Standard SMD Package

[JohnsonMiller]

Hi,

When you check the Altium libraries you may see many footprints with same name, for example there are many 0402 package and footprints, why it happens? and which we should use?

BR,

[mairomaster]

Normally the names might differ a bit. For example for chip resistors, by the IPC standard you have 3 versions - Least, Nominal and Most. Accordingly the names are:

RESC1005X40L
RESC1005X40N
RESC1005X40M

The difference between the 3 versions is the pad size. L has the smallest pads and is used for dense designs, where you don't have much space. M has the biggest pads and is used in designs where the reliability is very very important. N is the standard version which works in most cases and most PCB manufacturers are fine with. If I don't have a particular reason not to, I always stick to N.

There are different reasons for similar footprints as well. For example the chip capacitors have slightly different footprint sizes compared to the chip resistors for the same size (0402 for example). I forgot the specific reasons about that.

For some parts the particular manufacturer might be recommending specific custom footprint that best fits the particular part and slightly differs than the standard footprint for the package.

It is a long topic, but those were some points to help you understand some of the reasons.

[robertferanec]

very nice answer mairomaster +1.

For example the chip capacitors have slightly different footprint sizes compared to the chip resistors for the same size (0402 for example). I forgot the specific reasons about that.

My guess is, that capacitors are usually taller and the tin drop looks a little bit differently comparing to low profile resistors.

[JohnsonMiller]

Robert & Mairo, Thank you, but my question is not a little difference and I do understand the density prefixes, M,N, or L.
Question is footprint that does not fit to each other and difference is huge, for example check 0201 and 0402 packages, and in case of capacitor and resistor or conductor, they differ from each other. Then compare it R0201 package which Robert used in OpenRex design. I am a little bit confused, which footprint we can trust?

[mairomaster]

It is still not very clear to me. Do you want to know:

1. Which size of component you should use - for example if you need to use 0201 capacitors or 0402 capacitors.

Or

2. Why for a particular size of component, lets say 0402, you have very different footprints.

I am assuming it is 2. A simple rule to follow is if you have a resistor, use a resistor footprint, if you have a capacitor use a capacitor footprint, etc. Based on my experience and a lot of research, I recommend using standard IPC footprints for the chip components (resistors, capacitors, inductors). Such footprints you can generate yourself with the Altium IPC footprint wizard. Also you can find some on the web, but they are not always very reliable. If you have access to the Altium vault, you can get such from there as well.

[JohnsonMiller]

Thank you, case is 2.

[robertferanec]

Very often we use this document: https://www.ibselectronics.com/pdf/p.../smt_notes.pdf