PIC ICSP Instant SMD Connector with Pogo Pins

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PIC ICSP Instant SMD Connector with Pogo Pins

Author
Giorgos Lazaridis
May 5, 2012

The connector side by side to my PICKIT 3 programmer

I have began working with SMD chips and especially with my favorite QFN package some time ago, and i have already manage to radically reduce the size of my PCB to minimum, thanks to the tiny footprint of those packages. Slowly i began replacing my titanic through-hole parts with SMDs (whenever possible). One problem that arises with QFN PIC packages is that the microcontroller must be programmed after being soldered to the PCB. I know that there are QFN sockets that i can use to make a QFN chip programmer, but they are still very expensive to get, almost $100 each.

I turned using 0.1 pitch headers on each PCB, but this was totally inefficient, because this connector occupies more PCB space than the PIC itself. Taking also into account that the programming connector will only be used once, i decided to design something better, smaller and somehow faster for programming the PICs.

Pogo pins are here to help

I did not know the existence of pogo pins until i saw one interesting make from Limor, our beautiful engineer from NY. These pogo pins are called "pogo pins" because they are spring loaded. They have electrical conductivity between their two parts so they can be used as connectors.


I got two different sizes to test.	The pin extended	Apply force to the pin and you realize the spring-loaded action

The idea is simple: i will make an eagle library with the ICSP device which will actually have 5 pins, the MCLR/Vpp, positive and negative supply, and the serial Data and Clock pins. These are actually the 5 wires that the ICSP wire has. The package of this eagle device will be SMD of course, so that it will occupy only one side of the PCB (and not two like the through-hole connector), and it will have 0.05 pitch instead of 0.1 to further reduce the footprint:


The symbol for the ICSP connector that is used in the schematic	The PCB footprint for the PCB layout (top side)

You can download and use this Eagle library yourselves from the following link:

Download file
PIC ICSP SMD connector Eagle library files

I actually bought two different sizes of pogo pins for test, the big one had diameter 1.36mm and the small one had diameter 0.68mm and length 16mm. This is the size that fits my needs best (for the 0.05 pitch).

For the PCBs, i only had to print onto the copper the corresponding footprint for the pogo connector:

The pogo connector PCB

Now i had to make a PCB for the pogo pins. The PCB must have one 6 through-hole female connector for my PICKIT3 ICSP wire on one side, and the 5 pogo pins on the other side. One additional trick that i did is that i did not soldered the pogo pins all at the same height, instead their endings are inclined. I did this for easier placement onto the PCB, since the pins are touched one-by-one on the PCB rather than being touched all at once:


Bottom side of the PCB	There is a female connector on top side for the ICSP cable	The connector is ready to program a batch of chips out of the shelve...

And here are the Eagle files for this PCB:

Download file
ICSP Pogo Pins connector PCB layout and schematic

Keep in mind that the pitch is 0.05 which is rather small, and the pads are also very small. Soldering the pogo pins onto the PCB might be hard since they must be soldered parallel to each other and on one plane. You may wanna make 3 PCBs, one wto use for the connector and the other two for aligning the pogo pins during soldering.

In action!!!

Holes for aligning the pins... (Update May 21 2012)

I'm not a surgeon to have a steady hand. I would rather say that i am some sort of blacksmith in terms of hand stability. Therefore, i made another library for the PCB ICSP pads, and instead of SMD pads i used through-hole pads. I do not intend to drill those holes, i use them only for aligning the pogo pins. This idea works perfectly fine. As a matter of fact, i already used this connector to program 12 high power LED controllers for a project of an artist from puplik.org


This is the PCB that i programmed with this connector	A close look reveals the holes that i added to help in aligning the pogo pins	Besides these 8 PCBs, i successfully programmed and sent another 4 PCBs, a total of 12. The pogo connector works perfect!

And here is the new library file to download and use:

Download file
PIC ICSP SMD connector with alignment holes - Eagle library files

Enjoy!

Continue reading. Click here to view the references.

Comments

At 24 June 2012, 4:20:46 user George wrote: [reply @ George]

At 23 May 2012, 11:58:03 user George wrote: [reply @ George]

At 10 May 2012, 19:27:41 user Giorgos Lazaridis wrote: [reply @ Giorgos Lazaridis]

@tom Hello tom, the link is awesome! I did not knew it. But regarding the "wasting your time", i made because i had to program 12 PCB boards with SMD PICs, something which was very easy and fast indeed. I noticed what the problem was, and i solved it by removing a tiny amount of copper in the middle of the pad, like a punch. This was an amazing help for keeping the pogo pins stable, which i held with my left arm (i am right-handed) and programed them with my right arm easily. But i may give the tags a try afterall.

At 10 May 2012, 18:15:32 user tom wrote: [reply @ tom]

Hi George. You are probably wasting your time (and money) with pogo-pins. You have to be very patient and have very stable hands when you trying to program your mcu. On the other hand you can't use your adapter for debugging. What I suggest you is to use one of these. http://www.tag-connect.com/

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