Problem with SM caps

[James Arthur]

Your iron is way too cold. 750F/400C is the ticket. Using too cold an
iron makes the part stay very hot for far too long.

Cheers,

Phil Hobbs

I've had parts leap onto the iron--dancing and swimming in molten
solder while I tried to wipe 'em off--without damage. I don't
know why Charlie's would fail so easily. Something's wrong.

And you'd expect thermal shock cracks from soldering would create
opens, not shorts.

On low mass jobs I keep the iron on the cool side, but hot
enough to work quickly. A well-tinned iron helps.

I'm still puzzled by the "bits of metal holding the sides in"
Charlie wrote of earlier.

Cheers,
James Arthur

 

[Archimedes' Lever]

I desolder parts by laying a big iron tip across both ends, melting
everything in sight, and knocking the parts aside. Doesn't seem to
bother them.

You do everything on how it seems to you, John. That is a problem, but
I am sure you have also 'knocked that part aside' as well.

About the only damage I see from soldering abuse is ripped-off end
caps, and that seldom on PC boards.

Except that you obviousl;y have no clue what soldering abuse is.
The two irons violates several rules regarding PCB assemblies.

Ceramic Multi-layers Chip Capacitors DO get damaged, particularly by
high solder and reflow temps. They are meant for ONE solder operation.

If you are repairing a circuit, you should replace any removed chip
caps.

Despite them possibly appearing intact, they detach from their
termination end caps internally, ESPECIALLY when some know nothing dope
uses TWO irons at high temp to remove one.

The best way to perform a removal and still keep the part and its
operational parameters intact, is to use solder braid ON the solder joint
at each pad, ONE at a time. Quickly removing the main bulk of the solder
fixturing it in place. Then, the part can generally be removed clean and
relatively cool. I would still replace any chip cap, however, as I have
seen them get damaged from heat, and the problem become severely apparent
when working with HV chip caps.

Two irons for placement or removal of an SMD part is the stupidest
thing any assembler (that's barely what you rate) could ever do.

Despite any circuit level engineering you may posses, you certainly
lack a lot of knowledge in physics. The vapor phase, and now this
certainly proves that.

 

[Archimedes' Lever]

0402's have my production people climbing the stairs with torches and
pitchforks.

John

That is a clue not to use them on the underside of the assembly or
anywhere that staking would be required.

That or get better dispensing gear. AND better dispensing personnel.
After all, we are talking about a group of dolts that think a vapor phase
cleaning system involves immersion of the assembly in the bath. They
could easily, however, have learned that fault from you. Pretty sad that
the shit you ooze rubs off on others and stains the entire industry with
misinformation.

 

[Charlie E.]

Your iron is way too cold. 750F/400C is the ticket. Using too cold an
iron makes the part stay very hot for far too long.

Cheers,

Phil Hobbs

Yeah, but this one was DOOB (or out of tape!) I have tested this in
both the 1uF and 22pF caps. very, very weird!

Charlie

 

[Charlie E.]

Are you saying that the caps are shorted before you solder them?

How many ohms is "shorted"?

Maybe they're not caps!

John

Well, they are in the packaging that digikey sent them in, in a sealed
tape. But then, maybe DK did something wrong. the parts have no
markings on them. The resistors do have values on them.

Charlie

 

[Charlie E.]

Are you using a glue before soldering ?

I've had no trouble (except with my eyes) soldering 0805s by hand. Takes a
while to recover normal vision.

And the buggers tend to stick to the tip of the iron, so held 'em down at
one end (say with a toothpick) while soldering the other. Then do the other
end.

Sneezing is also a bad idea.

Graham

Hi All,
These are Murata caps, so you can see a picture at
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=490-3912-1-ND

but like I said, these appear to be shorted out of the box, so I don't
know what to do now. Will contact digikey in the morning, and see if
there is something I am doing wrong!

Charlie

 

[Ben Bradley]

That looks like an "SMD feedthrough (pat. pend.)"

Yes indeed, the two end terminals, marked 1 and 3 in the page
below, are electrically connected, and the capacitance is between
either of those and terminal 2, the 'center clip' area, or as called
in an earlier post, "the metal holding the sides in" (the above page
points to this datasheet):

http://search.murata.co.jp/Ceramy/image/img/PDF/ENG/L0111S0111NFM21P.pdf

No wonder the two endcaps are shorted together, it's designed that
way.

 

[Archimedes' Lever]

That looks like an "SMD feedthrough (pat. pend.)"

It is an EMI filter. Jeez! Learn how to read a datasheet.

 

[nospam]

These are Murata caps, so you can see a picture at
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=490-3912-1-ND

Chip EMI Filters Capacitor Type.

"NFM21PC Series: NFM21P is a 3-terminal structure component. This product
can be applied to large current DC power lines. NFM21P is
suitable for noise suppression of DC power lines where relatively large
current operates."


--

 

[Charlie E.]

Hi All,
Ok, after never before having an opportunity, I designed my new boards
with SM caps. Didn't think there would be any problems soldering
them, but have run into a real problem.

Every single dang one of them shorts out when I solder them down. They
are Murata 0805 caps, and the only thing I can think of, is that there
is this little metal 'clip' on each side that must be shorting the
pads together. if if remove one of the caps, it is definitely not
shorting internally.

I just used the standard 0805 footprints in the Orcad Layout library,
and haven't had any problems with the resistors, just these darned
caps! Has anyone else seen problems like this? Or am I just making
some simple newby mistake?

Thanks,
Charlie

Hi Everyone,
Ok, mystery solved. These things aren't caps, they are little EMI
filters! They popped up when I did my search of the Digikey database
when I was ordering, and in my error, I saw "filter, cap" and thought
that meant a filter cap, not a filter that contains a cap. Of course
DK is doing the right thing, and refunding my purchase and shipping my
replacements free, but they are also going into the web guys, and
making sure that a search for capacitors doesn't bring up filters!

Sorry to drive ya'll as crazy as I have been...

Charlie

 

[Charlie E.]

Two questions, zero answers. On that basis, I can't help much.

John

Hi John,
Thanks for your help. Yep, they are not caps, but 'filters' that came
up when I searched for caps. Mea culpa! I 'assumed' that if you
searched for caps, you got caps, and didn't get and examine the data
sheets for every part. I just needed a few bypass caps... :-(

Charlie

 

[legg]

Errm, I think the little metal 'clip' is supposed to be on each end.

That would do it.

RL

 

[legg]

Hi Everyone,
Ok, mystery solved. These things aren't caps, they are little EMI
filters! They popped up when I did my search of the Digikey database
when I was ordering, and in my error, I saw "filter, cap" and thought
that meant a filter cap, not a filter that contains a cap. Of course
DK is doing the right thing, and refunding my purchase and shipping my
replacements free, but they are also going into the web guys, and
making sure that a search for capacitors doesn't bring up filters!

Sorry to drive ya'll as crazy as I have been...

Charlie

This explains the metal 'clip' on the sides.

RL

 

[John Devereux]

Hi John,
Thanks for your help. Yep, they are not caps, but 'filters' that came
up when I searched for caps. Mea culpa! I 'assumed' that if you
searched for caps, you got caps, and didn't get and examine the data
sheets for every part. I just needed a few bypass caps... :-(

I was about to ask: Are you sure they are not ferrites?!

ROFL

 

[krw]

I desolder parts by laying a big iron tip across both ends, melting
everything in sight, and knocking the parts aside. Doesn't seem to
bother them.

We have a soldering iron that looks like a pair of tweezers. Both
ends get hot and one just plucks the parts off. I don't like using it
to solder parts back on because its tips are crap.

About the only damage I see from soldering abuse is ripped-off end
caps, and that seldom on PC boards.

I just lost some pads because I had to solder a resistor to the board
as a probe point. The scope probe got bumped and the whole mess came
off. I spent an hour soldering wires and gluing down PTH resistors to
get the board working again. :-(

 

[Archimedes' Lever]

Of course. But there's nothing keeping me from measuring a part I just
pulled.

Caps may "measure" at one value, but perform at an entirely different
way. HV caps cannot be "measured" to determine viability. They actually
have to be energized at HV voltages to detect a failure mode. Some are
detectable as they became wholly shorted.

Replace and be sure. Put that part back down that you removed in such
a lame way, or even 'the right way' makes it a used part, and your
product is no longer "new", nor does it carry the specified MTBF declared
for it.

I have you on this one, Johnny. You know NOTHING about chip caps and
heat or degreasers, after what you wrote.

 

[Archimedes' Lever]

, and caps having none at all.

That depends on the form factor, and what brand they are. There are
plenty of chip caps that have markings. Just not any that would be
visible to such a technically casual dipshit as yourself. It would
require that you actually pay attention to the details, instead of the
typical male 'Ram it, Cram it, Jam it, damn it' mentality. Added together
with that 'knows all' attitude, and you are seen as the half assed prick
that you are.

 

[Archimedes' Lever]

On parts with a lot of pins, I can sometimes cut the pins off the
part, and then desolder them one at a time.

That is the ONLY correct way to remove the part, if the part is not to
be reclaimed. So, you got one right. Someone in your employ must have
actually known what he was doing at one time, and instructed you.

Or just send it downstairs
to the production people, who have every rework gadget imaginable.

If they would remove the part in any way other than that you described,
they would be doing it incorrectly. The ONLY time heat should be applied
to the assembly is for BGA where the connections must all be reflowed at
once, or other such parts that need full reflow for removal. If the pins
are exposed, a proper rework tech will NOT apply heat to remove a part
which will not be salvaged.

 

[Archimedes' Lever]

What two irons? On my bench in my office. I only have room for one
Metcal.

You are the one that mentioned heating both pads together.

 

[Archimedes' Lever]

Two semisters at Tulane, both A's. How about you?

Numbers and grades have NOTHING to do with REAL grasp of the physical
realm. A quick viewing of "Goodwill Hunting" should have cleared that up
for you.

In other words, I'd bet that you can't shoot pool worth a shit either.
And yes, that would also be quite a tell.