On Wed, 6 Mar 2019 12:33:13 -0600, you wrote:
Thanks for the info Harvey. I have a new question. What is the closest
pads should be to each other? And if you are making a bunch of small
boards and transferring them to copper for etching what is the minimal
space between designs? In other words, what should the remaining border
width be? Seems I may have placed my circuits too close to the center
and have to shrink the width a little.
There's two limits, design and process.
Process limits simply say that you can't physically make the board
like that. Either too close to the edge, or holes too small, or
pads/traces too small.
Those limits vary with respect to the process, but typically 0.030 or
0.060 are decent limits (roughly 1/16 or 1/32) for pad to pad, and
spacing betwen tracks, but that's process....
Now, voltage wise, that determines the minimum track spacing as well.
I'm not sure of the limits here, you'd have to look that up. Ditto
with track current carrying capacity for width (varies also with
respect to the copper foil thickness).
You also want to allow for heat dissipation for things like resistors.
Typical power resistors are often at the end of longer leads and
spaced off the boards. Seen scorched boards because of resistors. Now
on the other hand, those resistor long leads will fail any sort of
vibration test. (military stuff used clamps for bulky parts like
that).
So for home analog stuff, not necessarily digital, you want a small
enough trace that you can put one between the pads of a DIP (more
requires finer stuff than can be happily done at home).
WIthout an autorouter (which is of limited use for home built boards),
I tend to use the airwires (unrouted traces) to determine which parts
need to be near which parts for shortest wire runs, then try to
manually route the shortest wires. It's a learning process...
Once you go to surface mount parts, the design rules start to change,
but I'm not sure where you are on this design.
Harvey
Thanks
On 3/6/2019 10:52 AM, Harvey White wrote:
On Wed, 6 Mar 2019 10:14:29 -0600, you wrote:
<snip>
? Ok, good info. So if I do my etching under my 24x24x14 carport
outside, I should be good and the carport should escape rusting too. I
think I can rest easy on the rust thing now as I have enough info on how
not to be careless. I have to also realize I am a noob and have to
design stuff to etch. Or download other peoples stuff to etch I probably
won't be etching all of the time to worry about it.
In a sense, there's really not a "design stuff to etch", but there are
things to consider in terms of process.
If you're using toner transfer, and especially just starting, I'd
suggest no thinner than about 12 mil traces, 16 being better.
Naturally that depends on the design.
Larger pads are better if possible. Normal traces could be 16 or 24,
but you'll get an idea of how much that is in terms of the board.
If you're using EAGLE (for example), draw a polygon around the entire
board on the bottom layer, following the dimension line. Name it
"GND" for the bottom (assuming you're doing single sided boards).
In EAGLE, the command to remove the effects (but not the polygon) is
RIPUP @
That's a ground fill, ground pour, etc. It fills some unused areas of
the board and reduces etchant use.
Mostly, for beginning stuff, larger traces are better because the
process can tolerate more pinholes and the like. Once you get down to
10 mil traces with 10 mil spacing, the process is less forgiving, and
you'll have to be a bit better at it.
A note on EAGLE (and likely some other programs), the size of the pad
is optimized for a board house, so it's rather thin in diameter. This
can be difficult when drilling holes and soldering. In a board house
produced board, this hole is automatically plated through and is more
sturdy as well as has more contact area for solder.
You may want to start making a library with larger pads for parts
depending on how you design things. I'd especially suggest this for
single sided boards, although the nature of the parts lead (through
board and then soldered) tends to hold things in place.
Harvey
