All,
At Harris we mount PWB to metal plates very often.
Two methods are used.
1. Blind vias for all non GND connections.
2. Dimpling the metal plate where the non GND connections are is
usually the least expensive method. Hopefully the PWB will
not change and you won't have to remake the plate.
We don't generally do controlled depth drilling. Most fabricators
are not very good at it or price our boards to fund their research.
Use the KISS method for all designs when possible. The second
approach I mentioned above satisfies this.
Regards,
Jerry Schwartz, CID
IPC Certified Interconnect Designer
"May the Schwartz be with you"
Jerry Schwartz, CID Designer 3
Harris Corporation GCSD Voice (321)-727-5474
P.O. Box 37, MS 1/9843 Fax (321)-729-5990
Melbourne, FL 32902-0037 Pager (321)-690-9797
mailto:[log in to unmask]
http://harris.com
-----Original Message-----
From: David Cary [mailto:[log in to unmask]]
Sent: Thursday, January 04, 2001 6:58 PM
To: [log in to unmask]
Subject: Re: [DC] Controlled depth drilling
Dear Roy Beckman,
I think I heard about something like this before ... ah, here it is.
_Surface-Mount Technology for PC Boards_ book by James K. Hollomon, Jr.
p. 317
<blockquote>
<p>
... NASA's Jet Propulsion Lab ...
One circuit in particular was fascinating. For a spacecraft, it was a relatively
large card. And, it was fully planar mounted with single-side population. The
back side of the board was bonded to a metallic plate. The circuit was part of
the electronics of the Voyager space probe. ... the metallic backside of the
substrate was used as an outer skin of the spacecraft, as well as a support and
a heat sink for the electronics. Therefore, surface mounting of the components
was a must if they were to achieve a smooth hole-free skin for the spacecraft.
</blockquote>
I wish I knew where to get more details on the Voyager space probe. Maybe Andrew
J Jenkins <[log in to unmask]> could help ?
You also might look into "blind vias".
...
One of our board shops has suggested an alternative strategy to handle
through-hole vias for a PCB mounted on a flat metal plate. They suggest that we
remove the bottom pads on all non-ground vias and then they will drill the
plated holes out to a depth of 0.010". (The finished hole sizes for these vias
are 0.012" and 0.018".) The previous strategy was to drill holes in the
mounting plate at the via locations.
Has anyone had any experience with this scenario?
Can you recommend any board shops that do this?
How reliable are the vias after this drilling?
Thanks for your feedback,
Roy
Roy H. Beckman, C.E.T., C.I.D.
Senior PCB Designer
...
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