On Fri, 17 May 2002 19:08:46 -0700, John Dammeyer wrote:
>For one project I'd like to fabricate a bed of nails
>tester/programmer panel.  Does anyone have any experience with
>those spring like pins.
>Where to get small qty, what size holes to install into. Etc.

John,

Interesting, I just got done converting a PIC16C926 based board
away from a spring contact programming setup. We had lots of
problems with intermittent contact and bad programming. Not such=

a large problem for flash based MCU's, but deadly on a tiny (1.5"=

x 2.5"), dense board with a TQFP64 PIC chip. Can you say "Program=

Error - trash the board"? The PC board layout could accept .1"
pin headers though, so we added the small cost of them (maybe 10=A2=

or so) and the problem is no more... glad I used the "stick a
header in the holes for programming my prototypes" method -- it
turns out that a permanent header was the most reliable solution=

and required no additional changes to the board.

I have used the spring pins before with success. One company is
(was) Augat Pylon. They are brand named Pogo contacts. Since
being acquired by Tyco, I'm not sure what their name is anymore.=

You should be able to do a google search and find their web=
 site.

The above mentioned board assembly is still being tested on a
"bed of nails" fixture, using Pogo contacts. Pylon also makes
blank test fixture enclosures and can provide applications
notes/help to get you started.

It seems the main problems I've run into are intermittent
contacts caused by PC board manufacturing variations which can
result in uneven pressure on the contact-to-board interface.
Oxidation and corrosion, as well as surface contaminants can also=

cause problems. It seems like every board assembly and test
fixture has it's own personality. I'm getting ready to design a
PC based bed-of-nails test fixture for a 9" x 11" board assembly,=

so I expect some interesting surprises along that road too.

Good luck!

Matt Pobursky
Maximum Performance Systems

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