tin whisker

[bkubicek]

Hi!
I think that some more info on tin whiskers, and these things could be quite interesting.
http://nepp.nasa.gov/whisker/video/index.html
I stumbled on this topic, while watching this NASA soldering tutorial:

It would be quite cool if the showed soldering methods are still "up to date".

[Stonent]

Hi!
I think that some more info on tin whiskers, and these things could be quite interesting.
http://nepp.nasa.gov/whisker/video/index.html
I stumbled on this topic, while watching this NASA soldering tutorial:

It would be quite cool if the showed soldering methods are still "up to date".

Those NASA soldering videos make me want to tear my hear out when watching.

"Looks like Bob on the other side of the room didn't wash his hands after coming out of the bathroom, we're going to have to wipe and sterilize our solder again"

[Monkeh]

Hi!
I think that some more info on tin whiskers, and these things could be quite interesting.
http://nepp.nasa.gov/whisker/video/index.html
I stumbled on this topic, while watching this NASA soldering tutorial:

It would be quite cool if the showed soldering methods are still "up to date".

Those NASA soldering videos make me want to tear my hear out when watching.

"Looks like Bob on the other side of the room didn't wash his hands after coming out of the bathroom, we're going to have to wipe and sterilize our solder again"

And this attention to detail is what keeps spacecraft, whether manned or otherwise, working..

[Stonent]

And this attention to detail is what keeps spacecraft, whether manned or otherwise, working..

I wouldn't think they'd be hand soldering everything for that though.

Now, two things I did get from the video that I liked. The resistor bending tool and bending the pins in the direction of the trace.

Also did not think about stressing the component. I've been known to take a component that is slightly askew and melt the solder on one side and pull it down by the pin while leaving the other side soldered down to straighten it. I do see how that could be a problem now and will be more mindful of it.

[Monkeh]

And this attention to detail is what keeps spacecraft, whether manned or otherwise, working..

I wouldn't think they'd be hand soldering everything for that though.

There's more hand work involved than you might think, it's not as if they produce large quantities of some of this stuff.. Plus repair (kinda worthwhile when the board cost six figures), modification..

[Stonent]

I hear they're looking into that new fangled 74 series logic now.   

[AndyC_772]

Interesting that he bends the resistor leads one way to retain the part in the board, then after cropping, bends them a completely different way. He even applies quite a bit of twisting force with that wooden stick during the clinch process, which I can't see being a particularly good technique for ensuring the component and its end caps don't get over-stressed.

[NickS]

Also did not think about stressing the component. I've been known to take a component that is slightly askew and melt the solder on one side and pull it down by the pin while leaving the other side soldered down to straighten it. I do see how that could be a problem now and will be more mindful of it.

I do that too and couldn't care less. Never had a failed resistor from it.
Mind you I'm not building spacecraft.....

[ElectroIrradiator]

Do keep in mind that components on a spacecraft may be subjected to very serious levels of thermal extremes. A component assembly may have to survive repeatedly being frozen down to the temperature of liquid Nitrogen. This could happen for instance if there is a temporary fault condition with the attitude control, or something similar. Same thing for literally being baked in the high noon Sun for a while...

[Stonent]

Do keep in mind that components on a spacecraft may be subjected to very serious levels of thermal extremes. A component assembly may have to survive repeatedly being frozen down to the temperature of liquid Nitrogen. This could happen for instance if there is a temporary fault condition with the attitude control, or something similar. Same thing for literally being baked in the high noon Sun for a while...

Possibly the temperature of solid nitrogen too.

[ddavidebor]

The fact is if a satellite turn around earth 40 times a day, you have 40 extreme temperature changes.

For everyday. For 15 year.

[grumpydoc]

Hi!
I think that some more info on tin whiskers, and these things could be quite interesting.
http://nepp.nasa.gov/whisker/video/index.html
I stumbled on this topic, while watching this NASA soldering tutorial:

It would be quite cool if the showed soldering methods are still "up to date".

The NASA video was interesting but does anyone outside NASA call a PCB a "PWB"??

[Monkeh]

Hi!
I think that some more info on tin whiskers, and these things could be quite interesting.
http://nepp.nasa.gov/whisker/video/index.html
I stumbled on this topic, while watching this NASA soldering tutorial:

It would be quite cool if the showed soldering methods are still "up to date".

The NASA video was interesting but does anyone outside NASA call a PCB a "PWB"??

Sometimes, it's an old term.

[Kjelt]

Pffff now at least I know why those products from nasa are so expensive, they take ages to assemble 
Come on use a semi cleanroom, gloves, bent it the right way the first time and you,re done in 10 seconds.
Are they using SMT nowadays or is that still too risky? If you have such thermal shocks, I wonder how SMT will hold up.

[Neilm]

Hi!
I think that some more info on tin whiskers, and these things could be quite interesting.
http://nepp.nasa.gov/whisker/video/index.html
I stumbled on this topic, while watching this NASA soldering tutorial:

It would be quite cool if the showed soldering methods are still "up to date".

The NASA video was interesting but does anyone outside NASA call a PCB a "PWB"??

IEC61010 still refers to PCBs as PWB.

[walshms]

Now, two things I did get from the video that I liked. The resistor bending tool and bending the pins in the direction of the trace.

US Military Wiring Specification WS-6536 revision C; can't remember for certain, but I think it was an Air Force spec.  Stringent as hell, but very highly reliable, especially in high vibration/high stress environments.  I used to assemble power supplies that had to meet the requirements of that spec and they were beasts... and yes, everything was hand soldered, inspected, tested, reworked as needed, cleaned within an inch of its life, tested a second time and then potted with a re-enterable compound before being tested yet again.

Also did not think about stressing the component. I've been known to take a component that is slightly askew and melt the solder on one side and pull it down by the pin while leaving the other side soldered down to straighten it. I do see how that could be a problem now and will be more mindful of it.

Amazing how easily some things can be damaged.  When it's got to be as reliable as it can possibly be, you don't mess around.

[walshms]

The fact is if a satellite turn around earth 40 times a day, you have 40 extreme temperature changes.

For everyday. For 15 year.

The International Space Station circles the earth about every 92 minutes, roughly 16 orbits per day.  Satellites higher up orbit slower... so it's not quite 40, but the extremes are indeed extreme.  Think in terms of up to ~200C swings, depending on the emissivity of the surface in question.  That's why most of the stuff up there has heaters built in.

[walshms]

Are they using SMT nowadays or is that still too risky? If you have such thermal shocks, I wonder how SMT will hold up.

Sure; SMT is commonly used now, but the requirements are probably just as painful to meet.  Proper centering on the pads.  Solder fillets on component legs that must show the entire outline of the component leg (no excess) and make a smooth transition to the pad.  Each and every one.  No nicks on component surfaces, or the component legs.  The slightest scratch is enough to cause an inspector to reject a board.

Think that's expensive?  Trust me on this -- it's far more expensive to send something up there that fails because the time wasn't spent on the ground to ensure it was right.  That's why teams spend up to 10-15 years preparing hardware before sending it where it can't be repaired...

[Kjelt]

Sure; SMT is commonly used now, but the requirements are probably just as painful to meet.  .........

Probably also gluedots to keep the components mechanically fixed without having mechanical stress on the solder joints?
They probably still use leaded solderpaste? 

[Stonent]

I think given the poor reliability that RoHS has added to electronics, I'm sure of it.

[ElectroIrradiator]

They probably still use leaded solderpaste? 

Yes, they do. Solder containing lead is still allowed for use in critical applications like aerospace, military and medical equipment.

[AndyC_772]

I should hope so. Lead leaching out of scrapped PCBs into drinking water supplies is less of a problem in space than it is on Earth!

[Stonent]

I should hope so. Lead leaching out of scrapped PCBs into drinking water supplies is less of a problem in space than it is on Earth!

Lead came from the earth in the first place.

[romantronixlab]

Since i have been reading information on tin whiskers why is formed etc. Ill post some pics for those lazy enough to search google and of course for the novices in the forum.

Removing lead from solder may seem a smart idea environmentally, but the resulting microscopic growths called tin whiskers could be just as problematic. - theguardian.com

Credited to the respective providers.
Tin Whisker Detached from RF Shield/Bracket which then bridged exposed conductor. nasa.gov


Millstone nuclear generating plant in Connecticut shut down when a circuit board monitoring a steam pressure line short-circuited. theguardian.com

nasa.gov
electronicstheory.com

[SeanB]

Had it on my car as well. Took the unit apart and had a little work on it with a soldering iron to check joints on connectors, and scrubbed it with IPA. Seems to have fixed it for now. Was rather annoying to drive with all the warning lights lit, including for diesel heating, EGR, ABS, SRS, overheat and oil pressure. They stayed on with key off as well.