Etched foil technology

Limitations—Practical Rule of Thumb. It is useful to have a practical limit to express an understanding of where the technologies may limit performance. In the case of etched linewidth, it has been expressed that the total of the resist thickness pins the etched foil thickness wonld limit the gap between the etched features. Therefore, for 1.2-mil dry-film resist over 1-oz copper foil, the total thickness is 2.6 mil. This conld be nsed as a practical limit for both the trace and gap. Further limits can be determined by the nndercnt and etch factor experienced for the same type of etched featnres. Therefore, nsing the R/B = 1 data from Table 34.2 (17= 0.525 mil), a 2.6-mil resist line wonld be 2.6 mil at the trace bottom and would have a 1.5-mil etched top reduction, leaving only a 1.1-mil top snrface. It mnst then be determined if these dimensions (with allowance for variations) are snfficient for the design functionality. 

Institute of Technology (Reese et al., 2003). Using optical lithography to etch away photolithographic resists on stainless steel foils, french pens were designed with a rectangular geometry of 6 p in depfh, 30 p in width with 30 p sidewalls at the tips. To add structural support, the features anterior to the tip were expanded out so that the width of the sidewalls increased to 120 p with a trench width set at 90 p. 

The whole process consists of a sequence of consecutive steps which allows separation into production modules. Some of them already exist and will just need slight modifications. Others have to be developed. At the very beginning, one makes use of the newly developed reel-to-reel etching technology for micro structured stainless-steel foils similar to the process described in [166], The structured foils are then coated with catalyst, structured again with a laser tool and finally folded by sheet metal forming to a reactor monolith. The readily mass-produced reactors will be sealed by laser welding. 

EMM can be applied to either Al films, typically deposited on SiCVSi substrates, or Al foils. The dimensions of metallic features are determined by the same rules the etch factor, the depth of porous-type anodization, the mask design, and process conditions. In addition to the fabrication of metallic microstructures, EMM can be used to produce microstructured ceramic substrates composed of porous AI2O3. For the fabrication of both types of 3D microstructures by localized porous-type anodization, the following technological problems have to be addressed the reliability of a mask material, the fidelity of the mask transfer, volumetric expansion of porous AI2O3 during anodization, and the effect of the mask design on the rate of porous-type anodization and on the completion of anodization of the entire thickness of Al without traces of Al islands. 

On one side the development is based on thin film and micro-patterning technologies. Wafer level and foil processes used to produce high density interconnect electronic modules, and wafer level packaging was adapted to micro fuel cell development to achieve the required miniaturisation and cost reduction. By using reactive ion etching, high aspect ratio capillary structures of the anode and cathode side flow fields were achieved. 

Foil H, Carstensen J, Christophersen M, Hasse G (2000) Parameter dependenee of pore formation in silieon within a model of local current bursts. Phys Stat Solid A 182 63-69 Kleimann P, Linnros J, Juhasz R (2001) Formation of three-dimensional microstructures by electrochemical etching of silicon. Appl Phys Lett 79 1727-1729 Kohler M (1999) Etching in microsystem technology. Wiley, Weinheim... 

DYCOstrate. A different approach to small via creation has been taken by Dyconex AG of Switzerland. After ground and power patterns are formed on the panel, and the panel is oxide-treated, polyimide-backed copper foil is laminated on the panel. Holes in the copper are formed by a chemical etching process, and the insulating polyimide material underneath the holes is removed by plasma etching. PWBs made in such a way are called DYCOstrate. In other, similar technologies, different dielectric materials are used, and they are removed by alkaUne solutions. The rest of the process is similar to that for SLC that is, holes are metallized and a thick copper deposition is made by electroless or galvanic plating, and the circuit pattern is formed by a tent-and-etch process (see Fig. 5.5). 

J.6.5.2 Resistive Foils. Other treatments can also be applied to the base foil for nse in mannfactnring inner-layer circnits with buried resistors. This technology can enable the creation of resistors on internal layers of a mnltilayer circnit, with removal of many of the resistors commonly assembled on the outside of the multilayer circuit. This can improve board reliability and free np space on the outside of the board for active components. These foils typically nse a resistive metal alloy coated onto the base foil. The laminate made with this foil can then be seqnentially imaged and etched to produce the desired circuit pattern along with resistive components. 

There are two basic etchant needs to be met. The first is traditional foil etching for print and etch, plate/tent and etch, and pattern plate and etch. Virtually all processes in the United States and Europe use constant-rate systems for alkaline ammonia or cupric chloride etchants for this purpose. The second need is developing technology for specific precision very-fine-line etching—including foil thinning and thin metallization clearout for HDI constructions and fine features. (See Sec. 34.7 for additional discussion and mention of additional chemistries that may be useful for these applications.)... 

Copper foils thinner than 5 micron will be demanded for the semi-additive process to generate 10 micron wide traces or finer since the beginning of 2000s. Two types of technologies have been developed to have ultra thin copper foils. The first one is the etch-down process used to reduce the copper thickness from standard thick RA copper foils. Through this process, foils 3-5 micron thick can be obtained from 12 micron RA copper foils.The second is the use of ultrathin foils. ED copper foils 1-5 micron thick have been commercialized with the carrier copper foils. Ultrathin copper layers have been built on the smooth surface of other copper foils with standard thickness. The carrier copper foils are removed mechanically after the lamination with the base layers. Ultra thin copper foils have been applied to adhesiveless laminates through casting or lamination processes. 

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