How Do 2 Layer PCBs Work

So I have been fooling around with a PCB in 123D Circuits. In order to connect a few compenents I had to use a second layer. Here is the circuit.

If I were to have this board made up which side do I solder on? Does it matter? Can I connect two times with a copper trace on either layer?

they work like, well, how a duplex printing works. You can "print" different "information" or circuity on either side. if you want to connect a line between the two pages, you use a via that goes through the board and connects the sides...

using SMD components, you can put one component on one side, and another component on the other side right behind one another.

if you use through hole components, which side you place the item on has to match up with how you placed it in your drawing....eg, if you placed an ic on the top layer, you'd need to place the IC on the top of the board, and solder it on the bottom side of the board, since the holes to all the way through the board.

on that particualar densign all the components are placed on the top, then you flip the PCB over and solder them from the bottom.

So are the holes for IC components essentially via's. Or do I have to add via's to my design

you may need to add vias to route signals and power from one side of the board to the other side. ic's that are through hole are technically vias I guess, in that they take up both sides.

the best way to figure it out into play with the software, the post what you got and what you want and get comments on it.....

Anything that is through-hole is also a via. You can connect either the top layer or the bottom layer to that pad.

This used to require you to solder both sides of the component leg, as the copper didn't go through the board. Vias would need little wires soldered into them too. These days everyone uses "plated through holes" which means they actually drill the holes before they put the copper on the board. This joins every hole to both layers.

If you are designing a board for home based etching/assembly, single sided is what you aim for. It it not trivial to do your own conductive vias at home. The holes you drill will not be conductive unless you add something to carry the connection through the board. Much easier to just make single sided boards with jumpers as needed if doing home fab.

If sending something out to a place like OSHPARK though... it's simple to make a double sided board with vias using EAGLE (cough) or something similar. And while there are definite design rules that you should follow with making PCB's... there are always exceptions. As long as you understand design rules... you can cope with making exceptions that don't make your board impossible to "make".

With all that unused real estate on the board, you could probably move things around so you don't need the "back" side traces at all. Or use jumpers as mentioned before.

pwillard:
If you are designing a board for home based etching/assembly, single sided is what you aim for. It it not trivial to do your own conductive vias at home. The holes you drill will not be conductive unless you add something to carry the connection through the board. Much easier to just make single sided boards with jumpers as needed if doing home fab.

It is possible to do fairly easily with through hole pins made for the purpose.

Tricky bit is accurate drilling and mask alignment.

I normally etch one side first drill some holes then do the other side..

In terms of good design practice (for purposes of manufacturability), it's best to have the parts all on one side. Particularly the SMD parts, since ones on the bottom need to get glued in place, adding extra steps to the manufacturing process. Even when doing hand assembly, it's easier if you don't have to flip it over and solder the other half.

Aligning the masks is easily done.
Tape the two masks back to back leaving the pocket assessable on one side.
Insert your PCB into the pocket.

Rather that jumpers, use SMD zero ohm resistors 1206 or 2010.
These are soldered on the foil side of your SS PCB

Might be of some interest.

We’ve started toaster oven reflow of 2 sided boards. So far, capillary action has been sufficient to hold SMD parts to the bottom of boards, example:

@Crossroads, what are the drill sizes used for the holes (vias also) in this board?

12 mil for signal vias, maybe 24 or 32 mil for ground plane vias (I need to open the file and look, I created the board a while ago) and 0.043" for the header thru holes to accept a 0.025" square pin.

Thank you.
.

SMT just being on a single side is still best if you can do it. Simpler, cheaper.

Depends how crowded - often my designs end up with decoupling caps under the chips so there is
room to route signals. For many BGA chips (not tried this yet) you are supposed to put decoupling
caps on reverse side of board so that they are as close as possible to the chip.

With a toaster oven and single-sided heating you don't normally get parts falling off the reverse side,
but I place the board on a multilayer stack of kitchen foil to help reflect heat and hold components
up when doing the second side, just in case. My technique is to watch the solder paste melt to ensure
I don't overheat, which helps prevent underside getting cooked too.

With regard to how double sided, vias, plating, etc. work, I found the following video very useful. It's 30 minutes long but goes through the whole process of how a PCB is manufactured.