Author Topic: Parallel Joining of PCBs  (Read 8072 times)

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Offline wigman27Topic starter

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Parallel Joining of PCBs
« on: December 27, 2014, 08:56:42 am »
Hi All,

I am working on a small project at the moment that requires me to join to small sections of PCB to make one long section, there are 8 contacts to be made, 4 on the front and 4 on the back.

This is what I have so far but I just cannot get the solder the bridge the gap, I have filed them so they butt up and also removed the solder mask but it just still won't bridge the gap, bloody typical, if it was a 0.65mm pin pitch I can short them no problems!! ^-^

I have seen some connectors I could use but I should be able to do it like this and reduce BOM if possible.

Any ideas??

Thanks

Lee
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Offline wreeve

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Re: Parallel Joining of PCBs
« Reply #1 on: December 27, 2014, 09:52:45 am »
It's hard to see in the photo but did you design the PCB to cut through the pad at the edge? Some disabling of DRCs will be required. Also you need to manually take into account the diameter of the routing bit so the boards butt up perfectly. Then you will be able to solder across; did exactly the same for a small project like this. Put a couple on the bottom as well if you need some mechanical stability.
« Last Edit: December 27, 2014, 10:10:01 am by wreeve »
 

Offline SL4P

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Re: Parallel Joining of PCBs
« Reply #2 on: December 27, 2014, 10:46:48 am »
Solder is not generally regarded as a mechanical connection - except in rare situations where the mechanical joint is self supporting and the solder simply provides the glue.

Run a thread of tinned wire across, or something that will give you mechanical continuity as well as electrical.

We've all done the solder blob in a pinch - but it's not something you want to leave for someone else to find - it makes you look like an unskilled hobbyist - sorry.
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Offline wreeve

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Re: Parallel Joining of PCBs
« Reply #3 on: December 27, 2014, 11:16:11 am »
you can get some neat connectors which do this BTW. JST make them I think. Depends if there is budget for them. If you butt up well and the boards are mechanically connected to the same chassis I am sure you will be OK; as it's been said it's not the best solution but small boards with good mounting you could get away with it!
 

Offline wigman27Topic starter

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Re: Parallel Joining of PCBs
« Reply #4 on: December 27, 2014, 11:46:23 am »
Thanks Guys,

Yes I agree, its certainly not the best method however I am trying to make use of and empty space on the PCB and trying to do it in the most economical way possible.

It is a PCB based LED cube and held fairly securely in most directions.

I have found these http://au.element14.com/avx-interconnect/009159008061916/card-edge-connector-open-ended/dp/2320399?ref=lookahead

But at 80c each, an 8 x 8 x 8 LED cube will need 96 of them, so you can understand my hesitation. If I can't make the PCB soloution work then I may have to abandon the idea and make the uprights out of a separate PCB. :-\  :(

you can get some neat connectors which do this BTW. JST make them I think. Depends if there is budget for them. If you butt up well and the boards are mechanically connected to the same chassis I am sure you will be OK; as it's been said it's not the best solution but small boards with good mounting you could get away with it!

What were the connectors you have seen?
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Offline hamdi.tn

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Re: Parallel Joining of PCBs
« Reply #5 on: December 27, 2014, 02:57:17 pm »
i saw such thing in T8 LED tube, it should work just consider better mechanical insertion when designing the board and pad really close to the edge, the led tube i saw didn't even use this Male Female insertion form to hold the board, just a regular edge with 4 pad i think.
 

Offline Richard Crowley

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Re: Parallel Joining of PCBs
« Reply #6 on: December 27, 2014, 03:12:37 pm »
We have seen a few examples of coupling boards with "solder bridges"  For example the "trellis" button matrix boards from AdaFruit.  Note how the "pads" extend beyond the board trim (rather like card-edge fingers).  Almost certainly designed with the pads extending beyond the board outline, and "chopped off" by the board outline trim.

http://www.adafruit.com/products/1616
 

Offline Yago

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Re: Parallel Joining of PCBs
« Reply #7 on: December 27, 2014, 04:16:12 pm »
The inside corners are radiused (from machining), could file them square so the pieces mate properly like Richard said.
 

Offline IconicPCB

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Re: Parallel Joining of PCBs
« Reply #8 on: December 27, 2014, 10:32:35 pm »
consider splicng the PCBs using hollow rivets.

Rivet the joints and ONLY THEN reflow with solder.
This will give you a cheap joint of excellent mechanical strength and an excellent electrical connection.

I had used this approach to build a length of approximately 2 meter out of four pieces
 

Offline Mad ID

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Re: Parallel Joining of PCBs
« Reply #9 on: December 27, 2014, 10:46:18 pm »
Also you need to manually take into account the diameter of the routing bit so the boards butt up perfectly. Then you will be able to solder across; did exactly the same for a small project like this. Put a couple on the bottom as well if you need some mechanical stability.

Not sure about this. How can we manually take into accoung if we don't know the size of the bit? The PCB fab does calculation so your board is cut correctly even if your board line is 1mil thick.
 

Offline wigman27Topic starter

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Re: Parallel Joining of PCBs
« Reply #10 on: December 27, 2014, 10:54:11 pm »
Thanks very much for you help everyone!

consider splicng the PCBs using hollow rivets.

Rivet the joints and ONLY THEN reflow with solder.
This will give you a cheap joint of excellent mechanical strength and an excellent electrical connection.

I had used this approach to build a length of approximately 2 meter out of four pieces

Do you have any examples of what you mean? That sounds like the go.

All or the examples I have seen use a much larger pad than what I'm trying to use also.

Thanks again.

Lee
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Offline SL4P

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Re: Parallel Joining of PCBs
« Reply #11 on: December 28, 2014, 12:24:42 am »
For dimensional stability/strength (i your aplication), how about your soldered finger - OK, then slide the whole PCB length (or just the joints filled with epoxy) into clear acrylic tubes.
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Offline ovnr

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Re: Parallel Joining of PCBs
« Reply #12 on: December 28, 2014, 12:47:45 am »
Not sure about this. How can we manually take into accoung if we don't know the size of the bit? The PCB fab does calculation so your board is cut correctly even if your board line is 1mil thick.

Then just assume the board fab uses a 1mm or 2mm bit - the latter is a safer choice!

Design everything so the minimum inner radius is at least that (ie, 0.5mm or 1mm), and you can be fairly sure the board fab will keep to your board outline. If you make it with square inner corners, it's not going to work.

And no, this is not a mechanically secure method. At least add some vias in the pads to anchor them to the PCB a bit more.
 

Offline sleemanj

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Re: Parallel Joining of PCBs
« Reply #13 on: December 28, 2014, 12:50:56 am »
If the pads are 2.54mm pitch, take a 2x4 male header, insert end of board A between the pins, solder, pull off the plastic from the header, insert board B, solder.
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Online langwadt

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Re: Parallel Joining of PCBs
« Reply #14 on: December 28, 2014, 01:27:49 am »
cut a pile of short pieces of tinned wire, tweezer and soldering iron
 

Offline IconicPCB

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Re: Parallel Joining of PCBs
« Reply #15 on: December 28, 2014, 03:52:40 am »
to ensure inner corners of PCB are going to clear a square mating part, sink a hole at with the center on top of the corner.
Make it a approximately a 2mm diameter hole .
This will ensure most router bits will in fact produce a corner which will be interference free as the drill clears the interfering residue.


 


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