Ask The Search Engineer

Search Engineer: I need a process to apply a low-resistance circuit to clear polycarbonate that can accept surface mounted components. —M.B. in Seattle

Dear M.B.: There are a couple of issues with producing circuits on clear polycarbonate. If your part is molded, then you'll need to metallize the part — such as electroless/electrolytic copper or dry processes like vacuum metallization and sputtering. The electroless process requires surface roughening. Vacuum metallization and sputtering provide thin films with good adhesion if you need to go through subsequent electroplating operations. The circuits can be defined by laser removal of the thin film or through printed circuit techniques. The circuit processes chosen must be compatible with the chemically sensitive polycarbonate. But attaching surface mount components may be a problem, since polycarbonate doesn't have sufficient temperature resistance to survive standard reflow soldering.

Dear Search Engineer: I have induction heat treat machines that hold the part to be heat-treated in a ceramic bushing. The ceramic bushing sits in a counterbored hole of a Garolite G-11 block and is retained with a nylon #8-32 x 3/8 inch setscrew. There are times when this setscrew actually melts in its hole. I'm searching for an inexpensive setscrew that can take the heat.—B.R. in Chicago

Dear B.R.: There are materials other than nylon I could suggest. For example, Craftech Industries (www.craftechind.com) offers headless plastic setscrews with flat, dog, half-dog, cup, cone or oval points. Drives are slotted or Allen sockets, and possible materials include PEEK, Radel R5000, Halar, and Ultem, all of which should handle higher temperatures than nylon. There's also stainless steel, polytheretherkeone (rated to 470F), or electrical grade virgin Teflon (melting point around 550F).

Dear S.E.: I am in the process of designing a plating pen, a hand-held pen similar to a felt-tip pen, used to deposit a plating solution on an object. The tip should wick the solution from the pen reservoir to the tip using capillary action. The catch is the tip is of relatively small dimension and needs to be machined to some close tolerances and unique shapes. Is there a material similar to felt that satisfies the requirements of machinability and wicking? —C.M. in Atlanta

Dear C.M.: Consider an old-fashioned fountain pen for your plating pen design. It could provide the capillary action without absorption. Modern calligraphy pens, available in stationary and office supply stores, already come in a wide variety of sizes and shapes. I would be surprised if the viscosity and other characteristics of your plating solution closely match the properties of ink but this holds true for the felt-tip concept, too. To get the performance you need, change some variables like the gap between the nibs, the length of the nibs, etc. until you get something that works. Best of all, the spring steel used to make these pens is easy to machine, should last longer than felt, and are easier to clean. Write on!

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