I say, Old Man,

If you have to, make 'em show you the screw spec and make damn sure that it
won't breakout or bottom out UNDER the board.  This is the usual mistake and why
I hate countersinks in THIN materials like PCBs.  Unless the screw is very
small, it is going to be thicker than 0.062 FR4 thickness.

From Bishop Graphics "The Design Aid" for 82 degree flathead screws here is what
the head depth is:

2-56  .051" thick
4-40  .067"  (just a bit thicker than the PCB!)
6-32  .083"
8-32  .100"

See what I mean?

Now, if you use a 100 degree flathead, things improve but not much, the 6-32 for
example is now .060"  Metric screws, I don't know about.

Also, as Kelly said, the heads tend to dig into the board as the edges are
sharp.  Nope, not my favorite.

Regards,

Bob Landman
H&L

(new to PCB design but been around electronics since vacuum tubes and phenolic
boards)





----- Original Message -----
From: Kelly M. Schriver <[log in to unmask]>
To: <[log in to unmask]>
Sent: September 26, 1999 7:08 PM
Subject: Re: [DC] PCB countersunk holes


> Hi Jack -
>
> The callout is adequate, assuming tolerances are stated elsewhere on the
> drawing.  Experience, from having attempted use of countersunk holes in both
> epoxyglass and polyimideglass boards, says someone is going to break some
> boards.  The laminate materials just don't hold up to the force applied by
> this type of fastening arrangement.
>
> I would suggest you explore your alternatives, such as a straight hole
> covered by a countersunk automotive trim washer or similar.
>
> Regards - Kelly
>
>
> -----Original Message-----
> From: Jack Olson <[log in to unmask]>
> To: [log in to unmask] <[log in to unmask]>
> Date: Friday, September 24, 1999 5:29 PM
> Subject: [DC] PCB countersunk holes
>
>
> >I have never been asked to provide countersink mounting holes on a PCB
> >before.
> >Since I have never had a drafting class, can I ask if any of you typically
> >do this?
> >I was just going to add a note to the fabrication dwg saying:
> >
> >x.) Countersink mounting holes (8X) 82 degrees x .230 on component side.
> >
> >Is this adequate?
> >Are there any "gotchas" I need to keep in mind?
> >
> >Jack (the new guy)
>