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Semi-unrelated question: On circuit boards of that era (roughly 1980 to

1990, plus or minus a little), I have noticed that the wider traces tend to have "wrinkles" in the foil. In the photo of the bottom of the motherboard, the power buses that run to about the middle of each card slot are showing the wrinkling, as well as a few of the wider traces that connect card slots A11-A13. On other boards, with even wider traces (0.25" or more), the "wrinkles" develop into a "snake" that zig- zags back and forth down the whole length of the trace. Was that done on purpose - if so, for what? Or was it a limitation of the board / etching technology, or...?

I have seen newer boards (usually power supplies) where some of the traces are deliberately not solder masked, so the whole trace gets plated with solder. Sometimes that is also done to the "heat sink" trace area for a high-power surface-mount component. Every once in a while I also see a spot where the trace wasn't up to the job, and they didn't want to spin the board, so there is a piece of wire soldered on top of the trace. But what I see on the older boards seems to be different than these; the wrinkles are *under* the solder resist. For a while I thought maybe there was a bus wire placed on the fiberglass (or whatever) before the copper went on, but now I don't like that idea as much.

Call the most negative side ground and run a wire from the most positive side into the station monitoring/alarm hardware. When you stop getting a couple of volts on that wire, you know the dish fell off.

Matt Roberds

Reply to
mroberds
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I think they used to tin the boards to use as etch resist, so the wrinkles are the tin on the tracks under the solder mask

-Lasse

Reply to
Lasse Langwadt Christensen

I think you mean this photo: The wrinkles are solder plated traces that have reflowed in the wave solder machine. Exposed copper is unacceptable because of the marine corrosion problem. Solder mask is insufficient protection, so all the traces are solder plated or solder coated. A motherboard this big picks up quite a bit of heat during wave soldering, which reflows the solder plate, which flows under the solder mask, and produces the ugly wrinkles in the photo. If left in the wave too long, it also sucks in additional solder from the pads. I can make the wrinkles less pronounced if I run the PCB through the wave solder machine faster, but then the multitude of connector pins are not properly soldered and need secondary touchup.

Yep. I did that for high current traces, where I wanted as low a trace resistance as possible. The problem is that the thickness is not controlled. With too thin a PCB, it can also cause the PCB to warp. Much as I detest secondary soldering operations, it's a necessary evil to clean up the mess left by such solder encrusted traces.

I've seen that on imported PC power supply products, where trace resistance might be a problem worth solving. More commonly, I've seen PC ATX power supplies with huge amounts of solder as if they were hand dip soldered, instead of wave soldered. Considering the low cost of such labor, it's probably a good alternative to automated methods.

Yep. Solder plated traces on the PCB using wave soldering. The solder wave heats the pads, and the solder flows under the solder mask. The quality and thickness of solder masks have improved substantially over the years.

Nope. That would be very difficult to produce.

Nope. We just look for the satellite audio feed to change and we know that the dish has sunk a few more mm into the lagoon (swamp). On the replacement dish, I have the electrolysis nightmare drastically reduced by insulating everything that might cause a problem with fiberglass shoulder washers. For example, the LNB feed struts are stainless steel, which is insulated from the aluminum scalar ring on the LNB.

Incidentally, the station has two AM BCB transmitters on site. Sometimes, the corrosion turns into a diode which rectifies the RF. I've never bothered to check the voltage across these rectifiers, but I have heard voices coming from the aluminum dishes, which indicates that it's time to tighten the rusted bolts.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558
Reply to
Jeff Liebermann

Back then, the mask layer was not as taut. During a through hole wave solder process, the hot molten solder can be hydraulically forced down a trace as it passes over the rolling solder fall.

Still see it on power supply boards with thu hole parts and heavy traces.

A lot of SMD these days means not many wave solder runs going on any more.

And I do not know if lead free wave soldering even happens at all.

Reply to
DecadentLinuxUserNumeroUno

Quite possibly the one scenario where hearing disembodied voices is a good thing.

Reply to
Ralph Barone

Yes.

Okay... makes sense. I didn't know that things could be done in that order (plating all the traces, then applying resist). I always thought the resist went right over the bare copper.

I think that's where I saw it, too. It's not common, in my experience.

What do you do when you hear voices when you're *not* at that station?

Matt Roberds

Reply to
mroberds

"Conductivity water" has a very low conductivity. If it's open to the atmosphere for more than few minutes it absorbs CO2, which hydrates to carbonic acid (H2CO3) producing enough ions to push the conductivity up to a couple of microSiemens/cm.

Tap water is closer to 300 microSiemens/cm so distilled water is about one hundred times less conductive than tap water, if still an order of magnitude or two more conductive than "conductivity water".

--
Bill Sloman, Sydney
Reply to
Bill Sloman

Ultrapure water as used in semiconductor processing is 18.2 megohm-cm at room temperature. I used to have an "18-meg water" tap in my lab sink at IBM.

Cheers

Phil Hobbs

Reply to
Phil Hobbs

What kind of plumbing is required for that? I would think that most materials would tend to leach into the water. On the other hand, if the water really is pH 7.000000, maybe it doesn't bother the pipes much.

Matt Roberds

Reply to
mroberds

It was all Kel-F, I think, or maybe a special grade of stainless steel.

It was great for cleaning optics with. ;)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net
Reply to
Phil Hobbs

Deionized water is also used as a cooling medium in big HVDC stations, There are hundreds of kilovolts (AC/DC) between the switch stack, all living in the same water circulation.

Reply to
upsidedown

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