Use a Solder Gun for Delicate Electronics

Semi-conductors, like LEDs and transistors can easily be damaged by too much heat. Low wattage soldering irons in the 15 to 25 Watt range are recommended. I have used my nearly 50 year old 100/140 Watt dual heat soldering gun for this job very successfully. This Instructable will illustrate how to do that safely and easily.

Materials

• 5/16 inch bolt and nut
• Short piece of #12 gauge solid copper wire

Tools

• Vise
• Vise-Grip adjustable pliers
• 4 inch angle head grinder with a metal cutting disc
• Grinder with a wheel

I have a low wattage soldering iron I bought for use with circuit boards and semi-conductors. It has gotten a lot of use and the point has worn away a bit. New points are not available for this soldering iron as they are for some models. I could file a sharper end on this soldering iron. It does not produce too much heat, but the point is now too broad and I get solder bridges between closely spaced solder points.

I want to attach a fine copper point made from #12 electrical wire to the tip of my 100/140 Watt soldering gun. The photo shows what I did. I made a split bolt to hold the wire securely near the soldering gun's tip.

I am holding a 5/16 inch bolt very firmly in a Vise-Grip pliers and the pliers is firmly mounted in my workbench vise. I need a cut straight down the middle of the bolt to a depth of about 1/2 inch.

I gently moved the cutting wheel up and down to trim away a little bit of the sides while watching to keep the slot centered down the middle of the bolt. I want the slot to fit a soldering gun tip as shown in the photo.

I want to keep the amount of metal in the split bolt to a minimum so more heat goes to the wire tip and less heat is used to heat the split bolt. Cut the bolt to length. Notice the cut from the upper surface of the bolt a bit to the right of the slot down the middle of the bolt. Smooth any rough edges.

With a 5/16 inch bolt long enough to hold while grinding on a wheel, thread on two nuts. One is to lock the nut to be ground so it remains with a few threads above the end of the bolt as in the first photo. Grind the nut until it is even with the end of the bolt as in the second photo. Test the nut on the split bolt and work the nut until it turns smoothly on the split bolt.

The first photo shows the pieces (split bolt, thinner nut, and copper wire) with a new soldering gun tip. The second photo shows how the pieces fit together. Use a pair of pliers to tighten the nut on the split bolt. The copper wire will be secure enough to heat up when the gun is in use, but will not be nearly as hot as a 100 Watt soldering gun.

The soldering tip is too close together at the end and the split bolt would short the two members. When the tip is installed on the soldering gun I always bend the tip so the included light reaches the end of the tip. This opens the legs of the tip so there is plenty of room for the split bolt.

Pull the trigger on the soldering gun to the first click and wait about 20 seconds for the precise new wire tip to heat up enough to melt solder and tin the new tip.

In use I find it works best if I place a little molten solder on the tip before touching the joint. The solder heats the joint and flows into it.

I am assembling a kit for a small binary clock. Power is provided to the circuit board through a mini-USB connector. This is the second time I have built this kit. The first time solder bridged the tiny joints closely spaced. With my new soldering tip on my dual wattage soldering gun I still had to be careful, but I made the joints without solder bridges forming.

The soldering gun does have a 1 in 5 duty cycle (20/80). For every minute the soldering gun is "on" it needs to cool four minutes. I need to remember to let the gun cool periodically.