Connector-less PCB test connections - Page 1
Forum section: electronics / projects

author: jmdejoanelli
author_rank: Contributor
timestamp: September 29, 2013, 03:43:07 am
content: Has anyone ever seen a connector-less test/debug/program connection for PCBs? The idea being that all you need on the PCB is a pattern of blank copper pads (i.e. zero cost to the product). Edge connection is not possible (that would certainly make things easier...), and the connector needs to be able to latch to the PCB (it's for a 45min soak test) without any elaborate fixtures.I found this:http://www.tag-connect.com/TC2030-MCP,which is perfect, but it's more expensive than I would have hoped (we need like 40 of them), so maybe someone has seen an alternative? I have a feeling Tag-Connect perhaps has some patents in place.Cheers,Josef

author: marshallh
author_rank: Unknown
timestamp: September 29, 2013, 03:51:02 am
content: You can build a bed of nails with a couple 2 layer pcbs and some pogo pins from china ebay.

author: FrankBuss
author_rank: Unknown
timestamp: September 29, 2013, 03:51:44 am
content: You can easily build your own connector with pogo pins. Adafruit has them (maybe cheaper elsewhere) and a nice video:http://www.adafruit.com/products/394So all you need for a fixture is 4 holes.

author: jmdejoanelli
author_rank: Contributor
timestamp: September 29, 2013, 03:57:55 am
content: The big question if I was to build my own is how to secure it to the PCB during the test cycle?

author: FrankBuss
author_rank: Unknown
timestamp: September 29, 2013, 04:06:09 am
content: Usually testing is fast, so just some bolts with which you can align it with the holes on the DUT, press it some seconds on the DUT and it should be done, as seen in the Adafruit video. If it needs longer, perhaps mount it permanently with some screws.

author: jmdejoanelli
author_rank: Contributor
timestamp: September 29, 2013, 04:10:56 am
content: Frank, the test is a thermal soak test, and the device needs to be powered (through my test connector) for approx. 45 mins. Also, about 40-50 devices are tested at once, so I'd need to pay 20-25 poor souls to stand there for 45mins holding the connections without some kind of latching system

author: IanB
author_rank: Super Contributor
timestamp: September 29, 2013, 04:17:07 am
content: You create a jig to hold the PCB in place during testing (some locating pegs perhaps), and you use some form of positive positioning system for the pogo pin test fixture (like gravity, with a suitable weight to hold it down and compress the pogo pins). You can use locating pegs to align the test fixture just as with the PCB.Here you have to become a mechanician, you have to design and make something. Not everything can be bought ready made.

author: FrankBuss
author_rank: Unknown
timestamp: September 29, 2013, 04:23:27 am
content: Maybe use bolts for aligning and then some spring clamps, instead of human hands

author: pickle9000
author_rank: Super Contributor
timestamp: September 29, 2013, 04:29:05 am
content: When I was a boy, sorry I couldn't resist but true actually. One method is to use a hinged fixture the pcb on one side and pins on the other. The most important thing here is to make sure you have a fair distance from the hinge to the pins because during closure you can get lateral movement of the pins. To hold the fixture shut can be anything from a screw to a hook does not really matter. Yes wood works (MDF) is easy to work with and cheap.If you are going for the screw-down method use standoffs to mount everything and some really long ones with foam over the shaft to do the screwing in part. Basically use the standoff as a screwdriver, it can save you minutes and those add up if you are doing a bunch. It's fairly difficult to hold the board in place and screw it in without a 3rd hand. A big time saving step is to use clips or an actual clamping assembly that's help in place by a single wingnut.Your imagination is the best guide.

author: jmdejoanelli
author_rank: Contributor
timestamp: September 29, 2013, 05:07:52 am
content: Some good ideas bouncing around here. Unfortunately, the PCB is mounted in a plastic base, and the plastic base, with PCB, is mounted on a vertical wall so that a FLIR camera can monitor the temperature. At the moment there is a soldered cable that comes out the back of the plastic base from the PCB, goes through the mounting wall/fixture and then test clips are individually connected to each wire (6 wires each x 40-50 devices). This takes AGES to set up each run.I just wanted to explore any simple and cheap options which might make this process easier/faster, without having to completely rebuild the whole test rig.If there aren't any simple options then perhaps I will have to redesign the whole test rig and go with the more traditional bed of nails test fixtures.

author: kolbep
author_rank: Frequent Contributor
timestamp: September 29, 2013, 05:39:15 am
content: Use the pogo pins idea, but have a strong magnet glued onto the back of your test jig.Another magnet on the back of the box, and the force will hold the jig in place.

author: SeanB
author_rank: Super Contributor
timestamp: September 29, 2013, 08:21:05 am
content: Can you put 2 holes in the board for a pair of wire clips to poke through, to hold the bakelite body that holds the pins onto the board. The pins just touch the pads, and the spring steel clips push through the holes and expand on the other side to hold the connector to the board. Just needs a space where the pads are, 2 holes and then it is easy to put in and remove. the springs are similar to those ears on a centronics connector, or even use the springs and the screw holders and have 2 slots to fit in the board. Bakelite is recommended as it is heat resistant but easy to machine and pretty cheap in a block form. Used to make electrical distribution frames, and lasts decades.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: September 29, 2013, 09:22:02 am
content: Edge connector - Zero cost on PCB ( don't bother with bevelled edges or hard gold) , readily available connectors in a variety of pitches and sizes.

author: jmdejoanelli
author_rank: Contributor
timestamp: September 29, 2013, 11:08:52 am
content: Can't use an edge connector unfortunately since the PCB will already be mounted in it's housing.Maybe I can see if we can change the entire process so that we can do the soak test before the PCB is housed. I didn't want to make any drastic changes like that though since it's only my first week at this company and I don't want to turn everything upside down, not that much anyway

author: amyk
author_rank: Super Contributor
timestamp: September 29, 2013, 11:39:26 am
content: Quote from: SeanB on September 29, 2013, 08:21:05 amI was thinking of this idea, but a little simpler: use spring wire with L-shaped ends, that are just wide enough to fit through holes in the board; spring tension does the rest.

author: Jon Chandler
author_rank: Frequent Contributor
timestamp: September 29, 2013, 02:27:48 pm
content: Sparkfun has posted a tutorial about "lock-in" pads for single row 0.1" headers. The idea is handy to keep the headers perpendicular to the PCB during soldering but they are so tight that the idea has been used for connectorless ICSP programming – a row of header pins is inserted into the pattern when needed. I know the pattern holds tight – it was only when I unplugged the ICSP cable that I discovered I has missed soldering it in place.Standard size holes are alternately set above and below the the baseline to achieve the lock-in design.For a standard 0.1" pitch header, here are the details:Pitch: 0.1"Offset: 0.01" between alternate holes (or ± 0.005 offset from baseline)Drill: 0.04" diameter (which is the customary size)The illustration shows this clearly. I apologize in advance for the size of the image. As far as I can determine, there's no way to set image size on an iPad.