In a message dated 04/19/2000 6:08:15 PM Central Daylight Time,
[log in to unmask] writes:

> Hello,
>          Below is a question sent to me. Does anyone have any suggestions?
>  Thanks
>  Rich
>
>  I do have a question that you might be able to help me with.  We have a
>  customer that is building something like an electronic hotel room key
>  (double sided board) which will be stored for up to 5 years prior to use...
>  and then the key will be used only once.  We are trying to figure out what
>  type of surface finish to tell them to use.  There is a single surface
>  mount IC mounted to the board... otherwise, there are contacts on one edge
>  that will be used to connect the key to the "lock" when it is used.  In
>  your experience of talking to the Tech Net people, have you come across a
>  solution to this type of requirement?  My first inclination is to use Ni /
>  Au plating with a thick (20+ microinches) deposition of Au.  Being a cheap
>  double sided board, they are really price conscious, so they want to keep
>  it as cheap as possible.  I don't know if HASL will provide a good contact
>  after that long on a shelf...

Hi Richard!

This question is pretty unique. Putting a reliability cap on, gold, because
of it's properties of not oxidizing would seem a good choice. But on the
other hand, how are these "hotel keys" going to be stored? Also, does a flash
gold plating drive the costs up that much? I've heard that flash doesn't cost
any more than HASL...

Are they going to be stored in a protected environment? Or are they going to
be in a cabinet or drawer at the check-in desk that might be exposed to the
occasional coffee spill or whatever? Assuming that these are going to be
throw-away cards, I would opt for using the cheapest finish that you can use,
and then advise that a mechanical means of cleaning the contacts on old keys
be used to prevent them from functioning.

I know some people will cringe, but in my Navy days flying on P-3's
(anti-submarine warfare and patrol aircraft) we were loaded with electronics.
When something didn't work right, the first thing our in-flight technician
did was pull a suspected board, take a pencil erasure and clean the finger
contacts and plug it back in. Many times that fixed things...believe it or
not. Most of the times these boards were finished with gold finger contacts...

So, from a completely practical point of view, and to keep costs down, use
the cheapest finish you can (since they are going to be a one time use only)
and maybe advise some sort of "freshing" of the contacts if the cards are
really old...

Of course this goes without saying that if I'm a customer at this hotel, and
I've been put up on the 15th floor and my key doesn't work and I have to go
all the way down back to the check-in desk that I won't be pissed, I can't
say that (GRIN).

But from my point of view, if the customer can't control the storing
conditions, it won't matter if the contacts are gold or tin/lead.

Just some random thoughts...

-Steve Gregory-

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