Optical design
- Wafer-level cameras require novel strategies for optical design and stray light management. Very few optical designers have WLC experience.
- Integration of actuators for autofocus, mechanical zoom or shutters is difficult or impossible.
- The lens material must be suitable for high-throughput imprint lithography, UV-curable, reflowable at 260°C, and must have long-term stability in harsh environments.
- Hybrid wafers from polymer lens material and glass substrates show issues during wafer-level integration (warping, bowing) due to thermal expansion mismatch. Glass-only solutions may have a competitive advantage.
- For chromatic correction, different lens materials (crown and flint glass types) must be available.
- Additonal material problems are introduced with antireflective coatings on polymers, apertures or baffle layers and IR cut filter.
- Optical testing of aspherical and free-form microlenses is extremely difficult.
- Wafer-level, high-throughput lens testing is mandatory to maintain high production yields.
- Opto-wafers are usually not perfectly planar. Bow, warp and double-sided optics make it especially difficult to mount a stack of 3–6 different wafers.
- Gluing and sealing for the wafer stack is not trivial in terms of reflow temperature restrictions.
- Dicing of the complete WLC stack consisting of different materials is complicated and significantly impacts yield.
- WLC technology and through-silicon via (TSV) technology is protected by numerous patents.
- The profit margins for mobile phone camera suppliers are already small. WLC manufacturers might simply not earn enough to finance the new technology ramp-up and to pay the license fees.
Thanks to R.C. for pointing me to this.
