SMT Resistor Issues

[owel]

I know Thin film types are less noisier than Thick film. But is there any noise advantage regarding the different sizes?
Which is better in terms of lower noise? (assuming the power rating isn't important).

1210
1206
0805

Any particular brand that are better? KOA, Vishay, etc???? 

And lastly, do you prefer a 1206 or 0805 for board designs? and why? 

Thanks in advance.

 

[Rochey]

there are specific voltages that can be driven through different sized smt resistors. I'll hunt for a link in a moment.
-- something along the lines of
http://www.vishay.com/doc?60031 (look for the working voltages bit)

0805's are great for board designs, as 0603's will also work.

As a commodity, the smaller the resistor (or capacitor) makes a big difference on cost and pcb size.

That's all I have for now

 

[jdbakker]

ObMrGrumpy: the Search engine sez http://www.groupdiy.com/index.php?topic=15650.0 and http://www.groupdiy.com/index.php?topic=9035.0 might be of interest.

Which is better in terms of lower noise? (assuming the power rating isn't important).

There is some evidence that smaller parts have more excess noise, as discussed in the threads I linked to.

(Another factor to keep in mind is that smaller parts will have less thermal mass, and will be more sensitive to self-heating induced resistance variations as discussed here).

Any particular brand that are better? KOA, Vishay, etc???

 
I've been very happy with the Susumu parts that Digi-Key carries. If you buy them in large quantities they're almost as cheap as thick film parts, especially if you take assembly cost into account.

(One way to cheat is to use MELFs; the bodies of normal axial resistors with end caps to facilitate SMD assembly. Vishay series MMU0102 is 0805-compatible; series MMA0204 fits 1206 footprints. Digi has a number of these in stock. An added advantage of MELFs is that their larger body makes it easier to dissipate heat, so ratings will be higher for the same footprint. Last week I hand-populated 200+ MMU0102s on a noise-critical proto, and I must say I find them easier to handle than regular 0805/1206 parts. As they're cylindrical they tend to be hard on most P&P-machines; your assembly house will hate you for using them. Also I find their larger contact area makes them more likely to tombstone than 0805s, but that's not an issue if you solder with one hand and hold them down with tweezers with the other.)

And lastly, do you prefer a 1206 or 0805 for board designs? and why?

Design-wise I don't much care, apart from the obvious reasons (max power, availability etc). If I'm hand populating I prefer either 0805 or 1206; as Susumu's thin film range is larger at the affordable end in 0805 than 1206 I tend to go for those. For hand-assembly I use huge PCB pads anyway as I'd rather be a pansy than have high blood pressure, so going for smaller parts doesn't buy me much board density. For stuff that must be tiny or anything that won't be assembled by me I go for 0603 (normal) or 0402/0201 (RF). Does that answer your question?

JDB.

 

[ppa]

I know these resistors since I have developed APP2050 SMD version, thin film are much better than thick film not only for the noise but for THD distortion. The problem of small resistors is their thermal distortion, the high quality thin film resistors have a very low thermal distortion as the PH type film resistors, but the standard cheap thick resistors have thermal distortion (3th harmonic). I use Vishay thin film res for the signal path and yageo for the other parts as sink currents ..etc...  

 

[owel]

Guys, thank you for the reply.  Very helpful.