per solder joint, 10 minutes per run at 10⁻⁷ mbar. Plus the whole foundation behind it, meaning reflectivity measurements on real surfaces, a thermal simulation model and a temperature profile validated against measurements.
The process now runs in the series production window with 33 sensors per chamber run. Surface reflectivity measurement has been a fixed part of process design ever since, whenever the material or cleaning step changes. That is exactly where the biggest lever on coupled-in power sits.
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