small ISP connectors - Page 1
Forum section: electronics / projects

author: Amper
author_rank: Frequent Contributor
timestamp: March 07, 2020, 05:16:35 pm
content: Hi!Im looking for a connector type i can use on small pcbs with 6-pin ISP. The board in question is 20x30mm and almost exclusively surface mount looking for the smallest "footprint" i can get. To this point the ISP connector is the single bulkiest component, which is sort of sad.A friend of mine usually uses micromatch for this purpose but they are still 5mm tall which would be alright if i cant get anything more suitable but id still like some other alternatives.Pogo pins are also a possibility but as this thing is a semi prototyping board that has to be re flashed in the field i dont like this idea here.Footprint should be small but it should also be mechanically sound enough to survive being treated sort of rough as a normal pin header would be.Open for any suggestions!

author: Fred27
author_rank: Unknown
timestamp: March 07, 2020, 05:33:48 pm
content: DoesTag Connectfit your requirements? It's basically pogo pins but with locating holes.

author: ataradov
author_rank: Super Contributor
timestamp: March 07, 2020, 05:45:06 pm
content: Tag-Connect requires a huge board area free of stuff.I really like 1.27mm pich connectors -https://www.ebay.com/itm/2-3-4-5-6-7-40P-Female-Sockets-Male-Pin-Header-1-27mm-Pitch-Connector-Double-Row/183945905661.They are small and the actual connector can be surrounded very closely by other components on the board, as long as they are not tall.

author: Amper
author_rank: Frequent Contributor
timestamp: March 07, 2020, 08:00:13 pm
content: well yes, but just having smaller pitch is not what im after. I need surface mount with compareably small print but most importannt is build height, 5mm is to much, 3mm would be ok, 2mm ideal. The connector should not purtrude above the other surface mount components as this will ruin the formfactor of a 100% surface mount board. Tag connect looks pretty much ideal, is there something with less pitch though? and smaller positioning pins? In case i can arrange it on a board, maybe i could just print a jig that will use a board edge for allignment. Thats not the exact thing im after, but at least close.Im still looking for some connector that will stay connected with no external force, maybe even snap in. It will be interesting for other problems as well where pogos will be not permanent enough or to bulky, like board stacking connectors for example.

author: ataradov
author_rank: Super Contributor
timestamp: March 07, 2020, 08:05:27 pm
content: For small connectors that would retain the cable, you need to look at FFC/FPC style connectors. They can be pretty small, but figuring out the cable part is a pain.

author: Amper
author_rank: Frequent Contributor
timestamp: March 07, 2020, 08:33:43 pm
content: Well, those are to small/ fumbly again ^^ Also not really made to be disconnected often.Basically micromatch would be ideal if it was 1.72mm pitch and not 2.54.

author: cgroen
author_rank: Unknown
timestamp: March 08, 2020, 03:20:20 pm
content: I use the tag-connect "no legs" variant on all I do. Its correct that you need 3 holes for mechanical steering, but at least you can use the space on the other side of the board where the 6 pads are. The "no legs" version has a small "clip" that you can mount on the connector on the other side of the board once the connector is inserted into the board if you need to to do "long term debugging".https://www.tag-connect.com/product/tc2030-ctx-nl-6-pin-no-legs-cable-with-10-pin-micro-connector-for-cortex-processors

author: fcb
author_rank: Super Contributor
timestamp: March 08, 2020, 03:37:13 pm
content: Quote from: cgroen on March 08, 2020, 03:20:20 pm+1 for Tag-Connect

author: cgroen
author_rank: Unknown
timestamp: March 08, 2020, 03:51:12 pm
content: Tag-connect "no leg":The 3 holes are 35 mil/0.89 mm each

author: Amper
author_rank: Frequent Contributor
timestamp: March 08, 2020, 04:31:07 pm
content: hah, right, i didnt realize you could use the back, thats a big plus.Just bought one, it seems pretty ideal to me, Thanks!

author: mariush
author_rank: Super Contributor
timestamp: March 08, 2020, 05:34:14 pm
content: Your problem made me wonder if you could have something like this:The connector could be a stack of 2-3 thin pcbs .. both sides with 3 1mm..1.27mm pins soldered flat to the circuit board.... and a middle pcb or something which could be pushed in between the two small boards so that it would push the boards onto the through hole half bits and make solid contact.Another option ... it's more expensive, but maybe you could just solder a microusb connector and be done with it? You have microusb with 5 pins (power, data and otg pin) and you could maybe use the housing as 6th wire?You'd require maybe a custom usb cable or your programmer would have to be customized to separate housing from ground. It's about 20 cents for the connector, in volume.

author: Amper
author_rank: Frequent Contributor
timestamp: March 08, 2020, 06:00:55 pm
content: Nice idea! Though some sort of spring will be necessary i think, at least if it is supposed to last for a lot of cycles.Micro usb is a nice idea but i dont really like special pinouts on standard connectors, technically i cant argue with it though.

author: cgroen
author_rank: Unknown
timestamp: March 08, 2020, 06:15:58 pm
content: Amper,use a tag connect and be done with it, no need to invent more or less practical solutions when one is readily available and tested. And NEVER use a USB connector or anything else standard for such a a thing, it will 100% sure end in disaster

author: Amper
author_rank: Frequent Contributor
timestamp: March 08, 2020, 07:37:15 pm
content: I wasnt the one suggesting new designsI think its allways a good idea to think of new ways, thats what sets you apart from all the other designers in their mental boxes. It just has to be a sound idea.

author: TomS_
author_rank: Frequent Contributor
timestamp: March 08, 2020, 08:22:51 pm
content: What about pogo pins in your own little custom programming adapter? Something where you place the board into, hold it down and program.You wouldn't even need any pads at all then as they could contact the IC legs directly (potentially), or you could put them anywhere it was convenient.

author: Amper
author_rank: Frequent Contributor
timestamp: March 09, 2020, 03:01:30 am
content: As i said in my first post, i want it to work in the field without much work, this is not for just flashing once and then selling a product, i want to change firmaware conveniently, so a cable connection with a plug would be optimal.

author: SiliconWizard
author_rank: Super Contributor
timestamp: March 09, 2020, 03:08:05 am
content: Yes, but very small SMD connectors are a nightmare reliability wise if you're going to plug/unplug more than a couple times. We had done this in the past on a very small board, this was breaking all the time - even if you're being very gentle.So yeah I also recommend a pogo-pin thing, either Tag-connect or something custom, as you prefer.

author: Dave
author_rank: Super Contributor
timestamp: March 09, 2020, 08:16:28 am
content: Quote from: cgroen on March 08, 2020, 03:51:12 pmThis one is not routed well. According to Tag Connect, no tracks or vias should be between the 6 exposed contacts.Source

author: cgroen
author_rank: Unknown
timestamp: March 09, 2020, 08:21:55 am
content: Well,until now, approx 50.000 boards does not agree on that (not of this exact design, but others using the same connector here, also with tracks between the 6 pads)I can't see what problem that should give you whatsoever, the pads are big compared to the "pogo" pins in the connector. The connector is very well centered with the 3 holes/pins

author: Amper
author_rank: Frequent Contributor
timestamp: March 09, 2020, 04:00:37 pm
content: Thats exactly the reason why i was asking ^^ A half size micro match would have been awesome, they are robust and survive many cycles, but well, if it doesnt exist im out of luck.I will also print some hook to go under a board, in case i want a semi permanent connection the side of the pogostick with the two pins will be on the boards edge, just two alf circles should give nice registration combined with the other one and having it on the edge will allow hooking under the board without having large holes around as with the original design.

author: IDEngineer
author_rank: Super Contributor
timestamp: March 10, 2020, 04:21:53 pm
content: If you want a commercial, lowest possible PCB real estate solution, take a look at Tag-Connect's boardedgesystem:https://www.tag-connect.com/product/ec-06-pcb-edge-connectorThis consumes nearly zero surface area. Its downside is increased cost of PCB fabrication for the castellated edge. Here's the board layout:

author: SiliconWizard
author_rank: Super Contributor
timestamp: March 10, 2020, 04:27:16 pm
content: Quote from: IDEngineer on March 10, 2020, 04:21:53 pmNice, hadn't seen this version of Tag-connect yet.

author: ataradov
author_rank: Super Contributor
timestamp: March 10, 2020, 05:07:09 pm
content: It is pretty flimsy and the pin that holds the board breaks that tiny PCB part away very easily. I would not use that for any sort of field handling.

author: Amper
author_rank: Frequent Contributor
timestamp: March 10, 2020, 05:11:57 pm
content: Yes, thats not really field stuff, but nevertheless interesting and nice to know, it could be useful otherwise. I could also imagine making some different sort of board cutout that will make it captive and use the edge. One downside will be higher board price if i remember correctly, they want more for cut in half plated areas.I got the tag-connect cable today and i have to say, im very glad i did it, it wasnt cheap @25€+shipping from ebay but no complaints quality wise and it really is small. Now i just have to hurry to get my boards done, i want to try this thing asap

author: cgroen
author_rank: Unknown
timestamp: March 10, 2020, 05:40:05 pm
content: Quote from: Amper on March 10, 2020, 05:11:57 pmAmper,you are right, they are not exactly cheap! When I order them, I usually get 5 at a time. But! This was until I made a little trick, I now place a piece of heatshrink on the Tag Connect right where the flat cable exits the black plastic. I have had a tendency to put pressure on the cable there when programming a bunch of boards, this will at some point wear the cable out. By placing the heatshrink this problem is now completely gone

author: IDEngineer
author_rank: Super Contributor
timestamp: March 10, 2020, 05:48:00 pm
content: Quote from: Amper on March 10, 2020, 05:11:57 pmIndeed, which is why I said "Its downside is increased cost of PCB fabrication for the castellated edge."

author: mrburnzie
author_rank: Regular Contributor
timestamp: March 11, 2020, 10:11:41 pm
content: Create pads on the bottom of the board and have it sit on another board with small pogo pins.That way you can place the pogo pins anywhere where you like. It's smd and can be placed near other components.

author: Amper
author_rank: Frequent Contributor
timestamp: March 12, 2020, 08:05:33 pm
content: "in the field" ist not nailbed terretory.

author: IDEngineer
author_rank: Super Contributor
timestamp: March 12, 2020, 08:09:07 pm
content: Had another thought about the edge connectors and their castellated holes. When PCB's are panelized they scribe break lines so the individual boards can be separated after stuffing and reflow. I wonder if you could design the board with "traditional" holes, and a scribe line running through them, such that you could then just snap off the edge leaving the castellated holes as shown in the illustration. That might be cheaper than asking the board shop to actually route and plate the edge of the board... drilling and plating holes anywhere inside the boundaries is just "more holes".

author: ataradov
author_rank: Super Contributor
timestamp: March 12, 2020, 08:11:56 pm
content: Quote from: IDEngineer on March 12, 2020, 08:09:07 pmNo, it is impossible. Or it would basically cost the same. They normally would not even attempt to scribe over copper layer, much less interrupted cut over holes.