Wanted: Tips on Designing PCBs

[owel]

So, I'm using Eagle to design PCBs. They have a free version and as long as the project can fit on a 4x3 PCB, I'll be okay.

First I layout the schematic... while laying out the schematic, I have to pick the component type/dimension/package from the hundreds of options available. TO-92, TO-3, To-220 packages are no problems. They're standard.

But resistors and capacitors, this is where I get tripped. Sometimes I would pick a component that's too big that when it came to the board design, I see my supposedly 1/4w resistor is sized as a 1W resistor. I picked the wrong part! Of course, in the schematic editor you can't tell it's the wrong part/package. You just see the symbol. The part names do not come with 1/4w or 1/2w designations.

So lately, what I've done is everytime I pick a new component in my schematic, say 470uf/50V capacitor, I go to digikey.com, look for it, open the PDF, get the lead spacings in millimeters, go back to Eagle, pick a capacitor with the right lead spacings (or bigger).

Well, it takes a long time just to insert one capacitor. (The payoff is when I etch and drill the PCB, the lead spacings are exact.)

Anyways, my question is "Is there an easier way? Is there a trick? Are there cheat sheets I can use? Am I doing it right, or am I making it more difficult because I don't know something about the software?"

Thanks
Owel

 

[Rochey]

Why not buy all your passive components in a batch? (e.g. 20 of every value all in a fixed size)

There's loads of companies on Ebay that do that kind of deal (in the UK at least). Once you recieve them measure them, and THEN start designing your board.

Resistor 'sets' are pretty cheap (under £20 in the UK), similar things can be done with capacitors. Typical companies that can do this are: http://www.fastcomponents.co.uk/ in the UK.

Http://www.uktronics.co.uk are good for surface mount resistors too.

Once you get all your specific parts in a single component size, it's easy in eagle.

Good Luck,

Rochey

 

[mcs]

[quote author="Rochey"]Once you get all your specific parts in a single component size, it's easy in eagle.[/quote]
But that's not really an option for electrolytics. I find the caps I need for a design to check the lead spacing and size. And if I don't have any I check the RS homepage... It's not easy/fast, but if you want the PCB and components to match I think you have to.

Best regards,

Mikkel C. Simonsen

 

[VacuumVoodoo]

I've created a "mylib" component library, as soon as i use a component with a certain foorprint i put it there with a more detailed description. It's a slow process in the beginning but once the library reaches critacl mass it makes things quick and easy.

Alex

 

[dale116dot7]

I do board layouts as about 30% of my job, so after a lot of time I've figured out how to do it in Protel 99SE. Many programs would be similar.

The schematic has a location for footprint, so I put in, say, for a 1/4 watt resistor: AXIAL0.4 which is a resistor footprint, .4" between legs. A 1 watt gets AXIAL0.7 and a 2 watt gets AXIAL0.8. Capacitors get RAD0.1 or RAD0.2. Electrolytics maybe ELECT-FC-2.5MM or ELECT-FC-5.0MM. Then I have a library of parts that are drawn up with these dimensions. If I'm going to use another new footprint that I don't have in my library, I draw the new component up and save it in the library, and when I need that footprint I just pull it up.

When I lay out a board with new parts (ones that I haven't used before) - I have the Digikey catalog right there - the lead spacings are right there. I also keep a spreadsheet of values I have in my home shop along with their footprints. I print it out and look at it when drawing up boards.

Hope that helps.

-Dale

 

[Bauman]

Almost all PCB programs are the same, some have more flexibility but here's what I do.

I create a library using as footprint names the value of the capacitor. So a 470uF/50V electro is CE470U50. CE is for CAPACITOR ELETROLYTIC. CTAN10U25 is a Tantalum 10uF/25V and so on. RES4 is a 400mils resistor, R5W is a 5W resistor. It takes a little time to grow your own lib but it worth the time.

One trick that can speed up this in Protel (maybe your software have this also...) is a command in some of the menus called MAKE LIB FROM PCB. What it does is to create a LIB file with all components you have placed on your pcb. So you can do a little research, find the sizes you use more and put them all in one pcb, generate the LIB from there and them edit the names. PRONTO!

hope this helps.

cheers!
Fabio

 

[owel]

Thanks for the tips... I guess it just takes time if you want it done right.

In summary, what I've noticed in all your tips is the need to create your OWN custom library (or compilation) instead of always picking from the general library.

I like the tip of typing in a more descriptive text, and even including supplier part numbers.

I like this tip from Bauman too. It's more descriptive.
>CE470U50. CE is for CAPACITOR ELETROLYTIC. CTAN10U25 is a Tantalum 10uF/25V and so on.

>I also keep a spreadsheet of values I have in my home shop along with their footprints. I print it out and look at it when drawing up boards.

Great tip. Could take some time to build.

Thanks to all for the great posts.