Introduction: Make a Good Dupont Pin-Crimp EVERY TIME!

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About: Electrical Engineer by training; Electronics Nerd before it was fashionable.

Anyone working with an Arduino, Raspberry PI, Beagle Bone, or any other multi-circuit-board project has become familiar with .025 X .025 in, square post pins and their mating connectors. The male pins are usually mounted to the circuit board with board to board wiring accomplished through mating connectors and wiring. These connectors usually consist of female pins that are individually crimped onto the wires which are then then inserted into multi-position connector shells.

These connector pins, also commonly called “Dupont Pins,” and are manufactured by AMP, Tyco, Molex, Samtec and a myriad of others.

Crimping Dupont female pins onto a wire requires a special crimping tool, precise techniques, and lots of time and patience! When I first started home-crimping these pins, I found that only about 1 in 10 came out right, with the rest defective in one way or another.

Thankfully, a few soles before me posted documentation, a few Instructables, and some YouTube videos that helped me get a started. Even at that, it took lots of trial and error and many crushed, damaged and unusable pins before I was able to get my failure rate under control.

Over time I studied my problems and came up with this guide and document to share some common crimp problems and solutions. In particular, you will see a very simple “Pin-Guide Tool” that you can make that will precisely position and hold the female Dupont pin inside of your hand crimping tool throughout the whole process. By using this Pin-Guide and a few other basic ideas, you too I can get a good crimp every time!

Step 1: Tools and Parts Needed

Above you can see the items you will need. Although not shown, a good wire stripper is also required. Take care in selecting and using the stripper as you will see soon, consistent strip length, free of nicks, is crucial to good Dupont pin crimp results.

Step 2: What Goes Wrong?

I studied my many failed crimps in an effort to figure out what was going wrong. I came up with the DEFECT TABLE shown above. This table helped me determine the root cause(s) for each defect which in turn, led me towards solutions.

While I don’t claim this list to be a 100% comprehensive, it does represent a good summary of my most common reoccurring problems.

Step 3: Wire Strip Length

The figure above shows the anatomy of a Dupont pin.It is seen that the total length of wire going into the pin should not exceed .2 in (5.0 mm). This means that when the wire is correctly and precisely positioned in the pin, the optimum wire-strip length is only 0.10 in (2.5 mm). A shorter strip length will compromise the conductor crimp while a longer strip length will either cause the wire to penetrate into the pin too deeply or lead to a degraded insulation crimp. For these reasons, I conclude that strip length is critical to achieving a good Dupont pin crimp.

  • While I’m sure there are precision wire strip tools out there, I don’t have one. Therefore, I check each strip length and carefully trim away any excess wire whenever my stripped length is too long.
  • As a reminder, take great care not to nick any of the conductors during the strip process as this will compromise the quality of the finished connection.

Tip: I found that recycled stranded-wire Ethernet cable is a good source for the interconnect wire.

Step 4: Pin Positioning Inside the Crimp-Tool

Improper pin-positioning within the crimp-tool tool was also a major reason for many of my crimp defects.

Perhaps I am just ‘all thumbs’, but once I thought I found the best spot to place the pin inside the crimper, I rarely seemed able to get it there. Furthermore, even when my pin placement was perfect, I frequently found that the pin would be pushed out of position or even rotated as a by-product of inserting the wire into the pin.

To solve this problem, I came up with a “PIN-GUIDE” tool. The Pin-Guide tool is nothing more than a strip of male pins onto to which the female pin to be crimped is placed. While simple, this Pin-Guide provides many benefits.

  1. The Pin-Guide provides a ‘handle’ for the pin so that placement into the crimper jaws is easier.
  2. The Pin-Guide precisely sets the position and depth of the pin relative to the crimper jaws. This serves to locate the CONDUCTOR-CRIMP zone and INSULATION-CRIMP zone in exactly the right spots within the crimp dies.
  3. Since the Pin-Guide ‘stays in place’ during the crimp cycle. it prevents the female pin from twisting, sliding, or moving while inserting the wire or performing the actual crimp cycle.
  4. The Pin-Guide also provides a ‘wire-stop’ that keeps the wire from going too far into the center of the female pin and obstructing the Mating-Pin Zone. Note that this fault only revealed when you find that you can’t plug the finished connector assembly onto the male PCB pins!

The Pin-Guide is easily fabricated from a 4-pin strip of male pins. The key to success however, is precisely setting the pin depth.

Step 5: Making the Pin-Guide

It’s easy to use the Pin-Guide. Just cut the female Dupont pin from the carrier and place it onto the Pin-Guide.

Step 6: Loading the Pin-Guide

Step 7: Selecting a Crimp Port

The SN28-B crimp tool has three different crimp-ports. Each port has a slightly different die shape and will form the pin differently. As noted in the figure, I found that I get the best results using “port 1” with wire up to and including AWG 22 Ga; I do not get good crimps with 22 Ga wire in position 2. Your results may vary however, as each crimp tool is adjustable; your setup maybe different than mine.

While the tool markings implies larger gauge wire may be used, I suspect that anything much larger than 22 Ga may not fit into the 0.1 inch spaced shells used for most Dupont pin connector assemblies.

Step 8: Loading the Dupont Pin Using the Pin-Guide Tool

As shown, with the female Dupont pin on PIN-GUIDE post #2, place the pin into the crimper jaws and close the jaws until they “click” and the pin is held in place. Be sure the pin is properly oriented and take care NOT to over compress the pin at this time as that will make wire insertion more difficult.

Step 9: Loading the Wire & Completing the Crimp

Next, carefully insert the stripped wire into the pin. As shown, be sure the wire is fully inserted and is not ‘hung-up’ during placement. While holding the wire in place, compress the crimper-handles to complete the crimp. Release and remove the completed crimp and perform a QC inspection.

After each crimp, it is important to perform a VISUAL INSPECTION as well as a QC PULL TEST of the pin-wire combination. A few examples follows that show you what to look for. Since the pins are small, I recommend you use a magnifying lens for all visual QC checks.

Step 10: Inspecting Your Work: Example A

Step 11: Inspecting Your Work: Example B

Step 12: Inspecting Your Work: Example C

Step 13: Loading Connector Shells

When the crimped pins are completed, they are easily inserted into the connector shells as shown. Pay attention to the photo details as pin orientation is important. Note that the pins will only lock-into the shell when inserted with the proper orientation.

Step 14: Summary of Pin-Crimp Steps

Step 15: Troubleshooting

As another aid to diagnose and trouble shoot common crimping issues, I offer the expanded trouble shooting table above.


CLOSING COMMENTS

This Instructable aims at helping you get solid, consistent Dupont pin termination results. I have focused on female-pins but similar steps can be applied to help you achieve good results for male-pins as well. I invite you all to review and tweak these ideas as you see fit to get them to work well for you.

Take care and Happy-Crimping!