I will add a couple of questions to the list:
1. what the designer does for conn vias where pressfit conn is also
soldered.
2. what will happen if we use solder conn vias for pressfit operation.

I will talk on this as well.

[log in to unmask]

> ----------
> From:         Larry Campbell[SMTP:[log in to unmask]]
> Sent:         September 23, 1997 10:43 AM
> To:   [log in to unmask]
> Subject:      [TECHNET] Press Fit -Reply
>
> 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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