SMT Package size

Hi there,

I am just putting together a bill of materials for a surface mount project.

I have created this putting together a range of different circuits.

I have the same value capacitors/resisters but at different cap sizes, so I have order multiple reels.

Is it ok to make all capacitors the same cap size, would this alter anything else?

Thanks so much,

Ben

What do you mean by size? Physical or value?

I try & use 0805 Rs & Cs to have some consistency & a shot at re-use of leftovers.
22pF, 100nF/0.1uF, can even get 1uF and 10uF in that size.
Same for resistors, 0805 has high enough power rating for many things.
Also not impossibly small to assemble/place by hand, vs 0603 & 0402.
1206 is a good size too, especially for LEDS.
1812 for PTC Resettable fuses between USB & the board Vcc.

I guess you differentiated between physical size and value in your original post, I just didn't quite understand why you would be asking.

One point to make, the smaller a ceramic capacitor (except C0G/NP0) is, the higher its voltage coefficient. So if you put 5V on a 6.3V 0402 and a 1210, you're going to get more capacitance from the 1210.

Thanks for the help.

I have been working with a prototyping assembly factory, so I have been using mainly 0603. Size is an important factor in my design so I am keen, if it is possible to make all the capacitors and resistors this size.

Although it may sound a strange question, I want to understand if I make all the components 0603 package size, will I be changing more than I realize?

I want to understand if I make all the components 0603 package size, will I be changing more than I realize?

The size 0603 only applies to components with two terminals like resistors, capacitors, diodes, LEDs and inductors. It does not apply to transistors, FETs or much else.

One thing to watch with small components is the power rating (resistors especially). An 0603 resistor typically has 100mW power rating - 0805 is higher at about 125mW, and 0612 (sideways 1206 with the terminals on the long sides) is even higher at 500mW.

So you need to know what kind of current is going to be flowing through your component to know how small you should go, and if it's safe to reduce the size to match others. Remember - P=I²R, so a 100? resistor with 100mA flowing through it would be 1W, so you'd really be looking at a 2512 that can give you 1.33W (yes, leave a little safety margin) for that. Yes, there are smaller resistors with that kind of power, but they cost more and aren't as common. I tend to go by a parametric search for the power rating I want, then find the size that has the largest number of components available.

Thanks majenko,

Thats really helpful... I need to go back and check my circuit.