Chip Scale Review - January February 2020

32 Chip Scale Review January • February • 2020 [] As such, the size tolerance equals the positional tolerance values. The lowest roughness value obtained by LIDE is approximately Ra ≈ 0.5µm. Although the bottom surface of the pockets created by LIDE does not meet optical standard requirements, most capping applications do not require such a low roughness. Cavity depth shows a standard deviation of 3.9µm and is therefore significantly larger than the other tolerances. The reason for this is suspected to be insufficient control of the mechanically-guided laser head relative to the substrate. Further investigations will show whether and to what extent better cavity depth tolerance can be achieved. Cost cont r ibut ions. To evaluate a new manufact u r i ng process, it is essential to consider its cost and, in particular, to understand its influencing factors. Even though LIDE is a very fast manufacturing process, it remains a direct writing technology. The pulse pitch is the main contributor to the overall cost. Fortunately, there is a tradeoff between an acceptable bottom surface roughness and a manufacturing cost to choose an optimal pulse pitch. In addition, wet etching used in LIDE is typically a batch process and does not contribute significantly to the overall process costs. Summary Glass capping wafers with steep side walls have been achieved with the help of laser-induced deep etching (LIDE) technology. The size tolerances of the cavities, their depth value (>300µm), as well as their position tolerance, have been measured. They are within specifications to accommodate WLP packaging. The bottom pocket surface roughness is Ra ≈ 0.5µm, well within what is necessary to accommodate the dies. In conclusion, we believe that LIDE t ech nology is a good cand idat e t o manufacture closed cavities for WLP, taking into account the fact that the steep side walls achieved allow higher population densities of the die packing. References 1. R. Ostholt, “Novel method for high- volume via formation in solid–core glass for IC substrates,” Chip Scale Review , Sep/Oct 2017, Vol. 21/5. 2. R. Tummala, “Future of Embedding and Fan-Out Technologies,” Chip Scale Review , Vol. 21 (2017) 20-28. 3. R. Ostholt, “Laser-induced deep etching of glass (LIDE) and its contribution to heterogeneous integration,” Semi 3D Summit 2019, Dresden, Germany. 4. J. Thomason, “Glass fibre strength— a review with relation to composite recycling,” (2016); https://www.mdpi. com/journal/fibers 5. Z. Zhang, C.P. Wong, “Design, Process and Reliability of Wafer Level Packaging,” from the book Micro- and Opto- Electronics Materials and Structures: Physics, Mechanics, Design, Reliability, Packaging , (pp. B135 – B150), Jan 2007. Biographies Roman Ostholt is Managing Director Electronics at LPKF Laser & Electronics AG, Garbsen, Germany. He earned a Dipl.-Ing. in Mechanical Engineering and a Dr.-Ing. at RWTH Aachen U. At LPKF Laser & Electronics AG he is responsible for the development of LIDE technology, for which he received an award at Productronica 2017. He is an inventor and co-inventor of multiple patents in that field. Email or Norbert Ambrosius is Team Leader Process Engineering at LPKF Laser & Electronics AG, Garbsen, Germany. He received a Dipl.-Ing. in Mechanical Engineering at RWTH Aachen U. and started his career as a project manager in the Technology Development department at LPKF Laser & Electronics AG, where he developed the LIDE process. In his current role, he is responsible for the process and technology development of LIDE technology. He is an inventor and co-inventor of multiple patents in that field. E-Tec Interconnect AG, Mr. Pablo Rodriguez, Lengnau Switzerland Phone : +41 32 654 15 50 , E-mail: