By no means should you press fit a connector or pin of any sort
into a platted thru hole that has intermal layer thermal layers, or
internal pads for that matter.  By pressing the pin into the hole
you run the risk of breaking the continuity of the PTH and not
make a connection to the internal layers, or possibly making
only intermittent connections internally.

>>> Eddie Brunker <[log in to unmask]> 09/23/97
09:50am >>>
I posted a question a few days ago about Press Fit Connectors.
I've started
to understand the answer myself.
Press Fit connectors are a mechanical means of making
contact with no soldering.
PTH connectors which go through a soldering process that
requires CAD layout
to have thermal relief to copper planes. This means a
connection to the via
which doesn't go all the way around the circumference but only
makes contact
in two or four points. This is to reduce the heat sinking effect of
the
copper plane on the via which would cool it during a thermal
cycle
(soldering operation) and thereby create potential defects.
Press Fit connectors can be mechanically inserted without
soldering
therefore the via can be connected to the plane along its full
circumference
with no thermal relief (a solid contact). This solid contact in turn
gives
lower inductance for power pins on a backplane.(Which is what
the designers
want).
I get the impression that Press Fit is used not just by Compact
PCI
protocall (in our case 6U card computers) but anyone heading
at high bus
speeds in a backplane. Obviously the speeds are going up and
this is to be
commended. But the trend of the assembly industry to use
Press Fit
connectors to address this is seriously worrying. Why should
the Design
fraternity dictate the assembly technique and not the end result
required.
In other words if they want reduced inductance why don't they
just specify
no thermal relief and let the assembly heads worry about the
means of
connection and whether soldering will be a problem.
APPLYING A FEW TONS OF PRESSURE TO AN ASSEMBLY to
attach a connector seems
to me to be primitive method. Yet this is the trend for
manufacture in the
future for high speed applications. Why is this basic method
being promoted
for the future? Do people out there have any means of
automating this
process within a line? How can rework ever be possible
considering the
assemblies are expensive board level computers worth
thousands of pounds
(dollars). What is the typical yield for such a process? How easy
is it to
destroy assemblies in a Press?
Does anyone out there use solid connection to vias on copper
planes for the
wave soldering process?
Has anybody done any trials on this?
Pressumably the thermal aspect can be sorted by sufficient
pre-heat. Do wave
solder machines need to use convection pre heat zones. Are
such machines
available?
It would be nice to see the design people told that there should
be a STOP
TO THIS BARBARIAN ASSEMBLY TECHNIQUE. It would be nice
to see the connector
manufacturers make connectors which provide shielding and
conform to Compact
PCI format and IEC1076 (or high speed bus formats) in Plated
Through Hole OR
Surface Mount packages.
Pressumably SURFACE MOUNT WOULD HAVE NO THERMAL
RELIEF DEMANDS as modern
Convection ovens have no problems dealing with solid contacts
to vias. So
why not develop the Surface Mount version of the connector?
Please, please, please there must be someone out there with
an opinion on this.
Thanks

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