Laser Bar Bonding

As opposed to single lasers, laser bars consist of several single edge-emitting lasers comprised in a silicon bar. Bundling the light results in significantly increased output power as needed in a wide range of applications.

Laser bars are high power products, applied wherever small and efficient light-emitting units are needed. They mainly serve as pumping sources for optical resonators of high power lasers. Another field of use can be found in medical appliances.

Laser bar bonding on heat sink
Cross section of bonded laser bar

What are the challenges?

Handling

Sensitive components with brittle materials and optically active areas
Delicate edges and facettes
Optics: highest magnification over the complete length of the laser bar/submount

Process

Perfect coplanarity required to ensure proper thermal management
Highest placement accuracy needed to ensure defined overhang
Solder materials are prone to oxidation, process gas integration required
Stacked mounting (lasers to submount) requires different solder materials with their appropriate profiles

Result:

Void free bonding to avoid cooling issues
Deformation of laser bar results in decreased emitting power (SMILE)
Thermal warpage shortens lifespan of the component

Deformation (SMILE) - The higher the SMILE value, the more affected is the beam quality of the optical system
Temperature distribution (HOTSPOT) - Faulty or inhomogeneous solder layers can cause local temperature fluctuations that may result in breakdown of single emitters
Warpage(STRESS) - Mechanical pressure or strain warpage may result in shortened lifespan

Error Cases

Deformation (SMILE)
the higher the SMILE value, the more affected is the beam quality of the optical system
Temperature distribution (HOTSPOT)
Faulty or inhomogeneous solder layers can cause local temperature fluctuations that may result in breakdown of single emitters
Warpage(STRESS)
mechanical pressure or strain warpage may result in shortened lifespan

The Finetech Solution

Tools & Modules

Laser bar tool

Automatic Bonding Force Module provides controlled forces and secure handling
Active and passive self-levelling tools guarantee even bond line, prevent SMILE effects
Unique fixed beam splitter, in combination with rotating placement arm, minimizes placement error
2-point-alignment of long narrow components by scanning with movable optics slide
Optical alignment with highest magnification
Process gas integration to reduce/avoid oxidation and increase quality of bonding
IPM allows comprehensive process control and reproducible processes
Full-automatic processes including substrate and component handling

Step-by-step: Complete Laser Bar Assembly Process

Pick-up laser bar from presentation
Align laser bar to sub-mount
Place and bond laser bar to sub-mount (i.e. using AuSn)
Pick-up sub-assembly
Align sub-assembly to heat sink (i.e. CS-mount)
Place and bond sub-assembly to heat sink (i.e. using Indium)
Mount N-contact sheet to top face of laser bar (z.B. InSn)

Process Gas Integration

Sophisticated support of AuSn and In joints under defined atmosphere
Employment of formic acid as process gas for shielding and reduction of oxide layers
Self-sufficient formic acid gas generation
Safe handling of fluid formic acid
Numerous standard and custom process gas integration methods with controlled injection and outlet
Automatic control of activation time and concentration for reproducible results

Integrated Process Management (IPM)

Integrated Process Management (IPM)
Principle of process gas integration
Operating software for bonding

The Integrated Process Management (IPM) is the center piece of a FINEPLACER^® system¹ - the place where it all comes together. IPM is more than just thermal management. It synchronizes the control of all process modules and their related parameters:

Controlled and precisely balanced interaction of top and bottom (pre-)heating and cooling
Control of temperature, time, force, power, energy, flow
Process-integrated camera and light control
Controlled process gas integration for reduced solder contamination, minimized surface tension effects and smooth spherical solder residues

IPM is very complex, yet easy to access. Via the GUI of the operating software, the user has perfect control of all required adjustments. Just drag 'n drop to define temperature ramps or activate process modules. All settings are represented in only one profile, making for a very intuitive work flow.

The operating software provides an ever-growing library of profiles for all kinds of processes. It also offers comprehensive data logging functions essential for statistical process control.

In combination with the system-to-system process transfer capability this is as easy as process development can get.

¹ _{FINEPLACER^® core offers co-ordinated top and bottom heating but does not support IPM}