# PCB design few questions

Quick couple of questions, I am designing my first PCB and want to have a few boards prototyped with OSH Park.

For a board I will be manually soldering components to, will I need to include a tCream layer or is this for automated soldering only?

And, do hobbyists generally make the surface mount pads a little larger than the components data sheet specifies, to help with soldering? Are there any other tips/tricks a first timer might like to know to make life easier?

And, for milled slots, i.e. two holes for a USB receptacle to mount to the board, do I need to include a note for these or is the data on the 'holes' layer sufficient?

• You don't need tcream. The other question will vary house by house, and is a question for OSH Park – Scott Seidman Jun 21 '15 at 14:11
• Even if you don't need it here, you should make sure it is correct, because this will make sure that any component footprints created for this project can be reused without surprises. – Simon Richter Jun 21 '15 at 18:46
• All great answers thanks for everyones help, sorry I can only pick one. Is it generally safe to use a generic package footprint for a component, for example this component being a 8-SOIC package, do you use an 8-SOIC footprint from spark fun or somewhere similar, or would you redesign it or at least double check the data sheet fits the one you have selected? – JoshNZ Jun 21 '15 at 20:34

The answer is no, you only include layers that they will use for manufacture.

I have always found Laen at OSH Park is extremely helpful and supportive, so I recommend you email if you have any concerns.

As for cutouts, it depends a little on how you are making the slot. I have used overlapping drill holes (not allowed at many PCB manufacturers, but OSH Park did it). Otherwise I have put slots on an outline layer.

OSH Park have extensive help under Support, for example creating slots is explained here.

For any devices which have pads under the package, I do extend them beyond the package boundary. Otherwise it is difficult to solder.

In general I don't make pads larger, but I often use Sparkfun libraries (at least for packages and footprints) which are pretty good.

The tCream layer contains the top side solder paste data for SMD, normally used to make stencils for printing the paste to the board before assembly. So I do not think that it will be necessary for a few prototype panels.

As for pads, it is recommended to use larger pads when hand-soldering because we need more space for the solder-iron. We was told back in class to add a couple tenth of a millimeter in both direction to the pads (red area below).

At thorugh-hole components, hole galvanization should be considered as follows:
drill_size= d + 0.3 mm where d is pin diameter.
The copper ring diameter around the hole should be drill_size + 0.5 mm.

These were advices from our teachers when I was desiging my first PCB.

Make the paste layer. Sometimes it's good to order the mask, put paste on the board and solder components with hot air. Also it's good for QFN. For manual soldering you don't need wider pads, you rather have to make wider spacing between the components, so the soldering iron will not touch what it shouldn't.

tCream layer or is this for automated soldering only? This is the Solder paste layer, which tells you where to apply solder paste. It can (and often is) used for soldering manually too. The paste/cream layer can be used to get a solder paste stencil from OSHStencil (I believe they are related to OSHPark), then use a squeegee to apply paste to the board, then reflow or use a hot air gun to solder.

make the surface mount pads a little larger...

In addition to Bence's answer above, make through hole pads larger as well. This helps greatly in the event some component fails and you need to remove/resolder the component. Having larger pads reduced the possibility of delamination.

milled slots

This is highly manufacturer specific. Some manufacturers do not support slots at all, some require it to be in a specific format. Talk to them.

Are there any other tips/tricks a first timer might like to know to make life easier?

• Once all your gerbers are ready, print them all out at 1:1 using your desktop printer. Lay out your critical components (SMD ICs, connectors) and make sure the pins all line up. This is an easy way to catch the most common footprint size issues.
• Use a vernier to actually measure the pin dia for all your through hole components, and check the drill holes dia in the drill file.