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Let's play Spot the Cold Solder.
(lemmy.ca)
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this post was submitted on 31 Dec 2023
154 points (94.8% liked)
Mildly Infuriating
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Care to elaborate, for those not as experienced as soldering? This isn't the most relatable post without some additional context.
For instance, my only experience soldering is with audio equipment (think wires and potentiometers), never with PCBs and I have no clue what you mean.
Solder is a low melting point metal used to join two metals, where the solder fills the gap and bonds to both metals. This is commonly used in electronics to bond components to the board. For a good solder joint, the solder must be brought up to the proper temperature, and the pads on the PCB (metal 1) and leads of the component (metal 2) need to be heated enough. Additionally, flux is added to the solder to remove oxides on the component leads and PCB pads to allow the solder to bond to the metal; oxides can prevent the solder from sticking.
A cold solder joint is one that does not reach the proper temperature and/or does not have enough flux, leading to the solder not bonding to the joint, having a scaly/bubbly/matte appearance, and a weaker more brittle joint. Flux also doesnt do as good a job at lower temperatures so it's important for the joint to get hot enough, and to heat the pads/component leads too
Then with my shitty ass soldering iron and skills I overheat the surrounding components while attempting to bring the soldering spot to temperature...
This is a circuit board from my slow cooker. It quit heating a week ago so I opened it up and found a broken wire. That was easily fixed.
I figured while I had it apart I should look at the display board and see if I can fix the missing segments. I resoldered the one pin but nothing changed.
Unfortunately my eyes arent what they used to be so the others someone pointed out will be a challenge.
5th pin down on the far left side in the picture.
There's no solder on the pin.
Most of the joints are questionable, that one is flat out bad.
Get some cheap magnifying glasses with a light.
Oh, that makes more sense. The heat from the malfunctioning cooker may have resoldered these points badly.
I was curious how like half the points were bad, and that could explain it.
e: especially since they’re all at the bottom half of the board. That was closest to the heating element, right?
That'd be about right. There's insulation inbetween.
Unlikely any heat from the slow cooker did anything. Solder melts at 370F. A slow cooker is never going to get anywhere close to that hot.
Strange that all the bad points are in the lower half of the board, and that most points in that half are bad, then.
e: could a malfunction make it heat beyond 370f?
It's most likely that it's related to the original manufacturing. These will be machine wave-soldered, not hand soldered, and having quality vary across the board isn't impossible if the setup/operators were less than ideal.
Perhaps. It still seems odd to me that this board was mounted vertically inline with the heating element and the bad parts I identified line up with that, before I knew that was the case:
Cold solder is what happens when the solder didn't quite reach the temperature needed to completely melt and do contact, so it looks brittle and would be potentially a faulty connection.
With that said I couldn't spot it in the pic
There are a bunch of questionable solder joints.
Like half the pins.
But the absolute worst is the 5th pin down on the far left side. There's so little solder used that you can see into the hole.
A few others are also a bit lacking as well. Almost all of the joints are ugly as sin...
!remindme 24h