2
\$\begingroup\$

I got a board for which I need several indicator LEDs and I cant decide on the best solution for the mechanical design of these.

The board and the casing currently have a gap of 15mm to each other. enter image description here

So far I came up with the following ideas to get the indicator LED's out of the case. enter image description here

a) solder the LED in through holes and bend it 90deg
b) put pad like for a SMD LED to the top and solder the LED flat to these
c) put a pad to the top and the bottom of the PCB (1.6mm PCB fits exactly to a standard 3mm LED)
d) SMD LED with light pipe
e) extend (unnecessarily) the whole PCB 15mm and use a 90deg SMD LED

So here are my questions:

  1. Did I forget any viable (or even better) solution?
  2. I want to make about 1000 of these. Is there a major difference in the assembly cost (I guess for example that b should be quit a struggle to solder in the right position)?
  3. What would be best practice in this case?
  4. For the 3 through hole LED solution - what is the best practice to cover / isolate the long free LED legs from each other or is this unnecessary?
\$\endgroup\$
  • \$\begingroup\$ C seems like it would double the assembly cost or time, hand soldered on both sides of the pcb. \$\endgroup\$ – Passerby Oct 31 '16 at 13:10
  • \$\begingroup\$ I think you left out "90deg SMT LED + light pipe", which I've used before successfully. \$\endgroup\$ – pjc50 Oct 31 '16 at 14:39
3
\$\begingroup\$

I would consider A acceptable- B and C are prone to failure by lifting pads if something presses on the LED. Only though if the LED is at a safe voltage relative to ground, because the LED insulation may not be adequate or it may break.

D. SMT LED plus a clear plastic light pipe is good in several ways. It removes the LED mechanically and electrically from the panel, and the LED can be assembled by machine with the rest of the PCB. There are many different types- the below photo is from Digikey. You can get multiples too, stacked if you like, that use less PCB area.

enter image description here

Extending the PCB E. is not a bad solution either. A small lens in the panel can be used. PCB area is pretty cheap compared to hand labor and you may be able to use the 'unnecessary' area to other advantage.

There are right-angle through-hole LED holders that could be applied to the extended PCB scenario, eg. Dialight type (below again from Digikey). Some are not prohibitively expensive.

enter image description here

I'm not a huge fan of these things- they seem to put crummy LEDs in them and they have the other disadvantages of non-insulated LEDs plus they cost some money. There are SMT versions too.

\$\endgroup\$
  • 1
    \$\begingroup\$ I often make my own custom light pipes when prototyping using hot-melt glue and plastic formers (sometimes with reflective tape too). It works quite well, and the diffuse nature of the glue gives the panel indicator a nice glow effect instead of the harsh point you get with a normal light pipe. Not something you'd want to do for 1000 units though ;) \$\endgroup\$ – Majenko Oct 31 '16 at 15:02
  • \$\begingroup\$ @Majenko I think auto-dispensed water-clear epoxy could be used for flat lenses in a panel, even in consumer quantities. Of course, injection molded acrylic light pipes might be preferable but the epoxy can create a seal. \$\endgroup\$ – Spehro Pefhany Oct 31 '16 at 15:27
  • \$\begingroup\$ I probably could, yes - especially if you included mouldings in the panel design to contain it nicely. \$\endgroup\$ – Majenko Oct 31 '16 at 15:28

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.