Hi JoAnn, watch for my comments below (---->)
> From [log in to unmask] Fri Jan 9 06:01:25 1998
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> Date: Fri, 9 Jan 1998 08:46:49 +0000
> Comments: Authenticated sender is <[log in to unmask]>
> From: JoAnn Amerson <[log in to unmask]>
> Subject: [DC] Spacing, etc questions
> To: [log in to unmask]
>
> Good morning folks! I have a few questions and would appreciate some feedback
> from others. I'd like to find out what others in the field are doing to either
> support our practices or re-vamp them.
>
> (1) Could someone explain why pad to conductor spacing is greater than
> conductor to conductor? If I only need to stay 8 mil away for the conductor,
> why do I need 10 mil or more from a pad on the same net? Or is this just one
> of the quirky things we do here?
----> If the pad is clear of soldermask (exposed) then your standard probably
is compensating for that. Soldermask openings are typically larger than
the copper pad, this to allow for the greater tolerance of the soldermask
process. If your soldermask is 4 mils larger than your pad, (providing a
2 mil anular ring), then your normal 8 mil clearance could be increased to
10 mils.
>
> (2) We are starting to use breakaway tabs on panelized boards more frequently
> but do not have a set keepaway distance. I'd like to know what others are
> using so that I can amend our guidelines. (Yes, I'm still trying for those
> brownie points! Reviews are next week.)
----> There are a couple of different types of break away methods, and I am unsure
which one you are using. You can use a 'V' groove or a slot. We use a 125
mil wide slot, which is 2 inches long max. We perferate the area between the
slots with 4 18 mil holes... if memory serves, these holes are about 25 mils
apart. A break away tab will use a number of these slots, depending on the
length of the break away.
>
> (3) What size via (drill and pad) are you using for low current signal track?
> We are using a .018 drill with a .038 pad diameter. It would be nice to be
> able to justify a smaller via and gain a little real estate.
----> An 18 hole with a 38 pad would be for us a good via for "low" technology
boards. As the density of your boards increases, you will have to decrease
the size of your via. However, an 18 drill usually allows your fab vendor
to stack 2 boards during the drill process (drill 2 boards at once). This
is a significant savings. A 38 diameter pad also allows you to use the pad
as an ICT test point. If you go to a smaller via, when you do ICT, you will
have to increase the pad size of a via if you want to use it for a test point.
Currently, the density of our boards would prohibit the use of such a large via.
We use a 10 mil finished hole in a 25 mil pad.
>
> I think this will do for now. I know there are no simple answers to these
> questions but if I could just get a feel what "the real world" is doing then
> maybe I can convince the others that it's not 1985 any longer. Of course I do
> still have one co-worker who INSISTS on using the RS-274D format for his Gerber
> files. He's been in the field alot longer than I have and I guess has a
> difficult time believing that I (a mere woman) could *possibly* know something
> he doesn't. Oh well.............
>
> Thanks in advance!
>
> JoAnn L. Amerson
> Design Librarian
> Red Lion Controls, Inc.
> E-mail: [log in to unmask]
> Voice: (717) 767-6961 ext 6308
>
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