ExpressPCB - some work-arounds...

[R O Tiree]

...that I've discovered in the last few days (even though I've been using it for years )

1.  In a thread a few months ago, I erroneously stated that you cannot change the clearance around pins/vias in a ground/power/signal plane.  Actually, you can do this, either immediately after selecting "New..." from the "File" menu, when a pop-up appears asking how many layers, etc, or you can do it retrospectively by clicking on the "Layout" menu and then selecting "Board Properties...".  There will be warnings about setting it either too small or too large, but I've increased mine to 15 mils without any issues from the default of 12 mils.

2.  In that same thread, someone asked about solder masking and I described the then current work-arounds that I was using - (a) constructing it the hard way in PaintShop Pro, with a grid-snap the same as ExpressPCB (which is not terribly accurate, as it turns out) or (b) inserting circles/squares on that plane and then deleting all traces, components, etc, leaving a bunch of circles/squares with holes in them (which is not ideal, because you get left with little raised bumps of solder-mask which will deflect your drill bit, unless you're really careful).  I've been hunting on the interwebs for months for a solution and, yesterday afternoon, I had one of those hed-desk moments, as the solution hit me.

It turns out that the simplest and most accurate way is to block-copy the entire circuit and then paste it into a new project.  Once you've done that, delete all the traces and planes from the project, leaving just the components.  Now select the "o?" icon (near the bottom in the toolbar down the left hand side of the window).  Click on any round pad and a little pop-up... pops up (!) and tells you the diameter of the pad and the diameter of the hole in it.  Then you hit the Pad menu (up near the top of that left-hand toolbar) and "Create New Pad".  Add about 5-6 mils to the pad size that you discovered a few seconds ago and select (for example) "BGA - round surface mount pad", bottom surface and then type in the new diameter you've just worked out.  Click on the pin you're interested in and you should see a little green circle appear around that pin (if you delete the component, you'll see that there's a solidly-filled circle in there, which is what we want.  Now press Ctrl+Z to get the component back again).  Sometimes, you'll find that this pad size actually exists already, in which case, all you need to do is select it from the list.  Repeat for all the round pads in your project.  For square pads, repeat the "o?" thing again to find out how big the pin pad is, add 5-6 mils, then select "Create New Pad" as before.  This time select "SMT - rectangular surface mount pad", bottom surface, type in the height and width that you just worked out, then click away until all the square pads of that size have a little green border around them.  Lastly, delete all the components and you should be left with a picture of the solder mask you need.  Make sure, as you delete each component in turn, that there are enough pads left behind for all the pins!  Save the file as "project_name_SMask" (or something similar, so you know for the future that it's a SM file) and then print it out in the normal way for photo-exposure.  I've assumed, here, that you normally work in inches.  If you work in mm, then the addition to each pad size works out at about 0.15mm.

OK, so it's not as simple as just selecting the relevant SM layer in Eagle and hitting "Print..." but there are those who love Eagle, and those who find it nowhere near as intuitive or just too daunting.  Of course, this method means it's a bit of a faff if you change the layout, but it only takes a few minutes to block-copy, paste, delete traces/planes, re-register the remaining components over the SM placements and then jiggle them around until they're all sorted again.  The solution for double-sided boards will be much more of a faff bu, essentially, just as simple... that said, if you're into double-sided, then you're probably going to have to bite the bullet and go with Eagle, in the long run.

[davent]

Neat ideas, thanks for sharing!

Played around a bit and found a few things to make life easier and speedier.

1. Rather then copying the whole layout you've created just highlight all your components and any stand alone pads and copy that group to a new worksheet. Easier then trying to go back in delete all the little bits and pieces of  traces, they never arrive.

2. On your new worksheet ungroup any components that have both square and round pads.

3. My component pads are for the most part all 75mil in diameter/square so created one round and one square  "85mil bottom surface mount pad" and placed one of each on the worksheet away from the layout.

4.Highlight every component and solo pad that requires the same size round solder mask pad plus highlight the new solder mask pad you created and placed on the worksheet. Double click the target solder mask pad, click the OK button in the balloon that pops up, every pad you had highlighted will now be changed to that bottom surface mount pad (solder mask pad) you targeted. Your components are now made up with bottom layer surface mount pads..

5, Go through do all the squares as a group. My off board pads are a different size so would create  new bottom surface mount SM pads to accomodate those and again change them as a group.

6. Because your solder mask pads are all on the bottom surface, when you go to print, simply check the Print Bottom Layer box and you're good to go. No need to delete the components, the outlines are on another layer so don't show up when you print.

Again, great ideas!
Thanks
dave

[R O Tiree]

How on earth did you find that little nugget, Dave?  Brilliant!  This method will make double-sided board solder-masks a snap!

I've also worked out a good way to ensure accurate registration.  I put a 0.4" x 0.4" cross at each corner of the board, made up of 0.010" bottom layer traces.  Copy those across as well as your components.  Then, when you have etched your board, you should find that those crosses are still there.  Once you've laminated the board with the solder mask, simply line up the crosses on the board with the crosses on the solder-mask artwork and you're good to go.