Through Hole Soldering?

[George Sephton]

Hi,
Im having real difficulty getting my head round this so I wondered if someone could clear this up for me.

I'm about to have a pcb fabbed and i'm thinking about through hole soldering...? Surface mount is easy as there's one side of pads so its easy to know where to solder, but through hole has 2 layers (in my case) and i'm trying to understand the pads. Are they connected on the top and bottom or not?
Take a look at this photo: http://www.sparkfun.com/commerce/images/products/00114-03-L.jpg

not that there is not bottom layer, it everything is on the top, so I've been assuming pads on the top and bottom aren't connected, ie if you have an LED the traces will need to be connected to the bottom pad cos obviously you can't solder to the top pad, however looking at this image of the pcb assembled, you can see very few of the components are soldered on the top: http://www.sparkfun.com/commerce/images/products/00114-04-L.jpg

I'm going to order with BatchPCB and my question is this? Are the through hole pads joined? Because at the moment all my through hole stuff has traces on the bottom layer connecting to the bottom pad, no top are uses and if it needs to be on the top a via is used dircetly after the pad...so do I need to do this or not? Can I have traces going to the top pad of say an LED and solder the LED from the bottom and still allow it to work?

Thanks,
George S.

 

[moxhamj]

"Can I have traces going to the top pad of say an LED and solder the LED from the bottom and still allow it to work?"

Short answer is "yes". Things that go all the way through are the pads of ICs, resistors, capacitors, leds, regulators etc. In fact, most components go all the way through - the exception is surface mount.

One problem soldering components is that you tip the board over and half of them fall out. I've just finished soldering a board where I cheated with some components (bypass caps, resistors) and soldered them from the top side.

HTH

 

[ylp88]

Looking at the unpopulated board, you can see three larger holes for the DC plus connector. If you look closely, you can see that the inner surface of the holes is metallic/grey in colour. This is a "plated through-hole" which provides a connection between the top and bottom layers, thus soldering on the bottom side pads will still have an electrical conenction to the pad which is directly above in on the top layer.

ylp88

 

[Andrew Cowan]

If you get 'through plated holes' (all PCB manufacturers do them), then the layers will be connected.

If you make your own board with homemade supplies, they probably won't. You then need to solder the top and bottom (hint - use turned pin sockets - they stand above the board!)

A

 

[Dippy]

George:
"Are the through hole pads joined? "
- YES, pukka manufacturers use PTH unless you ask otherwise.
This means the inner face of the hole is metal plated thus joining top pad to bottom pad.

If you want to join a top track to bottom track just insert a small pad in your CAD - assuming the pad is specified as a pinstack.
They are commonly calld 'vias'.

In CAD you can place pads on whatever layer you wish. However if you make the pad a pinstack or (maybe depending on your CAD) place it on the via layer (typically layer 0) this means the pad will apply to all layers - thus is will be drilled and PTH by default.

If you look at the bare PCB you linked you will see the inner faces of the holes are shiny - metal, not white emulsion paint

But you should really be checking with the manufacturer.

TIP: where possible use a component hole to act as a via. It means less drilling and that means lower cost for production. When using CAD manually route as much as possible. If you have experience you can cut track lengths and via counts down much better than MOR Autorouters. If you are just having some test boards done or a handful then thi won't matter much.

 

[George Sephton]

I did try ti cad my own board once but it went horribly wrong, so that clears things up. Atm I have a DIP that has all 16 traces come out from the bottom and each have a via that takes it all to the top layer. I guess this unecessary, thanks for clearing that up for me.

 

[Dippy]

"I guess this unecessary"
- for a proper PTH board yes it is unnecessary and costly when you have a million made

For home-brew you may need to do it, or do as most of us do (and Andrew) find a chip socket (e.g. turned-pin or wire-wrap) where you can get a soldering iron to the top-side too.

Horribly wrong? Practice dear boy

 

[Andrew Cowan]

For vias on a homemade board, either solder a component leg on the top and bottom (not possible on standard sockets and radial capacitors that are flush to the board).

Alternativly, for a via seperate from a component, insert a short bit of single core wire, and solder top and bottom.

A

 

[Dippy]

I think George could work that one out