Advancing Implantable Medical Device Reliability with Enhanced Laser Joining Technology

Laser joining is the gold standard for assembling high-performance, Class III implantable medical devices. This technology enables production of many medical innovations, from passive devices like guidewire assemblies to sophisticated active products including cardiac rhythm modulation (CRM) devices and brain-computer interfaces (BCIs).

Medical device manufacturers must know — with certainty — that device components will maintain their integrity once deployed within a patient. Laser joining addresses this critical need by offering a non-contact, particulate-free joining method, rapidly formed high-strength bonds, and exceptional precision and controllability. Figure 1 depicts several common medical devices manufactured using laser joining.

Fig. 1 - Examples of medical devices that require laser processing to ensure robust, high-quality joints (left) and an example implantable device with key joints highlighted (right).

Why Use Laser Joining?

Laser joining offers distinct advantages over other material joining technologies. Unlike conventional welding or joining methods (e.g., metal inert gas, tungsten inert gas, etc.), which tend to generate significant particulates and often require secondary processing or cleaning, laser joining is a clean process. Additionally, when properly controlled and refined, high-strength laser joints can be generated at high speeds. When laser joining is conducted via automated equipment, these joints are highly reproducible, very precise and visually appealing. Automated laser welding processes also enable tight control of a joint’s heat affected zone (HAZ), as shown in Figure 2. Finally, laser joining presents new opportunities for joining dissimilar materials, opening up novel possibilities for device manufacturers.¹

Fig. 2 - An illustration of laser welding’s heat affected zone compared to other forms of material joining.

How Does Laser Joining Work?

Effective laser joining is done with controlled delivery of laser energy along a given path or profile. Laser joining through keyhole management is a sophisticated welding technique that uses a high-energy laser spot to create a deep, narrow weld. In this process, the laser’s intense energy rapidly melts the material, forming a narrow, deep cavity called a keyhole. This keyhole is surrounded by a molten pool of material and maintained by the delicate balance of the laser’s energy input and heat dissipation. As the laser beam moves along the joint, it continuously melts material at the keyhole’s leading edge while the molten material flows around and fills in behind it, eventually solidifying to form a strong weld (or joint) in the material.

Compared to other welding methods, the keyhole method allows for deeper penetration and increased weld strength. This makes it particularly effective for joining thicker materials or when high welding depth is required. However, precise control over power densities and welding parameters is crucial to prevent defects such as porosity or excessive spattering and ensure a high-quality, durable weld. The difference is depicted in Figure 3.

Fig. 3 - A graph illustrating a side view (top) and top view (bottom) of a representative keyhole used when creating a laser weld.

Harnessing laser joining’s full potential also hinges on precise process control executed through proper motion control of the part about the laser spot. The location and amount of thermal energy the laser applies to the materials to form a high-integrity bond is instrumental in ensuring consistent, reproducible joints with minimal heat affected zones. By pairing advanced controller features such as spatial domain laser pulse control with superior electromechanics, device manufacturers can achieve unprecedented levels of part reproducibility in their assembly processes. These control features enhance joining processes, paving the way for increasingly complex and miniaturized implantable devices — and ultimately leading to better patient outcomes and expanded treatment options.

How Are High-Quality Laser Joints Created?

A typical laser welding workstation uses a laser source and a laser scanner. Laser sources are often selected to achieve the desired laser-to-material interaction. For instance, special consideration is given to highly reflective materials like copper or aluminum. In addition, very thin or thick materials will have different application requirements. A laser source provider can help ensure that a laser is the optimal choice for a specific application because the provider can take into account the targeted weld’s attributes, including penetration depth, weld width, heat affected zone, size, and speed requirements. Once the laser source is chosen, a laser scan head can be selected.

Fig. 4 - An image of a high-performance laser scan head (left) along with an exploded diagram of its internal components and laser beam path (right).

A laser scan head is typically composed of at least two high-dynamic motors (commonly referred to as galvanometers) coupled to mirrors with optimized reflectivity to the laser source. These motors also use high-resolution digital encoders so that their angular displacement can be controlled via a servo control loop. The mirrors guide a laser beam through an F-theta lens that linearizes the angular position of the mirrors to the displacement of the beam over the lens’s field of view, as shown in Figure 4. In the context of laser welding, laser scan heads provide several advantages including:

Optimum Beam Control and Positioning. The ability to quickly and accurately steer the beam enables consistent, repeatable welds even on intricate parts. Even at high speeds, laser scan heads can be used to execute complex weld patterns or geometries over the part.
Weld Keyhole Management. Oscillating or wobble patterns like the example in Figure 5 are commonly used to control the weld keyhole width and depth. Pulsing and power modulation can also manage heat input.
Process Monitoring. Off-axis cameras or through-axis vision can also precisely point the laser spot and manage the welding process in real time.

Fig. 5 - An example of an ellipse wobble pattern used when generating a weld path.

How Are Large Welds Created?

One common drawback of laser scan heads is their field of view. To maintain precision when locating the laser spot on the part, a scan head’s field of view may be limited to tens of millimeters in x and y dimensions along the work surface. Historically, this limits the size of weldable parts. However, recent motion control advancements enable seamless control of the laser spot’s movement over a virtually unlimited field of view.

Fig. 6 - Aerotech’s Automation1 controller controls laser scan heads and servo-based stages simultaneously to execute high-performance laser welds.

Coupling control of the laser scan head and high-precision servo stages eliminates the need to move the part to reach regions that extend beyond the laser scan head’s field of view. Modern motion controllers like the one shown in Figure 6 allow for the simultaneous motion of the laser scan head and servo stages to deliver high-quality joints across very large part surfaces.

Final Thoughts

Laser joining is essential for creating reliable, high-performance implantable medical devices that enhance patient safety and device longevity. The precise control and reproducibility offered by laser joining, particularly through keyhole management, ensures strong, clean joints with minimal heat affected zones. Advanced motion controllers that control laser scan heads and servo stages are equally essential. These components enable precise beam control, weld keyhole management, and the ability to create welds on larger parts. This level of control and precision will play a key role in implantable medical devices’ continued advancement. Laser joining will enable even more complex and miniaturized devices, ultimately expanding treatment options and improving patient outcomes.