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Almost done with drive circuit PCB

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LAN_403

Danielle

Sun May 27 2007, 11:09PM

Registered Member #632 Joined: Mon Apr 09 2007, 01:09AM
Location:
Posts: 267

I am half way done with my drive circuit and its looking bad I was wondering what I could do to make it better. It will be a combo of primary, secondary, or PWM H/Half bridge controller.
1180307408 632 FT0 Newpcb

How would I etch it Ive done toner but the traces are thin. Should I do a photographic method?
Also How do I bridge top to bottom on the holes where I bring the traces down, solder a wire through?
Thanks.

...

Sun May 27 2007, 11:52PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

I don't know much about surcites, so I can't comment.

It it were a circuit I have a ton of suggestions...

Danielle

Mon May 28 2007, 01:13AM

Registered Member #632 Joined: Mon Apr 09 2007, 01:09AM
Location:
Posts: 267

if not it
"It it were a circuit I have a ton of suggestions..."

...

Mon May 28 2007, 02:25AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

well...
1. Post a pic that has enough resolution to be able to discern the traces, and one without the silkscreen. (use proper img tags to make the thumbnail a link to the high res version)
2. The toner method can make traces plenty small for that board.
3. To bridge to top/bottom, the easiest way is to put in a piece of wire, or you can get small press-in ferrules to make it look better. The best solution is to design the board so that the traces always cross at a resistor or something.
4. When you do not have plated through holes (as would be case for a home etched board) it is very hard to solder components like electrolytic caps, LEDs, connectors, etc to the top layer, as when you put the component in it covers the top layer. Likewise, you should ensure that all such components are only have pads on the bottom layer.
5. Bigger traces are better think "squares and rectangles here, not lines".
6. See this thread for suggestions.

Danielle

Mon May 28 2007, 04:25AM

Registered Member #632 Joined: Mon Apr 09 2007, 01:09AM
Location:
Posts: 267

Here's a pdf of the circuit, but how would I solder caps that need top copper soldering to the board? or any other component that I cain't reach?

Thanks.
]1180326301_632_FT25907_tcdrive.pdf[/file]

...

Mon May 28 2007, 05:32AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

If you need to solder an electrolytic cap to a top layer, you can fold the pins out from under it and solder them out where you can get to them. Or you can put the cap in 1/2way, put a big blob of solder on it that is really hot, and jam the cap down, and pray that you don't get a cold joint. Or put the cap in from underneath.

Note however, that components that will be subject to a lot of stress (big caps/transistors, connectors, even LEDs sometimes) really need to be soldered to the bottom layer, as if they are aurface mounted they have very little mechanical strength--just the glue holding the copper to the board. When you solder them to the bottom layer you would have to break the solder joint to break the component off, where when it it on top you just need to pop the glue holding the trace to the fiberglass off.

IMHO, for such components, it is best to put a pad for it on the bottom layer, and then vias to get it back to the top layer.

Also, now that I can see the board itself, I have noticed a few things:
7. You need to make the pads for the vias bigger, as with such small ones it will be very had to get the top/bottom to line up well enough that for them to look decent. Also, when you drill the hole it has a tendency to rip that small bit of copper out. You have plenty of space, just put them out in the open and make a nice big bad.
8. The routing underneath the smd chips is too close, especially between the traces/pads for the pins--you are asking for shorts that are damn near impossible to find/fix. In fact right now there are already 2 touching traces next to the rightmost chip...
9. It is very hard to make a via work under a smd chip. You really should try to route the traces on the outside of the chips, not under them.
10. For a lot of the traces, there is no reason that you can't use a much larger trace--as mentioned earlier there is no point in making a trace smaller than it can be. Larger traces save enchant, are less likely to get eaten away when you etch, have less voltage drop, etc.

Danielle

Mon May 28 2007, 04:29PM

Registered Member #632 Joined: Mon Apr 09 2007, 01:09AM
Location:
Posts: 267

Thank you for the advice and I will revise the board but the free space is for my PWM, over temp, and over current. It is difficult to place all of them on the board I will try to keep the traces on top but I caint find good routs.

Thanks again.

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