Component/Footprint selection in EAGLE for PCB designing

Question

I'm a beginner and I want to build a basic PCB using EAGLE software. I want to only use SMD components but I have few doubts while using EAGLE:

1. I want to design a PCB schematic by using standard EAGLE rcl footprints, then complete a layout and ask a third party PCB manufacturer (e.g. JLCPCB) to print the PCB board and assemble those smd components themselves.
2. Now in this case I'm very confused by the fact that do I have to tell JLCPCB which rcl components they should put or I can just design the schematic & layout with eagle standard rcl footprints and JLCPCB will themself know which component to put?
3. Here my preference would be to just use standard SMD footprints (from rcl list in EAGLE) to make schematic & layout and I want to avoid components selection myself by searching it on Mouser or Digikey or other websites. I just want to create the layout and want JLCPCB to themself search components and assemble for me. Is it possible?

Answer 1

1. Just curious, did you model the circuit using software or solve it by hand? Did you build the circuit on a breadboard? You should validate your design in some way before you open EAGLE.

do I have to tell JLCPCB which rcl components they should put

In short yes.

You will need to give them a bill of materials (BOM). The BOM will have part designations for each component (e.g. R1, R2, C1, C2, etc.) that correspond to actual parts that will match the designations on your PCB footprints. Let's say you want R1 and R2 to both be 10kOhm resistors but you want R1 to be a 1/4 watt 1% tolerance 10kOhm resistor and you want R2 to be a 3 watt 5% tolerance 10kOhm resistor then you will need to have a two lines on your BOM; one for R1 and one for R2. Something like this:

Component Identifier Part Number
Resistor R1 R25w1p10
Resistor R2 R03w5p10

Then they will know to put the R25w1p10 resistor on your PCB where you have the footprint for R1 and the R03w5p10 resistor on your PCB where you have the footprint for R2. If you want R1 and R2 to be the same then you could do this:

Component Identifier Part Number
Resistor R1, R2 R25w1p10

Let's say you put a 0805 resistor footprint on your PCB design and you want a 10kOhm resistor to be placed there. Now it seems you are asking if you can leave the part number section of the BOM blank. Well if you look at digikey there are 192 10kOhm resistors in stock in a 0805 surface mount package. Which one should they pick for you? They range in price from $0.10 to $18.77, in power from 0.1W to 1W, and in tolerance from 0.01% to 10%. How can they just pick one for you? you have to determine what requirements you have for each component. This will narrow down the 192 options to something much more manageable. Then you can select each part for your design. This will take some time but it's not too difficult. It will also teach you a lot about what is out there which will help you with future designs.

3. I've never used JLCPCB but as Andy said they may have common parts in stock that you can have them put on your PCB. Even so, you will still need to tell them the specific parts to use from their selection.

Answer 2

I just want to create the layout and want JLCPCB to themself search components and assemble for me. Is it possible ?

It's possible but, quite likely to end in tears.

I don't know any designer that would approach it this way.

A designer would (for instance) decide that they need a 100 nF capacitor of C0G dielectric and voltage rating 630 volts then, because they don't know what footprint sizes this component comes in, they will go to Mouser or Digikey (to name a few) and find out what is available.

And' you'll instantly find that the smallest size doesn't cover 0402, 0603, 0805, 1206 or even 1210 but, if you didn't know this by finding out you'd almost certainly use the wrong footprint.

It's even more problematic for inductors so, do the sensible thing and browse the suppliers for the correct specification product and list that product in the bill of material.

Answer 3

Every assembly house I ever worked with preferred full manufacturer part numbers for all passive components provided with proper production data (BOM, assembly drawings, ...). So there is zero potential for misinterpretations and assumptions. And in case the part number is not available, the assembly house still has the full specification and can suggest alternatives.

I have to add that I'm speaking of professional high-volume jobs and our component library is also set up accordingly.

Maybe a shop like JLCPCB specialized for low cost and low volume prototypes has in-stock parts they'll prefer you to use.

You should just ask JLCPCB directly how they want your data. Many assembly houses provide BOM-templates for smooth processing, for example. Since proper production data is an art of its own, speaking to an assembly house is the best way to learn this stuff, anyway.