ExpressPCB layout newbie question

Go To Last Post
20 posts / 0 new
Author
Message
#1
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hi Freaks,

This is a very stupid question coming from a total ExpressPCB and layout newbie. I have an LM317 in a TO220 package. I am trying to create a through hole layout for it in Express PCB. Looking at the POD, I see that the leads are 0.07 inches in thickness and are separated by 0.1 inches. When I try to create a custom part in ExpressPCB, I found a 0.13 inch round pad with a 0.079 through hole. This won't work right since my pin to pin spacing will be 0.13 inches and I will be shorting the pins? Do I have to create a new pad which has a 0.079 inch hole but total diameter should be < 0.1 inches to maintain pad to pad spacing? Also how do I reduced the thickness of the ring around the hole in the pad?

Also any links with tutorials on ExpressPCB (where they show a simple board and have a step by step tutorial) would be very helpful.

Thanks for your patience and help.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I guess one option would be to use existing footprints and modify them. I also found one nice tutorial at
[url]

http://www.docstoc.com/docs/1171...
[/url]

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Use the layout for the part that comes with the package.

Under Component Manager, (Icon looks like an op amp), scroll way down the list, waaay down the list, to Semiconductor - TO-220, with mounting hole;
or To-220, without mounting hole.

Your choice.

I do not know of any good tutorials.

If you want me to e-mail you an example PCB let me know. Definitely not an expert design, but at least a starting point.

JC

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Use Eagle if you want a free PCB software....
Sparkfun has great setup files to create the proper files for a PCB house/...

I've loaded ExpressPCB on my pc to look at others boards to end up entirely disgusted with it and promptly removed it..

Go Eagle and don't look back ....

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

This reminds me of the early 1980's when there were many, many word processors around. Too many to count. Everyone had their favorite. Now you can count the major ones on one hand.

PCB layout software is similar. Lots out there to select from. Everybody has their own favorite.

ExpressPCB is the best, however. Everyone else is still playing catch up. :wink:

(Ducking for cover, but Krazatchu started it...)

JC

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

lol...

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Thanks, guys.

I am going with ExpressPCB for now.
JC, Can you please send me the layout you mentioned? Also do you have a schematic that goes with it? Thanks,again.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

With the ExpressPCB package, you can also easily define your own custom pads as well as your own components. Double click on a pad, and you will see a button to "create new pad".

Tom Pappano
Tulsa, Oklahoma

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Quote:
ExpressPCB is the best, however. Everyone else is still playing catch up. Wink

So far ExpressPCB has been meeting all (which is a *lot*) of my layout needs. Their service is terrific- now they just need to add routing capability to the inner layers.

Tom Pappano
Tulsa, Oklahoma

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

How critical is the yellow colored boundary that is drawn around the part on the silkscreen layer? Is it just for reference or does it also serve as a keep-out area for other components?

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Ok guys, here goes, my first simple layout. I have attached both the layout and schematic. Can you please look at it and let me know if I have anything blatantly wrong or just some minor corrections are needed?

I have created the layout for a power supply circuit I got from the Sparkfun website.

Thanks for your help.

Attachment(s): 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

That trace width is huge - 0.025 mils is fine for 1A. If you are planning to use a heat sink on the regulator, I would pick one now and make sure you leave enough space for it. Given the ground plane you have, I'd mount the regulator horizontally (TO220 with mounting hole) and use the plane as a sink - add some solid vias (not thermals) from the top pad under the regulator's tab to the ground plane to help transfer the heat.
/mike

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Maybe add some test-points to allow you to easily check voltages once the circuit it built.

You have plenty of board left, add some redundant pads for resistors in parallel with R1, R2 and R3 to allow you to 'fine tune' the voltage.

Connect JP2-1 to the Anode of D1, no sense letting a good idiot-diode go to waste.

Re-wire J1 to disconnect J2 to avoid possible contention between the power applied through J1 and J2

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hi Nikhil,

You have mail.

Check that you have adequate clearance on the traces. It looks a bit close on the switch and regulator pads.

You may want to include mounting holes in the corner of the board.

I would recommend you put your name or initials on the board, and a date and version number. If you make changes in the future, it will halp you easily recognize the board, the schematic that relates to it, etc.

I would label the connectors, and put V+ and Gnd by the appropriate pin. I tend to put the connectors along the edge of the board, as I find it easier to hook up cables or solder wires that don't have to dangle over and through various other components.

JC

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Thanks for your help, guys.

Quote:

Re-wire J1 to disconnect J2 to avoid possible contention between the power applied through J1 and J2

Can you please explain this a bit more? I didn't follow this.

@JC,
I got the email. I will look at it in detail.
Should I reduce my track width to get more clearance?
I could also follow n1ist's suggestion and go for narrower tracks.

Is there a problem (I am used to calling it current crowding based on process side) of overheating due to track width change from wider to narrower? I understand the track acts as a fuse.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

The LM317 puts out up to 1.5 A. You culd use a little smaller traces without a problem. It is hard to see the clearance on the posted photo. Make sure there is adequate clearance on the actual layout.

You can have a smaller trace connecting to the component's pads, then increase it to a larger trace for the majority of its length.

Changing trace width is an issue for high freq signals, not for this power supply.

For the voltages involved you do not need to worry about the voltage potential between traces or arcing between traces.

JC

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

a few thoughts that might help you start with expresspcb
(1) as far as a tutorial have you read the help with the program both pcb and schematic?...that pretty much explains it
(2) although this is a simple circuit, did you "link" your schematic to the pcb (you can link before or after but before saves a lot of rework) you started laying it out? if you step thru the netlist after you link I think it will illuminate some "things" ....like for example s1 maybe?....I do not believe expresspcb has any kind of netlist DRC running in the background during layout but viewing the netlist and wiring via the netlist is better than nothing (even if it is a simple pcb).you can also step thru the netlist and it will advise of some wiring errors.
(3) I assume you have all the parts used in the schematic in front of you so you can check the physical dimensions of the parts against what you drop on the pcb layout
(4) not sure what your yellow sik lines on the border are for..I think the default NEW pcb is what they call a miniboard 3.8" x 2.5" pcb and it will have violet outlines..
(5) try a few boards and learn expresspcb..it helps shield a pcb beginner from many $mistakes you can make submitting various files and other manufacturing design stuff involved in other pcb software....if and when you outgrow it you can learn the joy of gerber files, DRC mfg rules and checks...I think expresspcb is an excellant value (free)even if it has some quirks/bugs..once you discover them then you can discover the way around them and minimize them in the future... I use it AND I use Altium software($multiK) but this last year I have been doing about 3 expresspcbs a month..I really like dropping a design on a pcb, uploading on a Monday and testing a soldered board the same week for a very reasonable cost..very useful for debugging quickly a portion of a more complex design that later will be done in Altium possibly.
almost forgot...your pretty lucky learning pcb layout today since editing a pcb layout on a computer is childs play compared to making a change in the old days using taped up layouts on mylar......

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

...taking the masters to the litho service, mailing the negatives off to the pcb company, *then* waiting another agonizing 6 weeks to see the results!

Tom Pappano
Tulsa, Oklahoma

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Thanks,JC and bluegoo. I will make sure I have enough clearance.

Quote:

(1) as far as a tutorial have you read the help with the program both pcb and schematic?...that pretty much explains it

Yes, I read it. It is certainly very informative, but I was looking for a step by step tutorial. I ended up using the one in the link I posted. It is not extensive but enough to get a newbie like me started with PCB design.

Quote:

(2) although this is a simple circuit, did you "link" your schematic to the pcb (you can link before or after but before saves a lot of rework) you started laying it out? if you step thru the netlist after you link I think it will illuminate some "things" ....like for example s1 maybe?....I do not believe expresspcb has any kind of netlist DRC running in the background during layout but viewing the netlist and wiring via the netlist is better than nothing (even if it is a simple pcb).you can also step thru the netlist and it will advise of some wiring errors.

I did link my PCB to my schematic. I ran a schematic error check first to check for any open wires, double connections etc. That was very helpful.

Quote:

(3) I assume you have all the parts used in the schematic in front of you so you can check the physical dimensions of the parts against what you drop on the pcb layout

I do for this board but for my next board I don't. Is it absolutely necessary to have the parts before I send out the boards?

Quote:

(4) not sure what your yellow sik lines on the border are for..I think the default NEW pcb is what they call a miniboard 3.8" x 2.5" pcb and it will have violet outlines..

Those are the default lines that were in the layout when I first started the ExpressPCB. I assume those are necessary and serve as the board outline?

Quote:

5) try a few boards and learn expresspcb..it helps shield a pcb beginner from many $mistakes you can make submitting various files and other manufacturing design stuff involved in other pcb software....if and when you outgrow it you can learn the joy of gerber files, DRC mfg rules and checks...I think expresspcb is an excellant value (free)even if it has some quirks/bugs..once you discover them then you can discover the way around them and minimize them in the future... I use it AND I use Altium software($multiK) but this last year I have been doing about 3 expresspcbs a month..I really like dropping a design on a pcb, uploading on a Monday and testing a soldered board the same week for a very reasonable cost..very useful for debugging quickly a portion of a more complex design that later will be done in Altium possibly.
almost forgot...your pretty lucky learning pcb layout today since editing a pcb layout on a computer is childs play compared to making a change in the old days using taped up layouts on mylar......

That is a great idea. Thanks. I am planning to work my way slowly into PCB design and want to get good at it. Much much later when I am at that point, I will certainly look into other softwares but I guess the basics stay the same.

With this layout done, I will now start on my actual project layout. This one was just to get familiar with the software and techniques.

One more question:
When do you use the bottom layer for the board? Is it when you cannot possibly avoid crossing tracks on the top layer? I also noticed that the bottom copper layer had vertical tracks and the top layer had horizontal tracks. Is that a recommended style?

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

npat_avr wrote:

One more question:
When do you use the bottom layer for the board? Is it when you cannot possibly avoid crossing tracks on the top layer? I also noticed that the bottom copper layer had vertical tracks and the top layer had horizontal tracks. Is that a recommended style?

I think every pcb designer has their own methods..many of which have been learned after years of doing the "puzzle" that is pcb layout without a router. Most of my experience is prior to SMT so being that most parts were dip then and covered most of the component side it was easier to "fix" a pcb with a soldered wire if most of the wiring was on the Soldered side...as in the incorrect trace could be cut easily and removed. Also I think most designers tended to go in one direction on one side and the opposite on the other side. In the old days on a two sided board I tended to put the power traces and grnd bus (if one was required) on the comp side since I was pretty sure that was not going to change...with dip ic's that was easy to do. There was a time when some of the advanced autorouters started doing 45 degree routes on the innner layers and so forth that started to blur the "one way on one side and one way on the other". Today my experience is that SMT has thrown out all those easy to follow guidlines and SMT presents a basket full of new issues to deal with. I think that is one of the reasons why shape based autorouters are getting to be more popular....also keep in mind that todays smaller components and operating frequencies are a significant factor in pcb layout. No more production floor with lots of clipped component leads in the manual pcb assembly area! IN my early days (before doing pcbs) an experimentor had to learn more about "lead dress" that could doom a radio or amp project...today you almost have to be able to layout a pcb on a computer , send it to an outside vendor, and struggle with many components that are difficult to see the lead you solder with the naked eye and need special tweezers to pick up the component to get your project done..then get in sync with your mom's dinner plans so you can reflow solder the pcb in mom's oven!..mom's cookies just never smell as good as they used to!

I am probably a bit more critical than most about pcb design as I tend to look at a pcb as a work of art...(if you spent a week taping it up you would know that feeling) if looking at a pcb design makes me ill then it makes me wonder about the company that produced the product. Sloppy pcb design layout makes me wonder about "sloppy" engineering I can not easily see! I see lots of products by million $ companies these days that have pcbs that look like a "kid with an etch a sketch laid them out"...for a beginner thats understandable as in most things, practice and experience resolves that...