Using magnets with tiny SMD devices - any electronic concerns?

[N_Cook]

At the moment only diodes , but what about more sophisticated stuff?
Required a way of holding 2 of the tiniest (2mm long dimension) SMD
devices in registration , to solder together . Used a 6 pole rare earth
magnet from a VCR motor. Also broke a chip off to epoxy to the end of a
matchstick as a manipulator, for transfering to pcb and holding in place
while first solder dab.
Any devices a definite no-no for high local magnetism? , presumably some
SMD termination metal is not ferrous for one thing.

[pf...@aol.com]

I cannot imagine stray magnetism to be a concern for SMD devices these days. And given how many times very, very powerful magnets are used for cleaning materials and separating contamination artifacts from parts.

That being written:

a) There are magnet-based pick-and-place devices deployed for SMD devices already.
b) There are magnetic clamping and holding devices already deployed for boards and other parts. Their outstanding virtue is no moving parts.

NOTE: Reed and other sensitive mechanical relays using internal magnets may be damaged by excessive stray fields. So keep that in mind.

Otherwise, have-at.

http://hackaday.com/2011/02/24/magnetic-smd-pick-and-place/

Peter Wieck
Melrose Park, PA

[Michael Black]

WOuldn't an electromagnet be better? So you can turn it on as needed?
The good magnets are great, but lots of trouble removing them from
something.

Michael

[pf...@aol.com]

There is that, of course. And with neodymium magnets, switching them "off" is difficult. I was addressing the concept of magnetic fields in the first place.

I would also suggest AC on the electromagnet as that will naturally de-magnetize anything it touches - cf.: tape-head demagnetizers.

[N_Cook]

While at it, any problems with fine chip geometries in cameras, fancy
phones and computers, passing through airport X-ray scanners?

[pf...@aol.com]

I have been through many scanners all over the US, and the world. No issues, ever. Traveling with everything from high end cameras to sensitive medical equipment.

[whit3rd]

On Friday, March 24, 2017 at 1:31:11 PM UTC-7, pf...@aol.com wrote:
> On Friday, March 24, 2017 at 4:02:07 PM UTC-4, Michael Black wrote:
> > On Fri, 24 Mar 2017, N_Cook wrote:
> >
> > > At the moment only diodes , but what about more sophisticated stuff?

> > > Any devices a definite no-no for high local magnetism?

> > WOuldn't an electromagnet be better? So you can turn it on as needed?

> There is that, of course. And with neodymium magnets, switching them "off" is difficult. I was addressing the concept of magnetic fields in the first place.

> I would also suggest AC on the electromagnet as that will naturally de-magnetize anything it touches - cf.: tape-head demagnetizers.

I second this. It concerns me somewhat that the magnetic components might realign themselves
when you drop 'em, too; does anyone remember that silly little toy with magetized Scottie dogs?

Accidental magnetization can affect a relay or buzzer, but is unlikely to have any permanent
effect on the mainly-nickel magnetizables on surface mount devices.. The worst I can
imagine, is that a ferrite might leap to the magnet face and get a fracture from the impact.

[mike]

On 3/26/2017 3:29 PM, whit3rd wrote:
> On Friday, March 24, 2017 at 1:31:11 PM UTC-7, pf...@aol.com wrote:
>> On Friday, March 24, 2017 at 4:02:07 PM UTC-4, Michael Black wrote:
>>> On Fri, 24 Mar 2017, N_Cook wrote:
>>>
>>>> At the moment only diodes , but what about more sophisticated stuff?
>>>> Any devices a definite no-no for high local magnetism?
>
>>> WOuldn't an electromagnet be better? So you can turn it on as needed?
>
>> There is that, of course. And with neodymium magnets, switching them "off" is difficult. I was addressing the concept of magnetic fields in the first place.
>
>> I would also suggest AC on the electromagnet as that will naturally de-magnetize anything it touches - cf.: tape-head demagnetizers.
>

I'd worry a lot about that.
Transients from turning the electromagnet on and off can create voltage
in nearby conductors. Sensitive inputs might not like that. Hall Effect
sensors might not like magnetism either.

[N_Cook]

Perhaps not the voltage as such, but potentially destructive high dV/dt
, lowish voltage but very short duration

[pf...@aol.com]

On Sunday, March 26, 2017 at 9:18:50 PM UTC-4, mike wrote:

> I'd worry a lot about that.
> Transients from turning the electromagnet on and off can create voltage
> in nearby conductors. Sensitive inputs might not like that. Hall Effect
> sensors might not like magnetism either.

Good to raise the question - which deserves an answer that addresses it directly.

Magnetic fields are largely dissipated when bridged. Which is why horseshoe magnets, as one obvious example are bridged when shipped. A bar between N & S., that is. DO try this at home. Take the typical cartoon-type horseshoe magnet and iron filings (in a bag for the purposes of neatness). With the bar and without the bar.

When a magnetic parts-picker is holding its part, it is bridged. The electromotive coil is sitting between the two poles which are gapped at the proper size to pick up the part in question. The part-in-place dissipates extraneous fields, is demagnetized by the shifting field applied to it, and when the system shuts off (dropping the part) also absorbs and dissipates the transient - which ain't much nohow, anyway.

Thank goodness for high-school science. We learned things as they apply to real life every single day. And a lot of cool stuff, too. Such as making gunpowder (elementary), gun cotton (nitrocellulose, not so easy) and much more. The teacher ran the course parallel to our history courses with a little bit of physics thrown in. So, we made "Egyptian Ice" in hot weather, a Rhodesian hoist, Prince Rupert's drops, Archimedes' screw (as well as displacement and specific gravity experiments, split rocks without tools, and much much more.

Teaching that kind of science is probably a lost art - who would let little Jilly or Johnny around glacial sulphuric acid, much less the 'fixins' for gunpowder these days?

But I can tell you exactly how a Lift Pump works, how it is different from a Force Pump, and its lifting limits. And we learned about the differences between the Atkinson cycle and the Otto cycle in 1967.

As well as the ten (10) reindeer... How you can tell an American anywhere under any conditions... much longer, but related stories. The former is disclosable to the general public, the latter not - for obvious reasons.

[Chris Jones]

Some RF ferrites probably wouldn't like it. I remember reading warnings
about that. I doubt you would encounter those often.

[Chris Jones]

http://www.intersil.com/content/dam/Intersil/documents/an15/an1533.pdf

[bitrex]

The one you have to worry about is the one in the post office.

I've had packages containing prototypes likely seized before. Because
they looked scary.

Customer gets sent an empty box, "your package was damaged in shipping",
deny everything.

[pf...@aol.com]

OK - a few things.

a) Airport and shipping security are facts of life whether one is from the back of beyond or downtown NYC. Every manufacturer on the planet understands this.

b) Older devices would simply be immune to stray fields of the sorts found in airports, flying above 5,000 feet (cosmic rays), walking down the street (how many cell/bluetooth devices/routers/GPS devices and more do you think you are passing in, around and through on a moment-to-moment basis? Newer devices would be designed to be immune. After all, we are not discussing EMPs, just stray fields.

c) Magnetic fields propagate by the inverse-square. Twice the distance = the √ of the first distance. And so forth.

d) As previously noted, the magnetic field is bridged, and alternating.

e) As previously noted, the field is released when the part is placed - so there is no, repeat, no induced field beyond the shield (part) itself.

And as all sorts of these devices are already deployed all over the planet in many configurations without apparent untoward effects as of yet, I suggest that the need for paranoia is minimal.

https://www.youtube.com/watch?v=gp5JCrSXkJY

[Michael A. Terrell]

pf...@aol.com wrote:
> On Sunday, March 26, 2017 at 9:18:50 PM UTC-4, mike wrote:
>
>> I'd worry a lot about that.
>> Transients from turning the electromagnet on and off can create voltage
>> in nearby conductors. Sensitive inputs might not like that. Hall Effect
>> sensors might not like magnetism either.
>
> Good to raise the question - which deserves an answer that addresses it directly.
>
> Magnetic fields are largely dissipated when bridged. Which is why horseshoe magnets, as one obvious example are bridged when shipped. A bar between N & S., that is. DO try this at home. Take the typical cartoon-type horseshoe magnet and iron filings (in a bag for the purposes of neatness). With the bar and without the bar.
>
> When a magnetic parts-picker is holding its part, it is bridged. The electromotive coil is sitting between the two poles which are gapped at the proper size to pick up the part in question. The part-in-place dissipates extraneous fields, is demagnetized by the shifting field applied to it, and when the system shuts off (dropping the part) also absorbs and dissipates the transient - which ain't much nohow, anyway.

The tools to pick up SMD components use vacuum. Both manual, and
Pick-N-Place machines.


--
Never piss off an Engineer!

They don't get mad.

They don't get even.

They go for over unity! ;-)

[pf...@aol.com]

On Saturday, April 1, 2017 at 12:02:43 PM UTC-4, Michael Terrell wrote:

>
> The tools to pick up SMD components use vacuum. Both manual, and
> Pick-N-Place machines.

Not all of them.

http://hackaday.com/2011/02/24/magnetic-smd-pick-and-place/

[Michael A. Terrell]

pf...@aol.com wrote:
> On Saturday, April 1, 2017 at 12:02:43 PM UTC-4, Michael Terrell wrote:
>
>>
>> The tools to pick up SMD components use vacuum. Both manual, and
>> Pick-N-Place machines.
>
> Not all of them.
>
> http://hackaday.com/2011/02/24/magnetic-smd-pick-and-place/

That is a toy.

[pf...@aol.com]

It ain't nohow the only one.

[Michael A. Terrell]

So what, there are lots of cheap toys, just like the overpriced
garbage that your audiofools drool over. Have you ever seen a real, high
production Pick-N-Place machine with 20 or more component feeders?

How will a magnet handle the positioning of large, complex
components? Why don't you go on the news:sci.electronics.design
newsgroup so that you can tell the people who own and use real machines
what fools they are, to buy real tools. You were ranting about buying
cheap H-F tools the other day. You couldn't afford a real P-N-P machine,
or the reflow oven and all the other related machines for a modern PCB
manufacturing process.

Have you ever hand placed hundreds of tightly spaced components on a
real PC board? How about positioning ICs with hundreds of leads spaced
.015" apart, without causing solder bridges? How about hand placing 0201
components?

Stick to your real estate job and shotgunning 50 year old
amplifiers, where you know a few things.