What makes 0603 LEDs stick to probe?

[rogerk8]

Hi!

I had an interesting chat with a physisist colleague of mine this week.

Working with modern small electronic components I began to wonder why my extremely pointy probes, measureing the direction of the light emission diode, stuck so irritating hard to it that it could not break loose after I had established anode/cathode.

I also had trouble releasing it from the nippers with the purpose of soldering it to the tiny PCB pads.

So I asked my colleague why.

The too obvious reply was sticky dirt but neither him nor me really believed that.

Remember that these tiny LEDs weighs almost nothing.

We further speculated that there might be some magnetism in the probes like it is possible to magnetize something iron-like just by moving a magnet back and forth (which also is a strange phenomena because do you really have to move the magnet?).

I said that I don't believe that is the reason either and that is because the metal part of the LED is made of non-magnetic copper and tin so it doesn't matter if the probe or nippers is magnetic or not, I said.

Then he had an idea that perhaps things just stick to each other if they are really close to each other.

I did however refere to a scientific program I saw not so long ago that taught me that nothing really touches anything and this is due to the electromagnetic forces of the outermost electrons.

So what is the correct answer?

Roger

 

[CWatters]

Bit of googling...

http://www.freetronics.com/pages/surface-mount-soldering-with-a-toaster-oven#.VDJmoGctDmQ

You'll need to place parts that are small enough to lose in the palm of your hand and if the tweezers are even slightly magnetised the parts will stick to them and you'll go slowly insane. I bought some super-fine non-magnetic tweezers from - you guessed it - Jaycar. Part number TH1754, about $5.

http://forums.adafruit.com/viewtopic.php?f=42&t=13258&start=15

Ha! My tweezers are too magnetic-- I find even 0402s almost impossible to use.

http://www.hobbyelectronics.net/tec_smd-soldering.html

A good quality metal pair of tweezers is also essential. They should be none magnetic as most SMD components seem to be ferrous and “jump” up onto the tweezers when you move in for the grab, making it very difficult to pick the components up properly.

 

[rogerk8]

I now agree that they seem ferrous but what is it whith that copper/tin/lead/gold alloy that is ferrous?

Is there perhaps some iron involed also or what is it?

And if it's iron or some other ferrous material, why?

To me tinned copper should suffice.

Roger

 

[CWatters]

There are a lot of more exotic materials that are partially magnetic. Found several lists here..
http://chemistry.tutorvista.com/inorganic-chemistry/magnetic-materials.html#magnetic-materials-list

I also found a video by Vishay that says magnetic materials are very often used in capacitor manufacture but I've no idea which.
http://www.vishay.com/videos/capaci...c-mlccs-for-medical-applications-product-demo

 

[f95toli]

One candidate is nickel which is a very common "sticking layer" in electronics, a thin layer is deposited before the other metals to achieve better adhesion.
And nickel is of course ferromagnetic.