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OCTOBER 2020 I PCB007 MAGAZINE 83 MIT engineers have developed a robot designed to extend a chain-like appendage flexible enough to twist and turn in any necessary configuration, yet rigid enough to support heavy loads or apply torque to assemble parts in tight spaces. When the task is complete, the robot can retract the appendage and extend it again, at a different length and shape, to suit the next task. The appendage design is inspired by the way plants grow, which involves the trans- port of nutrients, in a fluidized form, up to the plant's tip. There, they are converted into solid material to produce, bit by bit, a sup- portive stem. Likewise, the robot consists of a "growing point," or gearbox, that pulls a loose chain of interlocking blocks into the box. Gears in the box then lock the chain units together and feed the chain out, unit by unit, as a rigid appendage. The researchers presented the plant-inspired "growing ro- bot" last year at the IEEE International Conference on Intelligent Robots and Systems (IROS) in Macau. They envision that grip- pers, cameras, and other sensors could be mounted onto the robot's gearbox, enabling it to meander through an aircraft's propul- sion system and tighten a loose screw or to reach into a shelf and grab a product without disturbing the organization of surrounding inventory, among other tasks. (Source: MIT) Flexible Yet Sturdy Robot Is Designed to 'Grow' Like a Plant ing process. Think of this as a surface where there are spots where there is very little, if any, roughening and where there could be areas of extreme roughness. This is not an optimum situation. In addition, failure to remove chromates and other soils effectively will lead to what we call differential etching. Essentially, this means that during the surface roughening step (after chromate and soil removal), by employing a micro-etch formulation, the roughening will be less than optimal due to incomplete chro- mate and other soil removal. This negatively impacts the adhesion of resists. Understand- ably, in those areas where organic soils and chromates remain, the micro-etchant will have compromised ability to provide a uniformly structured surface. Next Time In a future column, I will explore the rela- tionship between resist lamination parameters, developing, and etching. PCB007 Michael Carano is VP of technology and business development for RBP Chemical Technology. To read past columns or contact Carano, click here. One should understand that copper foil pro- ducers apply an anti-tarnish coating (general- ly a chromate-based conversion coating). This helps maintain that cosmetic copper color. However, as the first step in surface prepara- tion for inner layer processing, the chromate must be removed from the surface. Chromate thicknesses are somewhat non-uniform in practice. Regardless, before micro-etching the copper surface, it is highly recommended that the chromate be completely removed. This is accomplished with a mixture of strong miner- al acids. It is recommended that a formulated acidic cleaner with some solvation properties (surfactants, solvents) be used to remove or- ganic residues. Proper surface cleaning before micro-etch- ing or pumice treatment will minimize issues where the soils prevent uniform micro-rough- ening of the copper surface. My key point is chemical micro-etching, and pumice type treatments work best when the surface copper is free of organic soils and inorganic materials such as chromate coatings. The copper surface then is better able to obtain an acceptable sur- face roughness that will enhance resist adhe- sion. Failure to completely remove soils prior to pumice or chemical micro-etching will only prevent the uniformity of the surface roughen-

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