HB LED Eutectic Soldering
Posted by Rich Hueners on Tue, Nov 03, 2009 @ 06:41 PM
New HB LED applications require maximum thermal transfer to achieve ever higher and higher performance requirements. With that said, Eutectic Soldering provides the user high-quality, low-risk performance.
System Setup
For the purposes of this discussion, we will use Palomar's Automated Bonding Systems as examples of necessary system setups. The user will require an automated die attach (die bonding) machine with a Pulse Heat System (to perform the heat ramp and cool down that eutectic die attach die requires). Secondly, the user will require an automated wire bonder and ball bonder (Palomar's 8000 Hybrid Wire Bonder is recommended). Third, an Epoxy Dispenser will be required for "encapsulation". Currently, the Palomar MicroElectronics lab uses GPD Global's precision dispensing system for much of their encapsulation work. It is a terrific machine and not only a beauty to watch at work, but also aesthetically and acoustically pleasing.
Die Bonding details
The user will benefit greatly from a large work area combined with great accuracy (+/- 5 micron with Pulse Heat Eutectic processing). Additionally, the flexibility of the bonder will be an important factor. Flexibility can be defined as a wide range of options (pulse heat, steady state, handlers, etc), 8 tools available on-the-fly via turret and WIP and different tooling.
Palomar's 3500 Die Bonder has a 710 square inch work area with a Pulse Heat Stage/Profiling that includes:
- Temp up to 500'C
- Temp accuracy +/- 2'C
- Fast ramp, up to 100'C (no overshoot)
What is the Pulse Heat System? Very simply, it is a system to provide a heated platform for hard solder eutectic bonding (Au/Sn, Si, Ge). It "pulses heat" which means it raises temperature of heated area via HOT BAR; and it does this following a user-defined eutectic heat profile.
Palomar's Pulse Heat System gives a better eutectic attach, for this reason - improved performance through reduction in the following error:
You can see the "overshoot" in this graph. When performing HB LED attach, this error is very likely to damage the device. Having tight control over the Pulse Heat process is imperative!! The opportunity cost of getting it right the first time and making it repeatable pays for itself many times over. You get what you pay for in this context!
Here is Palomar's Pulse Heat Profile for contrast:
As you can see there is very tight control over the process. An excellent and consistent eutectic attach is the outcome with this Pulse Heat system/process.
The Die Bond Process performed in the Palomar MicroElectronics lab use advanced LED array programming tools and process experience. Here are some examples:
The Ball Bonder details
Much like the die bonder, large work area for the ball bonder is important and necessary: it gives the user the best possible access in HB LED die array applications. Palomar's automated 8000 Ball Bonder is both a wire bonder and ball bonder (and stud bumper). It can be argued that this is the industry's most advanced hardware and software tools for yield enhancement - the "smart" bonder. This ball bonder has a dual axis bond head. It's Zl and Zr optimize delivery of force and ultrasonics, enabling repeatable ball deformation and improved shear strength and looping control.
The wire bond process achieves high speed automated ball bonds that strings LED arrays and provide excellent looping. Here are some examples:
Testing
Test is accomplished through lighting up completed assemblies! This is a quick and easy test procedure.
