0201 SMD leds feasible project

[bask185]

A budy of mine had a question. I’m occupying myself with electronics for H0 gauge railway signal of several nations atm. Our own signal has a light speed indicator. (talking about that giant 8 )

It is essentially a 5x7 dot matrix with some dots left out.

A couple of commerial signals are in existance. These number displays can only display just one number. So my buddy wants to know if it is possible to display all of the numbers. One way or another.

A real life drawing shows that the number matrix is 800 x 460mm. So in H0 gauge that becomes 9.2x5.2mm

I looked for the smallest OLEDs on aliexpress but even the 0.42" is too big for this. So I thought that just maybe I can stuff 0201 LEDs close to eachother and see how that fits.

So I started doodeling in pcbnew and got to this. It barely fits and has 26 leds total.

I put my via’s on the smallest size for a 2 layer PCB made by JLCPCB and placed a couple of 'em. I do think that I’ll get some serious DRC issues when it comes to courtyards here

I am wondering if this ‘endeavor’ is feasible at al with JLCPCB’s SMT service that is.

My pad clearance is within JLC’s tollerances. That is good. But I think that my via’s are to close to the pads. And that JLC will complain about this for sure. But without the via’s I can’t possibly route the board.

If I change to a 4 layer PCB I do get to make smaller via’s. The distance between a pad and the via’s hole is 0.2mm. But I am not seeing a via to track clearence. The track to via hole clearence is also 0.2mm

PCB Manufacturing & Assembly Capabilities - JLCPCB

I could enlarge the design a little bit. Better have a slightly bulky signal with numbers than no numbers at all.

Penny for your thoughts?

Bas

[ML9104]

@bask185

Penny for your thoughts?

What you’re designing is a 5x7 matrix display. I’d look at it from that perspective when routing (vertical/horizontal grid, v and h on opposite sides).
Concerning placement for the best optical effect: try angling all the LEDs at 45 degrees. I think you’ll get a better “packing”.

And if JLPCB can’t mount them, someone else can.

Cheers.

[retiredfeline]

@bask185

that becomes 9.2x5.2mm

So unavoidably using ancient units for a moment, that’s 0.36 inch tall digits. That’s a standard 7 segment LED size if you don’t mind that the segments are not composed of dots. Is that heresy for those hobbyists?

[Piotr]

@bask185

Penny for your thoughts?

Never used any 0201 element but do the lighting point is in the 0201 LED center? If not than with LEDs positioned as you did it you will probably see that lines of lighting points are not strait.
I would consider doing front PCB without any electronic but with plated holes. I hope that if they were light by LED behind it you will se the whole hole lighting thank to being plated. May be LEDs should be in some distance behind and optically separated by something - may be the other PCB with bigger holes.

[kingcrediepcb]

Hi,
Whether the light is on or not?
Maybe I can help you. You can contact me.

[RaptorUK]

@bask185

If I change to a 4 layer PCB I do get to make smaller via’s. The distance between a pad and the via’s hole is 0.2mm. But I am not seeing a via to track clearence. The track to via hole clearence is also 0.2mm

What about splitting it to two stacked 0.8mm thick PCBs with holes in the top one to let the LEDs in the back one show through ? that way you have more PCB space to use for tracks/vias/etc.

[bask185]

try angling all the LEDs at 45 degrees. I think you’ll get a better “packing”.

Good idea, there is now a good spacing between the LEDs

Doing this also would solve this potential problem

do the lighting point is in the 0201 LED center?

I can put small via’s between 2 pads of the same net. So I can atleast group some anodes

But to route the rest may prove to be a difficult puzzle. For routing this dot matrix the ultimate solution would be in-pad vias. Solid vias running through the board. It seems my vendor does not have those

I would consider doing front PCB without any electronic but with plated holes.

I need to think about that. I am fan of using PCB as front ends. Silk texts are quite pritty nowadays. But PCB material is too thick to make the entire signal out of it. 0.6mm might suffice.

It could work if the signals have a square hole in which the PCB fits needless. The PCB would be a small part of the front end.

So this:

What about splitting it to two stacked 0.8mm thick PCBs with holes in the top one to let the LEDs in the back one show through ? that way you have more PCB space to use for tracks/vias/etc.

could be a viable solution. But I’d prefer to glue this pcb on to the 3D printed front end.

That’s a standard 7 segment LED size if you don’t mind that the segments are not composed of dots. Is that heresy for those hobbyists?

This is also a neat idea. It will be actual herasy for some of them. There are those who count the nails on a train…

Don’t you mean 0.20" ? I was lookin on aliexpress and found this 0.20" 7 segment
I don’t understand the measurements. It is labeled being 0.20" but it is 8mm tall and 7.2mm wide. According to Kicad the diagonal is.

This one does fit though barely:smiley:

The actual signal would be made by resin 3D printers, photo etched parts (brass) of laser cut material. What came to mind was to mount the LEDs upside down and make large enough holes for them. However 0201 is by far too small for that. That could work for the bigger lamps and 1206 leds I think .

So yeah to glue a dot matrix to this thing wouldn’t be a bad idea.

As you can see these signals are quite thin.

I also need to think about controlling the thing. With 5 columns and 7 rows an attiny 1616 would suffice I think.

Thank you for all your input so far,

Bas

[jmk]

Looking at your original effort of placement, you could get rid of at least 10 vias by routing the common all the way around the outside of the top layer. You would also collect the common of most of the centrally located LEDs, maybe only a group of three to via to the back layer. Then you have probably most of the the other to individually drop to the back.

How many and which are permanently coupled?
What LED footprint have you used?
What are the dimensions of the board?

I’m curious, and have time to play

[retiredfeline]

@bask185

It is labeled being 0.20" but it is 8mm tall and 7.2mm wide.

0.2" (5.08 mm) is the height of the digit, not the package, as you can see from its diagram.

[der.ule]

Not to deterr you from your efforts, but could the LTP-305 from Lite-On be something to consider ? The package it is a bigger than your envelope at (9.8x18.5mm) but the size of the LED matrix is only (5.08x7.62). The look very cute!

[jmk]

Biggest problem with 7 seg. displays is their depth. Seem to be mostly 6mm + PCB = 7.5mm + connector. Even thin PCB will give excessive depth.

[bask185]

How many and which are permanently coupled?

Well I have 7 rows and 5 columns. I thought to multiplex them so I don’t need 26 IO pins.

What LED footprint have you used?

EDIT: 0402 => 0201 without handsolder pads.

What are the dimensions of the board?

Undefined as of now, so I go for ‘as small as possible’ or ‘big enough’. Ideally I would like the attiny1616 in QFN-20 package also to be on the LED side (saves $ if I dont have to do double sides SMT assembly). And if the attiny has to go on the other side, so be it.

I want to have atleast 3 solder pads. 5V, GND and some data line to bit bang information to the attiny.

Biggest problem with 7 seg. displays is their depth

That 0.20" thing with castellated holes is just 3mm thick of which the PCB is 0.8mm. The outer size however is also a bottle neck. If you look how low these dot matrices are… the 7segment’s corners would stick out on the bottom + it is stil 3mm thick

If you look at the latter, a front end pcb with holes and a square cut-out hole like mentioned earlier is still on the table, JMk

Kind regards

Bas

[retiredfeline]

@bask185

There are those who count the nails on a train…

Oh well, everybody needs an obsession a hobby.

[jmk]

@retiredfeline

Oh well, everybody needs an obsession a hobby.

Yeah, some even mess around trying to place electronic components on copper plated fibre boards.

[bask185]

There is hope!! JLCPCB can manufactor plated via’s. So pads in vias can be done

[eelik]

But be aware of the price. At the moment they seem to charge extra for filled vias, and the board thickness must be >=0.8mm. PCBWay seems to do it without extra cost and with 0.6mm board and 4/4 mil track/spacing, at least if their automatic price calculation works.

[bask185]

@eelik

But be aware of the price

I am Dutch, we are ever aware of prices. It is in our nature

[davidsrsb]

This one 3.75mm deep

0900766b814a9f77.pdf

How do you solder 0201 leds, these things don’t like solder temperatures for very long and tiny packages must be worse

[bask185]

Not, you let the PCB supplier do it for you

[davidsrsb]

Given how fussy THT and 0805 SMD LEDs are about even 60/40 solder, I am surprised 0201 LEDs are even a thing.
LED III-V semiconductors don’t like heat