The company where I worked used a variety of tapes for many purposes in wire and cable manufacturing. One of the uses involves wraps for mechanical and electrical purposes, as well as laminated-metal tapes commonly used for shielding. One day, we received a visit by a supplier of such tapes.
The young salesman who showed up that day was very excited about a new tape his employer was producing for cable shielding. Rather than the conventional laminated construction, this new type of tape featured an electrodeposited aluminum coating. The advantages he touted included lower cost and lighter weight.
I asked about coating thickness. According to the product information, it was very thin. I was surprised by how thin it was. I then asked, "With a clear backing, how will an operator know which side is conductive?" As a note, laminated tapes use a tinted laminating adhesive, often blue, so you can easily distinguish the back from the front. This is an important matter, since the conductive side of a tape shield must be in contact with the drain wire.
Since I couldn’t tell much of a difference by looking at it, I noted that we should easily be able to determine the answer by using an ohmmeter or other continuity-testing device. We trotted off to the lab to do a quick test. To our mutual surprise, there was no discernible conductivity on either side of the tape. The electrodeposited coating was so thin that virtually none of the metal atoms were “holding hands.” The new tape had been manufactured and launched, apparently, without anyone recognizing this problem.
This entry was submitted by Peter M. Blackford and edited by Rob Spiegel.
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jmiller, that's what surprises me--that a company manufacturing a safety device can get away with no QA procedures, or at least, not the correct ones that would have caught this. And I think your comment regarding compartmentalization of responsibilities and job functions might go a long way toward explaining how that could happen.
Mind-boggling is the right word. There's been so many of these kinds of stories in Made by Monkeys lately, I'm starting to wonder if quality control just doesn't exist in some companies anymore.
Especially since at the surface this appears to be a faulty design. It's not like the electrical side was 1/2" too short or something. It literally wasn't there.
I came up against exactly that sort of problem during an analysis of why some sensors were not sensing correctly. The product used connections to a gold alloy plating on each side of a piece of material, except that the coating was nonconductive in that areq, while on some samples it had a high resistance. I quickly developed a test fixture to check the problem, and we discovered a sixty percent yoeild in the coating process. But we did not produce any more deffective parts.
A few years ago while developing a very sophisticated proof of concept prototype of a laser projection keyboard, I had mistakenly planned for conductive adhesive tape –a tape very similar to the one described here – which was to provide an electrical interconnect signal for one of the finger sensors of the assembly. Being a mechanical engineer, I neglected to consider the high resistance of the conductive adhesive, and the entire design concept was jeopardized because of my lack of experience.I had **assumed** that conductive adhesive would be conductive – and did not consider insufficient conductivity.
The tape was manufactured using Φ.002" conductive spheres potted and floating within a .0015" thick adhesive layer.Surely that would work.But it did not. There was nowhere near enough metal content floating in the adhesive, and the (poor conductivity / high resistance) rendered my entire design concept back to the drawing board.But the experience taught me much about laminates and conductive tapes.
Fast-forward now to is article, and read again, what the Salesman brought in: he said he had a new electrical shielding tape.From the content of the story, his company didn't make any claims about conductivity.
Point being, it really is the design engineers' responsibility to understand completely the characterization of all the elements going into a design.I wouldn't spend too much time slamming the quality of the tape manufacturer.If a component is not suitable for your design, MOVE ON, and find one that is.
We like to make fun of engineers, scientists and their quality departments. However, this could be a case of your young sales person not understanding a new product and trying to sell into the wrong application. Shielded cable needs to have a. Conductive sheath around the signal carrying cable. However, other products exist that are absorbing (not shielding) that can attenuate outside signals. Absorbers are isolated metal (iron or ferrite) particles imbedded in a matrix that is wrapped around the area or cable to be protected or even the area emitting the undesirable frequency.
This might be a case of "sold by monkeys" instraead of "Made by Monkeys".
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