Building A Probing PCB

When testing and debugging components on a printed circuit board (PCB), you'll need to be able to hold the PCB and at the same time hold your testing gear in the correct spot.  Sometimes, you need to test adjacent pins on an IC.  With small pin pitches, getting the necessary probes on adjacent pins can be a challenge.  Sometime you need to test a pad which test equipment can not easily be attached to without soldering on a temporary wire.  One way to address these challenges is to build a probing PCB.  The probing PCB has pogo pins at the pitch you need and each pogo pin on the PCB is connected via a trace to a single pin of a standard 0.1" (2.54mm) header.   Below is one example of how this can be easily accomplished.  The design and pogo pins used could be changed to meet your own requirements, but the concept is the same.

Designing the PCB

You'll need to design the PCB with the number of pogo pins and pitch for your application.  In this example the PCB has been designed to connect 3 pogo pins at 1 27mm pitch to a standard header at 0.1" (2.54mm) pitch.  The PCB contains a 3mm hole so that the entire PCB fixture can be easily connected and positioned using components from the PCBGRIP system.  As shown below, directly below the 3mm hole are the holes/pads for the pogo pins, and below those are the holes/pads for the standard header.  We designed the PCBs and had them manufactured at OSH Park.  The PCB design is shared here.

Other Components

To suite our 1.27mm pitch, we used P50-B1 pogo pins.  The minimum recommended spacing for these pogo pins is 1.27mm and the PCB hole diameter required is 0.9mm.

 

As we'll explain below, a long header is required  We used a 15mm long male header available from Canada RobitixSparkfun carries a 20mm long header which would work too.

To strengthen the assembly, protect the pogo pins from pending (they are fairly fragile), and make everything easy to attach to a 3mm rod, two identical PCBs are used, with a standard M3x0.5x6mm standoff in between.  The standoff is the 'meat' between the PCB 'bread' and the standoff provides a way of mechanically securing the lower PCB while at the same time providing a place to screw in a 3mm rod at the other end.  The machine screw shown below is M3x0.5x4mm with a Philips head. 

Putting It All Together

First attach the stand off to one of the PCBs with the machine screw.

The header is then placed between the PCBs and a 3mm rod with a stop nut secures the assembly together.

With the 15mm headers we used, we had to make sure that the header pin was flush with the bottom PCB, for enough protrusion of the header above the top PCB - see the left header pin in the following picture:

A Joining Plate was used hold the assembly while the headers were soldered to the top PCB.

 

The 3mm rod was removed and the assembly was secured against a Joining Plate .  With the PCB secure against the Joining Plate as shown in the picture below, we were assured that the pogo pins would be flush with the bottom PCB in the picture (top PCB when we use it).  The pogo pins and the unsoldered ends of the header were then soldered to the top PCB in the picture (bottom PCB when we use it).

 

The 3mm rod was reattached and the assembly held so that the pogo pins could be soldered to the top PCB in the picture below.

 

Then attach your test gear to the header and place the pogo pins on the parts that need to be tested.  We are using Cylinders and Variable Tees, along with 3mm rods in the pictures below to hold the probing PCB where we want it.