How to tell if chips overheat while soldering

Question

I am new to soldering and I am afraid that I am getting some of my chips too hot. I'm sure this will be less of an issue when I get more experience. I also ordered some DIP sockets but they won't arrive for a few months. In the mean time is there any way I can tell if I have damaged my chips? I am afraid that I won't by able to tell if I have made a mistake in the circuit on the protoboard or the chip is just damaged and malfunctioning. Generally speaking, can you destroy a chip with heat before it gets too hot to touch? I know datasheets list maximum temperatures but it seems like the temperature inside could get much hotter than the temperature you can feel on the outside.

Answer 1

First of all, it's unlikely that you will destroy your parts even if you hold the iron on the pins for a long time (over 5 seconds). Components are designed to withstand a good bit of heat and time (sometimes minutes) during mass production. However, an iron tip is usually hotter than the temperatures used in factory production, so there is risk of damaging a part if you hold the iron on it too long. Some spec sheets will give limits on soldering time, but these are usually aimed at mass production temperatures, not a hand soldering iron.

I, like many others here, have never fried a part from overheating it. But if you're working with a particularly sensitive part, there are a few techniques you can use to mitigate the risk of thermal damage (some CMOS or MOSFETs are known to be more easily damaged... CMOS technology is used in some digital logic ICs, for instance).

• Solder alternate pins, or give the chip time to cool off between pin
• Attach a thermal sink in between the chip and the solder joint to draw heat away before it damages the part. Note that this can make soldering more difficult as it will be harder to heat the actual joint.
• Use sockets (like you're doing already).
• Use a lower temperature (make sure to have a tip in good condition, and a little blob of solder already on the tip to help transfer heat--"tinning" the tip).

In general, though, if you spend no more than 2-3 seconds on the joint, you'll probably be OK. And for large wires, connectors, or ground planes, you may need to spend much more time on the joint to allow the solder to thoroughly wick and bond to all the surfaces. For joints with a lot of metal, try to keep the soldering time below 5-10s.

In terms of temperature, if you have an adjustable temperature iron, stay below 650°F for leaded solder, and 750°F for lead free. I will occasionally set the temperature to 800°F for large components or ground planes. You're better off finishing a joint in 5-10 seconds at a higher temperature than holding the heat on for much longer at a lower temperature. Long soldering times give the heat time to spread to the components where it can do damage.

How to tell if there's damage? If the component changes color, that's a bad sign. If the board browns or chars, that's also bad. The unfortunate reality is that you may do latent damage to a component by heating it too long and too hot. For example, a chip may initially work, but fail early, or some of its specs may be slightly off from their original design.

As an aside: Why is an iron tip hotter than temperatures used in mass production (and the temperatures noted in spec sheets)? During mass production, the entire board is usually heated, so the pcb, IC and joint are all at the same temperature. When you hand solder, the pcb and IC are much colder than the joint, and are constantly drawing heat away from the joint. Your iron must be much higher than the melting point of the solder to compete against these heat sinks.

Answer 2

It's all about knowing how to solder.

You should use a temperature controlled soldering station. Set temperature to 300°C and you'll be able to heat each pin of DIP chip for 2-3 seconds without damaging the chip. Guaranteed.

See PDF by Adafruit.

Answer 3

I have been soldering for a couple of years now, and I have not damaged a chip yet. I am usually a bit careless about how hot the chips get (which bad practice). I guess my point is not to worry about it too much, as long as you are not applying excessive heat to a pin for too long a period.

Answer 4

The best option at this point would be use the Datasheet of the specific chip and check between the pins, using a multimeter, whether it shows for the expected values. for eg. i am doing the same work, and whenever i solder a chip in this case lets consider a n-channel mosfet; i would check between gate pin and drain pin for High Resistence or Open Circuit. Also it will be really help you, if you could check some of the vids on youtube for the most common practices of soldering for noobs. Also keep the whole process, as you are starting now, VERY SLOW. take it easy on setting up the chip.

Answer 5

One thing that hasn't been mentioned is the eutectic point of solder. If a pin is ever over heated it's almost always due to someone over heating the solder, causing it to de-alloy which then shifts it's eutectic point to a higher temperature. The poor person then applies more heat, etc. etc. and soon they are dealing with a poor joint, de-alloyed solder and temperatures waaaay beyond they thought was possible.

The only way out of this is to add fresh solder (and MORE than was in the original melt), suck/wick the fresh and old out and start over.

The solder will start to look bad, not shiny and perhaps even granular.

Answer 6

I am afraid that I won't by able to tell if I have made a mistake in the circuit on the protoboard or the chip is just damaged and malfunctioning

you talking about a mistake? Then first get your diagram and check every node and a branch twice that they connected correctly and also verify that no other terminals were shorted or connected at the wrong place. Do it twice for every branch and a node in your diagram.

You better prepare a tabular checklist.That's the method that we are following in here.

You could use statistics and delta debugging techniques. And here , more statical methods will work. Such as guessing the devices which are more lead to fail. etc etc.

If your protoboard provide some test points, use them to test with the diagram.

Answer 7

These are my advices:

• Make sure that the surfaces are clean
  If the surfaces which you want to solder each other are dirty, the solder won't fold them up. Instead, it will become tiny beads.
• Use a high quality solder
  Half of a successful soldering is using qualified solder.
  When it was my first time to to do soldering, I though all solders are same and I bought the cheapest one in the market. All my solders were terrible. I thought that I was bad at soldering. After a while, I coincidentally happened to use my friends solder, and I was surprisingly soldering very good with that one. Then I bought a qualified solder, and my soldering became much better.
• Work in optimum temperature
  If the soldering iron is too hot, it will damage the element. If it is too cold, soldering time will increase, the element will be heated up for a longer period, so it will be damaged again. If you are inexperienced, I suggest you use a temperature controlled soldering iron. Refer datasheet of the element for optimum soldering temperature. If an optimum temperature is not specified, you may set your temperature to 300^oC.
• Try to be as fast as possible, don't exceed maximum soldering time
  You aim is to make the solder fold up the surfaces perfectly in minimum time. If you can't complete soldering in the maximum specified soldering time, let it cool down. You go on soldering other leads, and come back to the incomplete one later.
• Make the holes small
  Make the holes smalls so that the leads of the element lightly jams and stays fixed in the hole when you insert the element to its place on the PCB. If you make the hole radius large, the amounts of soldering time and the solder to use will increase, the element will be heat up more, and your PCB will not look good. It is also bad for high-frequency circuits.

Answer 8

Lots of excellent answers. My two cents based on my experience - may corroborate with what others have mentioned:

• Use a heat sink for the concerned pin - use the small crocodile clip (obviously strip away its plastic covering). If needed, attach a larger crocodile clip to this one. I did this for soldering header pins to my MSP430-F2013.
• Always use solder flux.
• Make sure (this is very very important) that your soldering iron tip is nicely shining and free of any dirt/black residue - you must tin it regularly before and after an actual solder operation. If the iron tip is not clean you will not get good heating - use something like a Dremel with abrasive attachment to get it back in 'shining form'.
• Use either a lint free damp cloth or better a good quality damp sponge to wipe the soldering iron before and after tinning.