Questions about SMD passive components

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

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Kurt Harders
PiN -Präsenz im Netz GITmbH
mailto:news@kurt-harders.de
http://www.pin-gmbh.com

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).

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 ?

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

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!

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

Probably X7R or Y5V ceramic.

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

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

My sympathies...

--

John Devereux

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

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

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

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

Alex

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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.