I am reviewing a prototype design that someone else made. In the design, they use this part. See image.

There are made holes in the PCB for the green marked plastic pins but only exposed surface copper for the red marked (cathode anode.)

When I look at this part I think that the cathode and anode should be through hole, but in the design they are surface mount.

Which alternative is correct? Alternative 1 or alternative 2, or are they both ok options?


enter image description here enter image description here

enter image description here

  • 2
    \$\begingroup\$ Are the metal and plastic pins the same length? \$\endgroup\$
    – Finbarr
    Sep 7, 2021 at 7:40
  • 2
    \$\begingroup\$ Your title needs major rework \$\endgroup\$
    – Mitu Raj
    Sep 7, 2021 at 7:41
  • 4
    \$\begingroup\$ You should ask this question to your colleague who made the prototype. Ask how he/she thinks the display should be mounted to the PCB. That is why we have design reviews. \$\endgroup\$ Sep 7, 2021 at 7:50
  • \$\begingroup\$ Considering that the display is 3.9mm thick those pins can't be more than 3mm. If you use double-stick tape for mounting they already could be above the board. If you mount by melting plastic and soldering pins then you'd need though-hole pads. But really, at $1.43 apiece you can buy a bunch and find what works for them \$\endgroup\$
    – Maple
    Sep 7, 2021 at 7:53
  • \$\begingroup\$ Finbarr: yes they seem to be mor eor less the same length. \$\endgroup\$
    – mannen
    Sep 7, 2021 at 8:03

2 Answers 2


If the metal tabs are bent flat, do they line up with the surface mount footprint? And can they be bent flat?

  • \$\begingroup\$ the footprint adds up as it is. I just noticed the holes for the plastic are not big enough for the plastic legs to fit true the hole. so the display must be surface mounted as the design is now. question is if it should be or if it is a bad design. maybe true hole positioning of the display would be better... \$\endgroup\$
    – mannen
    Sep 7, 2021 at 15:09

Almost certainly a mistake. The conic shape of the plastic pins is a strong hint they're meant to fit in a hole. And it would be very unusual for SMD tabs to be soldered edge-on, as this would be prone to mechanical failure.

Either the part comes in through-hole and surface-mount variants and this is the wrong one, or a mistake was made while drawing the footprint.

  • \$\begingroup\$ After looking a bit closer it seems that the holes in the PCB is somewhat smaler than the plastic legs from the display. Seems to be made to position the display correctly for the display to be surface mount soldered on the two metal pins (cathode anode). so in the end it will be soldered as well as rest on the plastic legs sitting in the hole. For me it is suprising that the display is solder mounted. Seems better to true hole mount it... So maybe it will work but i feel it is not the best solution since the solder (as mentioned) will be prone to failure. \$\endgroup\$
    – mannen
    Sep 7, 2021 at 15:02
  • \$\begingroup\$ @mannen you should clarify your colleague's intent. But if I were to mount this part as you suggest I would try to find a way to glue the screen to the PCB, and relieve the solder joint from rotational forces. \$\endgroup\$
    – DamienD
    Sep 7, 2021 at 15:44

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