I was working on a new connector design for 50 ohm impedance-matched coax connectors for Automotive Digital Satellite Radio receiving at 2.33 GHz. This application was very sensitive to electrical performance, with low insertion losses (i.e. a low impedance discontinuity, low dissipation factor, and low reflections from impedance mismatches), but was also very cost sensitive. The target electrical performance was compared with SMA connectors costing $25 each, but our target terminated cost was $1 each!
The SMA had screw machine components with PTFE Teflon insulators with dielectric constants around 2.1; gold-plated contacts and cable using foamed or expanded PTFE Teflon dielectric; a silver-plated center conductor, and dense outer braid and FEP Teflon jacket. Just the Teflon insulator was over my entire target cost! The less expensive engineering plastics usually had 3.4 to 4.5 dielectric constants which would increase my insertion loss and grow the size of the connector unacceptably to match the impedance.
My marketing was able to back off on the high-heat thermal capability requirements, to where we could use cable with the same center conductor, foamed polyethylene dielectric, cigarette wrap foil and loose braid, and polyethylene jacket. These material and construction changes provided better electrical performance at about 1/20th the cost per foot.
The connector optimization was more difficult. I created tables for a range of dielectric constant choices. This table created a sub-table at each dielectric value with a range center terminal outside diameters and outer conductor inside diameters. I then changed the color of all the corresponding characteristic impedance values in the table within +/- 2 ohms of nominal as green and +/- 5 ohms as orange printing. I could then visualize the sizes of my components for each dielectric choice down to around 1.0 for the dielectric constant of air.
This last observation kept striking me as so great electrically, and free. I came across articles in trade magazines of using ceramic discs as air/vacuum gap insulators in coax cables in space. Then it struck me (my aha moment) -- I could use cheaper nylon or polyester insulators, molded to hold the center terminals on ribs, and the effective dielectric constant was approximated as interpolated based upon volume of air at close to 1.0 and Nylon at 4.5 dielectric constant.
This further saved material volume, allowed use of much cheaper materials that could be injection molded instead of machined, and provided even better electrical performance than full density Teflon! If I targeted a slightly lower characteristic impedance, I could even tune and tweak the exact result by reducing the mold core sizes, effectively taking away air and increasing the dielectric constant. This worked like a charm. I also used deep-drawn brass outer shells at a much lower cost than diecast outer shells with an intermediate contact spring assembled.
We met our cost target, and we outperformed our competitor's connector that we estimated to have a much higher manufactured cost.
One other benefit of the "ribbed" insulator design was that it lent itself to injection molding, rather than machining. The core pin tooling in the molds became more robust than a skinny little pin. The mold builders were much happier with the tooling on the mold with this revised concept, the mold processing was much easier (larger process windows without damaging the core pins), and mold maintenance was much less frequent (cheaper).
—This entry was submitted by David T. Humphrey and edited by Rob Spiegel.
David Humphrey has a BS in mechanical engineering from the University of Delaware. He started working in the electronic connector industry right out of college, and has worked for various connector manufacturers over the past 22 years. This has included roles of manufacturing engineering, product engineering, application engineering, and design development engineering. Over the last 10 years, he has worked for Dentsply, an OEM dental equipment and supplies manufacturer, in various operations manufacturing engineering roles.
Tell us your experience in solving a knotty engineering problem. Send stories to Rob Spiegel for Sherlock Ohms.
Competition is the only way to get prices down for the consumer. In this case it was quite dramatic. The sad part is, one of your first sales will be to your competitor and they will soon have a competing tech. A sad, but true, state of affairs I have dealt with personally. Even if you patent it, it doesn't matter.
Continuing to innovate is the only way to exist in the industry.
1) Our competition was already tooled-up with a significant European investment in automation equipment locking them into their current design concept; unless, they again stepped-up to retooling the product. A 2.5 to 3.0MM $US retooling would be difficult, if not impossible for them to cost justify in this market which had far east competition eroding margins.
2) Many of the elements of how the ribs were designed were open sided features to latch the center conductor so the "air dielectric", if even recognized, would likely be viewed by competitors reverse-engineering our product as seredipity; rather than, intentional microwave-frequency electrical design optimization. Often these air pockets in the insulator were designed to be more open where center OD to outer ID was tight, which reduced the electrical impedance mismatch. But those "core-out sections" looked like convenient coring to reduce plastic use and reduce thicker walls that could increase mold warp or cooling cycle time. this air gap is not unususal in many PCB header connectors that just stabliize the pin at the PCB and where it mates to the other connector with open air between pin and outside conductor. This was just more unique to be able to mechanically stabilize the cable connector and use air gap techniques.
Product life cycles of most electronic connectors continues to shorten to where competition just missed this window, and needed to compete on the next big project. This unique center terminal latching approach, for better mechanical AND electrical performance, did have patents applied for, but that company moved away from that business market segment as not aligned with their core business and abandoned the application. That's OK, I have a number of other patents. (Did I say I also got out of that business commodity market with eroding margins.)
I also got the satisfaction of defining a very elegant design solution that got successfully commercialized for several years due to the highest electrical performance AND the lowest manufacturing cost due to the design. (As competition shifted from Europe to the Far East, our assembly was moved from mainland USA to Puerto Rico and even with burdened labor rates higher than the Far East, we were competititive with higher margins, but that's another whole story.)
I agree, James. Patents can be worked around. Even so, the cell phone legal wars indicate that many patents not only have some real strength, they also have value. These tech companies will pay billions to buy a company just for its patents. Samsung just paid a billion (it could go as high as $3 billion) for violating Apple's patents.
Yes, Obviously we were very happy with being able to meet that aggressive cost reduction target. One small, but potentially confusing, typographical error on the article. The 4th paragraph refers to $1 on the dieclectric where I was referring to the Dielectric constant of air as 1.0 (vacuum is exactly 1.00000, but air is very close) and air is of course free (unless filtered, dried, compressed, underwater, or in space).
That was my goal. Tap into that excellent high frequency dielectric constant performance for free, or as close as we could achieve and make the structure mechanically stable.
@David12345: Thanks for a great story. As your story shows, you can sometimes do more with standard, low-cost materials (and a little ingenuity) than with expensive, custom materials.
As you point out, we are constantly surrounded by a material that has a dielectric constant 50% lower than PTFE, and that costs 100% less.
The end of the article was particularily interesting to me. Any product improvement that makes the core pins bigger and easier to process is a big win for process engineers everywhere. Good job on the solution.
I enjoyed this hands-on article about the real nitty gritty of solving design and production problems. It's this sort of clever engineering that will help keep US companies competitive in the world market. Thanks.
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