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This question is related to the LED component HL-AM-2835H489W-S1-08HL-HR3 from HONGLITRONIC. The datasheet for this part can be found here.

This component has a SMD2835 SMD package that I have not used before. Please see the footprint drawing given in the datasheet page 2.

enter image description here

The LED itself is fairly symmetrical when viewed from the top. However, the pads are not symmetrical. The only question is, where exactly should the mid point be in the PCB footprint while taking the tolerance into consideration. It seems that the mid point won't be in the gap between the two pads but rather on the right side pad.

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    \$\begingroup\$ Why do you care about the midpoint at all. It's just a point to locate the component on the PCB and the rest of the component is located relative to that point. Some components are centered around pin 1. It doesn't matter. \$\endgroup\$
    – DKNguyen
    Commented Apr 27, 2023 at 23:24
  • \$\begingroup\$ Doesn't it matter for the pick and place machine that does assembly, where the centre point is? \$\endgroup\$
    – quantum231
    Commented Apr 28, 2023 at 1:26
  • \$\begingroup\$ I didn't concern myself with it at all when I was using an assembly service. But even if you were concerned it does not explain why you care if the midpoint is over a pad. I seem to recall the PP file I generated let me choose whether I wanted to use pin 1 or center, and I think the service asked me what I was using. Had nothing to do with the footprint file creation. \$\endgroup\$
    – DKNguyen
    Commented Apr 28, 2023 at 1:40
  • \$\begingroup\$ See, it does not matter to me if the mid point is over the pad. This is first time I have seen this for LED so was confused. Another question was how to locate the exact location of the mid point. The latter has been dealt with the answer from ron simpson. \$\endgroup\$
    – quantum231
    Commented Apr 28, 2023 at 1:55
  • \$\begingroup\$ This is unrelated to the question, but it's worth mentioning: asymmetrical footprints like this are usually--though not always!--meant to provide a larger area of contact to the PCB for whichever pin is connected to the die backside, for heat dissipation. Same reason as the large power pad in the center of many TSSOP, QFP, QFN, and such packages, and the large bond area on pin 2 of a D(²,³)PAK. \$\endgroup\$
    – Hearth
    Commented Apr 28, 2023 at 15:14

1 Answer 1

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enter image description here Center of footprint. Does that help?

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  • \$\begingroup\$ SMT components are usually positioned based on the center of the outline or footprint. AFAIK, only thru-hole components are located by pin 1. I have found that, unfortunately, some SMT LEDs are not very clearly marked. \$\endgroup\$
    – PStechPaul
    Commented Apr 28, 2023 at 1:02
  • \$\begingroup\$ yes, thanks for the drawing. The question however is also that, does it matter where I put the centre point of the PCB foot print? \$\endgroup\$
    – quantum231
    Commented Apr 28, 2023 at 1:27
  • \$\begingroup\$ The center point (0:0) is where the machine will place the part. If you hand solder, it does not matter but you should follow what everyone is doing. \$\endgroup\$
    – user338146
    Commented Apr 29, 2023 at 2:52

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