How to recognize cold February

how to recognize that solder is cold and what are the methods of its detection

When you touch the soldering iron with rosin, the tin flows down and you can see the lack of connection. When looking under a magnifying glass, you can see a heterogeneous structure, and in the extreme case, an evident border is visible. It is best to heat all suspected February one by one with a soldering iron, using a thin flux (0.7mm).

I think they feel in some systems and in some places as well as in some brands it just comes with time, how to recognize? rugged. non-shiny.appearance resembling tarnished aluminum and having a specific, difficult to describe, cracked circumference, which sometimes can be seen only under a magnifying glass in practice, cold February or otherwise their effects usually affect the most exposed places of coil connections on plates, heads on TV, all sockets in the equipment, especially in this more experienced Western practitioners know what I can talk about for so long

a spray, the so-called freezer, is used for this, but you can also use lighter gas to direct a sharp stream of gas to a suspicious place which will cause freezing then you will practically see cold February with the naked eye
greetings

offers a good magnifying glass and decent lighting of the workplace.

I was lucky when the TV stopped working, I turned it on and I immediately saw cold February (because they sparkled)

I could never recognize them

Sometimes the color goes from silvery to gray, this is cold February when overheated. You can make sure by soldering the point.

Well, I meet them sometimes. During the assembly of some arrangement ...
Sometimes they arise when the solder overheats, e.g. they hold soldering irons for too long, when there is too little flux and the like. If I want to improve some soldering, I use soldering irons and a piece of rosin and it is usually spox, sometimes you need to add some fresh tin 8)
greetings

Hello,
On the example of the CB radio - Alan 100 plus fault, I will show what cold February looks like and what may be the cause of their formation.
The failure manifested itself once in a quiet - once in a loud (normal) radio operation. Light blows against the casing brought a temporary improvement.

The reason was the cold (huffed) February of the R129 resistor right at the antenna output.







It also turned out that the antenna socket has some play - a slight left-right rotation of the socket was possible and this was most likely the cause of the defect. In addition to repairing the brazed joint, I fixed the socket thread with cyanoacrylate glue.

Regards

Somewhere I saw a description of such a method (I do not remember where - in "Young Technician" in the "At the workshop" section? In a book describing the construction of radio receivers and their repair?): Lightly tap the plate with an insulator rod and listen to interference - the closer to the cold solder , the lighter a tap is enough to make them audible - such a game of warm-cold until we find the right element and a badly soldered tip. Of course, if such a solder connects a bit, because if it does not, even when tapped, it is nothing. Sometimes it is possible to find cold solder, sometimes not - there are such malicious cases that a slight tapping away from the cold solder is enough, because the vibrations of the plate propagate so much that they focus on the cold solder ...

And another method (to be used when there is no connection at all) is to measure the voltages - everywhere - until you find a place where you can see the connection and the voltages are not equal - then you know that the connection contains solder that does not connect. Worse, if there is no direct voltage on such solder (e.g. both sides have a connection through a resistor to ground and thus the ground potential) - you can measure the resistance (if something does not match the diagram, it indicates a faulty solder), or with the system turned on touch the wire held by the insulator (as it is in the signal path, maybe you can hear something in the loudspeaker); you can also use a signal finder, but it does something only when you know that there is a signal at the input and there is no output.

As for measuring voltages: if the meter shows the voltage between the terminals (but the terminals, not the path to which they are soldered, nor the tin they are soldered to) of a capacitor, resistor, diode, it means that both terminals are connected; for a transistor, you can measure base-emitter and collector-emitter voltages. Zero voltage at any measurement does not mean that any solder is defective, but it is possible and it is probably worth taking a measurement to check it. The voltage between the tip of the component and the path to which it is soldered indicates no connection. But if, for example, the collector-emitter voltage is 0, and there is a voltage between the emitter and the path to which the collector is soldered, then collector soldering does not connect.

The very term "cold solder" comes from times when a soldering rod was still soldered with tin and usually with a high-power (and therefore temperature) soldering iron. Tin without flux and too high a temperature meant that even the "eye" looking connection did not conduct properly - there was an oxide layer at the contact point of the element's foot - pad. Often, this oxide was also formed during the operation of the device. This is one of the reasons why then it was fashionable to use rosin in large quantities - which some remember what PCB looked like at that time ...
Currently, the name remains, but it also applies to mechanical damage to the weld - either as in the example from Post 10, or resulting from the tin itself - the Chinese are in the lead, using lead-free tin with very poor mechanical properties and poor oxidation resistance in budget productions. I have had at least several dozen cases of modern equipment with such defects - the tin, about 2-3 years after the equipment was manufactured (!!!), simply turned into a gray - non-conductive - lump. It was enough to remove it with rosin or a better flux and put a new one, and the equipment suddenly miraculously revived ...
In the case of old equipment (over 20 years old), cold solder was also formed on the pads in the vicinity of elements that were heating during operation - frequent and repeated temperature changes (on - off) caused microcracks in some tin alloys, which over time caused a similar symptom as in the 10th post in the lower photo - the leg of the element was surrounded by a "wreath" of cracked tin.
In each case, "tapping" the PCB with the handle of the screwdriver helped to locate (at least narrow the search area) the place of the problem.

Evidently cold examples
solders

tin, after approx. 2-3 years from the production of the equipment (!!!), it simply turned into a gray - non-conductive - lump

Maybe this equipment was stored in a low temperature? At temperatures below 13.2 ° C tin recrystallization can occur (but it requires initiation, "contamination") - the metallic becomes gray, and the gray one is no longer a metal, hardly conducts electricity, and crumbles into a powder - this is called leprosy tin (the smallest fragment of such a powder "infects" the tin). The Russian army used to have a problem with that - the uniforms had tin buttons, and if they stayed in the cold for a long time, only powder was left from the buttons. And unfortunately, tin elements are found in historic objects (e.g. organ pipes were made of tin - if they are not kept warm, because the priest saves on heating the church, they turn into powder). The alloying elements change the temperature limit below which this can occur (and when the phenomenon of "leprosy" was discovered, chemists began to study it) - e.g. lead (and many others) lowers it - but in old items it was not used because it was not known. . If the Chinese had not thought about it, they could have used the tin without the additives that made it less susceptible to leprosy.

_jta_ wrote:

Maybe this equipment was stored in a low temperature? In temperature

In one - two cases - maybe. But in several dozen? From different clients? I doubt it. Anyway, from what we managed to suck off (after feeding the flux and melting some of the binder remained in the form of "tin", because the oxides had separated) it was visible to the naked eye that with the solder as such (even the worst silver) this alloy did not have much common. Still gray, dull ...

_jta_ wrote:

this is called tin leprosy

It is also known as "tin blight" - but it is more of pure tin. In combination with lead or other metals (silver, nickel, copper), this phenomenon no longer occurs.
For the first time, the "tin plague" was noticed during one of the first expeditions to the North Pole - where the tin plague ate all the tin cans (then they were made entirely of tin).

When heated with a soldering iron, the gray tin turns back to metallic (provided that it has been heated successfully). Maybe the Chinese gave too much lead?

Wikipedia writes about an expedition to the South Pole and tin cans soldered with kerosene (in 1910), but also about an earlier case with Russian army uniforms in the 1860s, and about a possibly false story about the problems with buttons that the army was supposed to have had. Napoleon (in the winter of 1812/1813).

_jta_ wrote:

When heated with a soldering iron, the gray tin turns back to metallic

Tin yes, oxide no. The oxide flows to the top (as long as you use a flux) and becomes "slag".

_jta_ wrote:

Wikipedia writes about an expedition to the South Pole and tin cans

I didn't use the wiki, from what I remembered from the chemistry lesson. It is possible that some distortion has arisen somewhere.
Anyway it does not matter. The main thing is that in the case I have described, there was no pure tin, or pure lead (I had a bit of a deal with lead and I know how to recognize it. It was definitely an alloy, but to me it looked like it was recovered from some plates, thrown into a soldering bath. on the wave (these PCBs were one-sided) and skimpy flux - such overheated contaminated tin for soldering.

Cold February is a slang term for everything soldered and not connected. I deal with cracked solder in most cases. They have never been cold, but during operation, temperature changes, vibrations of heavy elements and / or high current flowing, the tin delaminates and loses its conductivity. Lead-free especially. But I also call it cold February
A typical cold solder is the leg of the element covered with tin but not soldered. Such a thing arises when soldering at too low temperature, with a weak soldering iron, i.e. snot common among adepts of the art of soldering.