thinner/flusher connector for SODIMM and CM3+

[zontar]

Hello,
I am designing a carrier board for the CM3+. The obvious choice is to go with the same connector that is on the Dev Board or something similar, but I was wondering if there was a way to make the resulting carrier board + CM slimmer.

For example I've seen many video/usb connector that are soldered with half of the pins on the top and half on the bottom, so the resulting connector is (if you see the board sideways) positioned with its center line aligned to the board. This one is a HDMI connector on a small breakout board for example:

IMG_6541.jpg (98.55 KiB) Viewed 792 times

My idea was to build the carrier board U shaped and find a connector that would enable the CM3+ board to be connected in such a way that it would be flush with the carrier board, fitting in the "hole" the U shaped board. It would need to be like a vertical connector, but with fingers parallel ti the connector. This way I could reduce the thickness of the overall board since I am building a wearable device.

The concept is illustrated perfectly in my detailed physical mockup (!)

IMG_6544.jpg (52.13 KiB) Viewed 792 times

IMG_6543.jpg (65.35 KiB) Viewed 792 times

Searching on Digikey has yeld me only the usual connectors or very similar, but maybe I am searching for the wrong thing.
Thanks
Z

[RattusRattus]

Don't forget SODIMM connectors have mechanical retention on the SIDE of the module, so you would need to look at that as well


/Andy

[aBUGSworstnightmare]

Might exist ... But I've never ever seen one!

DDR2 slots are available in different heights; why can't you use them? Board space will habe to be payed anyhow. Regarding board height you will have heigher components too.

[zontar]

Andy, of course i will need to find something.

aBUGSworstnightmare, hello again. Yes I can see low profile connector, but they are always (correct me if wrong) built in such a way as to have the Module on top of the board, and allowing for a bit of space between them, it's a lot of millimeters. As for other components on the board, I will have one miniDP which is sunken into the board and a microUSB. Inductors are not very high, so I think the highest compo will be the SODIMM ensemble..

https://www.digikey.de/product-detail/e ... ND/1811082

Here also the horizontal one has a total height of 9.2mm, that's almost a centimeter!

But on the other hand, if I read this correctly:

https://www.digikey.de/product-detail/e ... ND/1891239

that's just 5.2mm.. maybe this connectors are the one to go, provided they allow for the space of the bottom side compos of the Module

Thanks!

[msl]

https://www.digikey.de/product-detail/e ... ND/1891239
that's just 5.2mm.. maybe this connectors are the one to go, provided they allow for the space of the bottom side compos of the Module

5.2mm height connector leaves enough space under CM3+, so I put SD card connector there and IC. But 5.2 is not your total height, because BCM metal lid pops higher. Using CM3 instead of CM3+ can save you some space.

What’s your target height and application, that you really want to slim down everything?

[zontar]

Hello msl,
yes I see that the CM has a the BCM soc sticking a little high. To be honest i think I could work also with a CM normal but I relaly don't know.
I plan to pack in the smallest case possible

• a custom built Carrier board
• a compute module (not lite)
• a 3K or 4K mA battery pack
• a small screen (3 or 4")

the slimmer, the better, but at the moment I am some months behind the point where I will think about the enclosure. My question was just to start prototyping the alpha release PCB, maybe setting off with the right foot.

Thanks for the nice idea
Z

[msl]

Hello msl,
yes I see that the CM has a the BCM soc sticking a little high. To be honest i think I could work also with a CM normal but I relaly don't know.
I plan to pack in the smallest case possible

• a custom built Carrier board
• a compute module (not lite)
• a 3K or 4K mA battery pack
• a small screen (3 or 4")

the slimmer, the better, but at the moment I am some months behind the point where I will think about the enclosure. My question was just to start prototyping the alpha release PCB, maybe setting off with the right foot.

Thanks for the nice idea
Z

Small 3-5” screens only allow to stack battery, only from ~6” it’s possible to place battery next to CM3 in order to save 3-4mm height. Also, consider USB connectors that soldered to board cut out, but remember to have cut outs in your case, because retaining leaves pop off connector outline when inserting connector.
Case is where I stuck at the moment, because I don’t like visible layers from FDM printers. With resin printer I can’t get straight parts. They are awesome right after printing is finished, but during curing process parts bend.
There is a picture of what I got in this post: viewtopic.php?f=73&t=282060&start=25#p1717431

[zontar]

Hi msl!
thanks, I've read the thread you posted. Looks very nice and 14mm is not too thick for me.
Could you suggest the SODIMM 200 connector that you used?

I am still not sure about the screen size but I doubt it will be more than 5". What are you using? Is it something low power and high visibility under the sun, by any chance?

Thanks for sharing your picture!

AS per the case I plan on prototyping it with a 3D printer at first, but then I plan to find somewhere an industrial designer, design a proper case and have it printed professionally.

Z

[msl]

Hi msl!
thanks, I've read the thread you posted. Looks very nice and 14mm is not too thick for me.
Could you suggest the SODIMM 200 connector that you used?

I am still not sure about the screen size but I doubt it will be more than 5". What are you using? Is it something low power and high visibility under the sun, by any chance?

Thanks for sharing your picture!

AS per the case I plan on prototyping it with a 3D printer at first, but then I plan to find somewhere an industrial designer, design a proper case and have it printed professionally.

Z

Connector is TE 1473005-4. And prepare good flux and soldering iron - it’s so easy to make a solder bridges on SODIMM connectors.
Display is 5” 720p IPS display. Brightness is 400cm/m2, it’s kinda readable under sunlight, but you’d prefer to have something better if brightness is main requirement.

[zontar]

Hi msl,
Thanks for the info on connector. Actually after some years learning how to solder (and not being very good at it) I've discovered that assembly in China is cheaper and more precise than what I can achieve. Time is a little bit longer i know, but the result is way better. So unless they are very simple soldering I prefer printing and assembly.

As per the display yes, brightness and readability under direct sunlight is a must. At the moment I use Ortustech, and they are pretty good. Once I also used JDisplay ones, but they had just 8 colour and it was a little bit too "CGA"..

Thanks
Z

[msl]

I've discovered that assembly in China is cheaper and more precise than what I can achieve. Time is a little bit longer i know, but the result is way better. So unless they are very simple soldering I prefer printing and assembly.

Is there particular company you’re going to use? Company-that-every-blogger-is-talking-about don’t solder any connectors

[Imperf3kt]

I've got an RC transmitter that has its chips embedded in the middle of the PCB, maybe you could find something similar for a sodimm socket?
No idea what term to search, unfortunately, but they really make circuit boards much thinner than they'd otherwise be.

If you're having trouble visualising that, imagine drilling a hole in the PCB, putting the microchips in said holez then soldering the wires to the sides of the hole.

[msl]

I've got an RC transmitter that has its chips embedded in the middle of the PCB, maybe you could find something similar for a sodimm socket?
No idea what term to search, unfortunately, but they really make circuit boards much thinner than they'd otherwise be.

If you're having trouble visualising that, imagine drilling a hole in the PCB, putting the microchips in said holez then soldering the wires to the sides of the hole.

I was obsessed by “slimmest Pi I the world” idea a month ago and concluded that there can be two options similar to what you mentioned:
- place CM3 and carrier board edge to edge (edge to edge in carrier cut out, ie carrier should extend to mechanically support CM3) and stitch/solder them with wires... 200 wires
Or
- same as above, but use two flex PCB instead of 200 wires for top and bottom contacts

[zontar]

Hi msl,

I usePCBWay, they are pretty decent and can solder also something with tiny connectors.
I suspect once they made a bridge over a very small form factor SOT-6 chip, but since I don't have a microscope I cannot be sure.
Their customer care is pretty efficient even though sometimes writing with them is a bit frustrating due to language incomprehensions.. but overall I think they are more than ok.

For the prices, you can have a quote in a few minutes if you have fabrication files. And for assembly the price is 30$ per assemblage under 5 units (independent of number of units) plus component cost.

Z

PS what is the company everyone is talking about?

[zontar]

Imperf3kt hello,

well yes. I can imagine it, but talking about a Compute Module.. i wanted a socket that enables mating the PCB and the Compute module horizontally at the same level.. me neither I don't know the term to search for.
Thanks,
Z

[msl]

PS what is the company everyone is talking about?

JLCPCB. They seem to give you nice price as long as you’re using only basic stock parts. And no connectors at all.

[zontar]

Hi,
I understand.
at PCBWay they do plenty of connectors (even fine pitched like the camera socket and with fine THP pins as the miniDisplayport at bottom) and pretty small compos with very close spaced pins (see unsoldered U2 on bigger board, which I suspected had a brigde).
They can do also electrical testing.
I am not endorsing them in any way apart from the fact that I am using them with more than enough satisfaction.

Chunky solder bridges are mine while trying to amend some "minor" design errors

This is my modified camera board, 27mm x 27mm

IMG_6562.jpg (74.79 KiB) Viewed 420 times

IMG_6563.jpg (89.68 KiB) Viewed 420 times

and this is some components tests on a bigger board (around 115 x 85 mm )

IMG_6564.jpg (76.9 KiB) Viewed 420 times

In the past I've also used LocoPCB but this is better IMHO.
Bye!
Z

[msl]

Hi,
I understand.
at PCBWay they do plenty of connectors (even fine pitched like the camera socket and with fine THP pins as the miniDisplayport at bottom) and pretty small compos with very close spaced pins (see unsoldered U2 on bigger board, which I suspected had a brigde).
They can do also electrical testing.
I am not endorsing them in any way apart from the fact that I am using them with more than enough satisfaction.
Bye!
Z

Thanks for sharing your experience. Hope to try one of PCBA services soon and not to exceed 150€ customs limit...

[zontar]

msl,
regarding customs, twice I've payed around 70 € for custom clearing (custom fees?) to DHL.
Then I've asked the support at PCBWay to declare the true value of the good, that is a few bucks for the PCB and a few for the components, or even less.. truth is apart from manual work and surcharge, the overall value of the final product is very low..

Result: last shipment: was declared as being worth less than a dozen €, so no custom fees whatsoever.

Z