(SCI TOM) Cold solder joints?

[Algorithm]

I have 2 different pieces of equipment that are experiencing this. after replacing the component/chip in question on that particular board, I noticed cold solder joints beginning to form where it was not like that before I worked on it. I dont mean nearby the desoldering, its on the other side of the board in a few places. It seems to be spreading through the board. alot of through-holes look pointy in places, instead of dome shaped... How could the board get hot enough to melt certain points all over the board? Anybody ever seen this before?

EDIT: I thought maybe the temp of the iron?
Maybe flux remnants? but how could it travel so far?

[Stab Frenzy]

That can't happen. Joints don't become cold, they're like that if you don't solder them properly in the first place. You probably just never really looked at the other ones closely before.

[Algorithm]

"That can't happen. Joints don't become cold, they're like that if you don't solder them properly in the first place. You probably just never really looked at the other ones closely before."

Well, say there is a product with cold solder joints in its future, when they show themselves, do they all go at once?
because the manufacturer had to use the same cheap solder on everything right? so every point potentially could be cold if manufacturing conditions permit?

Or is it cold from the get go, visually detectable?

I thought that originally, just assuming I overlooked them until I had replaced the part.
This is on a TOM, I replaced the z80. before, it would start up, but freeze shortly after.
I replaced the z80, afterwards, I noticed I desoldered a few of the tiny points in the process. So I dabbed more solder on there. Everything looked good. Then, I took a toothpick and ran it between each leg of the z80 with a paper towel to soak up any leftover flux. I inspected both sides of the board at this point, touched up a small bunch of 5 points that had tiny holes... plugged it up, tested it, it worked! no freeze! so I put it back in the case, when I try to power it on, no 7 segment displays... So I take it apart again, I notice a point behind the display completely bare, just a ring with a hole through it... + many more in places I am almost sure were there prior... That is the only relation I could make... how it all worked moments before I put it back together...

[meatballfulton]

Or is it cold from the get go, visually detectable?

Good joints should be shiny. Cold joints look dull grey.

[madtheory]

...dabbed...touched up...

From your description, it looks like your soldering technique is at fault. If you put new solder on top of old solder you will create dry joints. It also sounds like you heated the board itself too much, and removed the pads.

But I could be wrong, we'd need to see pictures.

[Algorithm]

Good joints should be shiny. Cold joints look dull grey.

Ok, what about air holes the size of a needle? thats what I meant by "cold". that might not be the most accurate term, I think I read that cold solder is an old term used widely for mysteriousness... This is good info either way though... Can solder go cold from weather? because some stuff left in humid cellars with unregulated temps seem to get discolored solder.

...dabbed...touched up...

From your description, it looks like your soldering technique is at fault. If you put new solder on top of old solder you will create dry joints. It also sounds like you heated the board itself too much, and removed the pads.

But I could be wrong, we'd need to see pictures.

Ok, now we are getting somewhere, so any cold joint with insufficient wetting, etc, needs to be removed completely and replaced with new? perfect...
you might be right about that too. I use an unregulated temp iron from the 80s... hard to believe a few moments could melt spots across the board, but the trace is doing its job I guess.
Any suggestions on a simple legit adjustable iron?

Thank you all for being patient with my lack of understanding.

[synthroom]

From here - http://en.wikipedia.org/wiki/Soldering

"Used solder contains some of the dissolved base metals and is unsuitable for reuse in making new joints. Once the solder's capacity for the base metal has been achieved it will no longer properly bond with the base metal, usually resulting in a brittle cold solder joint with a crystalline appearance.

"It is good practice to remove solder from a joint prior to resoldering—desoldering braids or vacuum desoldering equipment (solder suckers) can be used. Desoldering wicks contain plenty of flux that will lift the contamination from the copper trace and any device leads that are present. This will leave a bright, shiny, clean junction to be resoldered."

The quote above shows why touching up a joint is not a good practice.

You can't affect the solder on a joint that's across the board. If there are more spots on the board on second look, then you most certainly missed on first look.

[Algorithm]

Thanks for the replies everyone.
Now for another strange question, if there is an empty through hole, like a dead end?
If there is no solder in that hole, will it not work?



the 7 segment displays are not working after putting it back together.
it worked before the board went back into the case.

the q101 transistor is a npn 2n3904, Im seeing +5v on the collector...
does that seem right? someone keeps trying to tell me an npn does not work like that...
I tried to tell them that I think the 2n3904 is used as a switch for the leds...

Can anyone confirm or deny this?
Thanks ahead of time.

[synthparts]

Pics would help but it sounds like you destroyed some solder pads/circuit traces either soldering or desoldering...

[Algorithm]

continuity is good on every trace I touched...
& like I mentioned, after the z-80 was replaced, it worked.
it failed to work when it got bolted up in its case. after soldering was successful..

cant upload any pictures, but the schematic should not be too hard to find.
searching google for "tom 420 schematic" should work.