Mira, you are quite correct. "Hole flow" is what we in the West consider to be "current". Note that once upon a time, one could quite neatly blow their automobile battery up by trying to jump start the vbehiuncle, if it were Japanese, because they thought of current as electron flow, whereas we thought of it as hole flow. Because of this discrepancy, "Plus" menat one thing on on side of the other pond, and something entirely different on the other side...
>-----Original Message----- >From: [EMAIL PROTECTED] >[mailto:[EMAIL PROTECTED] On Behalf Of Mira >Sent: Wednesday, August 03, 2005 4:23 PM >To: [EMAIL PROTECTED]; Protel EDA Discussion List >Subject: Re: [PEDA] Vias. > >It's very interesting how a simple "via/current" >question ended up with a theoretical explanation where the >current flows. >Ivan, you just killed all my basic engineering knowledge. More >than 25 years ago the theory was that the current was a flow >of the electrons but the direction of the current is >considered the opposite of this flow i.e. from + to -. >Theory might have changed, who knows. > >Now back to the "via" question. >Brad, contact your PCB manufacturer and check what is the >smallest via they feel happy with and what is the plating >thickness they guarantee. >Starting from there and knowing your layer structure and PCB >thickness you can calculate how much current >(maximum) will flow through this via. If this is enough, use >it. If this is not enough, use 2 vias or use another hole size. >You may consider using blind vias or vias in pad if the design >is too dense but this depends also if your fab can manufacture it. >The other thing (if you are allowed to do) is to optimize the >placement. Then you won't need to pass the signal from layer >to layer and this will save you room for placing the traces. > >Mira > >--- Bagotronix Tech Support ><[EMAIL PROTECTED]> wrote: > >> [EMAIL PROTECTED] wrote: >> > And you both forgot that like water in a pipe, electrons will >> migrate to > the side of the via in which the flow is occuring, >> further reducing the > effective "trace width" of the via... >> >> I can't tell if aj is joking or serious... >> >> If we are going to use analogies to describe current flow, let's at >> least use correct ones. >> >> Current flow is the movement of electric charge through a >medium. The >> medium can be either conductive or non-conductive. >> If the medium is >> conductive, then you have "conduction current", as in >current flowing >> through a wire. If the medium is non-conductive, you have >> "displacement current", as in time-varying current flowing >through the >> dielectric of a capacitor. >> >> Electric charge consists of positive or negative charges. At the >> atomic level, a positive charge is an atom that is missing >one or more >> electrons from it's electron orbitals. The negative charge >is a lone >> electron that has broken away from the orbital it was in, >and is free >> to travel. Where does it go? It goes to the next >electron-deficient >> atom it encounters. It stays for a while, then hops to the >next atom. >> This process (electron >> drift) does not happen at the speed of light, as so many believe. >> What does happen is that the electric field travels through >the medium >> at nearly the speed of light (or some significant fraction >thereof). >> The actual electrons only travel a few meters per second. >> >> Here is the analogy that works: you remember that novelty >item with 5 >> steel balls suspended in a row by threads? You pull back one of the >> steel balls, let it go, and it swings back and hits the ball next to >> it. The ball on the other end of the row swings out and then swings >> back, while the >> 3 inner balls stay stationary. The silly thing keeps doing that >> "klak-klak" thing for a long time, until air resistance eventually >> robs it of the kinetic energy. In this analogy, the 2 end balls are >> electrons, the three middle balls are the conductor, and the kinetic >> energy is the electric field. Even though the end balls >> (electrons) are moving at only a >> some fraction of a meter per second, the speed at which the kinetic >> energy (electric field) is conducted through the middle balls >> (conductor) is much faster than that. >> >> So, the electrons will not pile up on a particular region of a via. >> What you may be thinking of is "skin effect". That happens when the >> electric field of a flowing current cannot penetrate equally through >> the depth of a conductor, and flows mostly on the surface of the >> conductor. This effect becomes worse as you go higher in >frequency. >> It results in a reduction of the effective cross-sectional area of a >> conductor. >> If you want to think of >> that as electron migration to the surface of the conductor, >that is a >> valid way to think of it. Maybe that's what you had in mind. Skin >> effect does not occur at DC, and is negligible at low frequencies in >> most cases. It does become a concern in high-power switching power >> supplies and high-tension AC power transmission lines. >> >> One last item: which way does current really flow? >> >> Answer: it flows from where there are negative charges >(electrons) to >> where there are positive charges (atoms missing an electron). >> Therefore current does not really flow from + to -, as we commonly >> analyze our circuits. Current actually flows from - to +. So why >> does our stuff work? >> Because unless you are working with the actual physics of >> semiconductors and materials, it doesn't really matter which way the >> current flows, as long as you choose one direction and stick with it. >> What most of us EE's >> (myself included) use is called "convential flow", which is + to -, >> but is incorrect theoretically. Some EE's use "electron >flow", which >> is - to +, and is correct theoretically. >> >> Put that in your academic pipe and smoke it ;-) >> >> Best regards, >> Ivan Baggett >> Bagotronix Inc. >> website: www.bagotronix.com >> >> >> [EMAIL PROTECTED] wrote: >> > And you both forgot that like water in a pipe, >> electrons will migrate to >> > the side of the via in which the flow is occuring, >> further reducing the >> > effective "trace width" of the via... >> > >> > aj >> >> >> >____________________________________________________________ >> You are subscribed to the PEDA discussion forum >> >> To Post messages: >> mailto:[email protected] >> >> Unsubscribe and Other Options: >> >http://techservinc.com/mailman/listinfo/peda_techservinc.com >> >> Browse or Search Old Archives (2001-2004): >> >http://www.mail-archive.com/[email protected] >> >> Browse or Search Current Archives (2004-Current): >> http://www.mail-archive.com/[email protected] >> >> > > >__________________________________________________ >Do You Yahoo!? >Tired of spam? 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