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Solder iron not hot enough for PC board

gary350

Well-Known Member
My pencil solder iron for circuit board is slow to melt solder then solder just sets on the pc board next the the wire doing nothing. If I hold it there 30 seconds it begins to try and stick. I think maybe a variac can be used to turn 120v up to 125v or 130v or so to get a little more heat.? I cleaned pencil solder iron tip its not hot enough for solder to stick to the clean copper tip? I used my solder gun to make solder stick to pencil solder iron tip still pencil solder iron will not solder PC board.
 

OBW0549

Active Member
Throw it out and get a new one; it's obviously defective. Solder should melt instantly on contact with the soldering iron; and the entire process of soldering a joint shouldn't need more than 3-5 seconds.
 

unclejed613

Well-Known Member
Most Helpful Member
i've tried using a variac with pencil irons, and always end up with the handle melting where the metal part is mounted to the handle. if you are using unleaded solder, or silver solder, both of those require higher temperatures. a typical 15 watt "dumb" iron won't be hot enough. maybe you should try a higher wattage, or a temperature controlled iron. keep in mind that while modern solder needs higher temperatures, the formulation for the glue that holds the copper traces on the PCB has not been improved, and will tend to lift off the board more often.
 

gophert

Well-Known Member
Most Helpful Member
Your copper pads may be partially oxidized. Brighten them up with a good quality pencil eraser, fine (400 to 800 grit) sandpaper or a scotchbrite pad. Solder just rolls around on an oxidized copper or oxidized tin surface. Solder will "wet-out" immediately on the freshly prepped copper surface.
 

gary350

Well-Known Member
I am using solder with lead. Solder iron is probably 20 years old but never been used more than 5 minutes. Pencil eraser works great on copper PC board.
 

audioguru

Well-Known Member
Most Helpful Member
Please tell us the details of your solder. I use Kester 63/37 rosin core solder with my temperature controlled Weller soldering iron. A solder joint takes one second.

My Weller soldering iron is at least 50 years old, I use it every day and is still being manufactured. Its tip lasts for many years.
Its pencil has the heater and temperature control built-in and it is powered from a 24VAC transformer.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
If it's an iron-plated bit that has had a lot of use, it may be hollow...

Normal solder slowly dissolves copper & if the iron plating has a pinhole in it, the copper core can gradually vanish, leaving an empty iron shell that is a very poor heat conductor.

If it's a bare copper bit then the iron has had it.
 

philomel

New Member
One tip to improve soldering is to wet the cleaning sponge with distilled water. If you use tap water the tip will get calcium on it and make soldering a real pain. Don't use drinking water, use distilled water. they are the same price~.99/gal.
 

gary350

Well-Known Member
OK problem is operator error and soldering iron is basically brand new solder does not want to stick to the tip.

I decided to build an LM386 amp then I found a complete amp kit on ebay $1.50 free postage. I cannot buy parts and make my own circuit board as easy and cheap as a kit so I bought 2 kits. Solder does not want to stick to the tip I had to go back and forth 10 times from solder to part to get enough solder to solder 1 end of a resistor. The more I worked with it the better it began to work. It took me about 45 minutes to solder parts to the first PC board. By the time I finished the first board solder was sticking better to the solder iron tip. I was getting better at using the solder iron and better at soldering parts to the PC board. It only took me 10 minutes to solder parts to the second PC board.

Next I need to search for a 120vac to 12vdc wall plug inverter power supply in my box of inverters. I have a new unopened package of earphones I can use. I am going to solder a ceramic mic to this also. Maybe I get it hooked up and tested before dark. I have not checked the circuit yet I'm not sure if it is wired for gain of 20, 50 or 200.

I don't have a lot of use for this but it is something FUN to do while I am a prisoner of the house it is 17 degrees outside and it rained non stop for 2 days had lots of flooding.

Ebay has 5 LM386 amps per PC board for $5 free postage. I was thinking it might be fun to buy 4 PC boards connect them in parallel 20 amps all 1/2W each = 10W output. LOL Is that crazy or what. LOL. Well I probably won't actually do that.



 
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audioguru

Well-Known Member
Most Helpful Member
Gary: "I decided to build an LM386 amp then I found a complete amp kit on ebay $1.50 free postage."
Audioguru: Are they Chinese bad copies or fakes?

Gary: "Next I need to search for a 120vac to 12vdc wall plug inverter power supply."
Audioguru; The datasheet for an LM386 shows that it works well with a supply of 9V but with 12V the extra voltage makes mostly much more heat, not much more speaker output power.

Gary: "I am going to solder a ceramic mic to this also."
The datasheet of the LM386 shows that its input resistance is much too low (50k ohms) for a ceramic mic. Use a properly powered electret mic instead.

Gary: "I was thinking it might be fun to buy 4 PC boards connect them in parallel 20 amps all 1/2W each = 10W output."
Audioguru: No. Amplifiers in parallel produce the same output power into one speaker as one amplifier.
 

gary350

Well-Known Member
Gary: "I decided to build an LM386 amp then I found a complete amp kit on ebay $1.50 free postage."
Audioguru: Are they Chinese bad copies or fakes?

Gary: "Next I need to search for a 120vac to 12vdc wall plug inverter power supply."
Audioguru; The datasheet for an LM386 shows that it works well with a supply of 9V but with 12V the extra voltage makes mostly much more heat, not much more speaker output power.

Gary: "I am going to solder a ceramic mic to this also."
The datasheet of the LM386 shows that its input resistance is much too low (50k ohms) for a ceramic mic. Use a properly powered electret mic instead.

Gary: "I was thinking it might be fun to buy 4 PC boards connect them in parallel 20 amps all 1/2W each = 10W output."
Audioguru: No. Amplifiers in parallel produce the same output power into one speaker as one amplifier.
The PC board says 5 to 12v. Ok I look for 9vdc PS tomorrow.

I though ceramic and electret mic are the same thing. I have 150 electret mics some very small and some larger. Does size make any difference?

Before I do anything I am going to draw a circuit of this LM386 amp.
 

audioguru

Well-Known Member
Most Helpful Member
The PC board says 5 to 12v.
The datasheet is in English, not in Chinese.

I though ceramic and electret mic are the same thing. I have 150 electret mics some very small and some larger. Does size make any difference?
An electret mic is a condenser mic with 48VDC permanently stored in its electret material. Then it has a Jfet inside that must be powered. The performance of most of them is excellent. I used a very small one from a cell phone and it works fine. Earplugs have a tiny electret MEMS mic that works fine.
A ceramic mic is very old and is similar to piezo. It sounds awful.

Before I do anything I am going to draw a circuit of this LM386 amp.
If the mic can hear the speaker then you will have acoustical feedback howling and squealing.
 

sagor1

Active Member
That soldering iron is a 40W iron, and should be hot enough to solder almost anything.
The tip is removable, and I suspect you have some oxidation of corrosion on it where there is heat transfer. Just like the old 100/140W Weller guns, one had to re-tightern the nuts on the tip to get the current flowing properly. In your case, it could be some "dirt" between the heating element and the tip.
Take the tip out and clean it all around.

If the tip seems fine, and no solder sticks to the tip itself, it could be you are using a non-flux solder. Even a copper tip will oxidize, preventing solder from sticking unless there is a bit of flux to etch off the oxidation. Same for iron plated tips, though I find that less of a problem (usually). Having an even coat (real thin) of solder on the tip makes it easier to flow the heat at the junction of the components/board.

The final possibility is that the soldering iron is defective, not heating up properly.

There are various tip cleaners out there, though I never use them . I usually just re-wet the tip with fresh solder then wipe it off with a wet sponge.

Good luck...
 

MichaelaJoy

Active Member
Radio Shack soldering irons are used "in a pinch", and should not be counted on for steady
soldering work. Especially not for ROHS stuff, where there's no lead to allow a lower temperature iron to be used.

If you're going to do a lot of soldering work, I suggest you invest in a temperature controlled soldering station.
One that comes with multiple tips.

Take a look here:
http://nymag.com/strategist/article/best-soldering-iron-stations.html

I have this station.
https://www.amazon.com/X-TRONIC-XTR-4040-XTS-Digital-Soldering-Station/dp/B003TC8EQS

It has served me well over the last 2 or so years, although I have to admit that the Hot air section isn't pushing air correctly.

The entire soldering iron handle is replaceable (I have broken one already) and is available for around $15.00 USD.
I bought two replacements. :)

For building breadboards with #28 wire wrap wire, I use a very fine tip and a temperature of 650 F
Change to a large tip, crank the temperature up to 700F and you should be good to go. :)
 

gary350

Well-Known Member
Good thing I made a circuit drawing. Circuit will need a 10k resistor for the electret mic. Why is there a 4.7K resistor between pin 3 & 4. Pin 7 is not connected. The pink color 1/8" plug is input wonder what type input they expect me to use. Output to speaker is 2 solder pins. I would rather have 1/8" plug for earphones. Too bad I soldered all the parts on the PC board already I could build it different on a different PC board. OK I can still use a electret mic with 10k resistor and test this to see how well it works. Then unsolder the pink plug then connect it to speaker pins with 2 wires for ear phones. I have 20 of those 1/8" plugs on order made they come in the mail soon then I don't have to unsolder the pink plug. I can solder 10K resistor and mic on bottom side of PC board.

 
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