Pad polarity? - Electronic Circuits Projects Diagrams Free

Rolf · 27th October 2007, 08:52 PM

Question:

Why is it when making a PCB is the square hole for a diode the cathode(negative) side but on an IC it indicates positive positive supply?
What about a photo diode?
Just need to make sure.

Hero999 · 27th October 2007, 11:12 PM

Because it makes it easier to identify the pins.

The same goes for a photodiode, it's no different than any other diode.

Aslo, the hole isn't actually square, it's the pad that's square and most people don't bother and use the same shape pad for all holes.

**3v0** · 27th October 2007, 11:26 PM

I have noticed that on ICs the square pad indicates pin 1.

Could it be that any relationship to polarity is due pin 1's assignment on parts like diodes and caps ?

Hero999 · 27th October 2007, 11:41 PM

Yes, pin one is normally positive.

**Krumlink** · 28th October 2007, 12:17 AM

On some pcbs i have designed, they have the positive pin being a square or a circle. I think it depends on the chip. I get my pcbs made at advanced circuits.

speakerguy79 · 28th October 2007, 02:08 AM

Am I weird for having a square pad for the + terminal on electrolytics?

Hero999 · 28th October 2007, 03:51 PM

No, I've seen this sort of thing used on electrolytics and any polarised component.

dknguyen · 28th October 2007, 11:42 PM

Quote:

Originally Posted by speakerguy79

Am I weird for having a square pad for the + terminal on electrolytics?

I thought that was standard?

mvs sarma · 29th October 2007, 09:34 AM

Quote:

Originally Posted by Rolf

Question:

Why is it when making a PCB is the square hole for a diode the cathode(negative) side but on an IC it indicates positive positive supply?
What about a photo diode?
Just need to make sure.

Cathode is a point where +ve voltage can come out (having entered at Anode.)

So we can't say that cathode is -ve.

Likewise, a negative voltage can enter at cathode and come out as -ve voltage at Anode.

Dean Huster · 29th October 2007, 11:56 AM

After working for Tektronix for several years, I adopted their standards of using a square pad for IC pin 1, capacitor positive and diode cathode, round pads for all the rest. When mounting resistors, I also make sure that all of them face the same direction, i.e., the tolerance band is always to the same edge of the board. Makes later reading of component values much faster and the board has a better appearance -- subtle, but still the eye does catch the difference.

Dean

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27th October 2007, 08:52 PM	(permalink)
Rolf	Pad polarity? Question: Why is it when making a PCB is the square hole for a diode the cathode(negative) side but on an IC it indicates positive positive supply? What about a photo diode? Just need to make sure.

27th October 2007, 11:12 PM	(permalink)
Hero999	Because it makes it easier to identify the pins. The same goes for a photodiode, it's no different than any other diode. Aslo, the hole isn't actually square, it's the pad that's square and most people don't bother and use the same shape pad for all holes. __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez

27th October 2007, 11:26 PM	(permalink)
3v0	I have noticed that on ICs the square pad indicates pin 1. Could it be that any relationship to polarity is due pin 1's assignment on parts like diodes and caps ?

27th October 2007, 11:41 PM	(permalink)
Hero999	Yes, pin one is normally positive. __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez

28th October 2007, 12:17 AM	(permalink)
Krumlink	On some pcbs i have designed, they have the positive pin being a square or a circle. I think it depends on the chip. I get my pcbs made at advanced circuits. __________________ MechTronics World of Warcraft is a disease Last edited by Krumlink; 28th October 2007 at 01:09 AM.

28th October 2007, 02:08 AM	(permalink)
speakerguy79	Am I weird for having a square pad for the + terminal on electrolytics?

28th October 2007, 03:51 PM	(permalink)
Hero999	No, I've seen this sort of thing used on electrolytics and any polarised component. __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez

29th October 2007, 11:56 AM	(permalink)
Dean Huster	After working for Tektronix for several years, I adopted their standards of using a square pad for IC pin 1, capacitor positive and diode cathode, round pads for all the rest. When mounting resistors, I also make sure that all of them face the same direction, i.e., the tolerance band is always to the same edge of the board. Makes later reading of component values much faster and the board has a better appearance -- subtle, but still the eye does catch the difference. Dean __________________ Dean Huster, Electronics Curmudgeon Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines). R.I.P.