How to mount LED in a product front panel

[VEGETA]

Hello,

kindly check the image here.



I am interested into learning how to mount LEDs on front panel like this and which part from Digikey can be used? I know he uses PCBs as front and under panel while the design PCB itself (green color) is in between..

more pics from here: https://www.axunworks.com/product-p341706.html

thanks

[ataradov]

This is just standard 3.5 mm LEDs mounted on the green board and poking though the top cover.

There is nothing like this that can be used with a single board and with an actual lens. But if you are ok with just a hole in the top panel PCB and light shining though, then you should search for  reverse-mount LEDs. Some of them are flush with the mounting surface, some will sit in the hole and may end up being flush with the panel surface.

Basically this https://dammedia.osram.info/media/img/osram-dam-2711021/s,x,760,y,0/00142087_0.jpg or this https://www.we-online.com/catalog/media/o135755v209%20Family_WL-SFRW.jpg

Although some seem to be more attractive, may be even suitable for direct use without additional lenses https://www.digikey.com/en/product-highlight/s/sunled/1206-reverse-mount-with-inner-dome-lens

[SiliconWizard]

Mounting TH LEDs like this is an annoyance in terms of production (if you have any kind of production to do, now if it's just prototypes, who cares.)

Usually easier to use SMD LEDs and light pipes to guide light to the front panel. Like this: https://www.lumex.com/lightpipe.html

[ledtester]

I've seen plastic spacers used to get the LED at exactly the correct height. Search for LED spacer/standoff or LED lamp holder.

[ataradov]

There are spacers, but then you will be running into an issue of designing your stuff around those spacers. Plus they are still annoying for mass production. Avoid if at all possible.

[VEGETA]

well, in my case the top cover PCB will be without any electric connections, just a matte black nice front panel. So I think it cannot host such reverse mounted LEDs.

I thought of spacers but these will need me to put them and solder the LEDs by hand rather that assembling them in PCB assembly factory.

Seems no option is perfect but I am ok with the result similar to picture in original post.

[AndyBeez]

What is the gap between the PCB and front panel surface?

You might be able to use 'lighthouse' PTH led: about 10mm high with a 2mm end diameter. Or for a short distance, there are press on plastic lenses for SMT leds. Google "smd 5050 led lens"

[Psi]

If you leave copper and soldermask off the PCB in an area on top and bottom you can shine light through the PCB substrate. It actually works really well and allows you to light up a pattern or shape that you can define on the PCB.
The PCB is diffuse enough that you don't get light hot spots.

You can do it with LEDs on a separate PCB, or reverse mount LEDs on the back of the main PCB.

You want to use high-intensity 20mA leds though, there's some light output loss in getting through the PCB.

The diffuse PCB also works well if you want to mix color with an RGB led.  the PLCC ones work great.

If you want to see it i can dig out my old one and make a short video of it lighting up the logo.

[VEGETA]

I prefer traditional way of either through hole LED with spacer or reverse mount smt one... but the reverse mount have to be mounted at the bottom side of the top cover PCB which needs me to run wires from main PCB to it. is there any better way?

how about just using regular through hole LED without spacer? just solder it and leave it. does it do any problem? i guess spacers are better.

as for SMT reverse mount ones, as mentioned, it will require me to have wires going from main PCB to the bottom side of the top cover PCB. has anyone done this before? assuming the product will be similar to that of the picture, it will not be inside an enclosure but rather having top and bottom cover PCB panels.

so assume I need 4 LEDs for indicating user choices... then I would need 4 power and 1 ground signal to run from main PCB to the bottom side of top panel PCB. the push button of choosing + the 4 LEDs will mostly be on the side not in the middle... so maybe I can have the wires coming from the middle of main PCB to middle of top cover PCB. then route them to the specified place on the bottom side of top PCB.

this way the wires will be hidden away from the user. but the problem is in the assembly stage since it will be kinda hard to do such short wires. I hoped for a more neat and cheap solution.

what do you think?

[Kean]

In your original photo it looks like they are using standard 3mm through hole LEDs, and I suspect they have LED spacers in place to avoid the LED getting "pushed in".  Common suppliers of these spacers are BIVAR and Essentra.

If you are making the front panel with a PCB, then it makes sense to leverage that and use reverse mount LEDs, and use appropriate length board to board SMD connectors.  You really don't want to be soldering wires between boards as that removes any assembly advantage of the reverse mount LEDs.

You need to work out the trade off between soldering some through hole LEDs vs SMD assembly of a second PCB.  Using an actively connected PCB for the front panel can certainly give you additional design options like capacitive touch buttons or better shielding.

[VEGETA]

as for reverse mount LEDs... can't I just use a ribbon cable with good enough length then after soldering either bend it to place or loctite it?

what type of connectors and cables are u suggesting?

[sokoloff]

You could also consider something like spring contacts to electrically connect the boards and using the backside of the panel PCB to have traces and hold the resistor and LED.

[Kean]

as for reverse mount LEDs... can't I just use a ribbon cable with good enough length then after soldering either bend it to place or loctite it?

what type of connectors and cables are u suggesting?

Of course you can use ribbon cable, but that would be an extra assembly task and time consuming.  Is this a one off, or a production design?

If I was designing it, I would be adding an SMD connector to the main PCB, and SMD pins to the rear of the front panel.  Obviously they need to be properly aligned just like the mounting holes.

Something like these (Harwin just as a quick example with pics, GCT, Samtec, etc are some other supplier options)
https://www.harwin.com/products/M20-7810345/
https://www.harwin.com/products/M20-8750342/

You can get different height mating connectors to suit the required distance between the PCBs.

[VEGETA]

as for reverse mount LEDs... can't I just use a ribbon cable with good enough length then after soldering either bend it to place or loctite it?

what type of connectors and cables are u suggesting?

Of course you can use ribbon cable, but that would be an extra assembly task and time consuming.  Is this a one off, or a production design?

If I was designing it, I would be adding an SMD connector to the main PCB, and SMD pins to the rear of the front panel.  Obviously they need to be properly aligned just like the mounting holes.

Something like these (Harwin just as a quick example with pics, GCT, Samtec, etc are some other supplier options)
https://www.harwin.com/products/M20-7810345/
https://www.harwin.com/products/M20-8750342/

You can get different height mating connectors to suit the required distance between the PCBs.

your suggestion is nice and can do the job for sure, not so expensive too.

however, the design will have stand-offs and can also get rubber feet. now how to match the lengths of all those?? not easy.

the design is still in, well, designing phase. but for sure going to be production one day.

[Kean]

Those example Harwin parts are 3.75mm tall for the female connector, and 9.9mm tall for the male header.
So those would suit 10mm or 11mm standoffs between the two PCBs, but versions of the male header can be found in a wide variety of lengths or even custom ordered if you have large enough requirements.

That female connector also supports top or bottom entry, so you can have holes beneath the connector and let slightly longer header pins poke through to the other side of the PCB, or even mount the female connector on the back side of the lower PCB if that suits the design requirements better.

There are heaps of other board-to-board connector choices depending on height, number of pins, and pitch/density requirements - but these types of 0.1" pitch are very common and cheap.  And most importantly they are available in a huge range of pin count and heights/lengths.

[AndyBeez]

So how and where are you having the front panel designed and manufactured?

[VEGETA]

So how and where are you having the front panel designed and manufactured?

well right now i am about to have another design (dreamcast power supply) delivered to me so I can test it and so on... once I wrap this up then I will try to dig into this design we are speaking of.

PCBs are made by PCBway, another option would be AllPCB. not going for others for price of course.

both have Matte Black PCBs so that is fine. as for the main PCB it could be just regular black or even make the bottom PCB panel the main PCB if possible. I just need to put some rubber feet if you know any good and cheap ones.

so the standoff should connect all these PCBs down to the rubber feet.

It is the first time I am doing something like this, and it is kinda not cheap to keep getting boards here due to customs and shipping.

[Jackster]

+1 for SMD LEDs with light pipes. Especially if your board is already 100% SMD. Don't want to add another process to your BOM (if this is a production run product).

That and they look nice and keep crap from getting into the housing. Easier to assemble the product too.

[VEGETA]

+1 for SMD LEDs with light pipes. Especially if your board is already 100% SMD. Don't want to add another process to your BOM (if this is a production run product).

That and they look nice and keep crap from getting into the housing. Easier to assemble the product too.

can you link to say a blue led with some 20mm light pipe? for reference. I assume they are installed by press fitting them right?



reverse leds seem nice too, but i thought of using those suggested smt board to board connectors not just for the led signals... but for mounting the PCBs together instead of standoffs.

like getting the appropriate female connectors with male pins, then put 4 of each corner plus 3 distributed in the middle for more sturdiness. anyone ever done that?

[thm_w]

I've seen plastic spacers used to get the LED at exactly the correct height. Search for LED spacer/standoff or LED lamp holder.

Tons available. I think its a viable option: https://www.lcsc.com/products/Photoelectric-Accessories_958.html
But if you don't want to hand solder a few boards, SMD option also good. Can either get board mount, or one that presses/clips into the panel (would look nicer).

https://www.aliexpress.us/item/2251832782960596.html

[Jackster]

+1 for SMD LEDs with light pipes. Especially if your board is already 100% SMD. Don't want to add another process to your BOM (if this is a production run product).

That and they look nice and keep crap from getting into the housing. Easier to assemble the product too.

can you link to say a blue led with some 20mm light pipe? for reference. I assume they are installed by press fitting them right?



reverse leds seem nice too, but i thought of using those suggested smt board to board connectors not just for the led signals... but for mounting the PCBs together instead of standoffs.

like getting the appropriate female connectors with male pins, then put 4 of each corner plus 3 distributed in the middle for more sturdiness. anyone ever done that?

I got mine from VCC.
https://vcclite.com/product-category/lightpipes/panelmountlinearlightpipes/
Digikey has them all. Sadly they are in freedom units but you should manage to find something close.
There are other brands that make them in metric.
My light pipes end up being about 1mm away from the LEDs which is ideal.

Yes they are press fit. I use hot glue on the other side though as my product gets abused. They sell little rubber things to go on the inside but I don't rate them.



As for the LEDs I used, I picked them based on stock availability at the time. Wanted a full reel so that limited my selection in 2020.
Any in the 0406-0603 range will do with 3-4mm light pipes.


Reverse LEDs can be nice but you get crap in the hole and the LED gets blocked... As someone else suggested, get the PCB host to route most the way through the FR4 and use the last layer as a defuser. If done right, it looks nice. But not very bright. Good luck with that in daylight.

[VEGETA]

sticking light pipes is another problem as well.

by reverse leds i meant those which can stick out to be flush with the board. so I can dig a hole in pcb to fit it.

[SiliconWizard]

Benefits of using SMD LEDs and light pipes, beyond making it cheaper/easier for production, is that they make it easier for waterproofing (or just dust protection), and they also avoid any direct mechanical coupling between the front panel and the PCB, which is way better in terms of long-term reliability.

One alternative of course if you still prefer TH LEDs for any reason, is to mount them on a separate PCB which will be mounted close to the panel, and connect this PCB to the main PCB via a cable. Makes it easier for production and avoids directly mechanical coupling, at least to the main PCB. A bit more expensive, although a small LED PCB would be dead cheap in any kind of quantities.

[VEGETA]

Benefits of using SMD LEDs and light pipes, beyond making it cheaper/easier for production, is that they make it easier for waterproofing (or just dust protection), and they also avoid any direct mechanical coupling between the front panel and the PCB, which is way better in terms of long-term reliability.

One alternative of course if you still prefer TH LEDs for any reason, is to mount them on a separate PCB which will be mounted close to the panel, and connect this PCB to the main PCB via a cable. Makes it easier for production and avoids directly mechanical coupling, at least to the main PCB. A bit more expensive, although a small LED PCB would be dead cheap in any kind of quantities.

ok, so light pipes are mounted on top of smt led (what size?) using pressing right?

I saw this one for example: https://www.digikey.com/en/products/detail/bivar-inc/VLP-600-R/4926905

so I need to make 3.1mm cut in the top pcb to fit this one... and on main pcb i need to do some cuts to press fit it? its 2 legs are 0.6mm of size, meaning 0.7mm holes?

how can i couple the smt led with the light pipe though? to make sure light travels good and the pressing is very firm.

and as a comparison, what kind of pricing between smt LED on main pcb + light pipe vs reverse mounted led on top pcb with smt board to board connectors? this is going to be a tough comparison i believe. i hope someone who tried them both to say his opinion and experience.

and there is this "flexible" one too: https://www.digikey.com/en/products/detail/bivar-inc/LC-1-0/3091462

but i guess the flexible one suits crammed designs where you need to route the pipe somewhere on another level, like from main pcb to a side panel.


Quick comparison for 100 boards:

Board to board connectors mentioned above + reverse LEDs = about 180$.
SMT LEDs + light pipe I mentioned = about 160$.

is this ok or am i missing something?

[ataradov]

Light pipes are mechanically mounted to the case and on the PCB side they just hover over the LED. That's the whole advantage - you do mechanical stuff separately from electrical stuff. Minor inaccuracies in LED positioning or board mount within the device won't matter.

The specific one you link has alignment pins that would need alignment holes in the PCB. This is not how this is usually done. But I guess if you are working with off the shelf components, you have to deal with whatever you can get.

And the description says "press fit", so I guess you are supposed to undersize the holes. But this does not sound interesting to me, I don't see how this is useful in any way. You will have more control with a through hole LED with a spacer. It makes more sense to me mechanically.