6 ms·

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 easie

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. They're around 3 cents (yes, $0.03) a piece on LCSC: https://www.lcsc.com/product-detail/_BAT-WIRELESS-_C5137195.html https://www.lcsc.com/product-detail/_BAT-WIRELESS-_C5137195.....

kevin_thibedeau 3y ago
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.
- kurthr 3y ago
  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.
- bsder 3y ago
  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.
  - hales 3y ago
    > 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. How do you do this? The centre pad is surrounded by the smaller pins. Are you snaking it out the diagonal corners?
    - bsder 3y ago
      It depends. 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. Machines will never notice, but humans sure will.
bsder 3y ago
Or just put a series resistor somewhere? 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.
jakeogh 3y ago
Nice, but not very good durability... pdf says 30 cycles.
- bsder 3y ago
  Those kinds of connectors are notorious for breaking on the first removal.
- fest 3y ago
  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).
- stavros 3y ago
  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.
- sannee 3y ago
  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.

kevin_thibedeau 3y ago

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.

kurthr 3y ago
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.
bsder 3y ago
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.
- hales 3y ago
  > 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. How do you do this? The centre pad is surrounded by the smaller pins. Are you snaking it out the diagonal corners?
  - bsder 3y ago
    It depends. 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. Machines will never notice, but humans sure will.

bsder 3y ago

Or just put a series resistor somewhere? 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.

jakeogh 3y ago

Nice, but not very good durability... pdf says 30 cycles.

bsder 3y ago
Those kinds of connectors are notorious for breaking on the first removal.
fest 3y ago
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).
stavros 3y ago
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.
sannee 3y ago
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.