AoE x-Chapters - 1x.1 Wire-&-Connectors

Wonderful stuff.

It's impressive how hard it is to shield low frequency AC mag fields.

As far as copper foil resistance goes, I just remember, for 1 oz,

but when you ask for 1 oz you rarely get 1 oz.

The experiments on the closed box of pcb are great! (pgs 16-17)

Win, is there any reference for the x_eff = ~ sqrt(x*D). This is not at all obvious to me. It's kinda counter-intuitive that a bigger box shields B-fields better.

George H.

Sorry, Win's original post dropped off my reader.

P.15, second column, discussing Helmholtz coils:

"driven with an ac current of 2App"

I found the '2App' confusing for a bit; would '2A p-p' be clearer?

Some metric comments; many metric people don't have the gut feeling of AWGs or mils.

Fig 1x.1: at least a few metric wire sizes would be nice to get some

Table 1x.1: mm^2 is used for wires

Some mm -dimensions with mils would be nice, we use currently 0.15 mm track/space design rules.

I don't think I knew about the 1dB per wire gauge rule. That's great...

Another rule that is handy to know is that adding 3 to the gauge very closely doubles the copper area. I guess that's where the 3dB comes in handy.

Also, some terminal blocks will say that you can use it for, say, 4 gauge wire but in fact, that only works for solid wire and usually not stranded wire because of the extra space used up.

Wow, an embarrassment of riches today. ;)

One other thing about Teflon wire is that it's a royal pain to strip using dikes. Irradiated PVC can be stripped in one motion with a pair of sharp cutters.

Prepreg isn't copper coated--the plating is on the cores. The cores are pre-cured, but the prepreg flows during lamination.

It's usually best to ask the board house what width to use for a 50-ohm line. FR-4 varies fairly widely in dielectric constant, and they know what brand they're using.

PCB propagation is faster on surface levels than inside, because the effective refractive index is ~sqrt((1+epsilon)/2) = 1.68 vs sqrt(epsilon) = 2.1.

I'd really like a couple more sentences on FFC/FPC cables. We use them all over the place, and they're great. The 1-mm ones are much less likely than the 0.5s to short out if you put them in a bit crooked. The jumpers you can buy are all made by taking wire and rolling it out flat, so they can carry lots of current, but if you get them made from plated Kapton, they are the undisputed champs at getting wires on and off cold plates.

Twisted pair helps crosstalk if you're really driving and receiving differentially, i.e. the odd mode, using Ethernet transformers, for instance. The even mode couples back and forth very easily.

I didn't know about the big-box effect. Cool!

Connector catalogues are full of things that they don't actually stock but would be happy to make for you if you order 100k pieces. Always check for ample distributor stock before designing in any part, but connectors _especially_.

You're _way_ too kind to the Black Magic folks. HoJo is completely up a pole on the subject of ground currents, among many other things. He had a video (since pulled down) on an electrostatic demo purporting to show ground currents following under the traces, but ten seconds calculation showed that his impedance levels were, like, six orders of magnitude away from where inductance would make any difference. The "ground plane" was made up of metal squares affixed to one side of a piece of glass, with the traces on the other side. The twists and turns of the "ground current" were governed entirely by corona discharge from the corners of the squares in the regions of highest E field. Yet he was giving this cockamamie magnetic explanation. The SNR of the Black Magic books is no more than 3 dB IMO.

JL and I had a fun go-round here on that some years back--we were competing to see if we could sell our copies to _somebody_. ;)

Cheers

Phil Hobbs

It was 2005!

Thread starts at

The now-videoless version of HoJo's page is at .

Cheers

Phil Hobbs

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As a euro-peon I've no clue what AWG sizes are, fwiw

NT

Some comments:

For leaded, you can also use Pin in Paste and laser soldering.

Also instead of wave, you can use selective soldering, which is more controlled than a broad wave

For connectors, fretting corrosion is the real killer.

Use decent amount of gold plating, and use the same plating for both plug and socket. Otherwise it makes no sense to add gold.

Also, too much gold is not better either. Just a waste of money

For fretting, to avoid it all together, use a bleading current so that the connection is always "current" driven at at least mA level. Reduces effects of fretting corrosion dramatically

For connectors, between 2 PCBs, use a floating connection. One PCB locked, the other able to float. That way mating is secure, and thermal expansion cycles does not wear out the connection

For the ac resistances, skin effect, maybe mention dowells equation, mostly used for transformers. Just a couple of layers in a winding can increase the DC resistance 100 fold

Cheers

Klaus

All my HoJo books are gone, so I successfully unloaded them somewhere.

Pity; in one copy I highlighted the dumb parts.

I'm about to battle a customer who believes a certain uP maker's recommendations on bypass caps. There is so much nonsense around signal integrity.

Near the flat-cable cross-talk measurements, maybe add a note that using a GND-signal-GND pattern is a good method to minimize cross talk. Impedance of a 0.05" FC is then close to 100 Ohms.

In the connector section add a warning against mixing e.g. tin and gold plated connectors. Maybe mention fretting?

Regards, Arie de Muijnck

Avoid SMD connectors, they rip off the traces of the PCB

For high quality connections, use pressfit, which also removes the leaded wave solder process

For best possible connections use gat tight connections. Press fit, crimping, splicing, wire wrap

Oh, and derate the connections to 50% current. Power dissipation in connectors kill them. Use high dimension wires to the connector to pull the heat away from the connection point. About connection points, use pins that have more than just one touch point

Mitigating EMC on cables can sometimes be solved just by flipping a bit. The bit that controls the slew rate/drive strength of the microcontroller (if that controller has that function)

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On page 17 where you start talking about connectors you state:

?The most unreliable components in any electronic system will be the following (worst first): 1. Connectors and cables. 2. Switches. 3. Potentiometers and trimmers.?

My experience with arcade games and monitor (tube and LED/LCD) repairs would fit electrolytic capacitors between #2 and #3. Or possibly even as

#2...

Is that not your experience too when repairing defective equipment?

Thanks for proving a draft to read, it is informative and I enjoy your style of humour, which makes for a more readable manual.

John :-#)#

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the

Experience from pump industry, electrolytics are number 1 field failure fai lure item, when mechanics is omitted

Robotic soldering is now available from some of the pcb assembly companies in the UK and no doubt elsewhere. It is mostly used where a few through- hole parts are needed on an otherwise surface mount board. For example Newbury Electronics offer this.

John

The mix of units is amusing, and we older Brits can mostly cope, but what of the rest of the world?

Cheers

Huh, Phil, I've been meaning to ask this for a while... but it seems to me you need a good pair of dikes, with sharp holes for each wire size. I've got these "paladin" strippers.. but I think someone bought them out. Can I send you some good strippers for your Birthday? :^)

George H. Irradiated PVC can be stripped in one motion with a pair