Questions on PCB terminology

Hi there - I've been running across a lot of PCB terminology lately, and thought I should make sure I'm not completely lost here:

NSMD vs. SMD pads: NSMD means that the hole in the solder mask is larger than the copper pad, while SMD means the hole in the solder mask is smaller than the copper pad.

blind via: via that only comes out one side of the PCB buried via: via that does not come out either side of PCB

Tented via: via with soldermask covering entire hole and pad, can be done on one or both sides capped via: via that has the holes covered on the top and bottom layers with copper (so that hole is not visible) plugged via: via that is filled with some nonconductive material (what kind of material is this?) filled via: via that is filled with solder encroached via: alot like a tented via, except that the hole is not completely covered with soldermask - only the majority of the via pad is covered with soldermask

How far off the mark am I on these? Can anybody give me an idea of added cost to low quantity PCB runs of all of these via types? I am mostly interested in how they'd effect runs of 4-8 layer PCBs that I'd be purchasing in 10-50 unit quantities. Also - what is the idea behind an encroached via? Is the idea that it's easier/cheaper to do than a tented via, while being nearly as effective in keeping solder from being wicked away from a surface mount pad?

Also - does anybody know of some master list that would explain all of this terminology (and all that I'm leaving out) to me? Maybe a killer book on the subject? I got my BSEE last May but this sort of stuff was never even mentioned in my classes.

Thanks!

-Michael

Reply to
Michael
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It is something you pick up as necessary and there are alot a terms meaning the same or different things depending on location/company/technology etc. There might be some standards but only big companies can afford to buy all these. Best to speak with your PCB supplier.

I can't be much help to you list below, my experience is mostly low cost basic 4 layer.

We have always used mask pads bigger than copper and referred to this as SMD pads. From what I remember the other was unusual and called mask defined pads, it may help gasketing of the paste screen, but we never used in our big volume factories and we managed fine.

Sounds about right, never used them though.

I would not advise doing tented on one side only, this leaves a contaminant trap for the PCB maker (subsequent quality problems) and if you are using vias as test points in a through hole flow solder process, the gas expansion will blow out the solder and not leave a nice solder dome to probe into.

I generally prefer to leave vias open as they can't always reliably close them (and there is not usually a test for it), but its always a bit of a topic when we goto a new PCB maker.

Havn't heard of this, sounds a bit dodgy having unsupported copper.

Has been offered, don't know what the material is, but tends to be an expensive process, we generally avoid it.

Not much of a term, more just 2 words ;-) its what happens when you leave the vias open in a flow solder process. In the old days of lead and HASL (hot air level solder leveled) you might have gotten a few filled vias. Guess you could try intrusive solder paste (just pushing solder paste down holes in the paste printing process) to achieve it over desired vias.

Havn't heard of this term, but I think we did this in our first move into open vias, and I have tried to replicate it in each new mfr we goto (it gives the best of both worlds). Basically the mask print was a little smaller than the hole and a little mask went down the hole to leave it open to gases but generally didn't take solder (bigger vias can flood up into BGAs in flow solder processes). Some (50% maybe) mfrs I have dealt with can't do this, or refuse to do it. I often thought it was due to wet ink or film mask processes, but never really got to the bottom of it due to language barriers. The first company that did it for us was UK based and no longer makes volume boards.

Under BGAs, a mask-hole clearance can make a via-ball short more likely after a flow solder process. Enchroached vias reduce the chance of solder upflow and if it happens makes any resulting dome smaller.

Tenting or not will make no difference atall to the price, its just a case if your CAD meets their design rules or not, depending on the company speed/volume they may or may not ask you if they can modify it. Alot of these minor issues are not important in small runs, but can cause huge losses to the PCB mfr in large volumes. For instance prototyping companies generally just follow your CAD/Gerber faithfully (I think), but most CAD programs cannot make good Gerber for volume MFR, and the mfr will pay special attention to acid traps, layer clearances (eg mask-pad, mask-edge etc), etching balance etc

Plugged vias is an extra process and will add cost.

Blind and buried vias I don't know, guess it means an extra drilling process for the inside layers instead of drilling after bonding, so would add cost.

Generally in small volumes extra processes machine setup+programming will add extra cost.

No, just ask your PCB mfr.

Whats a BSEE?

-- TonyS

Reply to
Tony

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