I think it will almost entirely eliminate the issue of people installing the LEDs backwards. The PCB labels the two LED terminals as C and A, for Cathode and Anode. So, given this, I switched back to the square-anode convention a few months ago and will be using it on all designs going forward. But based on my experience, among people who do not pay attention to the silkscreen, there are more people who instinctively put the longer leg to the square pad than people who would note that it's a diode and would instinctively put the shorter leg to the square pad. People who always follow the silkscreen will always be correct regardless of which pad is which shape. And they were mostly experienced builders, these weren't their first builds. 1 Greetings: Is there a standard on which pad to make square vs. In both cases, the silkscreen was also printed showing the flat side to help with orientation, so that wasn't a factor in either configuration. TP1, TP2 and two other circular pads (that appear to be referenced TPsomething) are 'test points' and if this circuit board is a medium to high volume then it's likely that the test points make contact with test equipment during manufacture to inject (or measure) certain.
In the 5 years previous, using square-anode, not one single person ever emailed me with that issue (nor anyone in the past year who was using older boards). Probably they connect to a 'bed of nails' test equipment. Since switching to square-cathode, I have had 4-5 people who emailed me saying the LED wasn't working, and in each case they had installed the LED backwards. Also, square and flat go together, so there's the mental hook there. SMD diodes have a range of anode/cathode identifiers. The pin nearest the flat edge will be the negative, cathode pin.
PCB ANODE CATHODE LED SQUARE ROUND PAD PDF
However, the footprint in the PDF is different from that described as being suitable for a resistor. The positive pad to its left connect to the anode of the led (square pad), and it also connect to the anode (round pad) of the diode. Sometimes the leads have been trimmed, try finding the flat edge on the LED’s outer casing. 2 The LED in question is described as 0805 dimensionally. Last year when I went through and updated all my libraries, I changed the convention to square pad for cathode since as BuGG said, it's a diode and should follow that convention. One is to identify the longer leg, which should indicate the positive, anode pin. Potentially useful data for other PCB designers:įor 5 years, my Eagle library had square pad for anode - so the same as a polarized capacitor, long leg goes to square. Make sure the anode(the long leg) goes in the round solder pad and the cathode(the short leg)goes in the square solder pad.
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