Use of heat sink when soldering transistors?

Question

Hello
I was about to solder several 2N2907 and 2N304 transistors to a PCB, but I was surprised to see the instructions for the kit I was assembling made no recommendation for the use of heat sinks. Can I safely solder these transistors onto the board without frying them, without the use of some sort of heat sink?

Answer 1

Heat sinks would never 'hurt' things. An alligator clip on the transistor lead off the PCB will take some heat away from the transistor die. BUT, so long as you don't hold the soldering iron for more than about 10 seconds on the lead/pad (more than enough time to get the solder to flow and make a joint), you shouldn't have to worry about frying the transistor.

Sometimes manufacturers have specifications for soldering in the datasheet. From TI's datasheet for the 2N2907:
"Lead temperature 1/16th inch from case for 10 seconds not to exceed 230 degrees C".
That's quite a bit of soldering iron energy.

What I do, when making a PCB, is: solder one lead of a transistor, then move to the lead of another part (resistor, cap, IC), then come back to the 2nd lead of the transistor, then move to another part, then finish the transistor -- instead of soldering C, B, and E; one after another.

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Answer 2

Soldering Heat Sink

Answer 3

Yes if you do not get them too hot in the process. The trick is to just get the joint hot enough for solder to flow fast enough the heat does migrate up to the transistor before you are done.
You can do this several ways. First use a low temperature solder like 63%--37% solder. This is the best solder to use in electronics on PCB's since it goes directly from the liqiud state to solid. This minimizes the danger of cold soldier joints.
Using 63% -- 37% solder also enables you to use a lower wattage(15 to 25 watts) lower temperature soldering iron as well further minimizing the danger of getting the component you are soldering too hot and damaging it.

The other way if you are fast enough is to use a higher temperature higher wattage( 25 to 50 watts) soldering iron, and get it on and off real fast as soon as the solder flows. But you have to be fast or else you will damage or destroy the component you are soldering.
You really have to pay attention and get on it and off it real fast using the second method.

You can get away without using a heat sink with Si transistors and diodes a lot more than you can using Ge transistors and diodes and components since silicon will stand a lot more heat than germanium transistors.

You also want to make sure your tip is electrically isolated as well. I've had soldering irons where when I measured the voltage on the tip I measured over 50 volts from the tip to ground. That will destroy most electronic components mounted on PCB's.
That is why I have gone, a long time ago, to cordless rechargeable soldering irons with iso tips to eliminate that problem; especially at work where every body and their brother or sister uses the soldering irons. I buy my own and keep them locked up when not using them or charging them for that reason. So I will know what kind of condition they are in.
Just remember you can get away with it a lot more when soldering silicon transistors and diodes not using a heat sink.
But with germanium transistors if at all possible use a heat sink.
Hope that helps.

Answer 4

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RE:
Use of heat sink when soldering transistors?
Hello
I was about to solder several 2N2907 and 2N304 transistors to a PCB, but I was surprised to see the instructions for the kit I was assembling made no recommendation for the use of heat sinks. Can I safely solder these transistors onto the board without frying them, without the use of some...

Answer 5

No heat sink required if you solder them properly. Using flux is the trick to getting the solder to flow quickly. You also need to be working with a clean tip on your iron. Better soldering irons have good temperature control and will adjust very quickly to keep the temp constant. Try and practice on some old boards to get the hang of it. Once you get the feel it is very easy to do.

Answer 6

You can safely solder those devices without a heat sink. Most components of that type are quite robust and can stand up to the thermal demands of soldering. Use a good iron with a clean, tinned tip. The cleaner the tip, the easier the heat transfer between iron and component.

Answer 7

just get good at soldering, you need to practice making good clean joints in a fraction of a second, then nothing gets warm. in industry the whole pcb board gets floated accross a solder bath to make all the joints, it literally like an oven roasting dish full of hot molten 60/40 tin lead solder, it skims over the top and then is cleaned with isopropyl alcohol or another chemical called CNP-30 to remove the residue flux etc. you'll be fine, just practice on resistors first, keep wiping the iron's tip clean on a damp (but not wet) sponge. put the iron onto the items to be soldered to heat them then feed the solder. NEVER put solder onto the iron then try to wipe it on the joint

Answer 8

sure, solder normally without a heatsink, just dont go overboard.
small iron, small solder, a little flux.
MIKE

Answer 9

I DON'T CARE WHAT YOUR SOLDERING ALWAYS USE A HEAT SINK NO MATTER WHAT CHEAP INSURANCE

Answer 10

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