What is Tag Connect (besides a bad idea)

Tag Connect is a programming header system where on a PCB you put down a foot print and then use a pogo pin system to make connection to footprint and program board.

This seems like a great idea on the surface. However there is no means to hold the pogo pins onto the PCB for development. Therefore Tag Connect came up with a back plate to lock the system in place.

This seem great until you realize the adapter sticks out like 2" from the PCB.

This means if you are like me and need to use a microscope or probe the bottom of board you are kind of hosed. As the height of the tag connect adapter is always in the way, especially if you turn board over.

For $45 per pogo pin header and with the height issue, holding in place issue, etc. I have come to hate the Tag Connect system.

So lets go back to the problem the tag connect solves and discuss it.

Problem

The problem is you need a way to program boards in factory, but without the cost of a header. Ideally the solution would be small footprint.

When we start looking how this problem has been solved before we know that test points are common on large volume production. Here a custom test fixture with pogo pins are made and often a panel of several boards are programmed in parallel. Here the Tag Connect is not ideal as it takes up more board real estate than needed.

Solution

A solution I often use is to just use a 10 pin 0.050" through hole connector.

Here the footprint area is less or about the same as the tag connect. You do not have to populate header, just plug connector into JTAG cable and press/hold into the holes on the PCB. This does the same thing as Tag Connect for programming and costs next to nothing.

Now many will note that yes it means you do not get the space on bottom of board for more parts which tag connect allows. The reality however if you use the tag connect locking system and due to the alignment holes no one uses space under the tag connect for parts. Note on a multi-layer board the through holes limit routing on those layers, but so does the alignment holes for Tag Connect, hence the tag connect offers very little advantages.

For factory programming I just have factory plug in the connector to JTAG cable and just press into holes and program, as shown above. I have made 1000s of boards this way with no complaints from contract manufacturers. For large volume production they can make pogo pin fixtures to contact pads easy enough.

For development I can solder in the connector, and since the ribbon cable is low height it is easy to turn board over and probe back side.

Note you can also do this with SMT 10pin 0.050" connector, however it is a bit harder for contract manufacture to make contact with pads without a connector installed. That is with SMT connector you will need a pogo pin test fixture for production.

6 pin Option

Another option is just to use a 6 pin 50mil (0.050") through hole connector:

This would have smaller footprint than the tag connect, just as easy use in the factory. You would need an adapter board to the standard 10 pin Cortex header. Keep reading and you will see the adapter board designed below can be used for this purpose.

The point is more that the Tag Connect has problems and is really not a good solution for production or development and that there are much better options.

Better Option

If you must use a tag connect consider making the pads through hole pads.

This will enable your developers to solder a real header in for development.

At this point you might ask, if I have the through holes then I can align pointed pogo pins on the holes and then I no longer need the 3 alignment holes and the footprint gets smaller. Yes this is true and why the Tag Connect is such a bad idea.

Note that the Tag connect adapter pogo pins might be small enough to go into holes of the through hole pads. So for production you might need a different pogo pin option. The adapter board board below with Mill-Max header does work, but the pogo pins stick through holes. Again for my production I just use the standard male headers in production and no pogo pins. Here for programming the tech just pushes male pins through hole and holds it there for the few seconds to program board.

Tag Connect Fixes

So many people still love the Tag Connect for production, I am not sure why but people use it. I have many customers that use it even after discussing why it is not ideal. Which is fine, but I still have a problem for development. The problem is that I need a way to connect debugger that has less height than the tag connect cable and does not come off.

The first idea I had was to use a Mill Max connector :

This connector is only about 6mm tall installed.

Hence it with this connector it might be possible to use self tapping screws and screw this to the device under test.

Yes, self tapping screws could damage the PCB with tag connect, but for development I normally solder a JTAG connector to PCB any way.

So I am not too concerned with damaging a development board.

Another idea was to stand a thin PCB vertical between the pads on the tag connect and solder it to the device under test.

I figure why not give this a try?

I figure the cost of the PCBs and the parts are still less than the Tag Connect programmer and it might actually work. If not it would allow an adapter board to solder jumper wires on easier.

Did I mention how much I dislike the Tag Connect... I still say just add the through hole 6 or 10 pin connector and get on with your life. It is cheaper and just as easy.

I will keep you guys updated on the progress once I received the boards.

Update 3-15-2021

I received the boards today and realized I did not have a tag connect PCB in the lab. So I used one of the boards as test subject.

I first bent a piece of stiff wire (from 100mil header) in a U shape and put through PCB (the board with tag connect).

I then attached the adapter board to the unit.

This allows direct solder connection to the Tag Connect. The wires add the mechanical strength such that the solder joint will not break. The wires are so stiff the PCB will break before solder connection.

On a non-plated mounting hole for Tag Connect might have more play in the connection than mine as my mounting holes were plated so that I could solder wires to mounting holes. However as a first test this worked very well.

Pogo Pin Option

The pogo pin connection system is shown below using the Mill-Max header.

The rods are just 100mill header pins. This allows the pins to be inserted into a PCB and bent to hold adapter on Tag Connect footprint.

Unlike the standard Tag Connect adapter this one is very low height, only about 12mm high installed.

6pin Adapter

If you decide that the Tag Connect footprint is a pain and just go with the 6 pin 50mil header.

Then this same PCB can be used as an adapter to the 10pin Cortex by soldering the 6pin female header on the board.

Conclusion

Tag Connect is a great idea in concept but is not very good given the alternatives. It is much cheaper and easier to just use a 6-pin or 10-pin 50mil header on your PCBs and move forward with life.

However if you have to use the tag connect consider using a PCB like the one above to fix some of the issues with the tag connect.