Jack:
Use a 4.1 to 4.35 standoff. seems simple enough to me :)
"Jack C. Olson" <[log in to unmask]>
Sent by: DesignerCouncil <[log in to unmask]>
03/21/2005 03:30 PM
Please respond to
"(Designers Council Forum)" <[log in to unmask]>; Please respond to
"Jack C. Olson" <[log in to unmask]>
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Subject
Re: [DC] Floating SMT components?
Caterpillar: Confidential Green Retain Until: 04/20/2005 Retention
Category: G90 - General Matters/Administration
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? (with no mechanical retaining feature)
Most people answered 2-2.5mils
Thanks for the feedback,
Jack (the "not an assembly guy" guy)
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03/18/2005 11:43 To
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"Jack C. Olson"
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Subject
Re: [DC] Floating SMT components?
Caterpillar: Confidential Green Retain Until: 04/17/2005
Retention Category: G90 -
General
Matters/Administration
Hi Jack-
Good question; no answer from me, but...
Just out of curiosity, what do you see as being "the surface of the
board"?
If you're worried about a mil or two of solder, then the difference
between
bare laminate vs. base conductor+ plating+finish vs. either/both with
soldermask added becomes significant... I only ask because that comes up
from time to time here. My answer is: "It depends... why do you ask?"
Since the board thickness usually has a 10% tolerance, if it's 1.5MM or
thicker PCB, I'd just leave solder under the connector out of the stackup,
but I'm lazy that way.
And I guess the connector config. would have a lot to do with it. Does it
have a mechanical retaining feature? If so, I say disregard the solder.
It's gonna be where it's gonna be within the tol. built into the snap,
lock, or whatnot.
-Chris
"Jack C. Olson"
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<[log in to unmask]> Subject: [DC]
Floating SMT components?
03/18/2005 12:08 PM
I have been asked a question that I've never read anything about before,
so
I'm hoping someone 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?
Jack
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