Instead of regular test points, I'm now adding u.fl/ipex connectors to my PCBs. They're small enough to not be in the way for most cases, and it's so much easier to just plug in a connector instead of messing around with probes.
I make my vias large enough to accept a 30AWG wire (15 mil hole). Slip in a precut/stripped wire, tack it with solder, trim to length, and you have an instant testpoint in a usually optimal location near the point of interest. Advantages are that you can't accidentally rip a pad off the board, it's accessible from both sides, and minimal board area is consumed.
If you're doing anything more than 2-4 layer PCBs, I'd make one more caveat... through-hole-via! It makes getting to test points much easier from both sides of the board, and if you're using pogo-pin testers, helps align the pins.
Unfortunately, if you're doing anything highspeed (>100MHz) or differential, then such vias (except at connectors) are highly frowned upon since they increase loading, crosstalk, imbalance, and reflections.
I would go further, adjust your footprints to accommodate a 30AWG wire being soldered to them.
Too many people blindly accept generated footprints that are meant for machines and not humans. They are far too dense and have too little overhang.
For QFNs, adding about .4-.6mm of exposed copper extension to all pins can make both testing and hand rework vastly easier. In addition, extending the thermal pad far enough that you can easily hit it with a soldering iron often makes heat gun rework tremendously easier.
While this won't work for giant BGAs, you can often figure out how to extend exposed copper for up to about a 36 ball (6x6) BGA. For example, there are some wonky packages for power transistors that are basically 4 ball (2x2) BGAs. Running the traces out diagonally with some extra exposed copper helps for both soldering and testing.
Sometimes the footprint is a DFN and the thermal pad can be directly routed out. That's the easy case.
A lot of the time, the thermal pad is GND. You can then connect the pad out through any GND pins. Quite often, if you need a thermal pad, there are multiple GND pins ganged right next to one another and you can route a tab out using them.
You can also put a piece of exposed copper on the back side connected to thermal vias that you can hit with a soldering iron. This is less optimal as it leaves an exposed copper pad on the opposite side of the board. However, if you have a lot of thermal vias attaching to the ground plane (ie. a LOT of thermal mass), it sure makes rework easier.
As a last resort, as you point out, you can try to sneak a trace out through the corner. That's generally less optimal as the trace size is pretty small.
The general lesson is "think about your footprints" and don't just blindly accept what the footprint generator gives you.
There are a lot of small "quality of life" things you can adjust on a footprint. Adding a line of silkscreen every 10th pin helps a bunch for debugging 100+ pin packages. Soldermask is a lot more accurate than silkscreen, so putting soldermask "L's" at the corners of your package helps for visual alignment. Putting pin numbers in silkscreen at corners is nice. Always sort your designators by X and Y. etc.
Most low-speed digital communication busses really need a series resistor inserted on their clock line for reliability anyway. If I'm on a prototype, I'll make those resistors 1206 which is plenty big enough to hit with test leads.
This is actually a common problem for test fixtures that involve miniature coaxial connectors (pretty much all of them are rated for few tens of mating cycles): even if the connector on device is used for assembly/repairs and goes through very few mating cycles, the automated test fixture used during manufacture of such a device is expected to last longer.
Most connector vendors have specialized connectors for test fixtures that last much longer (they are also a lot more expensive).
Wait, what? For IPEX? That's terrible, RC (drones) use those connectors a lot for video, I would hate my $300 transmitter going to the bin because I broke the connector. I guess that's why DJI puts screws above them, so they look more permanent.
That seems pretty reasonable for debugging no? And you can just replace them by hand, on your prototype board, in case you have been debugging so hard you managed to break one of them.
I have a bunch of these. They're great, except for being frustratingly "floppy" at times. Imagine huddling over a PCB carefully positioning all these probes, not daring to breathe... only for the slightest brush to send them all tumbling over like dominoes. More than a few curse words have been let loose over this gear, but I couldn't do without them.
It looks like they have new ones that address this: "The new SQ series of handsfree probes from Sensepeek have a lower point of gravity making them even more stable compared with the original SP series of handsfree probes."
Not related to the topic but it seems this marketing blurb has become the norm: They can't say they fixed something without claiming that it was already very good. I've come to hate this. No, they are not now "even more stable", "we made them more stable" because honestly they weren't that stable to begin with.
I would strongly recommend adding a couple of dial indicator stands to your kit. They are rather more bulky than the included arms, but as they're designed for holding precise mechanical measurement instruments they are rigid, stable and can be very finely adjusted.
I'm considering buying these. Are you saying they're floppy as in, the bendable part doesn't hold it's shape? or floppy as in, the magnet isn't strong enough and the whole thing falls down?
I'm assuming there's a magnet. I hope these aren't just using weight to hold their position....
One side has a magnet, and it firmly attaches the base board (steel). But the other side just has the pogo and is fixed there just by the weight of the thing. It works good if there's enough "bite" and the rest of the system applies force the right way. If not, we'll, it slides off.
In my case for example, it is excellent for test points but somewhat challenging with soldered SMD component pads and very challenging if the density is high.
If you're able to solder on and the signal can stand the stub, a little dot of copper tape on top of the IC and a tiny wire down to the lead in question and soldered on can help give an easier "hitbox". You can add the ground pad as well next to it and use the spring for the probe.
I assumed they were those bendable wire things like old style podium mic stands. Those tend to sort of stay where you put them, but not very precisely.
I find the magnet is usable but weaker then I'd like if the steel is under an ESD mat, which are usual 2mm thick. If anything they're a just little bit too long which means they can be slightly floppy in the cross-wise direction.
Thinking about it I might try a piece of low-profile bike chain and a copper wire and see if I can do better.
I mean the 'bendable' part. The nearest consistency I can think of would be a bag of sand. They are weighty but not rigid. They are not designed to hold their shape. Unfortunately this means that it takes very little sideways force to make them "flop" over.
Still, I can't recommend them highly enough. I use them all the time. Seriously, a PCBite plate with probes on-hand is now a permanent fixture on my main desk. If you do half as much fiddly electronics stuff as I do, they will pay for themselves. But you will also occasionally find them infuriating.
We have them at work too, like you said they are too floppy and you gotta be extremely careful not to touch anything, especially if the point you are testing is very tiny. Apart from that they are great but yeah, there needs to be a way to fix them in place.
I have bought the new SQ probes and went back to only buying the older version.
The new ones are heavier, but that makes it harder to put them at an angle, they fall over more quickly. And the probe heads are bigger so you can't put as many close together.
These really are lovely things. I only have the DMM ones, and rigged up a scope probe holder, but I'll be getting more of them.
The use of M4 screws on the older models at least is very helpful for DIYing custom fittings (even without the real SMD nuts, brass nuts can be soldered to PCB stripboard)
Interesting, I liked the flexibility of his idea to use coolant hoses, or 3d printed parts to make coolant hoses. But It may be that I just want to toss something together real quick instead of asking for a second set of hands or eyes. I wonder why he updated his design to the newer one you posted?
Came to upvote this. The station works unreasonably well. The needles are pointy enough that they deform solder/copper a little bit and stay put once placed (you can flex the arm to preload the needle).
You can buy it on the maker's website in the second link, with all the bits for ~50eur.
Naturally this is no good for high frequency, but it has saved me countless hours of soldering and removing fine wire in the lab.
Once I had a bunch of boards to test and rigged up a little temporary
"bed of nails"
________________ o
/ ____________ o <-- connector
| / _________o
| | / |
---T---T---T---T----[]
Where T = sewing pins and --- = thick polystyrene sheet
Use finest 30+ SWG wirewrap
The polystyrene gives a little bit of necessary springiness and as
long as you have two (preferably three) reliable anchor points near
the corners the pins will reliably find test points or the contact
points of SM resistors or caps.
Personally, I find the critical is to use good wire (the type used in transformers), use a good soldering station with right kind of tip, and plan a way to connect to your wires without destroying entire setup.
I solder the wires to a short piece of FFC tape ending with a connector. The tape and the connector are attached somewhere with apiece of double sided adhesive tape. The end of the tape with the wires is suspended in air nearby. I then individually solder the wires to the test points.
I can then connect my test tools (scope / logic analyser / PSU / DMM) directly to FFC connector easily. If I need more than one tool, I would usually use one of my breakout boards with connectors that make it easy to connect multiple test tools at the same time (for example supply power AND connect the scope, or maybe inject external signal to the chip on the board).
I would like to mention I don't do it frequently. This usually only happens when I am having fun with an existing device. My own devices usually have built in enough test points / test connectors to not require this kind of shenanigans. I would usually plan for one or more surface mount connectors that I will only solder if I need it for some reason.
Hot glue is good for strain relief. 30 gauge wire on tiny pads is going to be extremely fragile. Shifting the mechanical stress to the glue will make all of this more durable.
I prefer the UV hardening glue. Hot glue is a bit too messy for my taste, the glue gun takes too much space on my already full desk, and you need to wait for the thing to warm up.
They're around 3 cents (yes, $0.03) a piece on LCSC: https://www.lcsc.com/product-detail/_BAT-WIRELESS-_C5137195.....