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Electronic Design

Bob's Mailbox


...I especially enjoyed the article in the Sept. 26, 1991 issue regarding copper clad.  One application which I would like to add to your excellent collection is that of RF stripline design.

Being an old RF Dawg working in the area of 300 to 1000 MHz, I used to buy single-sided copper-clad boards of various thickness to do stripline design.  This was accomplished with a roll of 3M copper tape and an Xacto knife with plenty of spare blades for trimming the tape once it was on the board.  When my careful calculations were done, I would lay out a board using the copper tape and experimentally determine the effects of inter-trace spacing and trace shape.  Using this technique has saved my company lots of square feet of copper clad over the years, and lots of prototype pc-board layout.

Lawrence O. Richardson, P.E., Senior development engineer, Halliburton Logging Services, Houston, Texas

Sounds neat!  And versatile for breadboarding.-RAP

Dear Bob:

That was a great article on copper-clad board.  I use it to make microwave horn antennas.  You just need a big soldering iron, a pair of shears, and a waveguide flange.

Tom Webb, Texas Instruments, Dallas, Texas

Honk if you're a horn expert!  I'm not much of an RF man myself.-RAP

Hi Bob:

...Having just finished your column on the many uses of pc boards, let me add another trick.  Find the local store that deals in materials for STAINED GLASS.  One method for joining glass panels is sticky-back copper tape, available in several widths and very solderable.  Wrap that around the corners of a pc-board box, run a bead of solder along the seams, and I bet not much will get past that boundary.

There is a certain art to soldering copper foil using a big iron (>200W).  With practice, a pool of solder is formed and the iron is lifted slightly off the foil.  Then, as the solder is drawn along the foil and solder is fed in simultaneously, a very beautiful bead forms that's as smooth as silk.  Copper-sulfide crystals dissolved in water and rubbed over the solder will return it to its copper color.  This might be useful for a "presentation" box.  Oxalic acid is the standard stained glass copper flux.

Peter Doherty, Address unavailable.

Neat ideas.  Pretty, too!-RAP

Dear Bob:

...On the top floor of a department store called Seibu Loft in Shibuys, Tokyo, they sell lots of "artsy" stuff at exorbitant prices to Japanese yuppies and yuppie-wanna-bes...  I was in Japan recently on a business trip and lo and behold, they were selling lamps and clocks that used surplus pc boards (without any components on them) for the shades and faces.  Even more amusing were the prices-some were as high as 50,000 yen for a lamp.  Why didn't I think of that?...

...While I lived in Tokyo, I found myself in desperate need of a major project to keep from going totally bonkers, so I decided to try building some electrostatic speakers.  The speakers not only sound good, but due to the voltages used (about 1200 V dc with peak ac voltages that approach 4000), they also make great bug zappers.  Needless to say, good insulators are essential.  That's where FR-4 circuit-board material comes in.  The stuff works great!  My most recent project uses FR-4 as the insulating frame, which keeps the diaphragm under tension and supports the perforated metal sheets...

...Unfortunately, I didn't realize how difficult it is to saw FR-4 until after I bought it.  What a horrible job that was!  I ended up cutting the stuff with a carbide hacksaw blade, which I modified to fit my electric scroll saw.  You may want to warn your readers about the unhealthy effects of breathing the dust generated by sawing epoxy-fiberglass board.

Mark Rehorst, Fremont, Calif.

Good info.  I prefer using heavy tin snips to sawing (or see Duncan Moyer's letter below).-RAP

Hello Bob:

What's all this penny a square inch stuff, anyhow?  Being a long-time practicing frugal engineer, I was very intrigued by your article on copper-clad innovations.  I typically have to pay 10 times your mentioned price for the stuff when I can find it.  So PLEASE Pease, give me some tips or clues or contacts on your sources.

Thanks for the great column.  It's always refreshing to observe a member of our profession in firm contact with the real world.

John K. Carter, Norman, Okla.

For approximately 36-in.-by-4-in. strips of good G-10 at 1› per square inch, call Halted Specialties Co., 3500 Ryder St., Santa Clara, CA 95051; (408) 732-1573, VISA/MC.  For virgin 3-ft.-by-4-ft. sheets of FR-4 at 3› per square inch, call Advance Electronics, 1661 Industrial Way, Belmont, CA 94002; (415) 592-4550.-RAP

Dear Mr. Pease:

...We use a small paper cutter for cutting circuit board.  There is a tendency for the board to be pulled into the blade so square cuts are difficult, but not impossible.

We also use the paper cutter to cut thin aluminum.  Cutting both these materials does not destroy the edge on the cutter and we are still able to cut paper quite well.

We obtain, for free, scrap circuit board material from our local board fabricator.  He has a good supply of material that is, for the most part, too small for his use.  He does see a return, though, because he does our board manufacture.

Larger pieces of braid (outer braid on coaxial cable) make good hinges.  Solder-wick also works well for hinges, although it's difficult to keep solder from wicking into the hinge.

Duncan Moyer, Technical services manager, Radio Systems Technology Inc., Grass Valley, Calif.

Good techniques-thanks for sharing.-RAP

Dear Mr. Pease:

...Yes, copper-clad board is very useful to me as well.  I thought I'd add one more use to the bag of tricks.  When I need to epoxy two things together, I use a 2-in. square piece of copper-clad board as an epoxy palette.  The epoxy I use has resin and hardener in separate tubes, so I squirt the stuff onto the board and mix it with a hunk of 14AWG bus wire.  Copper-clad palette is great because it's so plentiful (around here) and the surface is clean as opposed to paper products.

I suppose it would work just as well for artistic painting.

Donald J. Delzer, Electronic design engineer, Tektronix Inc., Beaverton, Ore.

That stuff sure has many uses!-RAP


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