So i brought 0805 SMD capacitors and 0603 SMD resistors.
So my question is:
- Can i use them with 5v with no problem? What should i care about when using them?
Can i use them with 5v with no problem?
Yes the lowest working voltage for a capacitor I have seen is 6.5V so you should be fine. Resistors don't have a working voltage rating only a power rating.
What should i care about when using them?
Keep the resistor power dissipation within the rating.
So for capacitors i should take into account voltage and on resistors i should take into account Watts, am i right?
Yes that is right.
Thank you 
Resistors don't have a working voltage rating only a power rating.
Actually not true. Resistors do have a maximum safe working voltage rating but it's high enough to be taken for granted except for such applications as very high voltage voltage dividers and the such. I believe that 500vdc is a common max rating for standard 1/2 watt through hole resistors. I suspect the newer microscopic SMD resistors might have even lower max voltage ratings?
The resistors I have been using for many things tend to have voltage ratings of 50v or even sometimes as low as 25V, e.g:
I'm still curios, why there are so many sizes?
tsunamy_boy:
I'm still curios, why there are so many sizes?
Everything being equal (but not always possible) the smaller a component is the more components you can cram into a given PCB space. Miniaturization in space and weight has always been worth a premium in certain applications.
Some of the SMD sizes look like an ant with OCD organized his pepper flake connection on your PCB.
I'm amazed by the power-circuitry build onto the flexPCB of certain TFT displays, all
tiny MLCC's for the CoG display chip supply-rail generation and integrated into the
flex-pcb connector for the display.
Somewhat less tiny but still awesome is this: Seeeduino Film, maybe the first Arduino(TM) compatible board on FPC - Latest Open Tech From Seeed
But i'm still curious about why manufacturers use more than one SMD size, it looks like there's no reason for it
Two reasons
-
Historic the larger size was available first and production machinery was designed to cope. Then the smaller size came along, there was a reluctance to change because a) the production machinery would not cope and b) why change something that works you only have to get it re-qualified.
-
The larger ones will take more power and sometimes that is important.
The 0805 (larger) are now considered obsolete and the 0603 (smaller) are the default. There is an even smaller size 0402 (the "call that a component" size) coming along. It is all driven by mobile phone technology.
Oh i got it now.
Thanks for the help, have a great day you all 
I just picked up a grab bag of breakout boards at a ham radio swap meet. A few of the boards have lands for the first surface mount ICs. They look huge, now! Only about half the pin pitch of a DIP IC.
0402 coming along? I've been using them for over a year as a hobbyist, and they have been on motherboards and in phones for ages and ages.
The latest ones are as small as 0201, and even more impressive, 01005.
The different sizes are governed by several factors:
(1) power - high power means larger size required, so power circuitry tends to use the larger sizes
(2) speed - if you are talking about several GHz, everything behaves like RF signals whipping around in traces. A large physical size component is a massive burden on high-f design.
(3) space - if you have, say, a 64bit data bus and all of the lines need decoupling and terminating, there is simply not enough space to use a large size component - I've found in circuits I've designed in the past for HDMI, that even finding room for 0402 terminations in a tight space is not easy - no chance of fitting 0603 or above.
(4) cost - smaller components mean less real estate on the board = smaller board sizes = more functionality at lower cost.
In fact in many areas now if you look in a smart-phone for example, discrete RLC components are getting fewer and far between. Most of those that would have been there are now being integrated onto the silicon die in custom ASICs - have you ever tried to find datasheets for the ICs on a modern phone - many you never will as they are custom ICs.
The latest ones are as small as 0201, and even more impressive, 01005.
40-50y ago we did even smaller with hybrid integrated circuit (thick/thin film technology).
Today the PCB track widths (ie 3-4mils) and component sizes are being comparable with the old HIC technology.
Maybe it will come again - imagine the PCB provider will print/paint an R,L,C for you while fabricating your PCB. Trimming with laser. Doable even today..