Questions about SMD passive components

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Hello there !

I'm pretty much a newbie when it comes to finding and buying passive SMD
components. So, I went off and started a project that uses some
surface-mounted ICs, and these ICs now require some passive components for
bypass and filtering purposes.

Okay, so I need to find a surface-mounted resistor, and a surface-mounted
capacitor. How on Earth should I proceed in first finding a suitable
manufacturer, and a suitable product ? How should I select a component ? The
list of possible options/technologies/packages given is just overwhelming
and I don't even know where to start !

Please, if anyone could point me to the correct direction, for example, to a
website explaining the differences of the most common resistor/capacitor
technologies and with some sort of a "pick this resistor/capacitor
type/package for this kind of purpose" -guide.

If such guides are not available, then could someone at least state which
package (size/MELF/non-MELF/chip etc) should I use for a 30 ohm SMD resistor
and a 33pF/10uF capacitors :)

Greetings,
Antti Keskinen



Re: Questions about SMD passive components
Hallo Antti,


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Some simple rules: the value of esistors is printed for devices in the
sizes 1206 and 0805. I prefer 1206 for prototyping. There are only
little differences if you need resistors for digital purposes. Just
take the cheap ones :-).
capacitors are a little more complex, but if you need pF there is not
so much choice. Size again 1206, but there is no value printed on it,
so keep it sorted. µF is a bigger problem. If it may be a polarized
capacitor just choose an electrlytic one with sufficent valtage.
If it comes to the 100nF for ICs i take ceramic ones.

Hope that helps.

Näkemiin, Kurt

--
Kurt Harders
PiN -Präsenz im Netz GITmbH
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Re: Questions about SMD passive components
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It depends on (a) what other parameters are important for the part, and
(b) what your manufacturing prefers. My CM, for instance, "prefers"
0603 resistors - they stock every size as a standard part. Most 1206
parts are special order.

With resistors, you generally find that the larger parts have a higher
power rating. If you need 1/4W then you won't be using an 0603 resistor
:)

With some caps, you generally find that the larger parts have a higher
voltage rating.

If possible, pick one size (I'm standardized on 0603) and use this
preferentially - only specify a different package if you need a special
characteristic (like high-power resistors).


Re: Questions about SMD passive components
Hello !


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This isn't what I meant, exactly. You see, I know resistors come in specific
package sizes, such as the ones you listed above. It is the type of the
resistor, and technology, which puzzle me so greatly and make my strip my
hair out. Should I, for example, choose a thick film or a thin film resistor
to act as a serial resistor in an RC-circuit ? Or should it be a ceramic
resistor ? Can ceramic resistors be film-based at all ? What are metal film
resistors then ? Should I choose a similar type resistor to act as a signal
line terminator ?

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Again, it's not the size or the capacitance which puzzle me, since
capacitance category (pF, nF, uF) mostly goes hand-in-hand with the size.
It's the same with non-SMD capacitors. But, there are tantalum capacitors,
aluminium ones, ceramic ones, multi-layer ones etc etc. Which one should I
choose as a bypass capacitor for an IC then ? Should I use a similar
capacitor to filter an audio signal that exists an IC and enters another ?
Is such "filter capacitor" even needed ?

The problem is that with the current knowledge I have, I cannot efficiently
browse the manufacturer pages for capacitors or resistors. I don't know
which technology options I should tick in order to be even able to select
the resistance/capacitance ranges :)

Greetings,
Antti Keskinen



Re: Questions about SMD passive components

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<SNIP>
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I think you will find metal film tend to be the better ones (better
tolerance, temperature coefficient, noise). So use these unless you
have a good reason not to. You would need to be making an awful lot of
product in order for the slightly higher cost to be
significant. 0805's are about $15 for 5k!

<SNIP>
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It is hard to make general rules about capacitors, since they have so
many different parameters which may be irrelevant to you, or may be
critical in your particular application. Some non-obvious ones to be
aware of might be:

Ceramic
  voltage,temperature coefficient (C0G best, X7R OK, Y5V poor)

Alumininium Electrolytics
  lifetime vs temperature
  ripple current
  impedance

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Probably X7R or Y5V ceramic.

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Probably C0G. I think the other types could distort the signal if
there is significant voltage accross it.

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Depends on the application and what you mean by "filter" I think!
 
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My sympathies...

--

John Devereux

Re: Questions about SMD passive components
Hello Antti,

Don't worry too much about technology. Since you won't likely need
production quantities the first thing to do is find a place that sells
small quantities. In the US that would be Digikey, in Germany places
like Conrad, in Finland I wouldn't know.

Then see what they have and what is cheap. 1% resistors should be fine.
For the beginner it may be best to buy one of those assortments that
have all the common resistor values. Same for caps. With caps I'd start
with X7R which is the most common (and cheap) variety.

Manufacturers don't matter that much, you have to take what's available.
Size: I would not go smaller than 0805 in the beginning, until you have
some practice. And no coffee before soldering these ;-)

While at it you might buy some diodes and transistors in SOT23. The
cheap stuff like BAV99, MMBT2907, BSS123.

Also, you don't have to shell out lots of money for a new solder
station. I just use those pointy "ETS" tips in the regular Weller
station. Works fine.

Regards, Joerg

http://www.analogconsultants.com

Re: Questions about SMD passive components

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I need a morning cuppa to steady the hand.
Can always use circular movements to avoid the shakes.


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I like the wavetype tips , give a nice small ball of solder
that helps to melt the solder paste.

Alex



Re: Questions about SMD passive components

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Design with what is easily available from multiple easy to buy from
suppliers.
eg digikey , mouser , insert favourite supplier here etc






Re: Questions about SMD passive components
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The
a
resistor

I like Kemet and Vishay because they have a wide range of components and
good product selection guides with pictures.  They have app notes which help
explain the right part for the right application but which are not
exhaustive treatments on the subject.  Also look at app notes by Analog
Devices, National Semiconductor, and TI which have good help on how to
select the right type of passives.  Sometimes this information is in their
app notes on PCB design or noise control.  Many times the starting point for
selecting a passive component is what frequency will it be operating at.



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