Component libraries for schematic and layout design

Question

I've got much difficulties to find the footprint for the components I have in hand:

They don't have name (I buy them at somewhere similar to flea markets). Therefore, their proper footprints are unknown nor I don't know where to find such information. So far, I've been wondering if every component (such as resistor, cap, connector, header..) they all have standard footprints? where to find such information?

For the libraries available in CAD tools like eagle, proteus, orcad, they don't have the visualization (photo...) of the component so that I can guarantee the chosen footprint is suitable with the real one

For such reasons, I would like to know if there is an online or offline component library and browser which has:

• 1 photos of each component. This is meaningful since it may help to quickly verify if this component is the one the designer is having at hand or visually remember

• corresponding schematic

• corresponding footprint with some brief descriptions about pad size, distance between pads. This supports specific measurement information for the given photo

I am still at learning level in electronic design and have found EE SE is a great learning resource. Please pardon me if my questions does not make sense. In that case, your response would also help me to justify my understanding.

Answer 1

There are "standard" footprints for most IC packages, like DIP, SOIC, etc., but the library creators for the CAD programs may excercise their creativity in naming the footprints, so you may have to do some searching to find the appropriate footprint for your part.

When I first used Protel (now Altium), it seemed that the schematic library developers weren't allowed to talk to the PC footprint library developers, so the schematic part may call for a 14DIP footprint, while the PCB library had DIP-14!

You will, if you do any amount of PCB design, have to create your own footprints for many parts - when you do, save your footprints (and schematic parts) in your own libraries so they won't get over-written when you update the CAD program!!!

I would not complete a board layout until I had the actual parts in hand so I could verify that the footprints I was using matched the actual parts (and that I could really buy that part in that package!)

If you are uncertain about the size or shape of a footprint, place it on a PCB layout, then print it "life size", and see if the part really fits the printout.

Answer 2

SMD components and to some extent, through hole components have standard foot prints. If you have the component's reel, it is usually written on it. If not, you can measure the component with a caliper.

As for photographs of SMD passive components, they do not have much use. All capacitors of a certain size look the same, just with some color variations. And while most resistors have their resistance printed on them, some do not.

Inductors have few variants that are easily discernible (Printed, Ceramic, shielded types etc). A link to the component's datasheet would be much more useful in a component library.