I have been starting into PCB design with software and have noticed something that seems slightly troublesome to a beginner in it. Most datasheets when you look at them have a "recommended solder pad layout" (particularly for smt devices). I notice that the dimensions of the pads that come with the stock device library are different from those on the datasheets for the same device package. Is there a reason for this? It's usually not much of a difference, maybe 10-20 mils, but like I said, to someone who isn't familiar with the whole process, it bothers me to use the included library, and I find myself remaking all the pads to datasheet spec which adds a ton of work.

Thoughts?

 

Hi,

What software are you using?

 

Well, at the moment, FreePCB.

What I like about it:
1. It's free (the biggest plus, since I am not a company and can't afford $500 software)
2. Creating custom parts is really easy.
3. Nothing in this software seems really complicated.
4. Full CAM file generation

What I dislike about it:
1. Despite the ease of creating custom parts, if the part pads are even remotely complex, you might as well forget it. Even a DPAK with one large square pad and 2 small rectangles doesn't seem like it's happening. The custom part wizard pretty much assumes an equal size and spacing for all pads.

What I don't know enough about yet to decide if I like or dislike it:
1. Solder Mask stuff. It's hard to tell if the software automatically removes the mask from pads/vias.

I'm looking at other PCB software now, focusing mostly on free stuff (reference comment above about being poor). There is a free software that is made available by a board house that looks promising. However, if I can figure out how to overcome the shortfalls of freePCB, I do like the program.

 

The "pads" for SMD devices are usually a bit larger than the actual contact area of the component, this allows better solder flow. If you look at the data sheet for most SMD devices they will usually have a suggested pad size which is almost always larger.

Another software suite to try is http://www.diptrace.com It's free for up to 300 pins or 500 pins if it's for educational, student or non-profit use. I started out with the free version and it wasn't long until I went ahead and purchased the license for the unlimited version.

Personally I think it's easier to use than most others and I've made some great boards with it, some rather large.

 

How I make PCBs

I'm currently using PCB Express, which is also free. Another free package a lot of people like is Eagle Express, which is a crippled version of a commercial package.

Slight change of subject, ever use Gimp? It is a open source graphics package similar (but much more complex than) M/S Paint. Unlike Paint it will print out at 600DPI, the maximum resolution for printers. I use it to touch up the PCB Express outputs to something more like my personal standard.

How are you going to make the PCBs? Toner or photographic? There have been some really good threads on the subject in the past four months.

 

Hey thanks Marshall. I downloaded it after watching the videos on their website, it looked really great.

I decided to throw together a schematic to begin evaluating the software, and wouldn't you know it, the 3rd component I want to add isn't in the library. Ok, no problem... good chance to play with the Component Editor. The component I'm adding to the library is the On Semiconductor NCP3064 (SOIC).

The part I'm having trouble with is under the PIN manager, specifying the electric type (see attached image). I'm not sure what to classify the pins as. Vcc and GND I'm sure will be "Power" as will the ON/OFF pin. My guess is that Ipk (peak current sense) and the Comparator will be "Input". The others I'm not so sure of. Also, the column "type"... do I leave these as "blank" or do I need to specify them as well.

Thanks for the suggestion again.

@Bill, I'm designing PCBs to be made by a board house, not at home. I've decided that frankly... home PCB sounds like a giant pain in the rear and I just assume not mess with it. I've got me, my wife, and 4 pets crammed into an apartment, I don't need to add clutter and caustic materials on top of it.

 

Good luck! You will find it is going to be expensive. If I'm wrong let me know, resources are always nice to have.

PCB Express makes their software just so they can make boards to order, they didn't really mean for hobbiests to glom onto it. They can be easy, but I suspect local houses are better.

 

I'm a Linux guy, so I make schematic and PCB in Eagle, Eagle3D and finally rendered in Pov-Ray. That way I can "see" the board, and check component placement before I make the actual PCB.

And as Bill said, "...resources are always nice to have."

Good luck with your new software.

 

Here is another well kept secret pcb software, http://server.ibfriedrich.com/wiki/ibfwikien/index.php?title=Main_Page

It also does simulation similar to LTSpice, auto-layout, auto-router, 3-d board (to show what finished stuffed board will look like), makes Gerber and CNC-mill files, and is free! A lot of guy's on 'HomeBrew pcb' use it.

Also it has a 'front panel design' software, to layout project box panels.