PCB Layout -- A question of style

I believe it comes from the "convention" of always making pin 1 square and the other pins rounded... and anodes are usually made pin 1. Likewise, with polarized caps, I've seen the anodes square and the cathodes rounded, since again the anode was made pin 1. This does seem a little more consistent.

Were you taught this in school or at some company?

I did PCB layout for four companies going through school and they all did it the same way. Again, this was 40 years ago. I also remember it from a text on PCB layout that we used in school.

Jim

Squares for pin 1 on IC's and connector headers, round for the others. If I've got a polarized active or passive, like a diode or tantalum, I'll usually make the positive pad (for caps) square, and the cathode end of diodes square as well.

Sounds to me like a design hiccup.

Keep the peace(es).

--
Dr. Anton T. Squeegee, Director, Dutch Surrealist Plumbing Institute.
(Known to some as Bruce Lane, ARS KC7GR, 
kyrrin (a/t) bluefeathertech[d=o=t]calm -- www.bluefeathertech.com
"If Salvador Dali had owned a computer, would it have been equipped
with surreal ports?"

Early-on I saw it done it that way and have continued in that vein. The terminal that is marked on the part gets marked on the PCB. . ..

Since the tang on early transistors was the emitter (TO-5) it was the emitter that got marked.

Hello Jim,

On SMT that isn't done much anymore. At least I haven't seen it often. Mostly the identifier will be on the silk screen and it would be wherever the datasheet says is pin 1.

Regards, Joerg

The layout technician uses his program and only when he defines his own parts he will think about. It has become pretty meaningless as well with pick and place machines, who do not care how the pad looks. And through-hole parts are hardly used any more, seems just on the hobbyist level where it matters. Each one has his preferences, so even if you learned this once, now nobody knows about it any more. I have worked with both technologies in the 80s, making 2:1 sized layouts on those big blue grid sheets and I had a big collection of rub-on eyes and lines, but lately I have thrown all in the garbage, hadn't used it any more for ages. And I am happy about that!

--
ciao Ban
Bordighera, Italy

"RST Engineering (jw)" schreef in bericht news: snipped-for-privacy@corp.supernews.com...

the

cathode

I use square pads for:

pin 1 of an IC pin 1 of a boxheader/connector etc.

• side of polarized cap anode of a LED all pins of a TO220-78xx regulator.

For pth diodes, I use round pads for both anode/cathode.

--
Thanks, Frank.
(remove \'q\' and \'invalid\' when replying by email)

For small discrete components, arguably true, but I'd defy you to find me anyone who'd suggest that one differently shaped pad on a connector footprint or a many pin package could indicate anything other than "pin 1."

On very dense boards, much of the silkscreen is often completely obliterated due to packing components very tightly together. But I agree that silkscreens should indicate pin 1 as well.

What the hell does THAT mean?

It has become pretty meaningless as well with

I didn't ASK you about pick and place machines. There are places in this world where hand stuffing is still in vogue. Why don't you simply answer the question instead of telling us how other people do it?

And through-hole

The hell you say. Distributors are still selling equal amounts of SMD and TH parts.

Well, I used blue and red grid sheets in the '60s and still teach them as legacy methods to my college students. I also teach them how to lay out a board using tape and donuts. THEN and ONLY THEN do I introduce them to computer methods.

Now, I ask the frikkin question again (since there seems to be disagreement on both sides) what is the STANDARD convention for using square holes to indicate the lead of a component?

Jim

through-hole

now

on

more

Well said.

I agree it is, and generally always has been, a pretty useless thing to do - although I admit to having used square pads as pin identifiers in times past I did realise that it served no real purpose and was likely only to lead to confusion. As you say a square pad means nothing to SM or an auto pick and place. To hand stuffed PCB's the pad is generally on the other side - visible only with X-ray eyes. The purpose of the silk is for *exactly* the identifications previously mentioned although many seem to think the component ident. is there to make the board look 'professional'.

That's about as useful as asking them to design a 32 bit FPU using only NAND gates. Why not go back to the original method, and silk screen the etch resist on? If you REALLY wanted to teach them something useful, it would be to lay out a single sided PCB, black rub on tape or computer/ laser printer, and etch a real PCB from it. Teach them about under/ over etch, clearances, feature sizes etc.

Paul Burke

And you teach where, sir? And for how long? And how many of your students are working in the industry today?

You evidently have no clue as to how to introduce an absolutely green student with no prior knowledge of the art how it is done. Teaching button pushing on a computer is what got us to our sorry state of affairs in the industry today.

The first lesson is actually to use a resist pen on single sided copper and etch it themselves in a tray with ferric chloride. Everything else follows from that.

Jim

The principle is that it is impossible to build a cathedral on an outhouse foundation. THey will learn how many layers are necessary when they have to know that. It well may take a lifetime. Have you stopped learning?

Jim

Pad art used to serve a function in manual assembly, inspection and test/repair. As all are becoming increasingly rare, the imperative for standard practice evaporates.

The markings in the silk screen were more important in the first two functions - teckies dealing with solder-side were supposed to be able to figure out what they were looking at, regardless.

In manual assembly the longer or marked lead/end aligned with the marked receptacle/hole.

Producing designs that enhance manufacturability will become increasingly difficult, as the distance between design and mfring sites increases. This is one reason why design capability tends inevitably to follow mfring physical relocations.

The new designs you've examined may have been produced by individuals with little knowledge of or concern for mfring processes, having had no experience of them. RL

In more current designs, using higher volume assembly methods, locations of tooling holes and optical locating fiducials are probably more relevent than pad art. Copper patterns are more likely altered to improve solderability and test point access, than as visible guides for manual operations.

It's never really been 'style', unless it followed 'function'.

RL

As well as a differently shaped pad on pin 1 does.

With pick and place machines, I consider silkscreens to mainly serve the purpose of the design engineer insofar as debugging the prototype goes. :-) Thereafter, it's main purpose would be to help anyone repairing the board, although these days that often never happens (i.e., "troubleshooting" consists of swapping entire boards until a system comes back to life).

---Joel

Why not make them mine and smelt copper, roll into a foil etc? At this rate when will they learn how many layers are required to fan out 780 pin BGA?

--

    Boris Mohar

I know, but you're obnoxious, so I won't tell you.

I'm sure glad you're not *my* tracher.

John

We have a couple of semiautomatic p-n-p stations, where a computer guides an operator to pick up parts out of a carousel (or from reels) and place them. In that case, silkscreen outlines and polarization indicators are still necessary. We build things in 10's or sometimes

100's, and that's not enough to set up a full, all reel-fed, automatic p-n-p run.

The silkscreens are handy for our production test and inspection people, too. But for parts like 0603's and 0402's and such, placement of the legends, even 50 mils high, takes as much room as the parts.

John