Well. just to clarify since several people asked...

We have a mated pair of board to board connectors that are about 4mm once
the two boards are snapped together.
We noticed when looking at several boards that the plastic part of the
connector is not always flush to the board, like it is slightly riding on
the solder paste
We also have standoffs that are 4mm, but I was asked if we should design
our own 4.1mm standoffs to keep the pressure/warpage down.
So the board thickness tolerance is NOT an issue, we are concerned with the
space BETWEEN the boards.

So that just got me curious, how high do components sit above the surface
of a board?
Most people answered 2-2.5mils

Thanks for the feedback,
Jack (the "not an assembly guy" guy)



----- Message from "Blomberg, Rainer (FL51)"
<[log in to unmask]> on Fri, 18 Mar 2005 10:30:23 -0700 -----

          Subject: Re: Floating SMT components?


This sounds similar to a question about the solder height of LCC after
reflow...about 2.5 mils in that case.  I assume the connector lead joint to
be similar, but it's difficult to tell because you didn't indicate the
configuration or what is holding the connector body up in the first place
(without solder paste).  You could tell your ME the variation in distance
between boards is less than the board thickness tolerance and the connector
contact positioning tolerance.  If you had to have a number for him, my
estimation would be 1-2 mils, if it really mattered.  All the connectors we
work with are supported with a molded-in foot or end up "flush" to the
board
and that is within 2 mils of the surface.  Adding 2-mils to the total
connector position tolerance would be reasonable.

> Rainer G. Blomberg
> Honeywell -Space Systems Clearwater
> Staff Production Engineer
(727) 539-5534


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Jack C. Olson
Sent: Friday, March 18, 2005 12:07 PM
To: [log in to unmask]
Subject: [TN] Floating SMT components?

I have been asked a question that I've never read anything about before, so
I'm hoping some of you assembly gurus out there will know this...

We have a mechanical engineer who is trying to predict the distance between
boards after soldering SMT board-to-board connectors. We know the connector
mating height, but the question is:

"If the connector is sitting in solder-paste, how high will it stay above
the surface of the board?"

Common sense tells me the connector will not be flush to the surface, there
will be some solder under there, and I think we are using 6mil paste
screens. Has anyone had to document something like this before?

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