Laser-Welded Hermetic Seal Testing

One of our mottos at Accumet is to “trust the weld – with data.” By this, we mean that our design teams take every necessary step to ensure a solid, repeatable weld, that will hold up to the most rigorous of environmental conditions. We have previously explained the importance of laser welded hermetic seals and the process by which these seals are made. In our two-part blog we presented insight on understanding the materials that are ideally suited for packages, lids, and seals, which laser technology is right for the job, and which laser welded joint types are to best to use. But how exactly do we test the seals to ensure that they are free of leaks and other imperfections that might affect quality or long-term reliability? The answer depends upon the qualifications and certifications necessary to meet with standards associated with the application.

It’s worth mentioning that certain decisions about product structure, geometry and tolerances, made during the design process, will ultimately affect the outcome of the weld. Occasionally, this can result in defects, and thus a rework at the manufacturing floor and redesign loops. This re-work process takes time, which in turn pushes back the turnaround time and can result in an understandably angry client! To remedy these costly mistakes, it is important to understand the impact of product geometry on the manufacturing process. Anticipating welding capabilities during the exploration and analysis of the design space can reduce the amount of production, rework time, and ultimate costs.

Design and manufacturability assessment methods can support successful design evaluation by making information about the capabilities and limitations of the different manufacturing methods available to our clients. With this knowledge at hand, designers are able to evaluate design alternatives given the available manufacturability criteria. Depending on the relevant criteria for a client’s unique product, Accumet can subject these seals to one or multiple tests.

For military and space (NASA) applications, for example, a helium leak test (MIL-STD-883 Test Method 1014 for hybrids/microcircuits and MIL-STD-750 Method 1071 for discrete semiconductor devices) is performed to determine the quality of the hermiticity. But depending on the product, there are a number of tests which can be used independently or in concert with one another to identify previously unknown leaks in the weld. In addition to helium leak testing, these include water leak testing and thermal shock/temperature cycling testing.

• Helium leak testing is used to find small leaks or larger leaks in bigger volumes. Helium is well suited to leak testing applications due to its small molecular size and the fact that it is inert. It is also relatively safe to use (in comparison to hydrogen, for example) and, in most instances, non-reactive with the materials within the tested part. In leak testing, the helium is used as a tracer gas, its concentration is measured before the test, and observed throughout.
• Water leak testing is even more straightforward. The part being tested is attached to a fixture and submerged in water. If bubbles are detected, the weld is deemed faulty, the lid is removed, the is device re-inspected, and the process of resealing begins.
• Thermal shock/temperature cycling exposes the product to alternating low and high air temperatures to accelerate failures caused by repeated temperature variations during normal use conditions. The transition between temperature extremes occurs very rapidly, greater than 15 °C per minute. This conforms with MIL-STD-883J method 1010.9.

Over the past 50 years, Accumet has crafted a reputation for excellence in the field of advanced materials processing and laser services. As a one-stop-shop for everything from precision lapping and polishing to laser welding and critical component assembly, we have the capabilities and the supply chain integration to make your ideas and designs reality. We are also prepared to assist you with choosing the right materials and processes to suit your project's needs. This includes selecting and developing procedures for processing a wide range of materials from stainless steel and aluminum, to ceramics, plastics, and frozen epoxies. Our dedicated team of highly-skilled manufacturing consultants will guide you through the development process. From selecting the most suitable parts and substrates, all the way through to hermetic seal and thermal shock testing, Accumet's production experts will meet or exceed even the most demanding critical delivery schedule. Our mission is to deliver a quality product on a timely basis, and with that in mind, we encourage our engineering-driven customers to roll up their sleeves with us to work through design, prototyping and long-term production repeatability challenges.