I wanted probing tweezers for small SMD components on boards. Something like smart tweezers that I can connect to a multimeter. I had an extra Kelvin clip, that I got very cheap from ebay ( link ). You can easily get them for $5-6 a pair. I thought, why not to modify this into a tweezer. Here is what I wanted to achieve.
- Reverse the Spring action so that Clip tips are normally apart instead of being pressed at each other.
- Decrease the spring force. this will make easy one handed operation.
- Sharpen the clips nose for better contact with small SMD components.
- Insulate the probes to avoid touching around unnecessarily.
The results I got was better than what I was expecting. I could probe small SMD components. I could easily probe 0402 size ,though I only wanted it for 0805 sized components. I thought of sharing this with others as it may be helpful.
- Step 1 : Disassemble. I disassembled it easily. you only need to press the split plastic bushing on both sides.
I separated the clips to find a spring with long ends. I had to reverse the spring action by mounting the spring in opposite direction. The length of the spring was more that what would fit in opposite direction. So I thought of cutting it first. But I had a smaller spring in my junkbox, which was of a proper size that I needed to mount in these Kelvin clips. I had scored it from a floppy drive few days back. So I thought to give it a go. I had to bend the new spring so as to make it easy to put in the clip in opposite direction.
The one on left is the spring from the clip. the right one is from the floppy drive.
I had to Bend the new spring in way that it resembled the original spring. The right angled bend at the end of the keeps the spring straight when mounted inside the clip.
- Step 2 : Replace the spring. I replaced the spring and assembled the clip back so that the spring action is opposite. Instead of pushing the jaws inside, now it is pushing then outside. More like a tweezers now. I tested the tension was right for one handed operation.
As the spring was smaller than original one, it was prone to slipping out of the clip from the front, I drilled a small hole and put a screw in between to hold the spring in place.
- Step 3 : Make it sharper.I sharpened it using a file. The jaws were made of copper. So it was easy to file it. After some filing, it was now having nice sharp jaws, suitable for probing.
I also had to angle the jaws so that the tips of the jaws touched each other. One thing i learnt is that keep the jaws together preased tight, and then file it to make a sharp tip. this way, they are an exact match and bite well.
The sharp tips helps in poking on PCB as it can easily pinch through the solder mask, or oxidation on the parts terminals.
- Step 4 : Insulate: I took some heat shrink tube and put it on the jaws of the clip and then heated it with a hot air gun. It now fit nicely on the jaws, exposing only the tip enough for probing.
I used heat shrink tube of two diameters. One for the metal part and another with greater diameter for covering the plastic part and the metal.
I also colored one of the sides of the clip black, so it is easy to understand which side is the probe ground / negative terminal as connected to the Multimeter.
Step 5 : Test. Final part was to test it. I tried probing various sized components on a a board. here are the pics.
Some more pics. Here are some more pics of the assembly.
I am pretty satisfied with the results. I hope this was useful to you.