By Dr. Phil Garrou, Contributing Editor
Continuing our look at SEMICON Taiwan 2017, we’ll look at some of the papers dealing with laser processing for advanced packaging.
Habib Hichri examined the reliability of ultra fine line redistribution. Redistribution, developed in the 1990s to facilitate bumping or chips designed for peripheral interconnect, is now indispensable for WLCSP, fan out WLP and Embedded IC packaging.
The claim he best process is a dual damascene process flow creating the trenches and vias by laser ablation as shown below.
- Excimer laser ablation patterning does not require photosensitive materials
–allowing wider choice of dielectric materials
- Ablation patterning is performed after cure
- Significant reduction in lithography-related steps
–No photoresist application, develop or strip required
YE Yeh of ASE described their “Laser Technologies In Advanced Packaging and SiP Process” They offered the following use of lasers for their advanced packaging technologies.
Trumpf Lasers GmbH
Michael Lang of Trumpf Lasers discussed Laser application development for advanced packaging.
Ultra short pulse lasers enable extremely precise, cold ablation of different materials as shown below in the comparison of ns and ps lasers. Typical materials used in Advanced Packaging can be machined without heat-affected zone.
Nimrod Bar-Yaakov of Orbotech discussed laser via formation for Advanced Packaging.
They offered the following as key advantages of laser drilling for Advanced Packaging applications:
- Cost and process reduction: Direct material ablation saves photo-litho processes
- “Digital Patterning”: adjusts the drilling pattern according to the actual location of the die
- Same tool and process suites various substrate compositions
- Laser processing tools are panel format ready
They offered the following process flow for PoP laser ablation of TMV:
- Die placement and process variation can cause misalignment between fiducials and pattern
- Using actual pads pattern as registration targets can overcome this issue
They offered further visual evidence that thermal effects are reduced by using short pulsed lasers.
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