Pad polarity?

R

Rolf

Member

• Oct 27, 2007

• #1

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

Banned

• Oct 27, 2007

• #2

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

Coop Build Coordinator

Forum Supporter

• Oct 27, 2007

• #3

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

Banned

• Oct 27, 2007

• #4

Yes, pin one is normally positive.

 

Krumlink

New Member

• Oct 27, 2007

• #5

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.

 

Last edited: Oct 27, 2007

S

Speakerguy

Active Member

• Oct 27, 2007

• #6

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

 

Hero999

Banned

• Oct 28, 2007

• #7

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

 

dknguyen

Well-Known Member

Most Helpful Member

• Oct 28, 2007

• #8

speakerguy79 said:

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

Click to expand...

I thought that was standard?

 

mvs sarma

Well-Known Member

• Oct 29, 2007

• #9

Rolf said:

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.

Click to expand...

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.

 

D

Dean Huster

Well-Known Member

• Oct 29, 2007

• #10

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